nearby: snapshot as of cl/296436629

Signed-off-by: Alexey Polyudov <apolyudov@google.com>
Change-Id: I2cf5bf225b76f4c1541954651f3a7544a14e0cec

cpp/core/BUILD

@@ -0,0 +1,55 @@
+cc_library(
+    name = "core",
+    hdrs = [
+        "core.cc",
+        "core.h",
+    ],
+    visibility = [
+        "//googlemac/iPhone/Shared/Nearby/Connections:__pkg__",
+        "//location/nearby/setup/core/internal:__pkg__",
+    ],
+    deps = [
+        ":types",
+        "//core/internal",
+        "//platform:types",
+    ],
+)
+
+cc_library(
+    name = "types",
+    srcs = [
+        "payload.cc",
+        "strategy.cc",
+    ],
+    hdrs = [
+        "listeners.h",
+        "options.h",
+        "params.h",
+        "payload.h",
+        "status.h",
+        "strategy.h",
+    ],
+    visibility = [
+        "//core/internal:__pkg__",
+        "//location/nearby/setup/core/internal:__pkg__",
+    ],
+    deps = [
+        "//platform:types",
+        "//platform:utils",
+        "//platform/api",
+        "//platform/port:string",
+    ],
+)
+
+cc_library(
+    name = "check_compilation",
+    srcs = ["check_compilation.cc"],
+    deps = [
+        ":core",
+        ":types",
+        "//platform:types",
+        "//platform:utils",
+        "//platform/impl/sample",
+        "//platform/port:string",
+    ],
+)

cpp/core/check_compilation.cc

@@ -0,0 +1,119 @@
+
+#include <vector>
+
+#include "core/core.h"
+#include "core/listeners.h"
+#include "core/params.h"
+#include "core/payload.h"
+#include "core/status.h"
+#include "platform/byte_array.h"
+#include "platform/file_impl.h"
+#include "platform/impl/sample/sample_platform.h"
+#include "platform/port/string.h"
+#include "platform/ptr.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+class ResultListenerImpl : public ResultListener {
+ public:
+  void onResult(Status::Value status) override {}
+};
+
+class ConnectionLifecycleListenerImpl : public ConnectionLifecycleListener {
+ public:
+  void onConnectionInitiated(ConstPtr<OnConnectionInitiatedParams>
+                                 on_connection_initiated_params) override {}
+  void onConnectionResult(
+      ConstPtr<OnConnectionResultParams> on_connection_result_params) override {
+  }
+  void onDisconnected(
+      ConstPtr<OnDisconnectedParams> on_disconnected_params) override {}
+  void onBandwidthChanged(
+      ConstPtr<OnBandwidthChangedParams> on_bandwidth_changed_params) override {
+  }
+};
+
+class DiscoveryListenerImpl : public DiscoveryListener {
+ public:
+  void onEndpointFound(
+      ConstPtr<OnEndpointFoundParams> on_endpoint_found_params) override {}
+  void onEndpointLost(
+      ConstPtr<OnEndpointLostParams> on_endpoint_lost_params) override {}
+};
+
+class PayloadListenerImpl : public PayloadListener {
+ public:
+  void onPayloadReceived(
+      ConstPtr<OnPayloadReceivedParams> on_payload_received_params) override {}
+  void onPayloadTransferUpdate(ConstPtr<OnPayloadTransferUpdateParams>
+                                   on_payload_transfer_update_params) override {
+  }
+};
+
+void check_compilation() {
+  Core<sample::SamplePlatform> core;
+
+  const string name = "name";
+  const string service_id = "service_id";
+  const string remote_endpoint_id = "remote_endpoint_id";
+
+  core.startAdvertising(MakeConstPtr(new StartAdvertisingParams(
+      MakePtr(new ResultListenerImpl()), name, service_id,
+      AdvertisingOptions(Strategy::kP2PCluster,
+                         /* auto_upgrade_bandwidth= */ false,
+                         /* enforce_topology_constraints= */ false),
+      MakePtr(new ConnectionLifecycleListenerImpl()))));
+
+  core.stopAdvertising(MakeConstPtr(new StopAdvertisingParams()));
+
+  core.startDiscovery(MakeConstPtr(
+      new StartDiscoveryParams(MakePtr(new ResultListenerImpl()), service_id,
+                               DiscoveryOptions(Strategy::kP2PCluster),
+                               MakePtr(new DiscoveryListenerImpl()))));
+
+  core.stopDiscovery(MakeConstPtr(new StopDiscoveryParams()));
+
+  core.requestConnection(MakeConstPtr(new RequestConnectionParams(
+      MakePtr(new ResultListenerImpl()), name, remote_endpoint_id,
+      MakePtr(new ConnectionLifecycleListenerImpl()))));
+
+  core.acceptConnection(MakeConstPtr(new AcceptConnectionParams(
+      MakePtr(new ResultListenerImpl()), remote_endpoint_id,
+      MakePtr(new PayloadListenerImpl()))));
+
+  core.rejectConnection(MakeConstPtr(new RejectConnectionParams(
+      MakePtr(new ResultListenerImpl()), remote_endpoint_id)));
+
+  core.initiateBandwidthUpgrade(MakeConstPtr(new InitiateBandwidthUpgradeParams(
+      MakePtr(new ResultListenerImpl()), remote_endpoint_id)));
+
+  core.sendPayload(MakeConstPtr(new SendPayloadParams(
+      MakePtr(new ResultListenerImpl()),
+      std::vector<string>(1, remote_endpoint_id),
+      ConstifyPtr(
+          Payload::fromBytes(MakeConstPtr(new ByteArray("bytes", 5)))))));
+
+  core.cancelPayload(MakeConstPtr(
+      new CancelPayloadParams(MakePtr(new ResultListenerImpl()), 1)));
+
+  core.sendPayload(MakeConstPtr(new SendPayloadParams(
+      MakePtr(new ResultListenerImpl()),
+      std::vector<string>(2, remote_endpoint_id),
+      ConstifyPtr(Payload::fromFile(MakePtr(
+          new InputFileImpl("/some/arbitrary/file/path.txt", 1024)))))));
+
+  core.cancelPayload(MakeConstPtr(
+      new CancelPayloadParams(MakePtr(new ResultListenerImpl()), 2)));
+
+  core.disconnectFromEndpoint(
+      MakeConstPtr(new DisconnectFromEndpointParams(remote_endpoint_id)));
+
+  core.stopAllEndpoints(MakeConstPtr(
+      new StopAllEndpointsParams(MakePtr(new ResultListenerImpl()))));
+}
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/core.cc

@@ -0,0 +1,137 @@
+#include "core/core.h"
+
+#include <cassert>
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+template <typename Platform>
+Core<Platform>::Core()
+    : client_proxy_(new ClientProxy<Platform>()),
+      service_controller_router_(new ServiceControllerRouter<Platform>()) {}
+
+template <typename Platform>
+Core<Platform>::~Core() {
+  service_controller_router_->clientDisconnecting(client_proxy_.get());
+}
+
+template <typename Platform>
+void Core<Platform>::startAdvertising(
+    ConstPtr<StartAdvertisingParams> start_advertising_params) {
+  assert(!start_advertising_params->result_listener.isNull());
+  assert(!start_advertising_params->connection_lifecycle_listener.isNull());
+  assert(!start_advertising_params->service_id.empty());
+  assert(start_advertising_params->advertising_options.strategy.isValid());
+
+  service_controller_router_->startAdvertising(client_proxy_.get(),
+                                               start_advertising_params);
+}
+
+template <typename Platform>
+void Core<Platform>::stopAdvertising(
+    ConstPtr<StopAdvertisingParams> stop_advertising_params) {
+  service_controller_router_->stopAdvertising(client_proxy_.get(),
+                                              stop_advertising_params);
+}
+
+template <typename Platform>
+void Core<Platform>::startDiscovery(
+    ConstPtr<StartDiscoveryParams> start_discovery_params) {
+  assert(!start_discovery_params->result_listener.isNull());
+  assert(!start_discovery_params->discovery_listener.isNull());
+  assert(!start_discovery_params->service_id.empty());
+  assert(start_discovery_params->discovery_options.strategy.isValid());
+
+  service_controller_router_->startDiscovery(client_proxy_.get(),
+                                             start_discovery_params);
+}
+
+template <typename Platform>
+void Core<Platform>::stopDiscovery(
+    ConstPtr<StopDiscoveryParams> stop_discovery_params) {
+  service_controller_router_->stopDiscovery(client_proxy_.get(),
+                                            stop_discovery_params);
+}
+
+template <typename Platform>
+void Core<Platform>::requestConnection(
+    ConstPtr<RequestConnectionParams> request_connection_params) {
+  assert(!request_connection_params->result_listener.isNull());
+  assert(!request_connection_params->connection_lifecycle_listener.isNull());
+  assert(!request_connection_params->remote_endpoint_id.empty());
+
+  service_controller_router_->requestConnection(client_proxy_.get(),
+                                                request_connection_params);
+}
+
+template <typename Platform>
+void Core<Platform>::acceptConnection(
+    ConstPtr<AcceptConnectionParams> accept_connection_params) {
+  assert(!accept_connection_params->result_listener.isNull());
+  assert(!accept_connection_params->payload_listener.isNull());
+  assert(!accept_connection_params->remote_endpoint_id.empty());
+
+  service_controller_router_->acceptConnection(client_proxy_.get(),
+                                               accept_connection_params);
+}
+
+template <typename Platform>
+void Core<Platform>::rejectConnection(
+    ConstPtr<RejectConnectionParams> reject_connection_params) {
+  assert(!reject_connection_params->result_listener.isNull());
+  assert(!reject_connection_params->remote_endpoint_id.empty());
+
+  service_controller_router_->rejectConnection(client_proxy_.get(),
+                                               reject_connection_params);
+}
+
+template <typename Platform>
+void Core<Platform>::initiateBandwidthUpgrade(
+    ConstPtr<InitiateBandwidthUpgradeParams>
+        initiate_bandwidth_upgrade_params) {
+  service_controller_router_->initiateBandwidthUpgrade(
+      client_proxy_.get(), initiate_bandwidth_upgrade_params);
+}
+
+template <typename Platform>
+void Core<Platform>::sendPayload(
+    ConstPtr<SendPayloadParams> send_payload_params) {
+  assert(!send_payload_params->result_listener.isNull());
+  assert(!send_payload_params->remote_endpoint_ids.empty());
+  assert(!send_payload_params->payload.isNull());
+  // TODO(tracyzhou): Do sanity check on payload based on payload type.
+
+  service_controller_router_->sendPayload(client_proxy_.get(),
+                                          send_payload_params);
+}
+
+template <typename Platform>
+void Core<Platform>::cancelPayload(
+    ConstPtr<CancelPayloadParams> cancel_payload_params) {
+  assert(!cancel_payload_params->result_listener.isNull());
+  assert(cancel_payload_params->payload_id != 0);
+
+  service_controller_router_->cancelPayload(client_proxy_.get(),
+                                            cancel_payload_params);
+}
+
+template <typename Platform>
+void Core<Platform>::disconnectFromEndpoint(
+    ConstPtr<DisconnectFromEndpointParams> disconnect_from_endpoint_params) {
+  assert(!disconnect_from_endpoint_params->remote_endpoint_id.empty());
+
+  service_controller_router_->disconnectFromEndpoint(
+      client_proxy_.get(), disconnect_from_endpoint_params);
+}
+
+template <typename Platform>
+void Core<Platform>::stopAllEndpoints(
+    ConstPtr<StopAllEndpointsParams> stop_all_endpoints_params) {
+  service_controller_router_->stopAllEndpoints(client_proxy_.get(),
+                                               stop_all_endpoints_params);
+}
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/core.h

@@ -0,0 +1,83 @@
+#ifndef CORE_CORE_H_
+#define CORE_CORE_H_
+
+#include "core/internal/client_proxy.h"
+#include "core/internal/service_controller_router.h"
+#include "core/params.h"
+#include "platform/ptr.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+/*
+ * This class defines the API of the Nearby Connections Core library.
+ *
+ * Each passed-in Platform must provide a set of primitives with platform-
+ * specific implementations. The Platform class must provide factory functions
+ * for the following primitives:
+ *
+ *   SingleThreadExecutor
+ *   MultiThreadExecutor
+ *   ScheduledExecutor
+ *   Lock
+ *   CountDownLatch
+ *   AtomicBoolean
+ *   AtomicReference
+ *   SettableFuture
+ *   BluetoothAdapter
+ *   BluetoothClassicMedium
+ *   HashUtils
+ *   ThreadUtils
+ *   SystemClock
+ *   ConditionVariable
+ *
+ * The Platform class must also provide typedefs for the following subset of
+ * primitives to identify the concrete classes:
+ *
+ *   SingleThreadExecutorType
+ *   MultiThreadExecutorType
+ *   ScheduledExecutorType
+ *
+ * A sample Platform class can be found at
+ * //platform/impl/sample/sample_platform.h
+ */
+template <typename Platform>
+class Core {
+ public:
+  Core();
+  ~Core();
+
+  void startAdvertising(
+      ConstPtr<StartAdvertisingParams> start_advertising_params);
+  void stopAdvertising(ConstPtr<StopAdvertisingParams> stop_advertising_params);
+  void startDiscovery(ConstPtr<StartDiscoveryParams> start_discovery_params);
+  void stopDiscovery(ConstPtr<StopDiscoveryParams> stop_discovery_params);
+  void requestConnection(
+      ConstPtr<RequestConnectionParams> request_connection_params);
+  void acceptConnection(
+      ConstPtr<AcceptConnectionParams> accept_connection_params);
+  void rejectConnection(
+      ConstPtr<RejectConnectionParams> reject_connection_params);
+  void initiateBandwidthUpgrade(ConstPtr<InitiateBandwidthUpgradeParams>
+                                    initiate_bandwidth_upgrade_params);
+  void sendPayload(ConstPtr<SendPayloadParams> send_payload_params);
+  void cancelPayload(ConstPtr<CancelPayloadParams> cancel_payload_params);
+  void disconnectFromEndpoint(
+      ConstPtr<DisconnectFromEndpointParams> disconnect_from_endpoint_params);
+  void stopAllEndpoints(
+      ConstPtr<StopAllEndpointsParams> stop_all_endpoints_params);
+
+ private:
+  ScopedPtr<Ptr<ClientProxy<Platform> > > client_proxy_;
+  ScopedPtr<Ptr<ServiceControllerRouter<Platform> > >
+      service_controller_router_;
+};
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#include "core/core.cc"
+
+#endif  // CORE_CORE_H_

cpp/core/internal/BUILD

@@ -0,0 +1,102 @@
+cc_library(
+    name = "internal",
+    srcs = [
+        "ble_advertisement.cc",
+        "bluetooth_device_name.cc",
+        "internal_payload.cc",
+        "internal_payload.h",
+        "loop_runner.cc",
+        "loop_runner.h",
+        "offline_frames.cc",
+        "offline_frames.h",
+    ],
+    hdrs = [
+        "bandwidth_upgrade_handler.h",
+        "bandwidth_upgrade_manager.cc",
+        "bandwidth_upgrade_manager.h",
+        "base_bandwidth_upgrade_handler.cc",
+        "base_bandwidth_upgrade_handler.h",
+        "base_endpoint_channel.cc",
+        "base_endpoint_channel.h",
+        "base_pcp_handler.cc",
+        "base_pcp_handler.h",
+        "ble_advertisement.h",
+        "ble_compat.h",
+        "ble_endpoint_channel.cc",
+        "ble_endpoint_channel.h",
+        "bluetooth_device_name.h",
+        "bluetooth_endpoint_channel.cc",
+        "bluetooth_endpoint_channel.h",
+        "client_proxy.cc",
+        "client_proxy.h",
+        "encryption_runner.cc",
+        "encryption_runner.h",
+        "endpoint_channel.h",
+        "endpoint_channel_manager.cc",
+        "endpoint_channel_manager.h",
+        "endpoint_manager.cc",
+        "endpoint_manager.h",
+        "internal_payload_factory.cc",
+        "internal_payload_factory.h",
+        "medium_manager.cc",
+        "medium_manager.h",
+        "offline_service_controller.cc",
+        "offline_service_controller.h",
+        "p2p_cluster_pcp_handler.cc",
+        "p2p_cluster_pcp_handler.h",
+        "p2p_point_to_point_pcp_handler.cc",
+        "p2p_point_to_point_pcp_handler.h",
+        "p2p_star_pcp_handler.cc",
+        "p2p_star_pcp_handler.h",
+        "payload_manager.cc",
+        "payload_manager.h",
+        "pcp.h",
+        "pcp_handler.h",
+        "pcp_manager.cc",
+        "pcp_manager.h",
+        "service_controller.h",
+        "service_controller_router.cc",
+        "service_controller_router.h",
+        "wifi_lan_upgrade_handler.cc",
+        "wifi_lan_upgrade_handler.h",
+    ],
+    visibility = [
+        "//core:__pkg__",
+    ],
+    deps = [
+        "//core:types",
+        "//core/internal/mediums",
+        "//proto/connections:offline_wire_formats_portable_proto",
+        "//platform:logging",
+        "//platform:types",
+        "//platform:utils",
+        "//platform/api",
+        "//platform/port:down_cast",
+        "//platform/port:string",
+        "//proto:connections_enums_portable_proto",
+        "//net/proto2/compat/public:proto2_lite",
+        "//securegcm:ukey2",
+        "//absl/strings",
+    ],
+)
+
+cc_test(
+    name = "bluetooth_device_name_test",
+    srcs = ["bluetooth_device_name_test.cc"],
+    deps = [
+        ":internal",
+        "//platform:utils",
+        "//platform/port:string",
+        "//testing/base/public:gunit_main",
+    ],
+)
+
+cc_test(
+    name = "ble_advertisement_test",
+    srcs = ["ble_advertisement_test.cc"],
+    deps = [
+        ":internal",
+        "//platform/port:string",
+        "//testing/base/public:gunit_main",
+    ],
+)

cpp/core/internal/bandwidth_upgrade_handler.h

@@ -0,0 +1,50 @@
+#ifndef CORE_INTERNAL_BANDWIDTH_UPGRADE_HANDLER_H_
+#define CORE_INTERNAL_BANDWIDTH_UPGRADE_HANDLER_H_
+
+#include "core/internal/client_proxy.h"
+#include "proto/connections/offline_wire_formats.pb.h"
+#include "platform/api/count_down_latch.h"
+#include "platform/port/string.h"
+#include "proto/connections_enums.pb.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+// Defines the set of methods that need to be implemented to handle the
+// per-Medium-specific operations needed to upgrade an EndpointChannel.
+template <typename Platform>
+class BandwidthUpgradeHandler {
+ public:
+  virtual ~BandwidthUpgradeHandler() {}
+
+  // Reverts any changes made to the device in the process of upgrading
+  // endpoints.
+  virtual void revert() = 0;
+
+  // Cleans up in-progress upgrades after endpoint disconnection.
+  virtual void processEndpointDisconnection(
+      Ptr<ClientProxy<Platform> > client_proxy, const std::string& endpoint_id,
+      Ptr<CountDownLatch> process_disconnection_barrier) = 0;
+
+  // Initiates the upgrade for the endpoint and starts listening for upgraded
+  // incoming connections on the initiator side of the bandwidth upgrade.
+  virtual void initiateBandwidthUpgradeForEndpoint(
+      Ptr<ClientProxy<Platform> > client_proxy,
+      const std::string& endpoint_id) = 0;
+
+  // Processes the BandwidthUpgradeNegotiationFrames that come over the
+  // EndpointChannel on the non-initiator side of the bandwidth upgrade.
+  // TODO(ahlee): Rename parameters in the java code.
+  virtual void processBandwidthUpgradeNegotiationFrame(
+      ConstPtr<BandwidthUpgradeNegotiationFrame> bandwidth_upgrade_negotiation,
+      Ptr<ClientProxy<Platform> > to_client_proxy,
+      const std::string& from_endpoint_id,
+      proto::connections::Medium current_medium) = 0;
+};
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#endif  // CORE_INTERNAL_BANDWIDTH_UPGRADE_HANDLER_H_

cpp/core/internal/bandwidth_upgrade_manager.cc

@@ -0,0 +1,47 @@
+#include "core/internal/bandwidth_upgrade_manager.h"
+
+#include "proto/connections_enums.pb.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+template <typename Platform>
+BandwidthUpgradeManager<Platform>::BandwidthUpgradeManager(
+    Ptr<MediumManager<Platform> > medium_manager,
+    Ptr<EndpointChannelManager<Platform> > endpoint_channel_manager,
+    Ptr<EndpointManager<Platform> > endpoint_manager)
+    : endpoint_manager_(endpoint_manager),
+      bandwidth_upgrade_handlers_(),
+      current_bandwidth_upgrade_handler_() {}
+
+template <typename Platform>
+BandwidthUpgradeManager<Platform>::~BandwidthUpgradeManager() {
+  // TODO(ahlee): Make sure we don't repeat the mistake fixed in cl/201883908.
+}
+
+template <typename Platform>
+void BandwidthUpgradeManager<Platform>::initiateBandwidthUpgradeForEndpoint(
+    Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_id,
+    proto::connections::Medium medium) {}
+
+template <typename Platform>
+void BandwidthUpgradeManager<Platform>::processIncomingOfflineFrame(
+    ConstPtr<OfflineFrame> offline_frame, const string& from_endpoint_id,
+    Ptr<ClientProxy<Platform> > to_client_proxy,
+    proto::connections::Medium current_medium) {}
+
+template <typename Platform>
+void BandwidthUpgradeManager<Platform>::processEndpointDisconnection(
+    Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_id,
+    Ptr<CountDownLatch> process_disconnection_barrier) {}
+
+template <typename Platform>
+bool BandwidthUpgradeManager<Platform>::setCurrentBandwidthUpgradeHandler(
+    proto::connections::Medium medium) {
+  return false;
+}
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/bandwidth_upgrade_manager.h

@@ -0,0 +1,66 @@
+#ifndef CORE_INTERNAL_BANDWIDTH_UPGRADE_MANAGER_H_
+#define CORE_INTERNAL_BANDWIDTH_UPGRADE_MANAGER_H_
+
+#include <map>
+
+#include "core/internal/bandwidth_upgrade_handler.h"
+#include "core/internal/client_proxy.h"
+#include "core/internal/endpoint_channel_manager.h"
+#include "core/internal/endpoint_manager.h"
+#include "core/internal/medium_manager.h"
+#include "proto/connections/offline_wire_formats.pb.h"
+#include "platform/port/string.h"
+#include "platform/ptr.h"
+#include "proto/connections_enums.pb.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+// Manages all known {@link BandwidthUpgradeHandler} implementations, delegating
+// operations to the appropriate one as per the parameters passed in.
+template <typename Platform>
+class BandwidthUpgradeManager
+    : public EndpointManager<Platform>::IncomingOfflineFrameProcessor {
+ public:
+  BandwidthUpgradeManager(
+      Ptr<MediumManager<Platform> > medium_manager,
+      Ptr<EndpointChannelManager<Platform> > endpoint_channel_manager,
+      Ptr<EndpointManager<Platform> > endpoint_manager);
+  ~BandwidthUpgradeManager() override;
+
+  // This is the point on the initiator side where the
+  // current_bandwidth_upgrade_handler_ is set.
+  void initiateBandwidthUpgradeForEndpoint(
+      Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_id,
+      proto::connections::Medium medium);
+  // This is the point on the non-initiator side where the
+  // current_bandwidth_upgrade_handler_ is set.
+  // @EndpointManagerReaderThread
+  void processIncomingOfflineFrame(
+      ConstPtr<OfflineFrame> offline_frame, const string& from_endpoint_id,
+      Ptr<ClientProxy<Platform> > to_client_proxy,
+      proto::connections::Medium current_medium) override;
+  // @EndpointManagerReaderThread
+  void processEndpointDisconnection(
+      Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_id,
+      Ptr<CountDownLatch> process_disconnection_barrier) override;
+
+ private:
+  bool setCurrentBandwidthUpgradeHandler(proto::connections::Medium medium);
+
+  Ptr<EndpointManager<Platform> > endpoint_manager_;
+  typedef std::map<proto::connections::Medium,
+                   Ptr<BandwidthUpgradeHandler<Platform> > >
+      BandwidthUpgradeHandlersMap;
+  BandwidthUpgradeHandlersMap bandwidth_upgrade_handlers_;
+  Ptr<BandwidthUpgradeHandler<Platform> > current_bandwidth_upgrade_handler_;
+};
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#include "core/internal/bandwidth_upgrade_manager.cc"
+
+#endif  // CORE_INTERNAL_BANDWIDTH_UPGRADE_MANAGER_H_

cpp/core/internal/base_bandwidth_upgrade_handler.cc

@@ -0,0 +1,145 @@
+#include "core/internal/base_bandwidth_upgrade_handler.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+namespace base_bandwidth_upgrade_handler {
+
+template <typename Platform>
+class RevertRunnable : public Runnable {
+ public:
+  void run() {}
+};
+
+template <typename Platform>
+class InitiateBandwidthUpgradeForEndpointRunnable : public Runnable {
+ public:
+  void run() {}
+};
+
+template <typename Platform>
+class ProcessEndpointDisconnectionRunnable : public Runnable {
+ public:
+  void run() {}
+};
+
+template <typename Platform>
+class ProcessBandwidthUpgradeNegotiationFrameRunnable : public Runnable {
+ public:
+  void run() {}
+};
+
+}  // namespace base_bandwidth_upgrade_handler
+
+template <typename Platform>
+BaseBandwidthUpgradeHandler<Platform>::BaseBandwidthUpgradeHandler(
+    Ptr<EndpointChannelManager<Platform> > endpoint_channel_manager)
+    : endpoint_channel_manager_(endpoint_channel_manager),
+      alarm_executor_(),
+      serial_executor_(),
+      previous_endpoint_channels_(),
+      in_progress_upgrades_(),
+      safe_to_close_write_timestamps_() {}
+
+template <typename Platform>
+BaseBandwidthUpgradeHandler<Platform>::~BaseBandwidthUpgradeHandler() {}
+
+template <typename Platform>
+void BaseBandwidthUpgradeHandler<Platform>::revert() {}
+
+template <typename Platform>
+void BaseBandwidthUpgradeHandler<Platform>::processEndpointDisconnection(
+    Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_id,
+    Ptr<CountDownLatch> process_disconnection_barrier) {}
+
+template <typename Platform>
+void BaseBandwidthUpgradeHandler<Platform>::initiateBandwidthUpgradeForEndpoint(
+    Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_id) {}
+
+template <typename Platform>
+void BaseBandwidthUpgradeHandler<Platform>::
+    processBandwidthUpgradeNegotiationFrame(
+        ConstPtr<BandwidthUpgradeNegotiationFrame>
+            bandwidth_upgrade_negotiation,
+        Ptr<ClientProxy<Platform> > to_client_proxy,
+        const string& from_endpoint_id,
+        proto::connections::Medium current_medium) {}
+
+template <typename Platform>
+Ptr<EndpointChannelManager<Platform> >
+BaseBandwidthUpgradeHandler<Platform>::getEndpointChannelManager() {
+  return endpoint_channel_manager_;
+}
+
+template <typename Platform>
+void BaseBandwidthUpgradeHandler<Platform>::onIncomingConnection(
+    Ptr<IncomingSocketConnection> incoming_socket_connection) {}
+
+template <typename Platform>
+void BaseBandwidthUpgradeHandler<Platform>::runOnBandwidthUpgradeHandlerThread(
+    Ptr<Runnable> runnable) {}
+
+template <typename Platform>
+void BaseBandwidthUpgradeHandler<Platform>::runUpgradeProtocol(
+    Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_id,
+    Ptr<EndpointChannel> new_endpoint_channel) {}
+
+template <typename Platform>
+void BaseBandwidthUpgradeHandler<Platform>::
+    processBandwidthUpgradePathAvailableEvent(
+        const string& endpoint_id, Ptr<ClientProxy<Platform> > client_proxy,
+        ConstPtr<BandwidthUpgradeNegotiationFrame::UpgradePathInfo>
+            upgrade_path_info,
+        proto::connections::Medium current_medium) {}
+
+template <typename Platform>
+Ptr<EndpointChannel> BaseBandwidthUpgradeHandler<Platform>::
+    processBandwidthUpgradePathAvailableEventInternal(
+        const string& endpoint_id, Ptr<ClientProxy<Platform> > client_proxy,
+        ConstPtr<BandwidthUpgradeNegotiationFrame::UpgradePathInfo>
+            upgrade_path_info) {
+  return Ptr<EndpointChannel>();
+}
+
+template <typename Platform>
+void BaseBandwidthUpgradeHandler<Platform>::processLastWriteToPriorChannelEvent(
+    Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_id) {}
+
+template <typename Platform>
+void BaseBandwidthUpgradeHandler<Platform>::processSafeToClosePriorChannelEvent(
+    Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_id) {}
+
+template <typename Platform>
+std::int64_t BaseBandwidthUpgradeHandler<Platform>::calculateCloseDelay(
+    const string& endpoint_id) {
+  return 0;
+}
+
+template <typename Platform>
+std::int64_t
+BaseBandwidthUpgradeHandler<Platform>::getMillisSinceSafeCloseWritten(
+    const string& endpoint_id) {
+  return 0;
+}
+
+// TODO(ahlee): This will differ from the Java code as we don't have to handle
+// analytics in the C++ code.
+template <typename Platform>
+void BaseBandwidthUpgradeHandler<Platform>::
+    attemptToRecordBandwidthUpgradeErrorForUnknownEndpoint(
+        proto::connections::BandwidthUpgradeResult result,
+        proto::connections::BandwidthUpgradeErrorStage error_stage) {}
+
+// TODO(ahlee): This will differ from the Java code (previously threw an
+// UpgradeException).
+template <typename Platform>
+Ptr<BandwidthUpgradeNegotiationFrame::ClientIntroduction>
+BaseBandwidthUpgradeHandler<Platform>::readClientIntroductionFrame(
+    Ptr<EndpointChannel> endpoint_channel) {
+  return Ptr<BandwidthUpgradeNegotiationFrame::ClientIntroduction>();
+}
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/base_bandwidth_upgrade_handler.h

@@ -0,0 +1,189 @@
+#ifndef CORE_INTERNAL_BASE_BANDWIDTH_UPGRADE_HANDLER_H_
+#define CORE_INTERNAL_BASE_BANDWIDTH_UPGRADE_HANDLER_H_
+
+#include <cstdint>
+#include <map>
+
+#include "core/internal/bandwidth_upgrade_handler.h"
+#include "core/internal/client_proxy.h"
+#include "core/internal/endpoint_channel_manager.h"
+#include "proto/connections/offline_wire_formats.pb.h"
+#include "platform/api/count_down_latch.h"
+#include "platform/port/string.h"
+#include "platform/ptr.h"
+#include "proto/connections_enums.pb.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+namespace base_bandwidth_upgrade_handler {
+
+template <typename>
+class RevertRunnable;
+template <typename>
+class InitiateBandwidthUpgradeForEndpointRunnable;
+template <typename>
+class ProcessEndpointDisconnectionRunnable;
+template <typename>
+class ProcessBandwidthUpgradeNegotiationFrameRunnable;
+
+}  // namespace base_bandwidth_upgrade_handler
+
+// Base class for managing the upgrade of endpoints to a different medium for
+// communication (from whatever they were previously using).
+//
+// <p>The sequencing of the upgrade protocol is as follows:
+// <ul>
+//   <li>Initiator sets up an upgrade path, sends
+//       BANDWIDTH_UPGRADE_NEGOTIATION.UPGRADE_PATH_AVAILABLE to Responder over
+//       the prior EndpointChannel.
+//   <li>Responder joins the upgrade path, sends (without encryption)
+//       BANDWIDTH_UPGRADE_NEGOTIATION.CLIENT_INTRODUCTION over the new
+//       EndpointChannel, and sends
+//       BANDWIDTH_UPGRADE_NEGOTIATION.LAST_WRITE_TO_PRIOR_CHANNEL over the
+//       prior EndpointChannel.
+//   <li>Initiator receives BANDWIDTH_UPGRADE_NEGOTIATION.CLIENT_INTRODUCTION
+//       over the newly-established EndpointChannel, and sends
+//       BANDWIDTH_UPGRADE_NEGOTIATION.LAST_WRITE_TO_PRIOR_CHANNEL over the
+//       prior EndpointChannel.
+//   <li>Both wait to receive
+//       BANDWIDTH_UPGRADE_NEGOTIATION.LAST_WRITE_TO_PRIOR_CHANNEL from the
+//       other, and upon doing so, send
+//       BANDWIDTH_UPGRADE_NEGOTIATION.SAFE_TO_CLOSE_PRIOR_CHANNEL to each other
+//   <li>Both then wait to receive
+//       BANDWIDTH_UPGRADE_NEGOTIATION.SAFE_TO_CLOSE_PRIOR_CHANNEL from the
+//       other, and upon doing so, close the prior EndpointChannel.
+// </ul>
+template <typename Platform>
+class BaseBandwidthUpgradeHandler : public BandwidthUpgradeHandler<Platform> {
+ public:
+  BaseBandwidthUpgradeHandler(
+      Ptr<EndpointChannelManager<Platform> > endpoint_channel_manager);
+  ~BaseBandwidthUpgradeHandler();
+
+  void revert();
+  void processEndpointDisconnection(
+      Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_id,
+      Ptr<CountDownLatch> process_disconnection_barrier);
+  // Initiates the bandwidth upgrade and sends an UPGRADE_PATH_AVAILABLE
+  // OfflineFrame.
+  void initiateBandwidthUpgradeForEndpoint(
+      Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_id);
+  void processBandwidthUpgradeNegotiationFrame(
+      ConstPtr<BandwidthUpgradeNegotiationFrame> bandwidth_upgrade_negotiation,
+      Ptr<ClientProxy<Platform> > to_client_proxy,
+      const string& from_endpoint_id,
+      proto::connections::Medium current_medium);
+
+ protected:
+  // Represents the incoming Socket the Initiator has gotten after initializing
+  // its upgraded bandwidth medium.
+  class IncomingSocketConnection {
+   public:
+    virtual ~IncomingSocketConnection() {}
+
+    virtual string socketToString() = 0;
+    virtual void closeSocket() = 0;
+    // TODO(ahlee): Make sure to be careful with the ownership story of this.
+    // Leaning towards releasing to the caller.
+    virtual Ptr<EndpointChannel> getEndpointChannel() = 0;
+  };
+
+  // Called by the Initiator to setup the upgraded medium for this endpoint (if
+  // that hasn't already been done), and returns a serialized UpgradePathInfo
+  // that can be sent to the Responder.
+  // TODO(ahlee): This will differ from the Java code (previously threw an
+  // UpgradeException). Leaving the return type simple for the skeleton - I'll
+  // switch to a pair if the result enum is needed.
+  // @BandwidthUpgradeHandlerThread
+  virtual ConstPtr<ByteArray> initializeUpgradedMediumForEndpoint(
+      const string& endpoint_id) = 0;
+  // Called to revert any state changed by the Initiator to setup the upgraded
+  // medium for an endpoint.
+  // @BandwidthUpgradeHandlerThread
+  virtual void revertImpl() = 0;
+  // Called by the Responder to setup the upgraded medium for this endpoint (if
+  // that hasn't already been done) using the UpgradePathInfo sent by the
+  // Initiator, and returns a new EndpointChannel for the upgraded medium.
+  // @BandwidthUpgradeHandlerThread
+  // TODO(ahlee): This will differ from the Java code (previously threw an
+  // exception).
+  virtual Ptr<EndpointChannel> createUpgradedEndpointChannel(
+      const string& endpoint_id,
+      ConstPtr<BandwidthUpgradeNegotiationFrame::UpgradePathInfo>
+          upgrade_path_info) = 0;
+  // Returns the upgrade medium of the BandwidthUpgradeHandler.
+  // @BandwidthUpgradeHandlerThread
+  virtual proto::connections::Medium getUpgradeMedium() = 0;
+
+  Ptr<EndpointChannelManager<Platform> > getEndpointChannelManager();
+  // Common functionality to take an incoming connection and go through the
+  // upgrade process.
+  // @BandwidthUpgradeHandlerThread
+  void onIncomingConnection(
+      Ptr<IncomingSocketConnection> incoming_socket_connection);
+  void runOnBandwidthUpgradeHandlerThread(Ptr<Runnable> runnable);
+
+ private:
+  template <typename>
+  friend class base_bandwidth_upgrade_handler::RevertRunnable;
+  template <typename>
+  friend class base_bandwidth_upgrade_handler::
+      InitiateBandwidthUpgradeForEndpointRunnable;
+  template <typename>
+  friend class base_bandwidth_upgrade_handler::
+      ProcessEndpointDisconnectionRunnable;
+  template <typename>
+  friend class base_bandwidth_upgrade_handler::
+      ProcessBandwidthUpgradeNegotiationFrameRunnable;
+
+  void runUpgradeProtocol(Ptr<ClientProxy<Platform> > client_proxy,
+                          const string& endpoint_id,
+                          Ptr<EndpointChannel> new_endpoint_channel);
+  void processBandwidthUpgradePathAvailableEvent(
+      const string& endpoint_id, Ptr<ClientProxy<Platform> > client_proxy,
+      ConstPtr<BandwidthUpgradeNegotiationFrame::UpgradePathInfo>
+          upgrade_path_info,
+      proto::connections::Medium current_medium);
+  Ptr<EndpointChannel> processBandwidthUpgradePathAvailableEventInternal(
+      const string& endpoint_id, Ptr<ClientProxy<Platform> > client_proxy,
+      ConstPtr<BandwidthUpgradeNegotiationFrame::UpgradePathInfo>
+          upgrade_path_info);
+  void processLastWriteToPriorChannelEvent(
+      Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_id);
+  void processSafeToClosePriorChannelEvent(
+      Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_id);
+  std::int64_t calculateCloseDelay(const string& endpoint_id);
+  std::int64_t getMillisSinceSafeCloseWritten(const string& endpoint_id);
+  void attemptToRecordBandwidthUpgradeErrorForUnknownEndpoint(
+      proto::connections::BandwidthUpgradeResult result,
+      proto::connections::BandwidthUpgradeErrorStage error_stage);
+  Ptr<BandwidthUpgradeNegotiationFrame::ClientIntroduction>
+  readClientIntroductionFrame(Ptr<EndpointChannel> endpoint_channel);
+
+  Ptr<EndpointChannelManager<Platform> > endpoint_channel_manager_;
+  ScopedPtr<Ptr<typename Platform::ScheduledExecutorType> > alarm_executor_;
+  ScopedPtr<Ptr<typename Platform::SingleThreadExecutorType> > serial_executor_;
+  // Stores each upgraded endpoint's previous EndpointChannel (that was
+  // displaced in favor of a new EndpointChannel) temporarily, until it can
+  // safely be shut down for good in processLastWriteToPriorChannelEvent().
+  typedef std::map<string, Ptr<EndpointChannel> > PreviousEndpointChannelsMap;
+  PreviousEndpointChannelsMap previous_endpoint_channels_;
+  // Maps endpointId -> ClientProxy for which
+  // initiateBandwidthUpgradeForEndpoint() has been called but which have not
+  // yet completed the upgrade via onIncomingConnection().
+  typedef std::map<string, Ptr<ClientProxy<Platform> > > InProgressUpgradesMap;
+  InProgressUpgradesMap in_progress_upgrades_;
+  // Maps endpointId -> timestamp of when the SAFE_TO_CLOSE message was written.
+  typedef std::map<string, std::int64_t> SafeToCloseWriteTimestampsMap;
+  SafeToCloseWriteTimestampsMap safe_to_close_write_timestamps_;
+};
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#include "core/internal/base_bandwidth_upgrade_handler.cc"
+
+#endif  // CORE_INTERNAL_BASE_BANDWIDTH_UPGRADE_HANDLER_H_

cpp/core/internal/base_endpoint_channel.cc

@@ -0,0 +1,352 @@
+#include "core/internal/base_endpoint_channel.h"
+
+#include <cassert>
+
+#include "platform/synchronized.h"
+#include "proto/connections_enums.pb.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+namespace {
+
+std::int32_t bytesToInt(ConstPtr<ByteArray> bytes) {
+  const char* int_bytes = bytes->getData();
+
+  std::int32_t result = 0;
+  result |= (static_cast<std::int32_t>(int_bytes[0]) & 0x0FF) << 24;
+  result |= (static_cast<std::int32_t>(int_bytes[1]) & 0x0FF) << 16;
+  result |= (static_cast<std::int32_t>(int_bytes[2]) & 0x0FF) << 8;
+  result |= (static_cast<std::int32_t>(int_bytes[3]) & 0x0FF);
+
+  return result;
+}
+
+ConstPtr<ByteArray> intToBytes(std::int32_t value) {
+  char int_bytes[sizeof(std::int32_t)];
+  int_bytes[0] = static_cast<char>((value >> 24) & 0x0FF);
+  int_bytes[1] = static_cast<char>((value >> 16) & 0x0FF);
+  int_bytes[2] = static_cast<char>((value >> 8) & 0x0FF);
+  int_bytes[3] = static_cast<char>((value)&0x0FF);
+
+  return MakeConstPtr(new ByteArray(int_bytes, sizeof(int_bytes)));
+}
+
+ExceptionOr<ConstPtr<ByteArray> > readExactly(Ptr<InputStream> reader,
+                                              std::int64_t size) {
+  string buffer;
+  std::int64_t remaining_size = size;
+
+  while (remaining_size > 0) {
+    ExceptionOr<ConstPtr<ByteArray> > read_bytes = reader->read(remaining_size);
+    if (!read_bytes.ok()) {
+      if (Exception::IO == read_bytes.exception()) {
+        return ExceptionOr<ConstPtr<ByteArray> >(read_bytes.exception());
+      }
+    }
+    // Avoid leaks.
+    ScopedPtr<ConstPtr<ByteArray> > scoped_read_bytes(read_bytes.result());
+
+    // In Java, EOFException is a sub-variant of IOException.
+    if (scoped_read_bytes->size() == 0) {
+      return ExceptionOr<ConstPtr<ByteArray> >(Exception::IO);
+    }
+
+    buffer.append(scoped_read_bytes->getData(), scoped_read_bytes->size());
+    remaining_size -= scoped_read_bytes->size();
+  }
+
+  return ExceptionOr<ConstPtr<ByteArray> >(
+      MakeConstPtr(new ByteArray(buffer.data(), buffer.size())));
+}
+
+ExceptionOr<std::int32_t> readInt(Ptr<InputStream> reader) {
+  ExceptionOr<ConstPtr<ByteArray> > read_bytes =
+      readExactly(reader, sizeof(std::int32_t));
+  if (!read_bytes.ok()) {
+    if (Exception::IO == read_bytes.exception()) {
+      return ExceptionOr<std::int32_t>(read_bytes.exception());
+    }
+  }
+  // Avoid leaks.
+  ScopedPtr<ConstPtr<ByteArray> > scoped_read_bytes(read_bytes.result());
+
+  return ExceptionOr<std::int32_t>(bytesToInt(scoped_read_bytes.get()));
+}
+
+Exception::Value writeInt(Ptr<OutputStream> writer, std::int32_t value) {
+  return writer->write(intToBytes(value));
+}
+
+}  // namespace
+
+template <typename Platform>
+BaseEndpointChannel<Platform>::BaseEndpointChannel(const string& channel_name,
+                                                   Ptr<InputStream> reader,
+                                                   Ptr<OutputStream> writer)
+    : last_read_timestamp_(-1),
+      channel_name_(channel_name),
+      system_clock_(Platform::createSystemClock()),
+      reader_lock_(Platform::createLock()),
+      reader_(reader),
+      writer_lock_(Platform::createLock()),
+      writer_(writer),
+      encryption_context_(Platform::createAtomicReference(
+          Ptr<securegcm::D2DConnectionContextV1>())),
+      is_paused_lock_(Platform::createLock()),
+      is_paused_condition_variable_(
+          Platform::createConditionVariable(is_paused_lock_.get())),
+      is_paused_(Platform::createAtomicBoolean(false)) {}
+
+template <typename Platform>
+BaseEndpointChannel<Platform>::~BaseEndpointChannel() {
+  // WARNING: Make sure to never access reader_ and writer_ from here.
+  //
+  // They're owned by the specialized *Socket classes that are in turn
+  // owned by the *EndpointChannel children of this class, so by this point,
+  // they've been destroyed and now point to invalid memory.
+  //
+  // "Ugh!" is right -- this won't be a problem once we have a standardized
+  // Socket interface we can hold up in this class (instead of holding
+  // specialized implementations of that hypothetical interface in each child
+  // of this class).
+}
+
+template <typename Platform>
+ExceptionOr<ConstPtr<ByteArray> > BaseEndpointChannel<Platform>::read() {
+  Synchronized s(reader_lock_.get());
+
+  ExceptionOr<std::int32_t> read_int = readInt(reader_);
+  if (!read_int.ok()) {
+    if (Exception::IO == read_int.exception()) {
+      return ExceptionOr<ConstPtr<ByteArray> >(read_int.exception());
+    }
+  }
+
+  if (read_int.result() < 0) {
+    return ExceptionOr<ConstPtr<ByteArray>>(Exception::IO);
+  } else if (read_int.result() > kMaxAllowedReadBytes) {
+    return ExceptionOr<ConstPtr<ByteArray>>(Exception::IO);
+  }
+
+  ExceptionOr<ConstPtr<ByteArray> > read_bytes =
+      readExactly(reader_, read_int.result());
+  if (!read_bytes.ok()) {
+    if (Exception::IO == read_bytes.exception()) {
+      return ExceptionOr<ConstPtr<ByteArray> >(read_bytes.exception());
+    }
+  }
+
+  // This should be ScopedPtr usually, but because of the unique requirement of
+  // reassigning this variable when encryption is enabled, we can't make use of
+  // the power of ScopedPtr, and instead have to do manual memory management.
+  ConstPtr<ByteArray> read_bytes_result = read_bytes.result();
+
+  // If encryption is enabled, decode the message.
+  if (isEncryptionEnabled()) {
+    std::unique_ptr<string> decoded_bytes =
+        encryption_context_->get()->DecodeMessageFromPeer(
+            string(read_bytes_result->getData(), read_bytes_result->size()));
+    // Now that we are done using read_bytes_result, we should unconditionally
+    // destroy it, because we either reassign to the value of decoded_bytes, or
+    // short-circuit out of here on error.
+    read_bytes_result.destroy();
+    if (decoded_bytes == nullptr) {
+      return ExceptionOr<ConstPtr<ByteArray> >(
+          Exception::INVALID_PROTOCOL_BUFFER);
+    }
+    read_bytes_result = MakeConstPtr(
+        new ByteArray(decoded_bytes->data(), decoded_bytes->size()));
+  }
+
+  last_read_timestamp_ = system_clock_->elapsedRealtime();
+  return ExceptionOr<ConstPtr<ByteArray> >(read_bytes_result);
+}
+
+template <typename Platform>
+Exception::Value BaseEndpointChannel<Platform>::write(
+    ConstPtr<ByteArray> data) {
+  Synchronized s(writer_lock_.get());
+
+  // Avoid leaks.
+  ScopedPtr<ConstPtr<ByteArray> > scoped_data(data);
+
+  if (isPaused()) {
+    blockUntilUnpaused();
+  }
+
+  ConstPtr<ByteArray> data_to_write;
+  // If encryption is enabled, encode the message.
+  if (isEncryptionEnabled()) {
+    std::unique_ptr<string> message =
+        encryption_context_->get()->EncodeMessageToPeer(
+            string(scoped_data->getData(), scoped_data->size()));
+    assert(message != nullptr);
+    data_to_write =
+        MakeConstPtr(new ByteArray(message->data(), message->size()));
+  } else {
+    // Else, just make data_to_write point to the passed-in data.
+    data_to_write = scoped_data.release();
+  }
+  // Avoid leaks.
+  ScopedPtr<ConstPtr<ByteArray> > scoped_data_to_write(data_to_write);
+
+  Exception::Value write_exception = writeInt(
+      writer_, static_cast<std::int32_t>(scoped_data_to_write->size()));
+  if (Exception::NONE != write_exception) {
+    if (Exception::IO == write_exception) {
+      return write_exception;
+    }
+  }
+
+  write_exception = writer_->write(scoped_data_to_write.release());
+  if (Exception::NONE != write_exception) {
+    if (Exception::IO == write_exception) {
+      return write_exception;
+    }
+  }
+
+  Exception::Value flush_exception = writer_->flush();
+  if (Exception::NONE != flush_exception) {
+    if (Exception::IO == flush_exception) {
+      return flush_exception;
+    }
+  }
+
+  return Exception::NONE;
+}
+
+template <typename Platform>
+void BaseEndpointChannel<Platform>::close() {
+  //                      WARNING WARNING WARNING
+  //
+  // This block deviates from the corresponding Java code.
+  //
+  // In the corresponding Java code, close() calls
+  // close(proto::connections::DisconnectionReason) while here we do the
+  // opposite. This is because proto::connections::DisconnectionReason can be
+  // null in Java but not in C++.
+  Exception::Value reader_close_exception = reader_->close();
+  if (Exception::NONE != reader_close_exception) {
+    if (Exception::IO == reader_close_exception) {
+      // Add logging.
+    }
+  }
+  Exception::Value writer_close_exception = writer_->close();
+  if (Exception::NONE != writer_close_exception) {
+    if (Exception::IO == writer_close_exception) {
+      // Add logging.
+    }
+  }
+
+  closeImpl();
+
+  // TODO(tracyzhou): Add logging.
+}
+
+template <typename Platform>
+void BaseEndpointChannel<Platform>::close(
+    proto::connections::DisconnectionReason reason) {
+  //                      WARNING WARNING WARNING
+  //
+  // This block deviates from the corresponding Java code.
+  // Look at the corresponding block in the close() method above for details on
+  // the deviation.
+  close();
+
+  // TODO(tracyzhou): Add logging.
+}
+
+template <typename Platform>
+string BaseEndpointChannel<Platform>::getType() {
+  string subtype = isEncryptionEnabled() ? "ENCRYPTED_" : "";
+  switch (getMedium()) {
+    case proto::connections::Medium::BLUETOOTH:
+      return subtype + "BLUETOOTH";
+    case proto::connections::Medium::BLE:
+      return subtype + "BLE";
+    case proto::connections::Medium::MDNS:
+      return subtype + "MDNS";
+    case proto::connections::Medium::WIFI_HOTSPOT:
+      return subtype + "WIFI_HOTSPOT";
+    case proto::connections::Medium::WIFI_LAN:
+      return subtype + "WIFI_LAN";
+    default:
+      return "UNKNOWN";
+  }
+}
+
+template <typename Platform>
+string BaseEndpointChannel<Platform>::getName() {
+  return channel_name_;
+}
+
+template <typename Platform>
+void BaseEndpointChannel<Platform>::enableEncryption(
+    Ptr<securegcm::D2DConnectionContextV1> encryption_context) {
+  assert(!encryption_context.isNull());
+  encryption_context_->set(encryption_context);
+}
+
+template <typename Platform>
+bool BaseEndpointChannel<Platform>::isPaused() {
+  return is_paused_->get();
+}
+
+template <typename Platform>
+void BaseEndpointChannel<Platform>::pause() {
+  is_paused_->set(true);
+}
+
+template <typename Platform>
+void BaseEndpointChannel<Platform>::resume() {
+  is_paused_->set(false);
+  unblockPausedWriter();
+}
+
+template <typename Platform>
+std::int64_t BaseEndpointChannel<Platform>::getLastReadTimestamp() {
+  return last_read_timestamp_;
+}
+
+template <typename Platform>
+bool BaseEndpointChannel<Platform>::isEncryptionEnabled() {
+  return !encryption_context_->get().isNull();
+}
+
+template <typename Platform>
+void BaseEndpointChannel<Platform>::unblockPausedWriter() {
+  Synchronized s(is_paused_lock_.get());
+
+  // Notify to tell the thread calling wait() to check again.
+  // NOTE: There is only ever one thread blocked by wait() at a time, because
+  // EndpointChannel.write(Ptr<ByteArray>) is synchronized on writer. That means
+  // the first thread to call write(byte[]) will be blocked via
+  // blockUntilUnpaused() and all future threads will be blocked via
+  // synchronized(writer_lock_).
+  is_paused_condition_variable_->notify();
+}
+
+template <typename Platform>
+void BaseEndpointChannel<Platform>::blockUntilUnpaused() {
+  Synchronized s(is_paused_lock_.get());
+
+  // For more on how this works, see
+  // https://docs.oracle.com/javase/tutorial/essential/concurrency/guardmeth.html
+  while (is_paused_->get()) {
+    Exception::Value wait_succeeded = is_paused_condition_variable_->wait();
+    if (Exception::NONE != wait_succeeded) {
+      if (Exception::INTERRUPTED == wait_succeeded) {
+        // If we were interrupted, pass the interrupt up the stack and then exit
+        // immediately.
+        // Thread.currentThread().interrupt();
+        return;
+      }
+    }
+  }
+}
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/base_endpoint_channel.h

@@ -0,0 +1,112 @@
+#ifndef CORE_INTERNAL_BASE_ENDPOINT_CHANNEL_H_
+#define CORE_INTERNAL_BASE_ENDPOINT_CHANNEL_H_
+
+#include <cstdint>
+
+#include "core/internal/endpoint_channel.h"
+#include "platform/api/atomic_boolean.h"
+#include "platform/api/atomic_reference.h"
+#include "platform/api/condition_variable.h"
+#include "platform/api/input_stream.h"
+#include "platform/api/lock.h"
+#include "platform/api/output_stream.h"
+#include "platform/api/system_clock.h"
+#include "platform/byte_array.h"
+#include "platform/port/string.h"
+#include "platform/ptr.h"
+#include "proto/connections_enums.pb.h"
+#include "securegcm/d2d_connection_context_v1.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+template <typename Platform>
+class BaseEndpointChannel : public EndpointChannel {
+ public:
+  BaseEndpointChannel(const string& channel_name, Ptr<InputStream> reader,
+                      Ptr<OutputStream> writer);
+  ~BaseEndpointChannel() override;
+
+  ExceptionOr<ConstPtr<ByteArray> > read() override;
+
+  Exception::Value write(ConstPtr<ByteArray> data) override;
+
+  // Closes this EndpointChannel, without tracking the closure in analytics.
+  void close() override;
+
+  // Closes this EndpointChannel and records the closure with the given reason.
+  void close(proto::connections::DisconnectionReason reason) override;
+
+  // Returns a one-word type descriptor for the concrete EndpointChannel
+  // implementation that can be used in log messages; eg: BLUETOOTH, BLE,
+  // WIFI.
+  string getType() override;
+
+  // Returns the name of the EndpointChannel.
+  string getName() override;
+
+  // Enables encryption on the EndpointChannel.
+  void enableEncryption(
+      Ptr<securegcm::D2DConnectionContextV1> encryption_context) override;
+
+  // True if the EndpointChannel is currently pausing all writes.
+  bool isPaused() override;
+
+  // Pauses all writes on this EndpointChannel until resume() is called.
+  void pause() override;
+
+  // Resumes any writes on this EndpointChannel that were suspended when pause()
+  // was called.
+  void resume() override;
+
+  // Returns the timestamp (in elapsedRealtime) of the last read from this
+  // endpoint, or -1 if no reads have occurred.
+  std::int64_t getLastReadTimestamp() override;
+
+ protected:
+  virtual void closeImpl() = 0;
+
+ private:
+  // Used to sanity check that our frame sizes are reasonable.
+  static const std::int32_t kMaxAllowedReadBytes = 1048576;  // 1MB
+
+  bool isEncryptionEnabled();
+  void unblockPausedWriter();
+  void blockUntilUnpaused();
+
+  volatile std::int64_t last_read_timestamp_;
+
+  const string channel_name_;
+
+  ScopedPtr<Ptr<SystemClock> > system_clock_;
+
+  // The reader and writer are synchronized independently since we can't have
+  // writes waiting on reads that might potentially block forever.
+  ScopedPtr<Ptr<Lock> > reader_lock_;
+  // Not owned by this class, see the note in the destructor for a special
+  // restriction on usage.
+  Ptr<InputStream> reader_;
+
+  ScopedPtr<Ptr<Lock> > writer_lock_;
+  // Not owned by this class, see the note in the destructor for a special
+  // restriction on usage.
+  Ptr<OutputStream> writer_;
+
+  // An encryptor/decryptor. May be null.
+  ScopedPtr<Ptr<AtomicReference<Ptr<securegcm::D2DConnectionContextV1> > > >
+      encryption_context_;
+
+  ScopedPtr<Ptr<Lock> > is_paused_lock_;
+  ScopedPtr<Ptr<ConditionVariable> > is_paused_condition_variable_;
+  // If true, writes should block until this has been set to false.
+  ScopedPtr<Ptr<AtomicBoolean> > is_paused_;
+};
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#include "core/internal/base_endpoint_channel.cc"
+
+#endif  // CORE_INTERNAL_BASE_ENDPOINT_CHANNEL_H_

cpp/core/internal/base_pcp_handler.h

@@ -0,0 +1,507 @@
+#ifndef CORE_INTERNAL_BASE_PCP_HANDLER_H_
+#define CORE_INTERNAL_BASE_PCP_HANDLER_H_
+
+#include <cstdint>
+#include <map>
+#include <vector>
+
+#include "core/internal/bandwidth_upgrade_manager.h"
+#include "core/internal/client_proxy.h"
+#include "core/internal/encryption_runner.h"
+#include "core/internal/endpoint_channel_manager.h"
+#include "core/internal/endpoint_manager.h"
+#include "core/internal/pcp.h"
+#include "core/internal/pcp_handler.h"
+#include "core/listeners.h"
+#include "core/options.h"
+#include "core/status.h"
+#include "proto/connections/offline_wire_formats.pb.h"
+#include "platform/api/atomic_reference.h"
+#include "platform/api/count_down_latch.h"
+#include "platform/api/settable_future.h"
+#include "platform/api/system_clock.h"
+#include "platform/cancelable_alarm.h"
+#include "platform/port/string.h"
+#include "platform/prng.h"
+#include "platform/ptr.h"
+#include "proto/connections_enums.pb.h"
+#include "securegcm/ukey2_handshake.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+namespace base_pcp_handler {
+
+template <typename>
+class StartAdvertisingCallable;
+template <typename>
+class StopAdvertisingRunnable;
+template <typename>
+class StartDiscoveryCallable;
+template <typename>
+class StopDiscoveryRunnable;
+template <typename>
+class RequestConnectionRunnable;
+template <typename>
+class AcceptConnectionCallable;
+template <typename>
+class RejectConnectionCallable;
+template <typename>
+class ProcessEndpointDisconnectionRunnable;
+template <typename>
+class OnConnectionResponseRunnable;
+template <typename>
+class OnEncryptionSuccessRunnable;
+template <typename>
+class OnEncryptionFailureRunnable;
+
+}  // namespace base_pcp_handler
+
+// A base implementation of the PCPHandler interface that takes care of all
+// bookkeeping and handshake protocols that are common across all PCPHandler
+// implementations -- thus, every concrete PCPHandler implementation must extend
+// this class, so that they can focus exclusively on the medium-specific
+// operations.
+template <typename Platform>
+class BasePCPHandler
+    : public PCPHandler<Platform>,
+      public EndpointManager<Platform>::IncomingOfflineFrameProcessor {
+ public:
+  // TODO(tracyzhou): Add SecureRandom.
+  BasePCPHandler(
+      Ptr<EndpointManager<Platform> > endpoint_manager,
+      Ptr<EndpointChannelManager<Platform> > endpoint_channel_manager,
+      Ptr<BandwidthUpgradeManager<Platform> > bandwidth_upgrade_manager);
+  ~BasePCPHandler() override;
+
+  // We have been asked by the client to start advertising. Once we successfully
+  // start advertising, we'll change the ClientProxy's state.
+  Status::Value startAdvertising(
+      Ptr<ClientProxy<Platform> > client_proxy, const string& service_id,
+      const string& local_endpoint_name,
+      const AdvertisingOptions& advertising_options,
+      Ptr<ConnectionLifecycleListener> connection_lifecycle_listener) override;
+  void stopAdvertising(Ptr<ClientProxy<Platform> > client_proxy) override;
+
+  Status::Value startDiscovery(
+      Ptr<ClientProxy<Platform> > client_proxy, const string& service_id,
+      const DiscoveryOptions& discovery_options,
+      Ptr<DiscoveryListener> discovery_listener) override;
+  void stopDiscovery(Ptr<ClientProxy<Platform> > client_proxy) override;
+
+  Status::Value requestConnection(
+      Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_name,
+      const string& endpoint_id,
+      Ptr<ConnectionLifecycleListener> connection_lifecycle_listener) override;
+  Status::Value acceptConnection(
+      Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_id,
+      Ptr<PayloadListener> payload_listener) override;
+  Status::Value rejectConnection(Ptr<ClientProxy<Platform> > client_proxy,
+                                 const string& endpoint_id) override;
+
+  proto::connections::Medium getBandwidthUpgradeMedium() override;
+
+  // @EndpointManagerReaderThread
+  void processIncomingOfflineFrame(
+      ConstPtr<OfflineFrame> offline_frame, const string& from_endpoint_id,
+      Ptr<ClientProxy<Platform> > to_client_proxy,
+      proto::connections::Medium current_medium) override;
+
+  // Called when an endpoint disconnects while we're waiting for both sides to
+  // approve/reject the connection.
+  // @EndpointManagerThread
+  void processEndpointDisconnection(
+      Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_id,
+      Ptr<CountDownLatch> process_disconnection_barrier) override;
+
+  // Conforms to EncryptionRunner::ResultListener::onEncryptionSuccess().
+  // @EncryptionRunnerThread
+  void onEncryptionSuccessImpl(const string& endpoint_id,
+                               Ptr<securegcm::UKey2Handshake> ukey2_handshake,
+                               const string& authentication_token,
+                               ConstPtr<ByteArray> raw_authentication_token);
+
+  // EncryptionRunner::ResultListener::onEncryptionFailure().
+  // @EncryptionRunnerThread
+  void onEncryptionFailureImpl(const string& endpoint_id,
+                               Ptr<EndpointChannel> channel);
+
+ protected:
+  // The result of a call to startAdvertisingImpl() or startDiscoveryImpl().
+  class StartOperationResult {
+   public:
+    static Ptr<StartOperationResult> error(Status::Value status) {
+      return MakePtr(new StartOperationResult(status));
+    }
+
+    static Ptr<StartOperationResult> success(
+        const std::vector<proto::connections::Medium>& mediums) {
+      // Note: check here and not in the constructor, since for errors we have
+      // null mediums.
+      return MakePtr(new StartOperationResult(mediums));
+    }
+
+   private:
+    template <typename>
+    friend class base_pcp_handler::StartAdvertisingCallable;
+    template <typename>
+    friend class base_pcp_handler::StartDiscoveryCallable;
+
+    explicit StartOperationResult(Status::Value status)
+        : status_(status), mediums_() {}
+    explicit StartOperationResult(
+        const std::vector<proto::connections::Medium>& mediums)
+        : status_(Status::SUCCESS), mediums_(mediums) {}
+
+    // The status to be returned to the client.
+    Status::Value status_;
+    // If success, the mediums on which we are now advertising/discovering, for
+    // analytics.
+    std::vector<proto::connections::Medium> mediums_;
+  };
+
+  // Represents an endpoint that we've discovered. Typically, the implementation
+  // will know how to connect to this endpoint if asked. (eg. It holds on to a
+  // BluetoothDevice)
+  class DiscoveredEndpoint {
+   public:
+    virtual ~DiscoveredEndpoint() {}
+
+    virtual string getEndpointId() = 0;
+    virtual string getEndpointName() = 0;
+    virtual string getServiceId() = 0;
+    virtual proto::connections::Medium getMedium() = 0;
+  };
+
+  struct ConnectImplResult {
+    proto::connections::Medium medium;
+    Status::Value status;
+    Ptr<EndpointChannel> endpoint_channel;
+
+    explicit ConnectImplResult(Ptr<EndpointChannel> endpoint_channel)
+        : medium(proto::connections::Medium::UNKNOWN_MEDIUM),
+          status(Status::SUCCESS),
+          endpoint_channel(endpoint_channel) {}
+    ConnectImplResult(proto::connections::Medium medium, Status::Value status)
+        : medium(medium), status(status), endpoint_channel() {}
+  };
+
+  void runOnPCPHandlerThread(Ptr<Runnable> runnable);
+
+  Ptr<AdvertisingOptions> getAdvertisingOptions();
+
+  // @PCPHandlerThread
+  void onEndpointFound(Ptr<ClientProxy<Platform> > client_proxy,
+                       Ptr<DiscoveredEndpoint> endpoint);
+
+  // @PCPHandlerThread
+  void onEndpointLost(Ptr<ClientProxy<Platform> > client_proxy,
+                      Ptr<DiscoveredEndpoint> endpoint);
+
+  Exception::Value onIncomingConnection(
+      Ptr<ClientProxy<Platform> > client_proxy,
+      const string& remote_device_name, Ptr<EndpointChannel> endpoint_channel,
+      proto::connections::Medium medium);  // throws Exception::IO
+
+  virtual bool hasOutgoingConnections(Ptr<ClientProxy<Platform> > client_proxy);
+  virtual bool hasIncomingConnections(Ptr<ClientProxy<Platform> > client_proxy);
+
+  virtual bool canSendOutgoingConnection(
+      Ptr<ClientProxy<Platform> > client_proxy);
+  virtual bool canReceiveIncomingConnection(
+      Ptr<ClientProxy<Platform> > client_proxy);
+
+  // @PCPHandlerThread
+  virtual Ptr<StartOperationResult> startAdvertisingImpl(
+      Ptr<ClientProxy<Platform> > client_proxy, const string& service_id,
+      const string& local_endpoint_id, const string& local_endpoint_name,
+      const AdvertisingOptions& options) = 0;
+  // @PCPHandlerThread
+  virtual Status::Value stopAdvertisingImpl(
+      Ptr<ClientProxy<Platform> > client_proxy) = 0;
+
+  // @PCPHandlerThread
+  virtual Ptr<StartOperationResult> startDiscoveryImpl(
+      Ptr<ClientProxy<Platform> > client_proxy, const string& service_id,
+      const DiscoveryOptions& options) = 0;
+  // @PCPHandlerThread
+  virtual Status::Value stopDiscoveryImpl(
+      Ptr<ClientProxy<Platform> > client_proxy) = 0;
+
+  // @PCPHandlerThread
+  virtual ConnectImplResult connectImpl(
+      Ptr<ClientProxy<Platform> > client_proxy,
+      Ptr<DiscoveredEndpoint> endpoint) = 0;
+
+  virtual std::vector<proto::connections::Medium>
+  getConnectionMediumsByPriority() = 0;
+  virtual proto::connections::Medium getDefaultUpgradeMedium() = 0;
+
+  Ptr<EndpointManager<Platform> > endpoint_manager_;
+  Ptr<EndpointChannelManager<Platform> > endpoint_channel_manager_;
+  Ptr<BandwidthUpgradeManager<Platform> > bandwidth_upgrade_manager_;
+
+ private:
+  template <typename>
+  friend class base_pcp_handler::StartAdvertisingCallable;
+  template <typename>
+  friend class base_pcp_handler::StopAdvertisingRunnable;
+  template <typename>
+  friend class base_pcp_handler::StartDiscoveryCallable;
+  template <typename>
+  friend class base_pcp_handler::StopDiscoveryRunnable;
+  template <typename>
+  friend class base_pcp_handler::RequestConnectionRunnable;
+  template <typename>
+  friend class base_pcp_handler::AcceptConnectionCallable;
+  template <typename>
+  friend class base_pcp_handler::RejectConnectionCallable;
+  template <typename>
+  friend class base_pcp_handler::OnConnectionResponseRunnable;
+  template <typename>
+  friend class base_pcp_handler::ProcessEndpointDisconnectionRunnable;
+  template <typename>
+  friend class base_pcp_handler::OnEncryptionSuccessRunnable;
+  template <typename>
+  friend class base_pcp_handler::OnEncryptionFailureRunnable;
+
+  class ResultListenerFacade
+      : public EncryptionRunner<Platform>::ResultListener {
+   public:
+    explicit ResultListenerFacade(Ptr<BasePCPHandler<Platform> > impl)
+        : impl_(impl) {}
+
+    void onEncryptionSuccess(
+        const string& endpoint_id,
+        Ptr<securegcm::UKey2Handshake> ukey2_handshake,
+        const string& authentication_token,
+        ConstPtr<ByteArray> raw_authentication_token) override {
+      impl_->onEncryptionSuccessImpl(endpoint_id, ukey2_handshake,
+                                     authentication_token,
+                                     raw_authentication_token);
+    }
+
+    void onEncryptionFailure(const string& endpoint_id,
+                             Ptr<EndpointChannel> channel) override {
+      impl_->onEncryptionFailureImpl(endpoint_id, channel);
+    }
+
+   private:
+    Ptr<BasePCPHandler<Platform> > impl_;
+  };
+
+  class PendingConnectionInfo {
+   public:
+    static Ptr<PendingConnectionInfo> newIncomingPendingConnectionInfo(
+        Ptr<ClientProxy<Platform> > client_proxy,
+        const string& remote_endpoint_name,
+        Ptr<EndpointChannel> endpoint_channel, std::int32_t nonce,
+        std::int64_t start_time_millis,
+        Ptr<ConnectionLifecycleListener> connection_lifecycle_listener,
+        const std::vector<proto::connections::Medium>& supported_mediums);
+
+    static Ptr<PendingConnectionInfo> newOutgoingPendingConnectionInfo(
+        Ptr<ClientProxy<Platform> > client_proxy,
+        const string& remote_endpoint_name,
+        Ptr<EndpointChannel> endpoint_channel, std::int32_t nonce,
+        std::int64_t start_time_millis,
+        Ptr<ConnectionLifecycleListener> connection_lifecycle_listener,
+        Ptr<SettableFuture<Status::Value> > request_connection_result);
+
+    ~PendingConnectionInfo();
+
+    void setUKey2Handshake(Ptr<securegcm::UKey2Handshake> ukey2_handshake);
+
+    void localEndpointAcceptedConnection(const string& endpoint_id,
+                                         Ptr<PayloadListener> payload_listener);
+
+    void localEndpointRejectedConnection(const string& endpoint_id);
+
+   private:
+    template <typename>
+    friend class BasePCPHandler;
+    template <typename>
+    friend class base_pcp_handler::RequestConnectionRunnable;
+    template <typename>
+    friend class base_pcp_handler::AcceptConnectionCallable;
+    template <typename>
+    friend class base_pcp_handler::RejectConnectionCallable;
+    template <typename>
+    friend class base_pcp_handler::OnEncryptionSuccessRunnable;
+    template <typename>
+    friend class base_pcp_handler::OnEncryptionFailureRunnable;
+
+    PendingConnectionInfo(
+        Ptr<ClientProxy<Platform> > client_proxy,
+        const string& remote_endpoint_name,
+        Ptr<EndpointChannel> endpoint_channel, std::int32_t nonce,
+        bool is_incoming, std::int64_t start_time_millis,
+        Ptr<ConnectionLifecycleListener> connection_lifecycle_listener,
+        Ptr<SettableFuture<Status::Value> > request_connection_result,
+        const std::vector<proto::connections::Medium>& supported_mediums);
+
+    Ptr<ClientProxy<Platform> > client_proxy_;
+    const string remote_endpoint_name_;
+    // Can be released prior to destructor.
+    ScopedPtr<Ptr<EndpointChannel> > endpoint_channel_;
+    const std::int32_t nonce_;
+    const bool is_incoming_;
+    const std::int64_t start_time_millis_;
+    // Can be released prior to destructor.
+    ScopedPtr<Ptr<ConnectionLifecycleListener> > connection_lifecycle_listener_;
+
+    // Only set for outgoing connections. Can be released prior to destructor.
+    // TODO(b/77783039): Consider creating a one-time-use-only wrapper class
+    // around the Ptr<SettableFuture> that's passed in (that also implements the
+    // SettableFuture interface) so we can avoid the easy-to-forget calls to
+    // request_connection_result_.clear() peppered through multiple places in
+    // the code.
+    Ptr<SettableFuture<Status::Value> > request_connection_result_;
+
+    // Only (possibly) set for incoming connections.
+    const std::vector<proto::connections::Medium> supported_mediums_;
+
+    // If set, this is owned.
+    Ptr<securegcm::UKey2Handshake> ukey2_handshake_;
+  };
+
+  static Exception::Value writeConnectionRequestFrame(
+      Ptr<EndpointChannel> endpoint_channel, const string& local_endpoint_id,
+      const string& local_endpoint_name, std::int32_t nonce,
+      const std::vector<proto::connections::Medium>& supported_mediums);
+
+  static const std::int64_t kConnectionRequestReadTimeoutMillis;
+  static const std::int64_t kRejectedConnectionCloseDelayMillis;
+
+  template <typename T>
+  Ptr<Future<T> > runOnPCPHandlerThread(Ptr<Callable<T> > callable);
+
+  // The interface deviates from the Java code to convey a better ownership
+  // story. Ownership of 'connection_response_offline_frame' is transferred to
+  // the callee by calling this method.
+  void onConnectionResponse(
+      Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_id,
+      ConstPtr<OfflineFrame> connection_response_offline_frame);
+
+  // Returns true if the new endpoint is preferred over the old endpoint.
+  bool isPreferred(Ptr<DiscoveredEndpoint> new_endpoint,
+                   Ptr<DiscoveredEndpoint> old_endpoint);
+
+  bool shouldEnforceTopologyConstraints();
+  bool autoUpgradeBandwidth();
+
+  // Returns true if the incoming connection should be killed. This only happens
+  // when an incoming connection arrives while we have an outgoing connection to
+  // the same endpoint and we need to stop one connection.
+  bool breakTie(Ptr<ClientProxy<Platform> > client_proxy,
+                const string& endpoint_id, std::int32_t incoming_nonce,
+                Ptr<EndpointChannel> endpoint_channel);
+  // We're not sure how far our outgoing connection has gotten. We may (or may
+  // not) have called ClientProxy.onConnectionInitiated. Therefore, we'll call
+  // both preInit and preResult failures.
+  void processTieBreakLoss(Ptr<ClientProxy<Platform> > client_proxy,
+                           const string& endpoint_id,
+                           Ptr<PendingConnectionInfo> connection_info);
+
+  // Called when an incoming connection has been accepted by both sides.
+  //
+  // @param client_proxy The client
+  // @param endpoint_id The id of the remote device
+  // @param supported_mediums The mediums supported by the remote device. Empty
+  //        for outgoing connections and older devices that don't report their
+  //        supported mediums.
+  void initiateBandwidthUpgrade(
+      Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_id,
+      const std::vector<proto::connections::Medium>& supported_mediums);
+
+  // Returns the optimal medium supported by both devices.
+  proto::connections::Medium chooseBestUpgradeMedium(
+      const std::vector<proto::connections::Medium>& their_supported_mediums);
+
+  // This method should assume ownership of endpoint_id.
+  void processPreConnectionInitiationFailure(
+      Ptr<ClientProxy<Platform> > client_proxy,
+      proto::connections::Medium medium, const string& endpoint_id,
+      Ptr<EndpointChannel> endpoint_channel, bool is_incoming,
+      std::int64_t start_time_millis, Status::Value status,
+      Ptr<SettableFuture<Status::Value> > request_connection_result);
+  void processPreConnectionResultFailure(
+      Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_id);
+  Ptr<DiscoveredEndpoint> getDiscoveredEndpoint(const string& endpoint_id);
+
+  // Called when either side accepts/rejects the connection, but only takes
+  // effect after both have accepted or one side has rejected.
+  //
+  // NOTE: We also take in a 'can_close_immediately' variable. This is because
+  // any writes in transit are dropped when we close. To avoid having a reject
+  // write being dropped (which causes the other side to report
+  // onResult(DISCONNECTED) instead of onResult(REJECTED)), we delay our close.
+  // If the other side behaves properly, we shouldn't even see the delay
+  // (because they will also close the connection).
+  void evaluateConnectionResult(Ptr<ClientProxy<Platform> > client_proxy,
+                                const string& endpoint_id,
+                                bool can_close_immediately);
+
+  ExceptionOr<ConstPtr<OfflineFrame> > readConnectionRequestFrame(
+      Ptr<EndpointChannel> endpoint_channel);
+
+  void waitForLatch(const string& method_name, Ptr<CountDownLatch> latch);
+  Status::Value waitForResult(const string& method_name, std::int64_t client_id,
+                              Ptr<Future<Status::Value> > result_future);
+
+  ScopedPtr<Ptr<AtomicReference<proto::connections::Medium> > >
+      bandwidth_upgrade_medium_;
+  ScopedPtr<Ptr<typename Platform::ScheduledExecutorType> > alarm_executor_;
+  ScopedPtr<Ptr<typename Platform::SingleThreadExecutorType> > serial_executor_;
+  ScopedPtr<Ptr<SystemClock> > system_clock_;
+  Prng prng_;
+
+  // A map of endpoint id -> PendingConnectionInfo. Entries in this map imply
+  // that there is an active connection to the endpoint and we're waiting for
+  // both sides to accept before allowing payloads through. Once the fate of the
+  // connection is decided (either accepted or rejected), it should be removed
+  // from this map.
+  typedef std::map<string, Ptr<PendingConnectionInfo> > PendingConnectionsMap;
+  PendingConnectionsMap pending_connections_;
+  // A map of endpoint id -> DiscoveredEndpoint.
+  typedef std::map<string, Ptr<DiscoveredEndpoint> > DiscoveredEndpointsMap;
+  DiscoveredEndpointsMap discovered_endpoints_;
+  // A map of endpoint id -> alarm. These alarms delay closing the
+  // EndpointChannel to give the other side enough time to read the rejection
+  // message. It's expected that the other side will close the connection after
+  // reading the message (in which case, this alarm should be cancelled as it's
+  // no longer needed), but this alarm is the fallback in case that doesn't
+  // happen.
+  typedef std::map<string, Ptr<CancelableAlarm<Platform> > >
+      PendingRejectedConnectionCloseAlarmsMap;
+  PendingRejectedConnectionCloseAlarmsMap
+      pending_rejected_connection_close_alarms_;
+
+  // The active ClientProxy's advertising constraints. Null if the client hasn't
+  // started advertising. Note: this is not cleared when the client stops
+  // advertising because it might still be useful downstream of advertising (eg:
+  // establishing connections, performing bandwidth upgrades, etc.)
+  Ptr<AdvertisingOptions> advertising_options_;
+  // The active ClientProxy's connection lifecycle listener. Non-null while
+  // advertising.
+  Ptr<ConnectionLifecycleListener> advertising_connection_lifecycle_listener_;
+
+  // The active ClientProxy's discovery constraints. Null if the client
+  // hasn't started discovering. Note: this is not cleared when the client
+  // stops discovering because it might still be useful downstream of
+  // discovery (eg: connection speed, etc.)
+  Ptr<DiscoveryOptions> discovery_options_;
+
+  // This should have been a ScopedPtr, but we are making this a Ptr to manually
+  // control the order of destruction.
+  Ptr<EncryptionRunner<Platform> > encryption_runner_;
+};
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#include "core/internal/base_pcp_handler.cc"
+
+#endif  // CORE_INTERNAL_BASE_PCP_HANDLER_H_

cpp/core/internal/ble_advertisement.cc

@@ -0,0 +1,277 @@
+#include "core/internal/ble_advertisement.h"
+
+#include <algorithm>
+
+#include "absl/strings/ascii.h"
+#include "absl/strings/escaping.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+const std::uint32_t BLEAdvertisement::kServiceIdHashLength = 3;
+
+const std::uint32_t BLEAdvertisement::kVersionAndPcpLength = 1;
+// Should be defined as EndpointManager<Platform>::kEndpointIdLength, but that
+// involves making BLEAdvertisement templatized on Platform just for
+// that one little thing, so forego it (at least for now).
+const std::uint32_t BLEAdvertisement::kEndpointIdLength = 4;
+const std::uint32_t BLEAdvertisement::kEndpointNameSizeLength = 1;
+const std::uint32_t BLEAdvertisement::kBluetoothMacAddressLength = 6;
+const std::uint32_t BLEAdvertisement::kMinAdvertisementLength =
+    kVersionAndPcpLength + kServiceIdHashLength + kEndpointIdLength +
+    kEndpointNameSizeLength + kBluetoothMacAddressLength;
+const std::uint32_t BLEAdvertisement::kMaxEndpointNameLength = 131;
+
+const std::uint16_t BLEAdvertisement::kVersionBitmask = 0x0E0;
+const std::uint16_t BLEAdvertisement::kPCPBitmask = 0x01F;
+const std::uint16_t BLEAdvertisement::kEndpointNameLengthBitmask = 0x0FF;
+
+Ptr<BLEAdvertisement> BLEAdvertisement::fromBytes(
+    ConstPtr<ByteArray> ble_advertisement_bytes) {
+  if (ble_advertisement_bytes.isNull()) {
+    // TODO(ahlee): Logger.atDebug().log("Cannot deserialize BleAdvertisement:
+    // null bytes passed in.");
+    return Ptr<BLEAdvertisement>();
+  }
+
+  if (ble_advertisement_bytes->size() < kMinAdvertisementLength) {
+    // TODO(ahlee): Logger.atDebug().log("Cannot deserialize BleAdvertisement:
+    // expecting min %d raw bytes, got %d", kMinAdvertisementLength,
+    // ble_advertisement_bytes->size());
+    return Ptr<BLEAdvertisement>();
+  }
+
+  // Start reading the bytes.
+  const char* ble_advertisement_bytes_read_ptr =
+      ble_advertisement_bytes->getData();
+
+  // The first 3 bits are supposed to be the version.
+  Version::Value version = static_cast<Version::Value>(
+      (*ble_advertisement_bytes_read_ptr & kVersionBitmask) >> 5);
+  if (version != Version::V1) {
+    // TODO(ahlee): logger.atDebug().log("Cannot deserialize BleAdvertisement:
+    // unsupported Version %d", version);
+    return Ptr<BLEAdvertisement>();
+  }
+
+  PCP::Value pcp =
+      static_cast<PCP::Value>(*ble_advertisement_bytes_read_ptr & kPCPBitmask);
+  ble_advertisement_bytes_read_ptr++;
+  if (pcp != PCP::P2P_CLUSTER && pcp != PCP::P2P_STAR &&
+      pcp != PCP::P2P_POINT_TO_POINT) {
+    // TODO(ahlee): logger.atDebug().log("Cannot deserialize BleAdvertisement:
+    // unsupported V1 PCP %d", pcp);
+    return Ptr<BLEAdvertisement>();
+  }
+
+  // Avoid leaks.
+  ScopedPtr<ConstPtr<ByteArray> > scoped_service_id_hash(MakeConstPtr(
+      new ByteArray(ble_advertisement_bytes_read_ptr, kServiceIdHashLength)));
+  ble_advertisement_bytes_read_ptr += kServiceIdHashLength;
+
+  std::string endpoint_id(ble_advertisement_bytes_read_ptr, kEndpointIdLength);
+  ble_advertisement_bytes_read_ptr += kEndpointIdLength;
+
+  std::uint32_t expected_endpoint_name_length = static_cast<std::uint32_t>(
+      *ble_advertisement_bytes_read_ptr & kEndpointNameLengthBitmask);
+  ble_advertisement_bytes_read_ptr++;
+
+  // Check that the stated endpoint_name_length is the same as what we
+  // received (based off of the length of ble_advertisement_bytes).
+  std::uint32_t actual_endpoint_name_length =
+      computeEndpointNameLength(ble_advertisement_bytes);
+  if (actual_endpoint_name_length < expected_endpoint_name_length) {
+    // TODO(ahlee): Logger.atDebug().log("Cannot deserialize BleAdvertisement:
+    // expected endpointName to be %d bytes, got %d bytes",
+    // expected_endpoint_name_length, actual_endpoint_name_length);
+    return Ptr<BLEAdvertisement>();
+  }
+
+  std::string endpoint_name(ble_advertisement_bytes_read_ptr,
+                            expected_endpoint_name_length);
+  ble_advertisement_bytes_read_ptr += expected_endpoint_name_length;
+
+  // Avoid leaks.
+  ScopedPtr<ConstPtr<ByteArray> > scoped_bluetooth_mac_address_bytes(
+      MakeConstPtr(new ByteArray(ble_advertisement_bytes_read_ptr,
+                                 kBluetoothMacAddressLength)));
+  std::string bluetooth_mac_address;
+  // If the Bluetooth MAC Address bytes are unset or invalid, leave the string
+  // empty. Otherwise, convert it to the proper colon delimited format.
+  if (!isBluetoothMacAddressUnset(scoped_bluetooth_mac_address_bytes.get())) {
+    bluetooth_mac_address = hexBytesToColonDelimitedString(
+        scoped_bluetooth_mac_address_bytes.get());
+  }
+
+  return MakePtr(
+      new BLEAdvertisement(version, pcp, scoped_service_id_hash.release(),
+                           endpoint_id, endpoint_name, bluetooth_mac_address));
+}
+
+ConstPtr<ByteArray> BLEAdvertisement::toBytes(
+    Version::Value version, PCP::Value pcp, ConstPtr<ByteArray> service_id_hash,
+    const std::string& endpoint_id, const std::string& endpoint_name,
+    const std::string& bluetooth_mac_address) {
+  if (version != Version::V1) {
+    // TODO(ahlee): logger.atDebug().log("Cannot serialize BleAdvertisement:
+    // unsupported Version %d", version);
+    return ConstPtr<ByteArray>();
+  }
+
+  if (pcp != PCP::P2P_CLUSTER && pcp != PCP::P2P_STAR &&
+      pcp != PCP::P2P_POINT_TO_POINT) {
+    // TODO(ahlee): logger.atDebug().log("Cannot serialize BleAdvertisement:
+    // unsupported V1 PCP %d", pcp);
+    return ConstPtr<ByteArray>();
+  }
+
+  if (endpoint_name.size() > kMaxEndpointNameLength) {
+    // TODO(ahlee): logger.atDebug().log("Cannot serialize BleAdvertisement:
+    // expected an endpointName of at most %d bytes but got %d",
+    // kMaxEndpoingNameLength, endpoint_name.size());
+    return ConstPtr<ByteArray>();
+  }
+
+  std::uint32_t ble_advertisement_length =
+      computeAdvertisementLength(endpoint_name);
+  Ptr<ByteArray> ble_advertisement_bytes{
+      new ByteArray{ble_advertisement_length}};
+  char* ble_advertisement_bytes_write_ptr = ble_advertisement_bytes->getData();
+
+  // The first 3 bits are the Version.
+  char version_and_pcp_byte =
+      static_cast<char>((version << 5) & kVersionBitmask);
+  // The next 5 bits are the PCP.
+  version_and_pcp_byte |= static_cast<char>(pcp & kPCPBitmask);
+  *ble_advertisement_bytes_write_ptr = version_and_pcp_byte;
+  ble_advertisement_bytes_write_ptr++;
+
+  // The next 24 bits are the service id hash.
+  memcpy(ble_advertisement_bytes_write_ptr, service_id_hash->getData(),
+         kServiceIdHashLength);
+  ble_advertisement_bytes_write_ptr += kServiceIdHashLength;
+
+  // The next 32 bits are the endpoint id.
+  memcpy(ble_advertisement_bytes_write_ptr, endpoint_id.data(),
+         kEndpointIdLength);
+  ble_advertisement_bytes_write_ptr += kEndpointIdLength;
+
+  // The next 8 bits are the length of the endpoint name.
+  *ble_advertisement_bytes_write_ptr =
+      static_cast<char>(endpoint_name.size() & kEndpointNameLengthBitmask);
+  ble_advertisement_bytes_write_ptr++;
+
+  // The next x bits are the endpoint name. (Max length is 131 bytes).
+  memcpy(ble_advertisement_bytes_write_ptr, endpoint_name.data(),
+         endpoint_name.size());
+  ble_advertisement_bytes_write_ptr += endpoint_name.size();
+
+  // The next 48 bits are the bluetooth mac address. If bluetooth_mac_address is
+  // invalid or empty, we get back a null byte array.
+  // Avoid leaks.
+  ScopedPtr<ConstPtr<ByteArray> > scoped_bluetooth_mac_address_bytes(
+      bluetoothMacAddressToHexBytes(bluetooth_mac_address));
+  if (!scoped_bluetooth_mac_address_bytes.isNull()) {
+    memcpy(ble_advertisement_bytes_write_ptr,
+           scoped_bluetooth_mac_address_bytes->getData(),
+           kBluetoothMacAddressLength);
+  }
+  ble_advertisement_bytes_write_ptr += kBluetoothMacAddressLength;
+
+  return ConstifyPtr(ble_advertisement_bytes);
+}
+
+std::string BLEAdvertisement::hexBytesToColonDelimitedString(
+    ConstPtr<ByteArray> hex_bytes) {
+  // Convert the hex bytes to a string.
+  std::string colon_delimited_string(absl::BytesToHexString(
+      std::string(hex_bytes->getData(), hex_bytes->size())));
+  absl::AsciiStrToUpper(&colon_delimited_string);
+
+  // Insert the colons.
+  for (int i = colon_delimited_string.length() - 2; i > 0; i -= 2) {
+    colon_delimited_string.insert(i, ":");
+  }
+  return colon_delimited_string;
+}
+
+// TODO(ahlee): Rename to bluetoothMacAddressHexStringToBytes
+ConstPtr<ByteArray> BLEAdvertisement::bluetoothMacAddressToHexBytes(
+    const std::string& bluetooth_mac_address) {
+  std::string bt_mac_address(bluetooth_mac_address);
+
+  // Remove the colon delimiters.
+  bt_mac_address.erase(
+      std::remove(bt_mac_address.begin(), bt_mac_address.end(), ':'),
+      bt_mac_address.end());
+
+  // If the bluetooth mac address is invalid (wrong size), return a null byte
+  // array.
+  if (bt_mac_address.length() != kBluetoothMacAddressLength * 2) {
+    return ConstPtr<ByteArray>();
+  }
+
+  // Convert to bytes.
+  std::string bt_mac_address_bytes(absl::HexStringToBytes(bt_mac_address));
+  return MakeConstPtr(
+      new ByteArray(bt_mac_address_bytes.data(), bt_mac_address_bytes.size()));
+}
+
+bool BLEAdvertisement::isBluetoothMacAddressUnset(
+    ConstPtr<ByteArray> bluetooth_mac_address_bytes) {
+  for (int i = 0; i < bluetooth_mac_address_bytes->size(); i++) {
+    if (bluetooth_mac_address_bytes->getData()[i] != 0) {
+      return false;
+    }
+  }
+  return true;
+}
+
+std::uint32_t BLEAdvertisement::computeEndpointNameLength(
+    ConstPtr<ByteArray> ble_advertisement_bytes) {
+  return ble_advertisement_bytes->size() - kMinAdvertisementLength;
+}
+
+std::uint32_t BLEAdvertisement::computeAdvertisementLength(
+    const std::string& endpoint_name) {
+  return kMinAdvertisementLength + endpoint_name.size();
+}
+
+BLEAdvertisement::BLEAdvertisement(Version::Value version, PCP::Value pcp,
+                                   ConstPtr<ByteArray> service_id_hash,
+                                   const std::string& endpoint_id,
+                                   const std::string& endpoint_name,
+                                   const std::string& bluetooth_mac_address)
+    : version_(version),
+      pcp_(pcp),
+      service_id_hash_(service_id_hash),
+      endpoint_id_(endpoint_id),
+      endpoint_name_(endpoint_name),
+      bluetooth_mac_address_(bluetooth_mac_address) {}
+
+BLEAdvertisement::~BLEAdvertisement() {
+  // Nothing to do.
+}
+
+BLEAdvertisement::Version::Value BLEAdvertisement::getVersion() const {
+  return version_;
+}
+
+PCP::Value BLEAdvertisement::getPCP() const { return pcp_; }
+
+std::string BLEAdvertisement::getEndpointId() const { return endpoint_id_; }
+
+ConstPtr<ByteArray> BLEAdvertisement::getServiceIdHash() const {
+  return service_id_hash_.get();
+}
+
+std::string BLEAdvertisement::getEndpointName() const { return endpoint_name_; }
+
+std::string BLEAdvertisement::getBluetoothMacAddress() const {
+  return bluetooth_mac_address_;
+}
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/ble_advertisement.h

@@ -0,0 +1,95 @@
+#ifndef CORE_INTERNAL_BLE_ADVERTISEMENT_H_
+#define CORE_INTERNAL_BLE_ADVERTISEMENT_H_
+
+#include <cstdint>
+
+#include "core/internal/pcp.h"
+#include "platform/byte_array.h"
+#include "platform/port/string.h"
+#include "platform/ptr.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+// Represents the format of the Connections BLE Advertisement used in
+// Advertising + Discovery.
+//
+// <p>[VERSION][PCP][SERVICE_ID_HASH][ENDPOINT_ID][ENDPOINT_NAME_SIZE]
+//    [ENDPOINT_NAME][BLUETOOTH_MAC]
+//
+// <p>See go/connections-ble-advertisement for more information.
+class BLEAdvertisement {
+ public:
+  // Versions of the BLEAdvertisement.
+  struct Version {
+    enum Value {
+      V1 = 1,
+      // Version is only allocated 3 bits in the BLEAdvertisement, so this
+      // can never go beyond V7.
+    };
+  };
+
+  static Ptr<BLEAdvertisement> fromBytes(
+      ConstPtr<ByteArray> ble_advertisement_bytes);
+
+  static ConstPtr<ByteArray> toBytes(Version::Value version, PCP::Value pcp,
+                                     ConstPtr<ByteArray> service_id_hash,
+                                     const std::string& endpoint_id,
+                                     const std::string& endpoint_name,
+                                     const std::string& bluetooth_mac_address);
+
+  static const std::uint32_t kServiceIdHashLength;
+  static const std::uint32_t kMinAdvertisementLength;
+  // TODO(ahlee): Make sure names match for both Java and C++ implementations.
+  static const std::uint32_t kMaxEndpointNameLength;
+
+  ~BLEAdvertisement();
+
+  Version::Value getVersion() const;
+  PCP::Value getPCP() const;
+  ConstPtr<ByteArray> getServiceIdHash() const;
+  std::string getEndpointId() const;
+  std::string getEndpointName() const;
+  std::string getBluetoothMacAddress() const;
+
+ private:
+  static std::string hexBytesToColonDelimitedString(
+      ConstPtr<ByteArray> hex_bytes);
+  // TODO(ahlee): Rename to bluetoothMacAddressHexStringToBytes
+  static ConstPtr<ByteArray> bluetoothMacAddressToHexBytes(
+      const std::string& bluetooth_mac_address);
+  static std::uint32_t computeEndpointNameLength(
+      ConstPtr<ByteArray> ble_advertisement_bytes);
+  static std::uint32_t computeAdvertisementLength(
+      const std::string& endpoint_name);
+  static bool isBluetoothMacAddressUnset(
+      ConstPtr<ByteArray> bluetooth_mac_address_bytes);
+
+  static const std::uint32_t kVersionAndPcpLength;
+  static const std::uint32_t kEndpointIdLength;
+  static const std::uint32_t kEndpointNameSizeLength;
+  static const std::uint32_t kBluetoothMacAddressLength;
+  static const std::uint16_t kVersionBitmask;
+  static const std::uint16_t kPCPBitmask;
+  static const std::uint16_t kEndpointNameLengthBitmask;
+
+  BLEAdvertisement(Version::Value version, PCP::Value pcp,
+                   ConstPtr<ByteArray> service_id_hash,
+                   const std::string& endpoint_id,
+                   const std::string& endpoint_name,
+                   const std::string& bluetooth_mac_address);
+
+  const Version::Value version_;
+  const PCP::Value pcp_;
+  ScopedPtr<ConstPtr<ByteArray> > service_id_hash_;
+  const std::string endpoint_id_;
+  const std::string endpoint_name_;
+  const std::string bluetooth_mac_address_;
+};
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#endif  // CORE_INTERNAL_BLE_ADVERTISEMENT_H_

cpp/core/internal/ble_advertisement_test.cc

@@ -0,0 +1,343 @@
+#include "core/internal/ble_advertisement.h"
+
+#include <cstring>
+
+#include "platform/port/string.h"
+#include "gtest/gtest.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+namespace {
+
+const BLEAdvertisement::Version::Value version = BLEAdvertisement::Version::V1;
+const PCP::Value pcp = PCP::P2P_CLUSTER;
+const char endpoint_id[] = "AB12";
+const char service_id_hash_bytes[] = {0x0A, 0x0B, 0x0C};
+const char endpoint_name[] =
+    "How much wood can a woodchuck chuck if a wood chuck would chuck wood?";
+const char bluetooth_mac_address[] = "00:00:E6:88:64:13";
+
+TEST(BLEAdvertisementTest, SerializationDeserializationWorks) {
+  ScopedPtr<Ptr<ByteArray> > scoped_service_id_hash(new ByteArray(
+      service_id_hash_bytes, sizeof(service_id_hash_bytes) / sizeof(char)));
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_ble_advertisement_bytes(
+      BLEAdvertisement::toBytes(
+          version, pcp, ConstifyPtr(scoped_service_id_hash.get()), endpoint_id,
+          endpoint_name, bluetooth_mac_address));
+  ScopedPtr<Ptr<BLEAdvertisement> > scoped_ble_advertisement(
+      BLEAdvertisement::fromBytes(scoped_ble_advertisement_bytes.get()));
+
+  ASSERT_EQ(pcp, scoped_ble_advertisement->getPCP());
+  ASSERT_EQ(version, scoped_ble_advertisement->getVersion());
+  ASSERT_EQ(endpoint_id, scoped_ble_advertisement->getEndpointId());
+  ASSERT_EQ(sizeof(service_id_hash_bytes) / sizeof(char),
+            scoped_ble_advertisement->getServiceIdHash()->size());
+  ASSERT_EQ(0, memcmp(service_id_hash_bytes,
+                      scoped_ble_advertisement->getServiceIdHash()->getData(),
+                      scoped_ble_advertisement->getServiceIdHash()->size()));
+  ASSERT_EQ(endpoint_name, scoped_ble_advertisement->getEndpointName());
+  ASSERT_EQ(bluetooth_mac_address,
+            scoped_ble_advertisement->getBluetoothMacAddress());
+}
+
+TEST(BLEAdvertisementTest, SerializationDeserializationWorksWithGoodPCP) {
+  PCP::Value good_pcp = PCP::P2P_STAR;
+
+  ScopedPtr<Ptr<ByteArray> > scoped_service_id_hash(new ByteArray(
+      service_id_hash_bytes, sizeof(service_id_hash_bytes) / sizeof(char)));
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_ble_advertisement_bytes(
+      BLEAdvertisement::toBytes(
+          version, good_pcp, ConstifyPtr(scoped_service_id_hash.get()),
+          endpoint_id, endpoint_name, bluetooth_mac_address));
+  ScopedPtr<Ptr<BLEAdvertisement> > scoped_ble_advertisement(
+      BLEAdvertisement::fromBytes(scoped_ble_advertisement_bytes.get()));
+
+  ASSERT_EQ(good_pcp, scoped_ble_advertisement->getPCP());
+  ASSERT_EQ(version, scoped_ble_advertisement->getVersion());
+  ASSERT_EQ(endpoint_id, scoped_ble_advertisement->getEndpointId());
+  ASSERT_EQ(sizeof(service_id_hash_bytes) / sizeof(char),
+            scoped_ble_advertisement->getServiceIdHash()->size());
+  ASSERT_EQ(0, memcmp(service_id_hash_bytes,
+                      scoped_ble_advertisement->getServiceIdHash()->getData(),
+                      scoped_ble_advertisement->getServiceIdHash()->size()));
+  ASSERT_EQ(endpoint_name, scoped_ble_advertisement->getEndpointName());
+  ASSERT_EQ(bluetooth_mac_address,
+            scoped_ble_advertisement->getBluetoothMacAddress());
+}
+
+TEST(BLEAdvertisementTest,
+     SerializationDeserializationWorksWithEmptyEndpointName) {
+  std::string empty_endpoint_name;
+
+  ScopedPtr<Ptr<ByteArray> > scoped_service_id_hash(new ByteArray(
+      service_id_hash_bytes, sizeof(service_id_hash_bytes) / sizeof(char)));
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_ble_advertisement_bytes(
+      BLEAdvertisement::toBytes(
+          version, pcp, ConstifyPtr(scoped_service_id_hash.get()), endpoint_id,
+          empty_endpoint_name, bluetooth_mac_address));
+  ScopedPtr<Ptr<BLEAdvertisement> > scoped_ble_advertisement(
+      BLEAdvertisement::fromBytes(scoped_ble_advertisement_bytes.get()));
+
+  ASSERT_EQ(pcp, scoped_ble_advertisement->getPCP());
+  ASSERT_EQ(version, scoped_ble_advertisement->getVersion());
+  ASSERT_EQ(endpoint_id, scoped_ble_advertisement->getEndpointId());
+  ASSERT_EQ(sizeof(service_id_hash_bytes) / sizeof(char),
+            scoped_ble_advertisement->getServiceIdHash()->size());
+  ASSERT_EQ(0, memcmp(service_id_hash_bytes,
+                      scoped_ble_advertisement->getServiceIdHash()->getData(),
+                      scoped_ble_advertisement->getServiceIdHash()->size()));
+  ASSERT_EQ(empty_endpoint_name, scoped_ble_advertisement->getEndpointName());
+  ASSERT_EQ(bluetooth_mac_address,
+            scoped_ble_advertisement->getBluetoothMacAddress());
+}
+
+TEST(BLEAdvertisementTest,
+     SerializationDeSerializationFailsWithLongEndpointName) {
+  std::string long_endpoint_name(BLEAdvertisement::kMaxEndpointNameLength + 1,
+                                 'x');
+
+  ScopedPtr<Ptr<ByteArray> > scoped_service_id_hash(new ByteArray(
+      service_id_hash_bytes, sizeof(service_id_hash_bytes) / sizeof(char)));
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_ble_advertisement_bytes(
+      BLEAdvertisement::toBytes(
+          version, pcp, ConstifyPtr(scoped_service_id_hash.get()), endpoint_id,
+          long_endpoint_name, bluetooth_mac_address));
+
+  ASSERT_TRUE(scoped_ble_advertisement_bytes.get().isNull());
+}
+
+TEST(BLEAdvertisementTest,
+     SerializationDeserializationWorksWithEmojiEndpointName) {
+  std::string emoji_endpoint_name("\u0001F450 \u0001F450");
+
+  ScopedPtr<Ptr<ByteArray> > scoped_service_id_hash(new ByteArray(
+      service_id_hash_bytes, sizeof(service_id_hash_bytes) / sizeof(char)));
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_ble_advertisement_bytes(
+      BLEAdvertisement::toBytes(
+          version, pcp, ConstifyPtr(scoped_service_id_hash.get()), endpoint_id,
+          emoji_endpoint_name, bluetooth_mac_address));
+  ScopedPtr<Ptr<BLEAdvertisement> > scoped_ble_advertisement(
+      BLEAdvertisement::fromBytes(scoped_ble_advertisement_bytes.get()));
+
+  ASSERT_EQ(pcp, scoped_ble_advertisement->getPCP());
+  ASSERT_EQ(version, scoped_ble_advertisement->getVersion());
+  ASSERT_EQ(endpoint_id, scoped_ble_advertisement->getEndpointId());
+  ASSERT_EQ(sizeof(service_id_hash_bytes) / sizeof(char),
+            scoped_ble_advertisement->getServiceIdHash()->size());
+  ASSERT_EQ(0, memcmp(service_id_hash_bytes,
+                      scoped_ble_advertisement->getServiceIdHash()->getData(),
+                      scoped_ble_advertisement->getServiceIdHash()->size()));
+  ASSERT_EQ(emoji_endpoint_name, scoped_ble_advertisement->getEndpointName());
+  ASSERT_EQ(bluetooth_mac_address,
+            scoped_ble_advertisement->getBluetoothMacAddress());
+}
+
+TEST(BLEAdvertisementTest, SerializationFailsWithBadVersion) {
+  BLEAdvertisement::Version::Value bad_version =
+      static_cast<BLEAdvertisement::Version::Value>(666);
+
+  ScopedPtr<Ptr<ByteArray> > scoped_service_id_hash(new ByteArray(
+      service_id_hash_bytes, sizeof(service_id_hash_bytes) / sizeof(char)));
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_ble_advertisement_bytes(
+      BLEAdvertisement::toBytes(
+          bad_version, pcp, ConstifyPtr(scoped_service_id_hash.get()),
+          endpoint_id, endpoint_name, bluetooth_mac_address));
+
+  ASSERT_TRUE(scoped_ble_advertisement_bytes.get().isNull());
+}
+
+TEST(BLEAdvertisementTest, SerializationFailsWithBadPCP) {
+  PCP::Value bad_pcp = static_cast<PCP::Value>(666);
+
+  ScopedPtr<Ptr<ByteArray> > scoped_service_id_hash(new ByteArray(
+      service_id_hash_bytes, sizeof(service_id_hash_bytes) / sizeof(char)));
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_ble_advertisement_bytes(
+      BLEAdvertisement::toBytes(
+          version, bad_pcp, ConstifyPtr(scoped_service_id_hash.get()),
+          endpoint_id, endpoint_name, bluetooth_mac_address));
+
+  ASSERT_TRUE(scoped_ble_advertisement_bytes.get().isNull());
+}
+
+TEST(BLEAdvertisementTest, SerializationSucceedsWithEmptyBluetoothMacAddress) {
+  std::string empty_bluetooth_mac_address = "";
+
+  ScopedPtr<Ptr<ByteArray> > scoped_service_id_hash(new ByteArray(
+      service_id_hash_bytes, sizeof(service_id_hash_bytes) / sizeof(char)));
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_ble_advertisement_bytes(
+      BLEAdvertisement::toBytes(
+          version, pcp, ConstifyPtr(scoped_service_id_hash.get()), endpoint_id,
+          endpoint_name, empty_bluetooth_mac_address));
+  ScopedPtr<Ptr<BLEAdvertisement> > scoped_ble_advertisement(
+      BLEAdvertisement::fromBytes(scoped_ble_advertisement_bytes.get()));
+
+  ASSERT_EQ(pcp, scoped_ble_advertisement->getPCP());
+  ASSERT_EQ(version, scoped_ble_advertisement->getVersion());
+  ASSERT_EQ(endpoint_id, scoped_ble_advertisement->getEndpointId());
+  ASSERT_EQ(sizeof(service_id_hash_bytes) / sizeof(char),
+            scoped_ble_advertisement->getServiceIdHash()->size());
+  ASSERT_EQ(0, memcmp(service_id_hash_bytes,
+                      scoped_ble_advertisement->getServiceIdHash()->getData(),
+                      scoped_ble_advertisement->getServiceIdHash()->size()));
+  ASSERT_EQ(endpoint_name, scoped_ble_advertisement->getEndpointName());
+  ASSERT_EQ(empty_bluetooth_mac_address,
+            scoped_ble_advertisement->getBluetoothMacAddress());
+}
+
+TEST(BLEAdvertisementTest,
+     SerializationSucceedsWithInvalidBluetoothMacAddress) {
+  std::string bad_bluetooth_mac_address = "022:00";
+
+  ScopedPtr<Ptr<ByteArray> > scoped_service_id_hash(new ByteArray(
+      service_id_hash_bytes, sizeof(service_id_hash_bytes) / sizeof(char)));
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_ble_advertisement_bytes(
+      BLEAdvertisement::toBytes(
+          version, pcp, ConstifyPtr(scoped_service_id_hash.get()), endpoint_id,
+          endpoint_name, bad_bluetooth_mac_address));
+  ScopedPtr<Ptr<BLEAdvertisement> > scoped_ble_advertisement(
+      BLEAdvertisement::fromBytes(scoped_ble_advertisement_bytes.get()));
+
+  ASSERT_EQ(pcp, scoped_ble_advertisement->getPCP());
+  ASSERT_EQ(version, scoped_ble_advertisement->getVersion());
+  ASSERT_EQ(endpoint_id, scoped_ble_advertisement->getEndpointId());
+  ASSERT_EQ(sizeof(service_id_hash_bytes) / sizeof(char),
+            scoped_ble_advertisement->getServiceIdHash()->size());
+  ASSERT_EQ(0, memcmp(service_id_hash_bytes,
+                      scoped_ble_advertisement->getServiceIdHash()->getData(),
+                      scoped_ble_advertisement->getServiceIdHash()->size()));
+  ASSERT_EQ(endpoint_name, scoped_ble_advertisement->getEndpointName());
+  ASSERT_TRUE(scoped_ble_advertisement->getBluetoothMacAddress().empty());
+}
+
+TEST(BLEAdvertisementTest, DeserializationFailsWithNullBytes) {
+  ScopedPtr<Ptr<BLEAdvertisement> > scoped_ble_advertisement(
+      BLEAdvertisement::fromBytes(ConstPtr<ByteArray>()));
+
+  ASSERT_TRUE(scoped_ble_advertisement.get().isNull());
+}
+
+TEST(BLEAdvertisementTest, DeserializationFailsWithShortLength) {
+  // Serialize good data into a good BLE Advertisement.
+  ScopedPtr<Ptr<ByteArray> > scoped_service_id_hash(new ByteArray(
+      service_id_hash_bytes, sizeof(service_id_hash_bytes) / sizeof(char)));
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_ble_advertisement_bytes(
+      BLEAdvertisement::toBytes(
+          version, pcp, ConstifyPtr(scoped_service_id_hash.get()), endpoint_id,
+          endpoint_name, bluetooth_mac_address));
+
+  // Shorten the valid BLE Advertisement.
+  ScopedPtr<ConstPtr<ByteArray> > short_ble_advertisement_bytes(MakeConstPtr(
+      new ByteArray(scoped_ble_advertisement_bytes.get()->getData(),
+                    BLEAdvertisement::kMinAdvertisementLength - 1)));
+
+  // Fail to deserialize the short BLE Advertisement.
+  ScopedPtr<Ptr<BLEAdvertisement> > scoped_short_ble_advertisement(
+      BLEAdvertisement::fromBytes(short_ble_advertisement_bytes.get()));
+  ASSERT_TRUE(scoped_short_ble_advertisement.get().isNull());
+
+  // Make sure deserialization succeeds with the valid BLE Advertisement.
+  ScopedPtr<Ptr<BLEAdvertisement> > scoped_ble_advertisement(
+      BLEAdvertisement::fromBytes(scoped_ble_advertisement_bytes.get()));
+  ASSERT_FALSE(scoped_ble_advertisement.get().isNull());
+}
+
+TEST(BLEAdvertisementTest, DeserializationFailsWithWrongEndpointNameLength) {
+  // Serialize good data into a good BLE Advertisement.
+  ScopedPtr<Ptr<ByteArray> > scoped_service_id_hash(new ByteArray(
+      service_id_hash_bytes, sizeof(service_id_hash_bytes) / sizeof(char)));
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_ble_advertisement_bytes(
+      BLEAdvertisement::toBytes(
+          version, pcp, ConstifyPtr(scoped_service_id_hash.get()), endpoint_id,
+          endpoint_name, bluetooth_mac_address));
+
+  // Corrupt the EndpointNameLength bits.
+  std::string corrupt_ble_advertisement_bytes(
+      scoped_ble_advertisement_bytes->getData(),
+      scoped_ble_advertisement_bytes->size());
+  corrupt_ble_advertisement_bytes[8] ^= 0x0FF;
+  ScopedPtr<ConstPtr<ByteArray> > scoped_corrupt_ble_advertisement_bytes(
+      MakeConstPtr(new ByteArray(corrupt_ble_advertisement_bytes.data(),
+                                 corrupt_ble_advertisement_bytes.size())));
+
+  // And deserialize the corrupt BLE Advertisement.
+  ScopedPtr<Ptr<BLEAdvertisement> > scoped_ble_advertisement(
+      BLEAdvertisement::fromBytes(
+          scoped_corrupt_ble_advertisement_bytes.get()));
+  ASSERT_TRUE(scoped_ble_advertisement.isNull());
+}
+
+// Bytes at the end should be ignored so that they can be used as reserve bytes
+// in the future.
+TEST(BLEAdvertisementTest, DeserializationPassesWithLongLength) {
+  ScopedPtr<Ptr<ByteArray> > scoped_service_id_hash(new ByteArray(
+      service_id_hash_bytes, sizeof(service_id_hash_bytes) / sizeof(char)));
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_ble_advertisement_bytes(
+      BLEAdvertisement::toBytes(
+          version, pcp, ConstifyPtr(scoped_service_id_hash.get()), endpoint_id,
+          endpoint_name, bluetooth_mac_address));
+
+  // Add bytes to the end of the valid BLE advertisement.
+  ScopedPtr<ConstPtr<ByteArray> > long_ble_advertisement_bytes(MakeConstPtr(
+      new ByteArray(scoped_ble_advertisement_bytes.get()->getData(),
+                    BLEAdvertisement::kMinAdvertisementLength + 1000)));
+
+  // Deserialize the long BLE advertisement.
+  ScopedPtr<Ptr<BLEAdvertisement> > scoped_long_ble_advertisement(
+      BLEAdvertisement::fromBytes(long_ble_advertisement_bytes.get()));
+  ASSERT_FALSE(scoped_long_ble_advertisement.get().isNull());
+
+  // Make sure deserialization succeeds with the valid BLE Advertisement.
+  ScopedPtr<Ptr<BLEAdvertisement> > scoped_ble_advertisement(
+      BLEAdvertisement::fromBytes(scoped_ble_advertisement_bytes.get()));
+  ASSERT_FALSE(scoped_ble_advertisement.get().isNull());
+}
+
+TEST(BLEAdvertisementTest, DeserializationWorksWithLongEndpointName) {
+  // Serialize good data into a good BLE Advertisement.
+  ScopedPtr<Ptr<ByteArray> > scoped_service_id_hash(new ByteArray(
+      service_id_hash_bytes, sizeof(service_id_hash_bytes) / sizeof(char)));
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_ble_advertisement_bytes(
+      BLEAdvertisement::toBytes(
+          version, pcp, ConstifyPtr(scoped_service_id_hash.get()), endpoint_id,
+          endpoint_name, bluetooth_mac_address));
+
+  // Corrupt the EndpointNameLength bits and increase it past the accepted max
+  // length.
+  std::string corrupt_ble_advertisement_bytes(
+      scoped_ble_advertisement_bytes->getData(),
+      scoped_ble_advertisement_bytes->size());
+  corrupt_ble_advertisement_bytes[8] ^=
+      BLEAdvertisement::kMaxEndpointNameLength + 10;
+  ScopedPtr<ConstPtr<ByteArray> > scoped_corrupt_ble_advertisement_bytes(
+      MakeConstPtr(new ByteArray(corrupt_ble_advertisement_bytes.data(),
+                                 corrupt_ble_advertisement_bytes.size())));
+  // Increase the size of the advertisement so that there's enough data for the
+  // now-longer endpoint name.
+  ScopedPtr<ConstPtr<ByteArray> > long_ble_advertisement_bytes(MakeConstPtr(
+      new ByteArray(scoped_corrupt_ble_advertisement_bytes.get()->getData(),
+                    BLEAdvertisement::kMinAdvertisementLength + 1000)));
+
+  // And deserialize the changed BLE Advertisement.
+  ScopedPtr<Ptr<BLEAdvertisement> > scoped_ble_advertisement(
+      BLEAdvertisement::fromBytes(long_ble_advertisement_bytes.get()));
+  ASSERT_FALSE(scoped_ble_advertisement.isNull());
+}
+
+}  // namespace
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/ble_compat.h

@@ -0,0 +1,26 @@
+#ifndef CORE_INTERNAL_BLE_COMPAT_H_
+#define CORE_INTERNAL_BLE_COMPAT_H_
+
+#ifndef BLE_V2_IMPLEMENTED
+// Flip to true when BLE_V2 is fully implemented and ready to be tested.
+#define BLE_V2_IMPLEMENTED 0
+#endif
+
+#if BLE_V2_IMPLEMENTED
+
+#include "core/internal/mediums/ble_peripheral.h"
+#include "core/internal/mediums/discovered_peripheral_callback.h"
+#define BLE_PERIPHERAL location::nearby::connections::mediums::BLEPeripheral
+#define DISCOVERED_PERIPHERAL_CALLBACK \
+  location::nearby::connections::mediums::DiscoveredPeripheralCallback
+
+#else
+
+#include "platform/api/ble.h"
+#define BLE_PERIPHERAL location::nearby::BLEPeripheral
+#define DISCOVERED_PERIPHERAL_CALLBACK \
+  BLE<Platform>::DiscoveredPeripheralCallback
+
+#endif  // BLE_V2_IMPLEMENTED
+
+#endif  // CORE_INTERNAL_BLE_COMPAT_H_

cpp/core/internal/ble_endpoint_channel.cc

@@ -0,0 +1,55 @@
+#include "core/internal/ble_endpoint_channel.h"
+
+#include <string>
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+template <typename Platform>
+Ptr<BLEEndpointChannel<Platform> >
+BLEEndpointChannel<Platform>::createOutgoing(
+    Ptr<MediumManager<Platform> > medium_manager, const string& channel_name,
+    Ptr<BLESocket> ble_socket) {
+  return MakePtr(
+      new BLEEndpointChannel<Platform>(channel_name, ble_socket));
+}
+
+template <typename Platform>
+Ptr<BLEEndpointChannel<Platform> >
+BLEEndpointChannel<Platform>::createIncoming(
+    Ptr<MediumManager<Platform> > medium_manager, const string& channel_name,
+    Ptr<BLESocket> ble_socket) {
+  return MakePtr(
+      new BLEEndpointChannel<Platform>(channel_name, ble_socket));
+}
+
+template <typename Platform>
+BLEEndpointChannel<Platform>::BLEEndpointChannel(
+    const string& channel_name, Ptr<BLESocket> ble_socket)
+    : BaseEndpointChannel<Platform>(channel_name,
+                                    ble_socket->getInputStream(),
+                                    ble_socket->getOutputStream()),
+      ble_socket_(ble_socket) {}
+
+template <typename Platform>
+BLEEndpointChannel<Platform>::~BLEEndpointChannel() {}
+
+template <typename Platform>
+proto::connections::Medium BLEEndpointChannel<Platform>::getMedium() {
+  return proto::connections::Medium::BLE;
+}
+
+template <typename Platform>
+void BLEEndpointChannel<Platform>::closeImpl() {
+  Exception::Value exception = ble_socket_->close();
+  if (exception != Exception::NONE) {
+    if (exception == Exception::IO) {
+      // TODO(ahlee): Add logging.
+    }
+  }
+}
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/ble_endpoint_channel.h

@@ -0,0 +1,44 @@
+#ifndef CORE_INTERNAL_BLE_ENDPOINT_CHANNEL_H_
+#define CORE_INTERNAL_BLE_ENDPOINT_CHANNEL_H_
+
+#include "core/internal/base_endpoint_channel.h"
+#include "core/internal/medium_manager.h"
+#include "platform/api/ble.h"
+#include "platform/port/string.h"
+#include "platform/ptr.h"
+#include "proto/connections_enums.pb.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+template <typename Platform>
+class BLEEndpointChannel : public BaseEndpointChannel<Platform> {
+ public:
+  static Ptr<BLEEndpointChannel<Platform> > createOutgoing(
+      Ptr<MediumManager<Platform> > medium_manager, const string& channel_name,
+      Ptr<BLESocket> ble_socket);
+  static Ptr<BLEEndpointChannel<Platform> > createIncoming(
+      Ptr<MediumManager<Platform> > medium_manager, const string& channel_name,
+      Ptr<BLESocket> ble_socket);
+
+  ~BLEEndpointChannel() override;
+
+  proto::connections::Medium getMedium() override;
+
+ protected:
+  void closeImpl() override;
+
+ private:
+  BLEEndpointChannel(const string& channel_name, Ptr<BLESocket> ble_socket);
+
+  ScopedPtr<Ptr<BLESocket> > ble_socket_;
+};
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#include "core/internal/ble_endpoint_channel.cc"
+
+#endif  // CORE_INTERNAL_BLE_ENDPOINT_CHANNEL_H_

cpp/core/internal/bluetooth_device_name.cc

@@ -0,0 +1,292 @@
+#include "core/internal/bluetooth_device_name.h"
+
+#include <cstring>
+
+#include "platform/base64_utils.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+const std::uint32_t BluetoothDeviceName::kServiceIdHashLength = 3;
+
+const std::uint32_t BluetoothDeviceName::kMaxBluetoothDeviceNameLength = 147;
+// Should be defined as ClientProxy<Platform>::kEndpointIdLength, but that
+// involves making BluetoothDeviceName templatized on Platform just for
+// that one little thing, so forego it (at least for now).
+const std::uint32_t BluetoothDeviceName::kEndpointIdLength = 4;
+const std::uint32_t BluetoothDeviceName::kReservedLength = 7;
+const std::uint32_t BluetoothDeviceName::kMaxEndpointNameLength = 131;
+const std::uint32_t BluetoothDeviceName::kMinBluetoothDeviceNameLength =
+    kMaxBluetoothDeviceNameLength - kMaxEndpointNameLength;
+
+const std::uint16_t BluetoothDeviceName::kVersionBitmask = 0x0E0;
+const std::uint16_t BluetoothDeviceName::kPCPBitmask = 0x01F;
+const std::uint16_t BluetoothDeviceName::kEndpointNameLengthBitmask = 0x0FF;
+
+Ptr<BluetoothDeviceName> BluetoothDeviceName::fromString(
+    const std::string& bluetooth_device_name_string) {
+  ScopedPtr<Ptr<ByteArray> > scoped_bluetooth_device_name_bytes(
+      Base64Utils::decode(bluetooth_device_name_string));
+  if (scoped_bluetooth_device_name_bytes.isNull()) {
+    // TODO(reznor): logger.atDebug().log("Cannot deserialize
+    // BluetoothDeviceName: failed Base64 decoding of %s",
+    // bluetoothDeviceNameString);
+    return Ptr<BluetoothDeviceName>();
+  }
+
+  if (scoped_bluetooth_device_name_bytes->size() >
+      kMaxBluetoothDeviceNameLength) {
+    // TODO(reznor): logger.atDebug().log("Cannot deserialize
+    // BluetoothDeviceName: expecting max %d raw bytes, got %d",
+    // MAX_BLUETOOTH_DEVICE_NAME_LENGTH, bluetoothDeviceNameBytes.length);
+    return Ptr<BluetoothDeviceName>();
+  }
+
+  if (scoped_bluetooth_device_name_bytes->size() <
+      kMinBluetoothDeviceNameLength) {
+    // TODO(reznor): logger.atDebug().log("Cannot deserialize
+    // BluetoothDeviceName: expecting min %d raw bytes, got %d",
+    // MIN_BLUETOOTH_DEVICE_NAME_LENGTH, bluetoothDeviceNameBytes.length);
+    return Ptr<BluetoothDeviceName>();
+  }
+
+  // The first 3 bits are supposed to be the version.
+  Version::Value version = static_cast<Version::Value>(
+      (scoped_bluetooth_device_name_bytes->getData()[0] & kVersionBitmask) >>
+      5);
+
+  switch (version) {
+    case Version::V1:
+      return createV1BluetoothDeviceName(
+          ConstifyPtr(scoped_bluetooth_device_name_bytes.get()));
+
+    default:
+      // TODO(reznor): [ANALYTICIZE] This either represents corruption over the
+      // air, or older versions of GmsCore intermingling with newer ones.
+
+      // TODO(reznor): logger.atDebug().log("Cannot deserialize
+      // BluetoothDeviceName: unsupported Version %d", version);
+      return Ptr<BluetoothDeviceName>();
+  }
+}
+
+std::string BluetoothDeviceName::asString(Version::Value version,
+                                          PCP::Value pcp,
+                                          const std::string& endpoint_id,
+                                          ConstPtr<ByteArray> service_id_hash,
+                                          const std::string& endpoint_name) {
+  std::string usable_endpoint_name(endpoint_name);
+  if (endpoint_name.size() > kMaxEndpointNameLength) {
+    // TODO(reznor): logger.atWarning().log("While serializing Advertisement,
+    // truncating Endpoint Name %s (%d bytes) down to %d bytes", endpointName,
+    // endpointNameBytes.length, MAX_ENDPOINT_NAME_LENGTH);
+    usable_endpoint_name.erase(kMaxEndpointNameLength);
+  }
+  ScopedPtr<Ptr<ByteArray> > scoped_endpoint_name_bytes(
+      new ByteArray(usable_endpoint_name.data(), usable_endpoint_name.size()));
+
+  Ptr<ByteArray> bluetooth_device_name_bytes;
+  switch (version) {
+    case Version::V1:
+      bluetooth_device_name_bytes =
+          createV1Bytes(pcp, endpoint_id, service_id_hash,
+                        ConstifyPtr(scoped_endpoint_name_bytes.get()));
+      if (bluetooth_device_name_bytes.isNull()) {
+        return "";
+      }
+      break;
+
+    default:
+      // TODO(reznor): logger.atDebug().log("Cannot serialize
+      // BluetoothDeviceName: unsupported Version %d", version);
+      return "";
+  }
+  ScopedPtr<Ptr<ByteArray> > scoped_bluetooth_device_name_bytes(
+      bluetooth_device_name_bytes);
+
+  // BluetoothDeviceName needs to be binary safe, so apply a Base64 encoding
+  // over the raw bytes.
+  return Base64Utils::encode(
+      ConstifyPtr(scoped_bluetooth_device_name_bytes.get()));
+}
+
+Ptr<BluetoothDeviceName> BluetoothDeviceName::createV1BluetoothDeviceName(
+    ConstPtr<ByteArray> bluetooth_device_name_bytes) {
+  const char* bluetooth_device_name_bytes_read_ptr =
+      bluetooth_device_name_bytes->getData();
+
+  // The first 5 bits of the V1 payload are supposed to be the PCP.
+  PCP::Value pcp = static_cast<PCP::Value>(
+      *bluetooth_device_name_bytes_read_ptr & kPCPBitmask);
+  bluetooth_device_name_bytes_read_ptr++;
+
+  switch (pcp) {
+    case PCP::P2P_CLUSTER:  // Fall through
+    case PCP::P2P_STAR:     // Fall through
+    case PCP::P2P_POINT_TO_POINT: {
+      // The next 32 bits are supposed to be the endpoint_id.
+      std::string endpoint_id(bluetooth_device_name_bytes_read_ptr,
+                              kEndpointIdLength);
+      bluetooth_device_name_bytes_read_ptr += kEndpointIdLength;
+
+      // The next 24 bits are supposed to be the scoped_service_id_hash.
+      ScopedPtr<ConstPtr<ByteArray> > scoped_service_id_hash(
+          MakeConstPtr(new ByteArray(bluetooth_device_name_bytes_read_ptr,
+                                     kServiceIdHashLength)));
+      bluetooth_device_name_bytes_read_ptr += kServiceIdHashLength;
+
+      // The next 56 bits are supposed to be reserved, and can be left
+      // untouched.
+      bluetooth_device_name_bytes_read_ptr += kReservedLength;
+
+      // The next 8 bits are supposed to be the length of the endpoint_name.
+      std::uint32_t expected_endpoint_name_length = static_cast<std::uint32_t>(
+          *bluetooth_device_name_bytes_read_ptr & kEndpointNameLengthBitmask);
+      bluetooth_device_name_bytes_read_ptr++;
+
+      // Check that the stated endpoint_name_length is the same as what we
+      // received (based off of the length of bluetooth_device_name_bytes).
+      std::uint32_t actual_endpoint_name_length =
+          computeEndpointNameLength(bluetooth_device_name_bytes);
+      if (actual_endpoint_name_length != expected_endpoint_name_length) {
+        // TODO(reznor): logger.atDebug().log("Cannot deserialize
+        // BluetoothDeviceName: expected endpointName to be %d bytes, got %d
+        // bytes", expectedEndpointNameLength, actualEndpointNameLength);
+        return Ptr<BluetoothDeviceName>();
+      }
+
+      std::string endpoint_name(bluetooth_device_name_bytes_read_ptr,
+                                actual_endpoint_name_length);
+      bluetooth_device_name_bytes_read_ptr += actual_endpoint_name_length;
+
+      return MakePtr(new BluetoothDeviceName(Version::V1, pcp, endpoint_id,
+                                             scoped_service_id_hash.release(),
+                                             endpoint_name));
+    }
+    default:
+      // TODO(reznor): [ANALYTICIZE] This either represents corruption over the
+      // air, or older versions of GmsCore intermingling with newer ones.
+
+      // TODO(reznor): logger.atDebug().log("Cannot deserialize
+      // BluetoothDeviceName: unsupported V1 PCP %d", pcp);
+      return Ptr<BluetoothDeviceName>();
+  }
+}
+
+std::uint32_t BluetoothDeviceName::computeEndpointNameLength(
+    ConstPtr<ByteArray> bluetooth_device_name_bytes) {
+  return kMaxEndpointNameLength -
+         (kMaxBluetoothDeviceNameLength - bluetooth_device_name_bytes->size());
+}
+
+std::uint32_t BluetoothDeviceName::computeBluetoothDeviceNameLength(
+    ConstPtr<ByteArray> endpoint_name_bytes) {
+  return kMaxBluetoothDeviceNameLength -
+         (kMaxEndpointNameLength - endpoint_name_bytes->size());
+}
+
+Ptr<ByteArray> BluetoothDeviceName::createV1Bytes(
+    PCP::Value pcp, const std::string& endpoint_id,
+    ConstPtr<ByteArray> service_id_hash,
+    ConstPtr<ByteArray> endpoint_name_bytes) {
+  std::uint32_t bluetooth_device_name_length =
+      computeBluetoothDeviceNameLength(endpoint_name_bytes);
+  Ptr<ByteArray> bluetooth_device_name_bytes{
+      new ByteArray{bluetooth_device_name_length}};
+
+  char* bluetooth_device_name_bytes_write_ptr =
+      bluetooth_device_name_bytes->getData();
+
+  // The first 3 bits are the Version.
+  char version_and_pcp_byte =
+      static_cast<char>((Version::V1 << 5) & kVersionBitmask);
+  // The next 5 bits are the PCP.
+  version_and_pcp_byte |= static_cast<char>(pcp & kPCPBitmask);
+  *bluetooth_device_name_bytes_write_ptr = version_and_pcp_byte;
+  bluetooth_device_name_bytes_write_ptr++;
+
+  switch (pcp) {
+    case PCP::P2P_CLUSTER:  // Fall through
+    case PCP::P2P_STAR:     // Fall through
+    case PCP::P2P_POINT_TO_POINT:
+      // The next 32 bits are the endpoint_id.
+      if (endpoint_id.size() != kEndpointIdLength) {
+        // TODO(reznor): logger.atDebug().log("Cannot serialize
+        // BluetoothDeviceName: V1 Endpoint ID %s (%d bytes) should be exactly
+        // %d bytes", endpointId, endpointId.length(), ENDPOINT_ID_LENGTH);
+        return Ptr<ByteArray>();
+      }
+      memcpy(bluetooth_device_name_bytes_write_ptr, endpoint_id.data(),
+             kEndpointIdLength);
+      bluetooth_device_name_bytes_write_ptr += kEndpointIdLength;
+
+      // The next 24 bits are the service_id_hash.
+      if (service_id_hash->size() != kServiceIdHashLength) {
+        // TODO(reznor): logger.atDebug().log("Cannot serialize
+        // BluetoothDeviceName: V1 ServiceID hash (%d bytes) should be exactly
+        // %d bytes", serviceIdHash.length, SERVICE_ID_HASH_LENGTH);
+        return Ptr<ByteArray>();
+      }
+      memcpy(bluetooth_device_name_bytes_write_ptr, service_id_hash->getData(),
+             kServiceIdHashLength);
+      bluetooth_device_name_bytes_write_ptr += kServiceIdHashLength;
+
+      // The next 56 bits are reserved, and should all be zeroed out, so do
+      // that and then jump over 56 bits to position things for the next write.
+      memset(bluetooth_device_name_bytes_write_ptr, 0, kReservedLength);
+      bluetooth_device_name_bytes_write_ptr += kReservedLength;
+
+      // The next 8 bits are the length of the endpoint_name.
+      *bluetooth_device_name_bytes_write_ptr = static_cast<char>(
+          endpoint_name_bytes->size() & kEndpointNameLengthBitmask);
+      bluetooth_device_name_bytes_write_ptr++;
+
+      // The remaining bits are filled with the endpoint_name.
+      memcpy(bluetooth_device_name_bytes_write_ptr,
+             endpoint_name_bytes->getData(), endpoint_name_bytes->size());
+      bluetooth_device_name_bytes_write_ptr += endpoint_name_bytes->size();
+
+      break;
+    default:
+      // TODO(reznor): logger.atDebug().log("Cannot serialize
+      // BluetoothDeviceName: unsupported V1 PCP %d", pcp);
+      return Ptr<ByteArray>();
+  }
+
+  return bluetooth_device_name_bytes;
+}
+
+BluetoothDeviceName::BluetoothDeviceName(Version::Value version, PCP::Value pcp,
+                                         const std::string& endpoint_id,
+                                         ConstPtr<ByteArray> service_id_hash,
+                                         const std::string& endpoint_name)
+    : version_(version),
+      pcp_(pcp),
+      endpoint_id_(endpoint_id),
+      service_id_hash_(service_id_hash),
+      endpoint_name_(endpoint_name) {}
+
+BluetoothDeviceName::~BluetoothDeviceName() {
+  // Nothing to do.
+}
+
+BluetoothDeviceName::Version::Value BluetoothDeviceName::getVersion() const {
+  return version_;
+}
+
+PCP::Value BluetoothDeviceName::getPCP() const { return pcp_; }
+
+std::string BluetoothDeviceName::getEndpointId() const { return endpoint_id_; }
+
+ConstPtr<ByteArray> BluetoothDeviceName::getServiceIdHash() const {
+  return service_id_hash_.get();
+}
+
+std::string BluetoothDeviceName::getEndpointName() const {
+  return endpoint_name_;
+}
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/bluetooth_device_name.h

@@ -0,0 +1,86 @@
+#ifndef CORE_INTERNAL_BLUETOOTH_DEVICE_NAME_H_
+#define CORE_INTERNAL_BLUETOOTH_DEVICE_NAME_H_
+
+#include <cstdint>
+
+#include "core/internal/pcp.h"
+#include "platform/byte_array.h"
+#include "platform/port/string.h"
+#include "platform/ptr.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+// Represents the format of the Bluetooth device name used in Advertising +
+// Discovery.
+//
+// <p>See go/nearby-offline-data-interchange-formats for the specification.
+class BluetoothDeviceName {
+ public:
+  // Versions of the BluetoothDeviceName.
+  struct Version {
+    enum Value {
+      V1 = 1,
+      // Version is only allocated 3 bits in the BluetoothDeviceName, so this
+      // can never go beyond V7.
+    };
+  };
+
+  static Ptr<BluetoothDeviceName> fromString(
+      const std::string& bluetooth_device_name_string);
+
+  static std::string asString(Version::Value version, PCP::Value pcp,
+                              const std::string& endpoint_id,
+                              ConstPtr<ByteArray> service_id_hash,
+                              const std::string& endpoint_name);
+
+  static const std::uint32_t kServiceIdHashLength;
+
+  ~BluetoothDeviceName();
+
+  Version::Value getVersion() const;
+  PCP::Value getPCP() const;
+  std::string getEndpointId() const;
+  ConstPtr<ByteArray> getServiceIdHash() const;
+  std::string getEndpointName() const;
+
+ private:
+  static Ptr<BluetoothDeviceName> createV1BluetoothDeviceName(
+      ConstPtr<ByteArray> bluetooth_device_name_bytes);
+  static std::uint32_t computeEndpointNameLength(
+      ConstPtr<ByteArray> bluetooth_device_name_bytes);
+  static std::uint32_t computeBluetoothDeviceNameLength(
+      ConstPtr<ByteArray> endpoint_name_bytes);
+  static Ptr<ByteArray> createV1Bytes(PCP::Value pcp,
+                                      const std::string& endpoint_id,
+                                      ConstPtr<ByteArray> service_id_hash,
+                                      ConstPtr<ByteArray> endpoint_name_bytes);
+
+  static const std::uint32_t kMaxBluetoothDeviceNameLength;
+  static const std::uint32_t kEndpointIdLength;
+  static const std::uint32_t kReservedLength;
+  static const std::uint32_t kMaxEndpointNameLength;
+  static const std::uint32_t kMinBluetoothDeviceNameLength;
+
+  static const std::uint16_t kVersionBitmask;
+  static const std::uint16_t kPCPBitmask;
+  static const std::uint16_t kEndpointNameLengthBitmask;
+
+  BluetoothDeviceName(Version::Value version, PCP::Value pcp,
+                      const std::string& endpoint_id,
+                      ConstPtr<ByteArray> service_id_hash,
+                      const std::string& endpoint_name);
+
+  const Version::Value version_;
+  const PCP::Value pcp_;
+  const std::string endpoint_id_;
+  ScopedPtr<ConstPtr<ByteArray> > service_id_hash_;
+  const std::string endpoint_name_;
+};
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#endif  // CORE_INTERNAL_BLUETOOTH_DEVICE_NAME_H_

cpp/core/internal/bluetooth_device_name_test.cc

@@ -0,0 +1,198 @@
+#include "core/internal/bluetooth_device_name.h"
+
+#include <cstring>
+
+#include "platform/base64_utils.h"
+#include "platform/port/string.h"
+#include "gtest/gtest.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+namespace {
+
+const BluetoothDeviceName::Version::Value version =
+    BluetoothDeviceName::Version::V1;
+const PCP::Value pcp = PCP::P2P_CLUSTER;
+const char endpoint_id[] = "AB12";
+const char service_id_hash_bytes[] = {0x0A, 0x0B, 0x0C};
+const char endpoint_name[] = "RAWK + ROWL!";
+
+TEST(BluetoothDeviceNameTest, SerializationDeserializationWorks) {
+  ScopedPtr<Ptr<ByteArray> > scoped_service_id_hash(new ByteArray(
+      service_id_hash_bytes, sizeof(service_id_hash_bytes) / sizeof(char)));
+
+  std::string bluetooth_device_name_string = BluetoothDeviceName::asString(
+      version, pcp, endpoint_id, ConstifyPtr(scoped_service_id_hash.get()),
+      endpoint_name);
+  ScopedPtr<Ptr<BluetoothDeviceName> > scoped_bluetooth_device_name(
+      BluetoothDeviceName::fromString(bluetooth_device_name_string));
+
+  ASSERT_EQ(pcp, scoped_bluetooth_device_name->getPCP());
+  ASSERT_EQ(version, scoped_bluetooth_device_name->getVersion());
+  ASSERT_EQ(endpoint_id, scoped_bluetooth_device_name->getEndpointId());
+  ASSERT_EQ(sizeof(service_id_hash_bytes) / sizeof(char),
+            scoped_bluetooth_device_name->getServiceIdHash()->size());
+  ASSERT_EQ(0,
+            memcmp(service_id_hash_bytes,
+                   scoped_bluetooth_device_name->getServiceIdHash()->getData(),
+                   scoped_bluetooth_device_name->getServiceIdHash()->size()));
+  ASSERT_EQ(endpoint_name, scoped_bluetooth_device_name->getEndpointName());
+}
+
+TEST(BluetoothDeviceNameTest,
+     SerializationDeserializationWorksWithEmptyEndpointName) {
+  std::string empty_endpoint_name;
+
+  ScopedPtr<Ptr<ByteArray> > scoped_service_id_hash(new ByteArray(
+      service_id_hash_bytes, sizeof(service_id_hash_bytes) / sizeof(char)));
+
+  std::string bluetooth_device_name_string = BluetoothDeviceName::asString(
+      version, pcp, endpoint_id, ConstifyPtr(scoped_service_id_hash.get()),
+      empty_endpoint_name);
+  ScopedPtr<Ptr<BluetoothDeviceName> > scoped_bluetooth_device_name(
+      BluetoothDeviceName::fromString(bluetooth_device_name_string));
+
+  ASSERT_EQ(pcp, scoped_bluetooth_device_name->getPCP());
+  ASSERT_EQ(version, scoped_bluetooth_device_name->getVersion());
+  ASSERT_EQ(endpoint_id, scoped_bluetooth_device_name->getEndpointId());
+  ASSERT_EQ(sizeof(service_id_hash_bytes) / sizeof(char),
+            scoped_bluetooth_device_name->getServiceIdHash()->size());
+  ASSERT_EQ(0,
+            memcmp(service_id_hash_bytes,
+                   scoped_bluetooth_device_name->getServiceIdHash()->getData(),
+                   scoped_bluetooth_device_name->getServiceIdHash()->size()));
+  ASSERT_EQ(empty_endpoint_name,
+            scoped_bluetooth_device_name->getEndpointName());
+}
+
+TEST(BluetoothDeviceNameTest, SerializationFailsWithBadVersion) {
+  BluetoothDeviceName::Version::Value bad_version =
+      static_cast<BluetoothDeviceName::Version::Value>(666);
+
+  ScopedPtr<Ptr<ByteArray> > scoped_service_id_hash(new ByteArray(
+      service_id_hash_bytes, sizeof(service_id_hash_bytes) / sizeof(char)));
+
+  std::string bluetooth_device_name_string = BluetoothDeviceName::asString(
+      bad_version, pcp, endpoint_id, ConstifyPtr(scoped_service_id_hash.get()),
+      endpoint_name);
+
+  ASSERT_TRUE(bluetooth_device_name_string.empty());
+}
+
+TEST(BluetoothDeviceNameTest, SerializationFailsWithBadPCP) {
+  PCP::Value bad_pcp = static_cast<PCP::Value>(666);
+
+  ScopedPtr<Ptr<ByteArray> > scoped_service_id_hash(new ByteArray(
+      service_id_hash_bytes, sizeof(service_id_hash_bytes) / sizeof(char)));
+
+  std::string bluetooth_device_name_string = BluetoothDeviceName::asString(
+      version, bad_pcp, endpoint_id, ConstifyPtr(scoped_service_id_hash.get()),
+      endpoint_name);
+
+  ASSERT_TRUE(bluetooth_device_name_string.empty());
+}
+
+TEST(BluetoothDeviceNameTest, SerializationFailsWithShortEndpointId) {
+  std::string short_endpoint_id("AB1");
+
+  ScopedPtr<Ptr<ByteArray> > scoped_service_id_hash(new ByteArray(
+      service_id_hash_bytes, sizeof(service_id_hash_bytes) / sizeof(char)));
+
+  std::string bluetooth_device_name_string = BluetoothDeviceName::asString(
+      version, pcp, short_endpoint_id,
+      ConstifyPtr(scoped_service_id_hash.get()), endpoint_name);
+
+  ASSERT_TRUE(bluetooth_device_name_string.empty());
+}
+
+TEST(BluetoothDeviceNameTest, SerializationFailsWithLongEndpointId) {
+  std::string long_endpoint_id("AB12X");
+
+  ScopedPtr<Ptr<ByteArray> > scoped_service_id_hash(new ByteArray(
+      service_id_hash_bytes, sizeof(service_id_hash_bytes) / sizeof(char)));
+
+  std::string bluetooth_device_name_string = BluetoothDeviceName::asString(
+      version, pcp, long_endpoint_id, ConstifyPtr(scoped_service_id_hash.get()),
+      endpoint_name);
+
+  ASSERT_TRUE(bluetooth_device_name_string.empty());
+}
+
+TEST(BluetoothDeviceNameTest, SerializationFailsWithShortServiceIdHash) {
+  char short_service_id_hash_bytes[] = {0x0A, 0x0B};
+
+  ScopedPtr<Ptr<ByteArray> > scoped_short_service_id_hash(
+      new ByteArray(short_service_id_hash_bytes,
+                    sizeof(short_service_id_hash_bytes) / sizeof(char)));
+
+  std::string bluetooth_device_name_string = BluetoothDeviceName::asString(
+      version, pcp, endpoint_id,
+      ConstifyPtr(scoped_short_service_id_hash.get()), endpoint_name);
+
+  ASSERT_TRUE(bluetooth_device_name_string.empty());
+}
+
+TEST(BluetoothDeviceNameTest, SerializationFailsWithLongServiceIdHash) {
+  char long_service_id_hash_bytes[] = {0x0A, 0x0B, 0x0C, 0x0D};
+
+  ScopedPtr<Ptr<ByteArray> > scoped_long_service_id_hash(
+      new ByteArray(long_service_id_hash_bytes,
+                    sizeof(long_service_id_hash_bytes) / sizeof(char)));
+
+  std::string bluetooth_device_name_string = BluetoothDeviceName::asString(
+      version, pcp, endpoint_id, ConstifyPtr(scoped_long_service_id_hash.get()),
+      endpoint_name);
+
+  ASSERT_TRUE(bluetooth_device_name_string.empty());
+}
+
+TEST(BluetoothDeviceNameTest, DeserializationFailsWithShortLength) {
+  char bluetooth_device_name_bytes[] = {'X'};
+
+  ScopedPtr<Ptr<ByteArray> > scoped_bluetooth_device_name_bytes(
+      new ByteArray(bluetooth_device_name_bytes,
+                    sizeof(bluetooth_device_name_bytes) / sizeof(char)));
+
+  ScopedPtr<Ptr<BluetoothDeviceName> > scoped_bluetooth_device_name(
+      BluetoothDeviceName::fromString(Base64Utils::encode(
+          ConstifyPtr(scoped_bluetooth_device_name_bytes.get()))));
+
+  ASSERT_TRUE(scoped_bluetooth_device_name.isNull());
+}
+
+TEST(BluetoothDeviceNameTest, DeserializationFailsWithWrongEndpointNameLength) {
+  // Serialize good data into a good Bluetooth Device Name.
+  ScopedPtr<Ptr<ByteArray> > scoped_service_id_hash(new ByteArray(
+      service_id_hash_bytes, sizeof(service_id_hash_bytes) / sizeof(char)));
+
+  std::string bluetooth_device_name_string = BluetoothDeviceName::asString(
+      version, pcp, endpoint_id, ConstifyPtr(scoped_service_id_hash.get()),
+      endpoint_name);
+
+  // Base64-decode the good Bluetooth Device Name.
+  ScopedPtr<Ptr<ByteArray> > scoped_bluetooth_device_name_bytes(
+      Base64Utils::decode(bluetooth_device_name_string));
+  // Corrupt the EndpointNameLength bits (120-127) by reversing all of them.
+  std::string corrupt_bluetooth_device_name_bytes(
+      scoped_bluetooth_device_name_bytes->getData(),
+      scoped_bluetooth_device_name_bytes->size());
+  corrupt_bluetooth_device_name_bytes[15] ^= 0x0FF;
+  // Base64-encode the corrupted bytes into a corrupt Bluetooth Device Name.
+  ScopedPtr<Ptr<ByteArray> > scoped_corrupt_bluetooth_device_name_bytes(
+      new ByteArray(corrupt_bluetooth_device_name_bytes.data(),
+                    corrupt_bluetooth_device_name_bytes.size()));
+  std::string corrupt_bluetooth_device_name_string(Base64Utils::encode(
+      ConstifyPtr(scoped_corrupt_bluetooth_device_name_bytes.get())));
+
+  // And deserialize the corrupt Bluetooth Device Name.
+  ScopedPtr<Ptr<BluetoothDeviceName> > scoped_bluetooth_device_name(
+      BluetoothDeviceName::fromString(corrupt_bluetooth_device_name_string));
+
+  ASSERT_TRUE(scoped_bluetooth_device_name.isNull());
+}
+
+}  // namespace
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/bluetooth_endpoint_channel.cc

@@ -0,0 +1,55 @@
+#include "core/internal/bluetooth_endpoint_channel.h"
+
+#include <string>
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+template <typename Platform>
+Ptr<BluetoothEndpointChannel<Platform> >
+BluetoothEndpointChannel<Platform>::createOutgoing(
+    Ptr<MediumManager<Platform> > medium_manager, const string& channel_name,
+    Ptr<BluetoothSocket> bluetooth_socket) {
+  return MakePtr(
+      new BluetoothEndpointChannel<Platform>(channel_name, bluetooth_socket));
+}
+
+template <typename Platform>
+Ptr<BluetoothEndpointChannel<Platform> >
+BluetoothEndpointChannel<Platform>::createIncoming(
+    Ptr<MediumManager<Platform> > medium_manager, const string& channel_name,
+    Ptr<BluetoothSocket> bluetooth_socket) {
+  return MakePtr(
+      new BluetoothEndpointChannel<Platform>(channel_name, bluetooth_socket));
+}
+
+template <typename Platform>
+BluetoothEndpointChannel<Platform>::BluetoothEndpointChannel(
+    const string& channel_name, Ptr<BluetoothSocket> bluetooth_socket)
+    : BaseEndpointChannel<Platform>(channel_name,
+                                    bluetooth_socket->getInputStream(),
+                                    bluetooth_socket->getOutputStream()),
+      bluetooth_socket_(bluetooth_socket) {}
+
+template <typename Platform>
+BluetoothEndpointChannel<Platform>::~BluetoothEndpointChannel() {}
+
+template <typename Platform>
+proto::connections::Medium BluetoothEndpointChannel<Platform>::getMedium() {
+  return proto::connections::Medium::BLUETOOTH;
+}
+
+template <typename Platform>
+void BluetoothEndpointChannel<Platform>::closeImpl() {
+  Exception::Value exception = bluetooth_socket_->close();
+  if (exception != Exception::NONE) {
+    if (exception == Exception::IO) {
+      // TODO(tracyzhou): Add logging.
+    }
+  }
+}
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/bluetooth_endpoint_channel.h

@@ -0,0 +1,45 @@
+#ifndef CORE_INTERNAL_BLUETOOTH_ENDPOINT_CHANNEL_H_
+#define CORE_INTERNAL_BLUETOOTH_ENDPOINT_CHANNEL_H_
+
+#include "core/internal/base_endpoint_channel.h"
+#include "core/internal/medium_manager.h"
+#include "platform/api/bluetooth_classic.h"
+#include "platform/port/string.h"
+#include "platform/ptr.h"
+#include "proto/connections_enums.pb.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+template <typename Platform>
+class BluetoothEndpointChannel : public BaseEndpointChannel<Platform> {
+ public:
+  static Ptr<BluetoothEndpointChannel<Platform> > createOutgoing(
+      Ptr<MediumManager<Platform> > medium_manager, const string& channel_name,
+      Ptr<BluetoothSocket> bluetooth_socket);
+  static Ptr<BluetoothEndpointChannel<Platform> > createIncoming(
+      Ptr<MediumManager<Platform> > medium_manager, const string& channel_name,
+      Ptr<BluetoothSocket> bluetooth_socket);
+
+  ~BluetoothEndpointChannel() override;
+
+  proto::connections::Medium getMedium() override;
+
+ protected:
+  void closeImpl() override;
+
+ private:
+  BluetoothEndpointChannel(const string& channel_name,
+                           Ptr<BluetoothSocket> bluetooth_socket);
+
+  ScopedPtr<Ptr<BluetoothSocket> > bluetooth_socket_;
+};
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#include "core/internal/bluetooth_endpoint_channel.cc"
+
+#endif  // CORE_INTERNAL_BLUETOOTH_ENDPOINT_CHANNEL_H_

cpp/core/internal/client_proxy.cc

@@ -0,0 +1,590 @@
+#include "core/internal/client_proxy.h"
+
+#include <cstdlib>
+#include <limits>
+#include <sstream>
+#include <utility>
+
+#include "platform/api/hash_utils.h"
+#include "platform/base64_utils.h"
+#include "platform/prng.h"
+#include "platform/synchronized.h"
+#include "proto/connections_enums.pb.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+namespace client_proxy {
+
+template <typename K, typename V>
+void eraseOwnedPtrFromMap(std::map<K, Ptr<V>>& m, const K& k) {
+  typename std::map<K, Ptr<V>>::iterator it = m.find(k);
+  if (it != m.end()) {
+    it->second.destroy();
+    m.erase(it);
+  }
+}
+
+}  // namespace client_proxy
+
+template <typename Platform>
+const std::int32_t ClientProxy<Platform>::kEndpointIdLength = 4;
+
+template <typename Platform>
+ClientProxy<Platform>::ClientProxy()
+    : lock_(Platform::createLock()), client_id_(Prng().nextInt64()) {}
+
+template <typename Platform>
+ClientProxy<Platform>::~ClientProxy() {
+  reset();
+}
+
+template <typename Platform>
+std::int64_t ClientProxy<Platform>::getClientId() const {
+  return client_id_;
+}
+
+template <typename Platform>
+std::string ClientProxy<Platform>::generateLocalEndpointId() {
+  // 1) Concatenate the DeviceID with this ClientID.
+  // 2) Compute a hash of that concatenation.
+  // 3) Base64-encode that hash, to make it human-readable.
+  // 4) Use only the first 4 bytes of that Base64 encoding.
+
+  std::ostringstream client_id_str;
+  client_id_str << getClientId();
+
+  ScopedPtr<Ptr<HashUtils>> hash_utils(Platform::createHashUtils());
+  ScopedPtr<ConstPtr<ByteArray>> id_hash(
+      hash_utils->sha256(Platform::getDeviceId() + client_id_str.str()));
+
+  return Base64Utils::encode(id_hash.get()).substr(0, kEndpointIdLength);
+}
+
+template <typename Platform>
+void ClientProxy<Platform>::reset() {
+  Synchronized s(lock_.get());
+
+  stoppedAdvertising();
+  stoppedDiscovery();
+  removeAllEndpoints();
+}
+
+template <typename Platform>
+void ClientProxy<Platform>::startedAdvertising(
+    const std::string& service_id, const Strategy& strategy,
+    Ptr<ConnectionLifecycleListener> connection_lifecycle_listener,
+    const std::vector<proto::connections::Medium>& mediums) {
+  Synchronized s(lock_.get());
+
+  advertising_info_.destroy();
+  advertising_info_ =
+      MakePtr(new AdvertisingInfo(service_id, connection_lifecycle_listener));
+}
+
+template <typename Platform>
+void ClientProxy<Platform>::stoppedAdvertising() {
+  Synchronized s(lock_.get());
+
+  if (isAdvertising()) {
+    advertising_info_.destroy();
+  }
+}
+
+template <typename Platform>
+bool ClientProxy<Platform>::isAdvertising() {
+  Synchronized s(lock_.get());
+
+  return !advertising_info_.isNull();
+}
+
+template <typename Platform>
+std::string ClientProxy<Platform>::getAdvertisingServiceId() {
+  Synchronized s(lock_.get());
+
+  if (!isAdvertising()) {
+    return "";
+  }
+
+  return advertising_info_->service_id;
+}
+
+template <typename Platform>
+void ClientProxy<Platform>::startedDiscovery(
+    const std::string& service_id, const Strategy& strategy,
+    Ptr<DiscoveryListener> discovery_listener,
+    const std::vector<proto::connections::Medium>& mediums) {
+  Synchronized s(lock_.get());
+
+  discovery_info_.destroy();
+  discovery_info_ = MakePtr(new DiscoveryInfo(service_id, discovery_listener));
+}
+
+template <typename Platform>
+void ClientProxy<Platform>::stoppedDiscovery() {
+  Synchronized s(lock_.get());
+
+  if (isDiscovering()) {
+    discovered_endpoint_ids_.clear();
+    discovery_info_.destroy();
+  }
+}
+
+template <typename Platform>
+bool ClientProxy<Platform>::isDiscoveringServiceId(
+    const std::string& service_id) {
+  Synchronized s(lock_.get());
+
+  return isDiscovering() && service_id == discovery_info_->service_id;
+}
+
+template <typename Platform>
+bool ClientProxy<Platform>::isDiscovering() {
+  Synchronized s(lock_.get());
+
+  return !discovery_info_.isNull();
+}
+
+template <typename Platform>
+std::string ClientProxy<Platform>::getDiscoveryServiceId() {
+  Synchronized s(lock_.get());
+
+  if (!isDiscovering()) {
+    return "";
+  }
+
+  return discovery_info_->service_id;
+}
+
+template <typename Platform>
+void ClientProxy<Platform>::onEndpointFound(const std::string& endpoint_id,
+                                            const std::string& service_id,
+                                            const std::string& endpoint_name,
+                                            proto::connections::Medium medium) {
+  Synchronized s(lock_.get());
+
+  if (isDiscoveringServiceId(service_id)) {
+    if (discovered_endpoint_ids_.find(endpoint_id) !=
+        discovered_endpoint_ids_.end()) {
+      // TODO(tracyzhou): Add logging.
+      return;
+    }
+    discovered_endpoint_ids_.insert(endpoint_id);
+    discovery_info_->discovery_listener->onEndpointFound(MakeConstPtr(
+        new OnEndpointFoundParams(endpoint_id, service_id, endpoint_name)));
+  }
+}
+
+template <typename Platform>
+void ClientProxy<Platform>::onEndpointLost(const std::string& service_id,
+                                           const std::string& endpoint_id) {
+  Synchronized s(lock_.get());
+
+  if (isDiscoveringServiceId(service_id)) {
+    std::set<std::string>::const_iterator it =
+        discovered_endpoint_ids_.find(endpoint_id);
+    if (it == discovered_endpoint_ids_.end()) {
+      return;
+    }
+    discovered_endpoint_ids_.erase(it);
+    discovery_info_->discovery_listener->onEndpointLost(
+        MakeConstPtr(new OnEndpointLostParams(endpoint_id)));
+  }
+}
+
+template <typename Platform>
+void ClientProxy<Platform>::onConnectionInitiated(
+    const std::string& endpoint_id, const std::string& endpoint_name,
+    const std::string& authentication_token,
+    ConstPtr<ByteArray> raw_authentication_token, bool is_incoming_connection,
+    Ptr<ConnectionLifecycleListener> connection_lifecycle_listener) {
+  Synchronized s(lock_.get());
+
+  ScopedPtr<ConstPtr<ByteArray>> scoped_raw_authentication_token(
+      raw_authentication_token);
+
+  // Whether this is incoming or outgoing, the local and remote endpoints both
+  // still need to accept this connection, so set its establishment status to
+  // PENDING.
+  connection_establishment_statuses_.insert(
+      std::make_pair(endpoint_id, ConnectionMetadata(is_incoming_connection)));
+
+  // Remember the ConnectionLifecycleListener for this endpoint.
+  connection_lifecycle_listeners_.insert(
+      std::make_pair(endpoint_id, connection_lifecycle_listener));
+
+  // Notify the client.
+  //
+  // Note: we allow devices to connect to an advertiser even after it stops
+  // advertising, so no need to check isAdvertising() here.
+  connection_lifecycle_listeners_.find(endpoint_id)
+      ->second->onConnectionInitiated(
+          MakeConstPtr(new OnConnectionInitiatedParams(
+              endpoint_id, endpoint_name, authentication_token,
+              scoped_raw_authentication_token.release(),
+              is_incoming_connection)));
+}
+
+template <typename Platform>
+void ClientProxy<Platform>::onConnectionResult(const std::string& endpoint_id,
+                                               Status::Value status) {
+  Synchronized s(lock_.get());
+
+  if (!hasPendingConnectionToEndpoint(endpoint_id)) {
+    // TODO(tracyzhou): Add logging.
+    return;
+  }
+
+  // Notify the client.
+  connection_lifecycle_listeners_.find(endpoint_id)
+      ->second->onConnectionResult(
+          MakeConstPtr(new OnConnectionResultParams(endpoint_id, status)));
+  if (Status::SUCCESS == status) {
+    // Mark ourselves as connected. Payloads should now be allowed.
+    typename ConnectionEstablishmentStatusesMap::iterator it =
+        connection_establishment_statuses_.find(endpoint_id);
+    if (it != connection_establishment_statuses_.end()) {
+      it->second.status = ConnectionEstablishmentStatus::CONNECTED;
+    }
+  } else {
+    // Otherwise, clean up.
+    onDisconnected(endpoint_id, false /* notify */);
+  }
+}
+
+template <typename Platform>
+void ClientProxy<Platform>::onBandwidthChanged(const std::string& endpoint_id,
+                                               std::int32_t quality) {
+  Synchronized s(lock_.get());
+
+  ConnectionLifecycleListenersMap::iterator it =
+      connection_lifecycle_listeners_.find(endpoint_id);
+  if (it != connection_lifecycle_listeners_.end()) {
+    it->second->onBandwidthChanged(
+        MakeConstPtr(new OnBandwidthChangedParams(endpoint_id, quality)));
+  }
+}
+
+template <typename Platform>
+void ClientProxy<Platform>::onDisconnected(const std::string& endpoint_id,
+                                           bool notify) {
+  Synchronized s(lock_.get());
+
+  connection_establishment_statuses_.erase(endpoint_id);
+
+  client_proxy::eraseOwnedPtrFromMap(payload_listeners_, endpoint_id);
+
+  ConnectionLifecycleListenersMap::iterator it =
+      connection_lifecycle_listeners_.find(endpoint_id);
+  if (it != connection_lifecycle_listeners_.end()) {
+    if (notify) {
+      it->second->onDisconnected(
+          MakeConstPtr(new OnDisconnectedParams(endpoint_id)));
+    }
+    it->second.destroy();
+    connection_lifecycle_listeners_.erase(it);
+  }
+}
+
+template <typename Platform>
+bool ClientProxy<Platform>::isConnectedToEndpoint(
+    const std::string& endpoint_id) {
+  Synchronized s(lock_.get());
+
+  typename ConnectionEstablishmentStatusesMap::iterator it =
+      connection_establishment_statuses_.find(endpoint_id);
+  if (it == connection_establishment_statuses_.end()) {
+    return false;
+  }
+  const ConnectionMetadata& metadata = it->second;
+  return metadata.status == ConnectionEstablishmentStatus::CONNECTED;
+}
+
+template <typename Platform>
+std::vector<std::string> ClientProxy<Platform>::getConnectedEndpoints() {
+  Synchronized s(lock_.get());
+
+  std::vector<std::string> connected_endpoints;
+
+  for (typename ConnectionEstablishmentStatusesMap::iterator it =
+           connection_establishment_statuses_.begin();
+       it != connection_establishment_statuses_.end(); it++) {
+    const std::string& endpoint_id = it->first;
+    const ConnectionMetadata& metadata = it->second;
+    if (ConnectionEstablishmentStatus::CONNECTED == metadata.status) {
+      connected_endpoints.push_back(endpoint_id);
+    }
+  }
+  return connected_endpoints;
+}
+
+template <typename Platform>
+std::vector<std::string> ClientProxy<Platform>::getPendingConnectedEndpoints() {
+  Synchronized s(lock_.get());
+
+  std::vector<std::string> pending_connected_endpoints;
+
+  for (typename ConnectionEstablishmentStatusesMap::iterator it =
+           connection_establishment_statuses_.begin();
+       it != connection_establishment_statuses_.end(); it++) {
+    const std::string& endpoint_id = it->first;
+    const ConnectionMetadata& metadata = it->second;
+    if (ConnectionEstablishmentStatus::CONNECTED != metadata.status) {
+      pending_connected_endpoints.push_back(endpoint_id);
+    }
+  }
+  return pending_connected_endpoints;
+}
+
+template <typename Platform>
+std::int32_t ClientProxy<Platform>::getNumOutgoingConnections() {
+  Synchronized s(lock_.get());
+
+  std::int32_t num_outgoing_connections = 0;
+
+  for (typename ConnectionEstablishmentStatusesMap::iterator it =
+           connection_establishment_statuses_.begin();
+       it != connection_establishment_statuses_.end(); it++) {
+    const ConnectionMetadata& metadata = it->second;
+    if (ConnectionEstablishmentStatus::CONNECTED == metadata.status &&
+        !metadata.is_incoming) {
+      num_outgoing_connections++;
+    }
+  }
+  return num_outgoing_connections;
+}
+
+template <typename Platform>
+std::int32_t ClientProxy<Platform>::getNumIncomingConnections() {
+  Synchronized s(lock_.get());
+
+  std::int32_t num_incoming_connections = 0;
+
+  for (typename ConnectionEstablishmentStatusesMap::iterator it =
+           connection_establishment_statuses_.begin();
+       it != connection_establishment_statuses_.end(); it++) {
+    const ConnectionMetadata& metadata = it->second;
+    if (ConnectionEstablishmentStatus::CONNECTED == metadata.status &&
+        metadata.is_incoming) {
+      num_incoming_connections++;
+    }
+  }
+  return num_incoming_connections;
+}
+
+template <typename Platform>
+bool ClientProxy<Platform>::hasPendingConnectionToEndpoint(
+    const std::string& endpoint_id) {
+  Synchronized s(lock_.get());
+
+  typename ConnectionEstablishmentStatusesMap::iterator it =
+      connection_establishment_statuses_.find(endpoint_id);
+  if (it == connection_establishment_statuses_.end()) {
+    return false;
+  }
+  const ConnectionMetadata& metadata = it->second;
+  return metadata.status != ConnectionEstablishmentStatus::CONNECTED;
+}
+
+template <typename Platform>
+bool ClientProxy<Platform>::hasLocalEndpointResponded(
+    const std::string& endpoint_id) {
+  Synchronized s(lock_.get());
+
+  return connectionEstablishmentStatusesContains(
+             endpoint_id,
+             ConnectionEstablishmentStatus::LOCAL_ENDPOINT_ACCEPTED) ||
+         connectionEstablishmentStatusesContains(
+             endpoint_id,
+             ConnectionEstablishmentStatus::LOCAL_ENDPOINT_REJECTED);
+}
+
+template <typename Platform>
+bool ClientProxy<Platform>::hasRemoteEndpointResponded(
+    const std::string& endpoint_id) {
+  Synchronized s(lock_.get());
+
+  return connectionEstablishmentStatusesContains(
+             endpoint_id,
+             ConnectionEstablishmentStatus::REMOTE_ENDPOINT_ACCEPTED) ||
+         connectionEstablishmentStatusesContains(
+             endpoint_id,
+             ConnectionEstablishmentStatus::REMOTE_ENDPOINT_REJECTED);
+}
+
+template <typename Platform>
+void ClientProxy<Platform>::localEndpointAcceptedConnection(
+    const std::string& endpoint_id, Ptr<PayloadListener> payload_listener) {
+  Synchronized s(lock_.get());
+
+  if (hasLocalEndpointResponded(endpoint_id)) {
+    // TODO(tracyzhou): Add logging.
+    return;
+  }
+
+  appendConnectionEstablishmentStatus(
+      endpoint_id, ConnectionEstablishmentStatus::LOCAL_ENDPOINT_ACCEPTED);
+  payload_listeners_.insert(std::make_pair(endpoint_id, payload_listener));
+}
+
+template <typename Platform>
+void ClientProxy<Platform>::localEndpointRejectedConnection(
+    const std::string& endpoint_id) {
+  Synchronized s(lock_.get());
+
+  if (hasLocalEndpointResponded(endpoint_id)) {
+    // TODO(tracyzhou): Add logging.
+    return;
+  }
+
+  appendConnectionEstablishmentStatus(
+      endpoint_id, ConnectionEstablishmentStatus::LOCAL_ENDPOINT_REJECTED);
+}
+
+template <typename Platform>
+void ClientProxy<Platform>::remoteEndpointAcceptedConnection(
+    const std::string& endpoint_id) {
+  Synchronized s(lock_.get());
+
+  if (hasRemoteEndpointResponded(endpoint_id)) {
+    // TODO(tracyzhou): Add logging.
+    return;
+  }
+
+  appendConnectionEstablishmentStatus(
+      endpoint_id, ConnectionEstablishmentStatus::REMOTE_ENDPOINT_ACCEPTED);
+}
+
+template <typename Platform>
+void ClientProxy<Platform>::remoteEndpointRejectedConnection(
+    const std::string& endpoint_id) {
+  Synchronized s(lock_.get());
+
+  if (hasRemoteEndpointResponded(endpoint_id)) {
+    // TODO(tracyzhou): Add logging.
+    return;
+  }
+
+  appendConnectionEstablishmentStatus(
+      endpoint_id, ConnectionEstablishmentStatus::REMOTE_ENDPOINT_REJECTED);
+}
+
+template <typename Platform>
+bool ClientProxy<Platform>::isConnectionAccepted(
+    const std::string& endpoint_id) {
+  Synchronized s(lock_.get());
+
+  return connectionEstablishmentStatusesContains(
+             endpoint_id,
+             ConnectionEstablishmentStatus::LOCAL_ENDPOINT_ACCEPTED) &&
+         connectionEstablishmentStatusesContains(
+             endpoint_id,
+             ConnectionEstablishmentStatus::REMOTE_ENDPOINT_ACCEPTED);
+}
+
+template <typename Platform>
+bool ClientProxy<Platform>::isConnectionRejected(
+    const std::string& endpoint_id) {
+  Synchronized s(lock_.get());
+
+  return connectionEstablishmentStatusesContains(
+             endpoint_id,
+             ConnectionEstablishmentStatus::LOCAL_ENDPOINT_REJECTED) ||
+         connectionEstablishmentStatusesContains(
+             endpoint_id,
+             ConnectionEstablishmentStatus::REMOTE_ENDPOINT_REJECTED);
+}
+
+template <typename Platform>
+void ClientProxy<Platform>::onPayloadReceived(const std::string& endpoint_id,
+                                              ConstPtr<Payload> payload) {
+  Synchronized s(lock_.get());
+
+  // Avoid leaks.
+  ScopedPtr<ConstPtr<Payload>> scoped_payload(payload);
+
+  if (isConnectedToEndpoint(endpoint_id)) {
+    payload_listeners_.find(endpoint_id)
+        ->second->onPayloadReceived(MakeConstPtr(new OnPayloadReceivedParams(
+            endpoint_id, scoped_payload.release())));
+  }
+}
+
+template <typename Platform>
+void ClientProxy<Platform>::onPayloadTransferUpdate(
+    const std::string& endpoint_id,
+    const PayloadTransferUpdate& payload_transfer_update) {
+  Synchronized s(lock_.get());
+
+  if (isConnectedToEndpoint(endpoint_id)) {
+    payload_listeners_.find(endpoint_id)
+        ->second->onPayloadTransferUpdate(
+            MakeConstPtr(new OnPayloadTransferUpdateParams(
+                endpoint_id, payload_transfer_update)));
+  }
+}
+
+template <typename Platform>
+bool ClientProxy<Platform>::operator==(const ClientProxy<Platform>& rhs) {
+  return this->getClientId() == rhs.getClientId();
+}
+
+template <typename Platform>
+bool ClientProxy<Platform>::operator<(const ClientProxy<Platform>& rhs) {
+  return this->getClientId() < rhs.getClientId();
+}
+
+template <typename Platform>
+void ClientProxy<Platform>::removeAllEndpoints() {
+  Synchronized s(lock_.get());
+
+  // Note: we may want to notify the client of onDisconnected() for each
+  // endpoint, in the case when this is called from stopAllEndpoints(). For now,
+  // just remove without notifying.
+  for (ConnectionLifecycleListenersMap::iterator it =
+           connection_lifecycle_listeners_.begin();
+       it != connection_lifecycle_listeners_.end(); it++) {
+    it->second.destroy();
+  }
+  connection_lifecycle_listeners_.clear();
+
+  for (PayloadListenersMap::iterator it = payload_listeners_.begin();
+       it != payload_listeners_.end(); it++) {
+    it->second.destroy();
+  }
+  payload_listeners_.clear();
+
+  connection_establishment_statuses_.clear();
+}
+
+template <typename Platform>
+bool ClientProxy<Platform>::connectionEstablishmentStatusesContains(
+    const std::string& endpoint_id,
+    typename ConnectionEstablishmentStatus::Value status_to_match) {
+  typename ConnectionEstablishmentStatusesMap::iterator it =
+      connection_establishment_statuses_.find(endpoint_id);
+  if (it == connection_establishment_statuses_.end()) {
+    return false;
+  }
+  const ConnectionMetadata& metadata = it->second;
+  return (metadata.status & status_to_match) != 0;
+}
+
+template <typename Platform>
+void ClientProxy<Platform>::appendConnectionEstablishmentStatus(
+    const std::string& endpoint_id,
+    typename ConnectionEstablishmentStatus::Value status_to_append) {
+  typename ConnectionEstablishmentStatusesMap::iterator it =
+      connection_establishment_statuses_.find(endpoint_id);
+  if (it == connection_establishment_statuses_.end()) {
+    return;
+  }
+  ConnectionMetadata& metadata = it->second;
+  metadata.status = static_cast<typename ConnectionEstablishmentStatus::Value>(
+      metadata.status | status_to_append);
+}
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/client_proxy.h

@@ -0,0 +1,241 @@
+#ifndef CORE_INTERNAL_CLIENT_PROXY_H_
+#define CORE_INTERNAL_CLIENT_PROXY_H_
+
+#include <cstdint>
+#include <map>
+#include <set>
+#include <vector>
+
+#include "core/listeners.h"
+#include "core/strategy.h"
+#include "platform/api/lock.h"
+#include "platform/byte_array.h"
+#include "platform/port/string.h"
+#include "platform/ptr.h"
+#include "proto/connections_enums.pb.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+template <typename Platform>
+class ClientProxy {
+ public:
+  static const std::int32_t kEndpointIdLength;
+
+  ClientProxy();
+  ~ClientProxy();
+
+  std::int64_t getClientId() const;
+
+  std::string generateLocalEndpointId();
+
+  // Clears all the runtime state of this client.
+  void reset();
+
+  // Marks this client as advertising with the given callbacks.
+  void startedAdvertising(
+      const std::string& service_id, const Strategy& strategy,
+      Ptr<ConnectionLifecycleListener> connection_lifecycle_listener,
+      const std::vector<proto::connections::Medium>& mediums);
+  // Marks this client as not advertising.
+  void stoppedAdvertising();
+  bool isAdvertising();
+  std::string getAdvertisingServiceId();
+
+  // Marks this client as discovering with the given callback.
+  void startedDiscovery(const std::string& service_id, const Strategy& strategy,
+                        Ptr<DiscoveryListener> discovery_listener,
+                        const std::vector<proto::connections::Medium>& mediums);
+  // Marks this client as not discovering at all.
+  void stoppedDiscovery();
+  bool isDiscoveringServiceId(const std::string& service_id);
+  bool isDiscovering();
+  std::string getDiscoveryServiceId();
+
+  // Proxies to the client's DiscoveryListener.onEndpointFound() callback.
+  void onEndpointFound(const std::string& endpoint_id,
+                       const std::string& service_id,
+                       const std::string& endpoint_name,
+                       proto::connections::Medium medium);
+  // Proxies to the client's DiscoveryListener.onEndpointLost() callback.
+  void onEndpointLost(const std::string& service_id,
+                      const std::string& endpoint_id);
+
+  // Proxies to the client's ConnectionLifecycleListener.onConnectionInitiated()
+  // callback.
+  void onConnectionInitiated(
+      const std::string& endpoint_id, const std::string& endpoint_name,
+      const std::string& authentication_token,
+      ConstPtr<ByteArray> raw_authentication_token, bool is_incoming_connection,
+      Ptr<ConnectionLifecycleListener> connection_lifecycle_listener);
+  // Proxies to the client's ConnectionLifecycleListener.onConnectionResult()
+  // callback.
+  void onConnectionResult(const std::string& endpoint_id, Status::Value status);
+
+  void onBandwidthChanged(const std::string& endpoint_id, std::int32_t quality);
+
+  // Removes the endpoint from this client's list of connected endpoints. If
+  // notify is true, also calls the client's
+  // ConnectionLifecycleListener.onDisconnected() callback.
+  void onDisconnected(const std::string& endpoint_id, bool notify);
+
+  // Returns true if it's safe to send payloads to this endpoint.
+  bool isConnectedToEndpoint(const std::string& endpoint_id);
+  // Returns all endpoints that can safely be sent payloads.
+  std::vector<std::string> getConnectedEndpoints();
+  // Returns all endpoints that are still awaiting acceptance.
+  std::vector<std::string> getPendingConnectedEndpoints();
+  // Returns the number of endpoints that are connected and outgoing.
+  std::int32_t getNumOutgoingConnections();
+  // Returns the number of endpoints that are connected and incoming.
+  std::int32_t getNumIncomingConnections();
+  // If true, then we're in the process of approving (or rejecting) a
+  // connection. No payloads should be sent until isConnectedToEndpoint()
+  // returns true.
+  bool hasPendingConnectionToEndpoint(const std::string& endpoint_id);
+  // Returns true if the local endpoint has already marked itself as
+  // accepted/rejected.
+  bool hasLocalEndpointResponded(const std::string& endpoint_id);
+  // Returns true if the remote endpoint has already marked themselves as
+  // accepted/rejected.
+  bool hasRemoteEndpointResponded(const std::string& endpoint_id);
+  // Marks the local endpoint as having accepted the connection.
+  void localEndpointAcceptedConnection(const std::string& endpoint_id,
+                                       Ptr<PayloadListener> payload_listener);
+  // Marks the local endpoint as having rejected the connection.
+  void localEndpointRejectedConnection(const std::string& endpoint_id);
+  // Marks the remote endpoint as having accepted the connection.
+  void remoteEndpointAcceptedConnection(const std::string& endpoint_id);
+  // Marks the remote endpoint as having rejected the connection.
+  void remoteEndpointRejectedConnection(const std::string& endpoint_id);
+  // Returns true if both the local endpoint and the remote endpoint have
+  // accepted the connection.
+  bool isConnectionAccepted(const std::string& endpoint_id);
+  // Returns true if either the local endpoint or the remote endpoint has
+  // rejected the connection.
+  bool isConnectionRejected(const std::string& endpoint_id);
+
+  // Proxies to the client's PayloadListener.onPayloadReceived() callback.
+  void onPayloadReceived(const std::string& endpoint_id,
+                         ConstPtr<Payload> payload);
+  // Proxies to the client's PayloadListener.onPayloadTransferUpdate() callback.
+  void onPayloadTransferUpdate(
+      const std::string& endpoint_id,
+      const PayloadTransferUpdate& payload_transfer_update);
+
+  // Operator overloads when comparing Ptr<ClientProxy>.
+  bool operator==(const ClientProxy<Platform>& rhs);
+  bool operator<(const ClientProxy<Platform>& rhs);
+
+ private:
+  struct ConnectionEstablishmentStatus {
+    enum Value {
+      PENDING = 0,
+      LOCAL_ENDPOINT_ACCEPTED = 1 << 0,
+      LOCAL_ENDPOINT_REJECTED = 1 << 1,
+      REMOTE_ENDPOINT_ACCEPTED = 1 << 2,
+      REMOTE_ENDPOINT_REJECTED = 1 << 3,
+      CONNECTED = 1 << 4,
+    };
+  };
+
+  struct AdvertisingInfo {
+    const std::string service_id;
+    Ptr<ConnectionLifecycleListener> connection_lifecycle_listener;
+
+    AdvertisingInfo(
+        const std::string& service_id,
+        Ptr<ConnectionLifecycleListener> connection_lifecycle_listener)
+        : service_id(service_id),
+          connection_lifecycle_listener(connection_lifecycle_listener) {}
+  };
+
+  struct DiscoveryInfo {
+    const std::string service_id;
+    ScopedPtr<Ptr<DiscoveryListener> > discovery_listener;
+
+    DiscoveryInfo(const std::string& service_id,
+                  Ptr<DiscoveryListener> discovery_listener)
+        : service_id(service_id), discovery_listener(discovery_listener) {}
+  };
+
+  struct ConnectionMetadata {
+    const bool is_incoming;
+    typename ConnectionEstablishmentStatus::Value status;
+
+    explicit ConnectionMetadata(bool is_incoming)
+        : is_incoming(is_incoming),
+          status(ConnectionEstablishmentStatus::PENDING) {}
+  };
+
+  void removeAllEndpoints();
+
+  bool connectionEstablishmentStatusesContains(
+      const std::string& endpoint_id,
+      typename ConnectionEstablishmentStatus::Value status_to_match);
+  void appendConnectionEstablishmentStatus(
+      const std::string& endpoint_id,
+      typename ConnectionEstablishmentStatus::Value status_to_append);
+
+  ScopedPtr<Ptr<Lock> > lock_;
+  const std::int64_t client_id_;
+
+  // If set, we are currently advertising and accepting connection requests for
+  // the given service_id.
+  Ptr<AdvertisingInfo> advertising_info_;
+
+  // If set, we are currently discovering for the given service_id.
+  Ptr<DiscoveryInfo> discovery_info_;
+
+  /**
+   * Map of endpoint_ids -> ConnectionMetadata. ConnectionMetadata.status may be
+   * either ConnectionEstablishmentStatus::PENDING, a combination of
+   * ConnectionEstablishmentStatus::LOCAL_ENDPOINT_ACCEPTED:
+   * ConnectionEstablishmentStatus::LOCAL_ENDPOINT_REJECTED and
+   * ConnectionEstablishmentStatus::REMOTE_ENDPOINT_ACCEPTED:
+   * ConnectionEstablishmentStatus::REMOTE_ENDPOINT_REJECTED, or
+   * ConnectionEstablishmentStatus::CONNECTED. Only when this is set to
+   * CONNECTED should you allow payload transfers.
+   */
+  typedef std::map<std::string, ConnectionMetadata>
+      ConnectionEstablishmentStatusesMap;
+  ConnectionEstablishmentStatusesMap connection_establishment_statuses_;
+
+  /**
+   * Map of endpoint_ids -> ConnectionLifecycleListeners. Every endpoint in here
+   * is guaranteed to at least be in
+   * ConnectionEstablishmentStatus::PENDING -- the precise status can be found
+   * from the corresponding entry in connection_establishment_statuses.
+   */
+  typedef std::map<std::string, Ptr<ConnectionLifecycleListener> >
+      ConnectionLifecycleListenersMap;
+  ConnectionLifecycleListenersMap connection_lifecycle_listeners_;
+
+  /**
+   * Map of endpoint_ids -> PayloadListeners. Every endpoint in here is
+   * guaranteed to at least be in
+   * ConnectionEstablishmentStatus::LOCAL_ENDPOINT_ACCEPTED -- the
+   * precise status can be found from the corresponding entry in
+   * connection_establishment_statuses.
+   */
+  typedef std::map<std::string, Ptr<PayloadListener> > PayloadListenersMap;
+  PayloadListenersMap payload_listeners_;
+
+  /**
+   * A cache of endpoint ids that we've already notified the discoverer of. We
+   * check this cache before calling onEndpointFound() so that we don't notify
+   * the client multiple times for the same endpoint. This would otherwise
+   * happen because some mediums (like Bluetooth) repeatedly give us the same
+   * endpoints after each scan.
+   */
+  std::set<std::string> discovered_endpoint_ids_;
+};
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#include "core/internal/client_proxy.cc"
+
+#endif  // CORE_INTERNAL_CLIENT_PROXY_H_

cpp/core/internal/encryption_runner.cc

@@ -0,0 +1,437 @@
+#include "core/internal/encryption_runner.h"
+
+#include <cinttypes>
+#include <cstdint>
+
+#include "platform/base64_utils.h"
+#include "platform/byte_array.h"
+#include "platform/cancelable_alarm.h"
+#include "platform/exception.h"
+#include "platform/logging.h"
+#include "absl/strings/ascii.h"
+
+namespace {
+
+std::int64_t kTimeoutMillis = 15 * 1000;  // 15 seconds
+std::int32_t kMaxUkey2VerificationStringLength = 32;
+std::int32_t kTokenLength = 5;
+securegcm::UKey2Handshake::HandshakeCipher kCipher =
+    securegcm::UKey2Handshake::HandshakeCipher::P256_SHA512;
+
+}  // namespace
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+namespace {
+
+// Transforms a raw UKEY2 token (which is a random ByteArray that's
+// kMaxUkey2VerificationStringLength long) into a kTokenLength string that only
+// uses A-Z0-9 for each character.
+string toHumanReadableString(ConstPtr<ByteArray> token) {
+  string result = Base64Utils::encode(token).substr(0, kTokenLength);
+  absl::AsciiStrToUpper(&result);
+  return result;
+}
+
+template <typename Platform>
+bool handleEncryptionSuccess(
+    const string& endpoint_id, Ptr<securegcm::UKey2Handshake> ukey2_handshake,
+    Ptr<typename EncryptionRunner<Platform>::ResultListener> result_listener) {
+  ScopedPtr<Ptr<securegcm::UKey2Handshake>> scoped_ukey2_handshake(
+      ukey2_handshake);
+
+  std::unique_ptr<string> verification_string =
+      scoped_ukey2_handshake->GetVerificationString(
+          kMaxUkey2VerificationStringLength);
+  if (verification_string == nullptr) {
+    return false;
+  }
+
+  ScopedPtr<ConstPtr<ByteArray>> raw_authentication_token(MakeConstPtr(
+      new ByteArray(verification_string->data(), verification_string->size())));
+
+  result_listener->onEncryptionSuccess(
+      endpoint_id, scoped_ukey2_handshake.release(),
+      toHumanReadableString(raw_authentication_token.get()),
+      raw_authentication_token.release());
+
+  return true;
+}
+
+template <typename Platform>
+class CancelableAlarmRunnable : public Runnable {
+ public:
+  CancelableAlarmRunnable(Ptr<ClientProxy<Platform>> client_proxy,
+                          const string& endpoint_id,
+                          Ptr<EndpointChannel> endpoint_channel)
+      : client_proxy_(client_proxy),
+        endpoint_id_(endpoint_id),
+        endpoint_channel_(endpoint_channel) {}
+
+  void run() override {
+    NEARBY_LOG(INFO,
+               "Timing out encryption for client %" PRId64
+               " to endpoint %s after %" PRId64 " ms",
+               client_proxy_->getClientId(), endpoint_id_.c_str(),
+               kTimeoutMillis);
+    endpoint_channel_->close();
+  }
+
+ private:
+  Ptr<ClientProxy<Platform>> client_proxy_;
+  const string endpoint_id_;
+  Ptr<EndpointChannel> endpoint_channel_;
+};
+
+template <typename Platform>
+class ServerRunnable : public Runnable {
+ public:
+  ServerRunnable(Ptr<ClientProxy<Platform>> client_proxy,
+                 Ptr<typename Platform::ScheduledExecutorType> alarm_executor,
+                 const string& endpoint_id,
+                 Ptr<EndpointChannel> endpoint_channel,
+                 Ptr<typename EncryptionRunner<Platform>::ResultListener>
+                     encryption_result_listener)
+      : client_proxy_(client_proxy),
+        alarm_executor_(alarm_executor),
+        endpoint_id_(endpoint_id),
+        endpoint_channel_(endpoint_channel),
+        encryption_result_listener_(encryption_result_listener) {}
+
+  void run() override {
+    CancelableAlarm<Platform> timeout_alarm(
+        "EncryptionRunner.startServer() timeout",
+        MakePtr(new CancelableAlarmRunnable<Platform>(
+            client_proxy_, endpoint_id_, endpoint_channel_)),
+        kTimeoutMillis, alarm_executor_);
+
+    std::unique_ptr<securegcm::UKey2Handshake> server =
+        securegcm::UKey2Handshake::ForResponder(kCipher);
+    // Java code throws a HandshakeException.
+    if (server == nullptr) {
+      logException();
+      handleHandshakeOrIOException(timeout_alarm);
+      return;
+    }
+
+    // Message 1 (Client Init)
+    ExceptionOr<ConstPtr<ByteArray>> client_init = endpoint_channel_->read();
+    if (!client_init.ok()) {
+      if (Exception::IO == client_init.exception()) {
+        logException();
+        handleHandshakeOrIOException(timeout_alarm);
+        return;
+      }
+    }
+
+    ScopedPtr<ConstPtr<ByteArray>> scoped_client_init(client_init.result());
+
+    securegcm::UKey2Handshake::ParseResult parse_result =
+        server->ParseHandshakeMessage(
+            string(scoped_client_init->getData(), scoped_client_init->size()));
+
+    // Java code throws a HandshakeException / AlertException.
+    if (!parse_result.success) {
+      logException();
+      if (parse_result.alert_to_send != nullptr) {
+        handleAlertException(parse_result);
+      }
+      handleHandshakeOrIOException(timeout_alarm);
+      return;
+    }
+
+    NEARBY_LOG(INFO, "In startServer(), read UKEY2 Message 1 from endpoint %s",
+               endpoint_id_.c_str());
+
+    // Message 2 (Server Init)
+    std::unique_ptr<string> server_init = server->GetNextHandshakeMessage();
+
+    // Java code throws a HandshakeException.
+    if (server_init == nullptr) {
+      logException();
+      handleHandshakeOrIOException(timeout_alarm);
+      return;
+    }
+
+    Exception::Value write_exception = endpoint_channel_->write(
+        MakeConstPtr(new ByteArray(server_init->data(), server_init->size())));
+    if (Exception::NONE != write_exception) {
+      if (Exception::IO == write_exception) {
+        logException();
+        handleHandshakeOrIOException(timeout_alarm);
+        return;
+      }
+    }
+
+    NEARBY_LOG(INFO, "In startServer(), wrote UKEY2 Message 2 to endpoint %s",
+               endpoint_id_.c_str());
+
+    // Message 3 (Client Finish)
+    ExceptionOr<ConstPtr<ByteArray>> client_finish = endpoint_channel_->read();
+
+    if (!client_finish.ok()) {
+      if (Exception::IO == client_finish.exception()) {
+        logException();
+        handleHandshakeOrIOException(timeout_alarm);
+        return;
+      }
+    }
+
+    ScopedPtr<ConstPtr<ByteArray>> scoped_client_finish(client_finish.result());
+    parse_result = server->ParseHandshakeMessage(
+        string(scoped_client_finish->getData(), scoped_client_finish->size()));
+
+    // Java code throws an AlertException or a HandshakeException.
+    if (!parse_result.success) {
+      logException();
+      if (parse_result.alert_to_send != nullptr) {
+        handleAlertException(parse_result);
+      }
+      handleHandshakeOrIOException(timeout_alarm);
+      return;
+    }
+
+    NEARBY_LOG(INFO, "In startServer(), read UKEY2 Message 3 from endpoint %s",
+               endpoint_id_.c_str());
+
+    timeout_alarm.cancel();
+
+    if (!handleEncryptionSuccess<Platform>(endpoint_id_,
+                                           MakePtr(server.release()),
+                                           encryption_result_listener_.get())) {
+      logException();
+      handleHandshakeOrIOException(timeout_alarm);
+      return;
+    }
+  }
+
+ private:
+  void logException() {
+    NEARBY_LOG(ERROR, "In startServer(), UKEY2 failed with endpoint %s",
+               endpoint_id_.c_str());
+  }
+
+  void handleHandshakeOrIOException(CancelableAlarm<Platform>& timeout_alarm) {
+    timeout_alarm.cancel();
+    encryption_result_listener_->onEncryptionFailure(endpoint_id_,
+                                                     endpoint_channel_);
+  }
+
+  void handleAlertException(
+      const securegcm::UKey2Handshake::ParseResult& parse_result) {
+    Exception::Value write_exception = endpoint_channel_->write(
+        MakeConstPtr(new ByteArray(parse_result.alert_to_send->data(),
+                                   parse_result.alert_to_send->size())));
+    if (Exception::NONE != write_exception) {
+      if (Exception::IO == write_exception) {
+        NEARBY_LOG(WARNING,
+                   "In startServer(), client %" PRId64
+                   " failed to pass the alert error message to endpoint %s",
+                   client_proxy_->getClientId(), endpoint_id_.c_str());
+      }
+    }
+  }
+
+  Ptr<ClientProxy<Platform>> client_proxy_;
+  Ptr<typename Platform::ScheduledExecutorType> alarm_executor_;
+  const string endpoint_id_;
+  Ptr<EndpointChannel> endpoint_channel_;
+  ScopedPtr<Ptr<typename EncryptionRunner<Platform>::ResultListener>>
+      encryption_result_listener_;
+};
+
+template <typename Platform>
+class ClientRunnable : public Runnable {
+ public:
+  ClientRunnable(Ptr<ClientProxy<Platform>> client_proxy,
+                 Ptr<typename Platform::ScheduledExecutorType> alarm_executor,
+                 const string& endpoint_id,
+                 Ptr<EndpointChannel> endpoint_channel,
+                 Ptr<typename EncryptionRunner<Platform>::ResultListener>
+                     encryption_result_listener)
+      : client_proxy_(client_proxy),
+        alarm_executor_(alarm_executor),
+        endpoint_id_(endpoint_id),
+        endpoint_channel_(endpoint_channel),
+        encryption_result_listener_(encryption_result_listener) {}
+
+  void run() override {
+    CancelableAlarm<Platform> timeout_alarm(
+        "EncryptionRunner.startClient() timeout",
+        MakePtr(new CancelableAlarmRunnable<Platform>(
+            client_proxy_, endpoint_id_, endpoint_channel_)),
+        kTimeoutMillis, alarm_executor_);
+
+    std::unique_ptr<securegcm::UKey2Handshake> client =
+        securegcm::UKey2Handshake::ForInitiator(kCipher);
+
+    // Java code throws a HandshakeException.
+    if (client == nullptr) {
+      logException();
+      handleHandshakeOrIOException(timeout_alarm);
+      return;
+    }
+
+    // Message 1 (Client Init)
+    std::unique_ptr<string> client_init = client->GetNextHandshakeMessage();
+
+    // Java code throws a HandshakeException.
+    if (client_init == nullptr) {
+      logException();
+      handleHandshakeOrIOException(timeout_alarm);
+      return;
+    }
+
+    Exception::Value write_init_exception = endpoint_channel_->write(
+        MakeConstPtr(new ByteArray(client_init->data(), client_init->size())));
+    if (Exception::NONE != write_init_exception) {
+      if (Exception::IO == write_init_exception) {
+        logException();
+        handleHandshakeOrIOException(timeout_alarm);
+        return;
+      }
+    }
+
+    NEARBY_LOG(INFO, "In startClient(), wrote UKEY2 Message 1 to endpoint %s",
+               endpoint_id_.c_str());
+
+    // Message 2 (Server Init)
+    ExceptionOr<ConstPtr<ByteArray>> server_init = endpoint_channel_->read();
+
+    if (!server_init.ok()) {
+      if (Exception::IO == server_init.exception()) {
+        logException();
+        handleHandshakeOrIOException(timeout_alarm);
+        return;
+      }
+    }
+
+    ScopedPtr<ConstPtr<ByteArray>> scoped_server_init(server_init.result());
+    securegcm::UKey2Handshake::ParseResult parse_result =
+        client->ParseHandshakeMessage(
+            string(scoped_server_init->getData(), scoped_server_init->size()));
+
+    // Java code throws an AlertException or a HandshakeException.
+    if (!parse_result.success) {
+      logException();
+      if (parse_result.alert_to_send != nullptr) {
+        handleAlertException(parse_result);
+      }
+      handleHandshakeOrIOException(timeout_alarm);
+      return;
+    }
+
+    NEARBY_LOG(INFO, "In startClient(), read UKEY2 Message 2 from endpoint %s",
+               endpoint_id_.c_str());
+
+    // Message 3 (Client Finish)
+    std::unique_ptr<string> client_finish = client->GetNextHandshakeMessage();
+
+    // Java code throws a HandshakeException.
+    if (client_finish == nullptr) {
+      logException();
+      handleHandshakeOrIOException(timeout_alarm);
+      return;
+    }
+
+    Exception::Value write_finish_exception =
+        endpoint_channel_->write(MakeConstPtr(
+            new ByteArray(client_finish->data(), client_finish->size())));
+    if (Exception::NONE != write_finish_exception) {
+      if (Exception::IO == write_finish_exception) {
+        logException();
+        handleHandshakeOrIOException(timeout_alarm);
+        return;
+      }
+    }
+
+    NEARBY_LOG(INFO, "In startClient(), wrote UKEY2 Message 3 to endpoint %s",
+               endpoint_id_.c_str());
+
+    timeout_alarm.cancel();
+
+    if (!handleEncryptionSuccess<Platform>(endpoint_id_,
+                                           MakePtr(client.release()),
+                                           encryption_result_listener_.get())) {
+      logException();
+      handleHandshakeOrIOException(timeout_alarm);
+      return;
+    }
+  }
+
+ private:
+  void logException() {
+    NEARBY_LOG(ERROR, "In startClient(), UKEY2 failed with endpoint %s",
+               endpoint_id_.c_str());
+  }
+
+  void handleHandshakeOrIOException(CancelableAlarm<Platform>& timeout_alarm) {
+    timeout_alarm.cancel();
+    encryption_result_listener_->onEncryptionFailure(endpoint_id_,
+                                                     endpoint_channel_);
+  }
+
+  void handleAlertException(
+      const securegcm::UKey2Handshake::ParseResult& parse_result) {
+    Exception::Value write_exception = endpoint_channel_->write(
+        MakeConstPtr(new ByteArray(parse_result.alert_to_send->data(),
+                                   parse_result.alert_to_send->size())));
+    if (Exception::NONE != write_exception) {
+      if (Exception::IO == write_exception) {
+        NEARBY_LOG(WARNING,
+                   "In startClient(), client %" PRId64
+                   " failed to pass the alert error message to endpoint %s",
+                   client_proxy_->getClientId(), endpoint_id_.c_str());
+      }
+    }
+  }
+
+  Ptr<ClientProxy<Platform>> client_proxy_;
+  Ptr<typename Platform::ScheduledExecutorType> alarm_executor_;
+  const string endpoint_id_;
+  Ptr<EndpointChannel> endpoint_channel_;
+  ScopedPtr<Ptr<typename EncryptionRunner<Platform>::ResultListener>>
+      encryption_result_listener_;
+};
+
+}  // namespace
+
+template <typename Platform>
+EncryptionRunner<Platform>::EncryptionRunner()
+    : alarm_executor_(Platform::createScheduledExecutor()),
+      server_executor_(Platform::createSingleThreadExecutor()),
+      client_executor_(Platform::createSingleThreadExecutor()) {}
+
+template <typename Platform>
+EncryptionRunner<Platform>::~EncryptionRunner() {
+  // Stop all the ongoing Runnables (as gracefully as possible).
+  client_executor_->shutdown();
+  server_executor_->shutdown();
+  alarm_executor_->shutdown();
+}
+
+template <typename Platform>
+void EncryptionRunner<Platform>::startServer(
+    Ptr<ClientProxy<Platform>> client_proxy, const string& endpoint_id,
+    Ptr<EndpointChannel> endpoint_channel,
+    Ptr<ResultListener> result_listener) {
+  server_executor_->execute(MakePtr(new ServerRunnable<Platform>(
+      client_proxy, alarm_executor_.get(), endpoint_id, endpoint_channel,
+      result_listener)));
+}
+
+template <typename Platform>
+void EncryptionRunner<Platform>::startClient(
+    Ptr<ClientProxy<Platform>> client_proxy, const string& endpoint_id,
+    Ptr<EndpointChannel> endpoint_channel,
+    Ptr<ResultListener> result_listener) {
+  client_executor_->execute(MakePtr(new ClientRunnable<Platform>(
+      client_proxy, alarm_executor_.get(), endpoint_id, endpoint_channel,
+      result_listener)));
+}
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/encryption_runner.h

@@ -0,0 +1,73 @@
+#ifndef CORE_INTERNAL_ENCRYPTION_RUNNER_H_
+#define CORE_INTERNAL_ENCRYPTION_RUNNER_H_
+
+#include "core/internal/client_proxy.h"
+#include "core/internal/endpoint_channel.h"
+#include "platform/byte_array.h"
+#include "platform/port/string.h"
+#include "platform/ptr.h"
+#include "securegcm/ukey2_handshake.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+// Encrypts a connection over UKEY2.
+//
+// <p>NOTE: Stalled EndpointChannels will be disconnected after {TIMEOUT_MILLIS}
+// milliseconds. This is to prevent unverified endpoints from maintaining an
+// indefinite connection to us.
+template <typename Platform>
+class EncryptionRunner {
+ public:
+  EncryptionRunner();
+  ~EncryptionRunner();
+
+  class ResultListener {
+   public:
+    virtual ~ResultListener() {}
+
+    // @EncryptionRunnerThread
+    virtual void onEncryptionSuccess(
+        const string& endpoint_id,
+        Ptr<securegcm::UKey2Handshake> ukey2_handshake,
+        const string& authentication_token,
+        ConstPtr<ByteArray> raw_authentication_token) = 0;
+
+    // Encryption has failed. The remote_endpoint_id and channel are given so
+    // that any pending state can be cleaned up.
+    //
+    // <p>We return the EndpointChannel because, at this stage, simultaneous
+    // connections are a possibility. Use this channel to verify that the state
+    // you're cleaning up is for this EndpointChannel, and not state for another
+    // channel to the same endpoint.
+    //
+    // @EncryptionRunnerThread
+    virtual void onEncryptionFailure(const string& endpoint_id,
+                                     Ptr<EndpointChannel> channel) = 0;
+  };
+
+  // @AnyThread
+  void startServer(Ptr<ClientProxy<Platform> > client_proxy,
+                   const string& endpoint_id,
+                   Ptr<EndpointChannel> endpoint_channel,
+                   Ptr<ResultListener> result_listener);
+  // @AnyThread
+  void startClient(Ptr<ClientProxy<Platform> > client_proxy,
+                   const string& endpoint_id,
+                   Ptr<EndpointChannel> endpoint_channel,
+                   Ptr<ResultListener> result_listener);
+
+ private:
+  ScopedPtr<Ptr<typename Platform::ScheduledExecutorType> > alarm_executor_;
+  ScopedPtr<Ptr<typename Platform::SingleThreadExecutorType> > server_executor_;
+  ScopedPtr<Ptr<typename Platform::SingleThreadExecutorType> > client_executor_;
+};
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#include "core/internal/encryption_runner.cc"
+
+#endif  // CORE_INTERNAL_ENCRYPTION_RUNNER_H_

cpp/core/internal/endpoint_channel.h

@@ -0,0 +1,69 @@
+#ifndef CORE_INTERNAL_ENDPOINT_CHANNEL_H_
+#define CORE_INTERNAL_ENDPOINT_CHANNEL_H_
+
+#include <cstdint>
+
+#include "platform/byte_array.h"
+#include "platform/exception.h"
+#include "platform/port/string.h"
+#include "platform/ptr.h"
+#include "proto/connections_enums.pb.h"
+#include "securegcm/d2d_connection_context_v1.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+class EndpointChannel {
+ public:
+  virtual ~EndpointChannel() {}
+
+  virtual ExceptionOr<ConstPtr<ByteArray> >
+  read() = 0;  // throws Exception::IO, Exception::INTERRUPTED
+
+  virtual Exception::Value write(
+      ConstPtr<ByteArray> data) = 0;  // throws Exception::IO
+
+  // Closes this EndpointChannel, without tracking the closure in analytics.
+  virtual void close() = 0;
+
+  // Closes this EndpointChannel and records the closure with the given reason.
+  virtual void close(proto::connections::DisconnectionReason reason) = 0;
+
+  // Returns a one-word type descriptor for the concrete EndpointChannel
+  // implementation that can be used in log messages; eg: BLUETOOTH, BLE, WIFI.
+  virtual string getType() = 0;
+
+  // Returns the name of the EndpointChannel.
+  virtual string getName() = 0;
+
+  // Returns the analytics enum representing the medium of this EndpointChannel.
+  virtual proto::connections::Medium getMedium() = 0;
+
+  // Enables encryption on the EndpointChannel.
+  //
+  // This method takes ownership of the passed-in 'connection_context'.
+  virtual void enableEncryption(
+      Ptr<securegcm::D2DConnectionContextV1> connection_context) = 0;
+
+  // True if the EndpointChannel is currently pausing all writes.
+  virtual bool isPaused() = 0;
+
+  // Pauses all writes on this EndpointChannel until resume() is called.
+  virtual void pause() = 0;
+
+  // Resumes any writes on this EndpointChannel that were suspended when pause()
+  // was called.
+  virtual void resume() = 0;
+
+  // Returns the timestamp of the last read from this endpoint, or -1 if no
+  // reads have occurred.
+  // TODO(tracyzhou): Clarify units of timestamp.
+  virtual std::int64_t getLastReadTimestamp() = 0;
+};
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#endif  // CORE_INTERNAL_ENDPOINT_CHANNEL_H_

cpp/core/internal/endpoint_channel_manager.cc

@@ -0,0 +1,299 @@
+#include "core/internal/endpoint_channel_manager.h"
+
+#include "core/internal/ble_endpoint_channel.h"
+#include "core/internal/bluetooth_endpoint_channel.h"
+#include "platform/synchronized.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+template <typename Platform>
+EndpointChannelManager<Platform>::EndpointChannelManager(
+    Ptr<MediumManager<Platform> > medium_manager)
+    : lock_(Platform::createLock()),
+      medium_manager_(medium_manager),
+      channel_state_(new ChannelState()) {}
+
+template <typename Platform>
+EndpointChannelManager<Platform>::~EndpointChannelManager() {
+  Synchronized s(lock_.get());
+
+  // TODO(tracyzhou): logger.atDebug().log("Initiating shutdown of
+  // EndpointChannelManager.")
+  channel_state_.destroy();
+  // TODO(tracyzhou): logger.atDebug().log("EndpointChannelManager has shut
+  // down.");
+}
+
+template <typename Platform>
+Ptr<EndpointChannel>
+EndpointChannelManager<Platform>::createOutgoingBluetoothEndpointChannel(
+    const string& channel_name, Ptr<BluetoothSocket> bluetooth_socket) {
+  return BluetoothEndpointChannel<Platform>::createOutgoing(
+      medium_manager_, channel_name, bluetooth_socket);
+}
+
+template <typename Platform>
+Ptr<EndpointChannel>
+EndpointChannelManager<Platform>::createIncomingBluetoothEndpointChannel(
+    const string& channel_name, Ptr<BluetoothSocket> bluetooth_socket) {
+  return BluetoothEndpointChannel<Platform>::createIncoming(
+      medium_manager_, channel_name, bluetooth_socket);
+}
+
+template <typename Platform>
+Ptr<EndpointChannel>
+EndpointChannelManager<Platform>::createOutgoingBLEEndpointChannel(
+    const string& channel_name, Ptr<BLESocket> ble_socket) {
+  return BLEEndpointChannel<Platform>::createOutgoing(medium_manager_,
+                                                      channel_name, ble_socket);
+}
+
+template <typename Platform>
+Ptr<EndpointChannel>
+EndpointChannelManager<Platform>::createIncomingBLEEndpointChannel(
+    const string& channel_name, Ptr<BLESocket> ble_socket) {
+  return BLEEndpointChannel<Platform>::createIncoming(medium_manager_,
+                                                      channel_name, ble_socket);
+}
+
+template <typename Platform>
+void EndpointChannelManager<Platform>::registerChannelForEndpoint(
+    Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_id,
+    Ptr<EndpointChannel> endpoint_channel) {
+  Synchronized s(lock_.get());
+
+  // Just in case there was a previous channel, unregister (and, thus, close) it
+  // now.
+  unregisterChannelForEndpoint(endpoint_id);
+
+  setActiveEndpointChannel(client_proxy, endpoint_id, endpoint_channel);
+
+  // TODO(tracyzhou): Add logging.
+}
+
+#ifdef BANDWIDTH_UPGRADE_MANAGER_IMPLEMENTED
+template <typename Platform>
+Ptr<EndpointChannel>
+EndpointChannelManager<Platform>::replaceChannelForEndpoint(
+    Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_id,
+    Ptr<EndpointChannel> endpoint_channel) {
+  Synchronized s(lock_.get());
+
+  ScopedPtr<Ptr<EndpointChannel> > scoped_previous_endpoint_channel(
+      channel_state_->getChannelForEndpoint(endpoint_id));
+  if (scoped_previous_endpoint_channel.isNull()) {
+    // TODO(tracyzhou): Add logging.
+    return Ptr<EndpointChannel>();
+  }
+
+  setActiveEndpointChannel(client_proxy, endpoint_id, endpoint_channel);
+
+  // TODO(tracyzhou): Add logging.
+
+  return scoped_previous_endpoint_channel.release();
+}
+#endif
+
+template <typename Platform>
+bool EndpointChannelManager<Platform>::encryptChannelForEndpoint(
+    const string& endpoint_id,
+    Ptr<securegcm::D2DConnectionContextV1> encryption_context) {
+  Synchronized s(lock_.get());
+
+  ScopedPtr<Ptr<EndpointChannel> > scoped_endpoint_channel(
+      channel_state_->getChannelForEndpoint(endpoint_id));
+  if (scoped_endpoint_channel.isNull()) {
+    // TODO(tracyzhou): Add logging.
+    return false;
+  }
+
+  // We found the requested EndpointChannel, so encrypt it.
+  encryptChannel(endpoint_id, scoped_endpoint_channel.get(),
+                 encryption_context);
+
+  // Then update 'endpoint_id' to use this new 'encryption_context' here
+  // onwards.
+  //
+  // Remember to manage the memory of the returned
+  // Ptr<securegcm::D2DConnectionContextV1> responsibly, even though we don't
+  // need what's returned.
+  ScopedPtr<Ptr<securegcm::D2DConnectionContextV1> >(
+      channel_state_->updateEncryptionContextForEndpoint(endpoint_id,
+                                                         encryption_context));
+  return true;
+}
+
+template <typename Platform>
+Ptr<EndpointChannel> EndpointChannelManager<Platform>::getChannelForEndpoint(
+    const string& endpoint_id) {
+  Synchronized s(lock_.get());
+
+  return channel_state_->getChannelForEndpoint(endpoint_id);
+}
+
+template <typename Platform>
+void EndpointChannelManager<Platform>::setActiveEndpointChannel(
+    Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_id,
+    Ptr<EndpointChannel> endpoint_channel) {
+#ifdef BANDWIDTH_UPGRADE_MANAGER_IMPLEMENTED
+  // If the endpoint is currently encrypted, encrypt this new
+  // 'endpoint_channel'.
+  if (channel_state_->isEndpointEncrypted(endpoint_id)) {
+    encryptChannel(
+        endpoint_id, endpoint_channel,
+        channel_state_->getEncryptionContextForEndpoint(endpoint_id));
+  }
+#endif
+
+  // Then update 'endpoint_id' to use this new 'endpoint_channel' here onwards.
+  //
+  // Remember to manage the memory of the returned Ptr<EndpointChannel>
+  // responsibly, even though we don't need what's returned.
+  ScopedPtr<Ptr<EndpointChannel> >(
+      channel_state_->updateChannelForEndpoint(endpoint_id, endpoint_channel));
+}
+
+template <typename Platform>
+void EndpointChannelManager<Platform>::encryptChannel(
+    const string& endpoint_id, Ptr<EndpointChannel> endpoint_channel,
+    Ptr<securegcm::D2DConnectionContextV1> encryption_context) {
+  // TODO(tracyzhou): Add logging.
+  endpoint_channel->enableEncryption(encryption_context);
+}
+
+///////////////////////////////// ChannelState /////////////////////////////////
+
+template <typename Platform>
+EndpointChannelManager<Platform>::ChannelState::~ChannelState() {
+  while (!endpoint_id_to_metadata_.empty()) {
+    typename EndpointIdToMetadataMap::iterator it =
+        endpoint_id_to_metadata_.begin();
+    // TODO(tracyzhou): Add logging.
+    removeEndpoint(it->first,
+                   proto::connections::DisconnectionReason::SHUTDOWN);
+  }
+}
+
+template <typename Platform>
+bool EndpointChannelManager<Platform>::ChannelState::isEndpointEncrypted(
+    const string& endpoint_id) {
+  return !getEncryptionContextForEndpoint(endpoint_id).isNull();
+}
+
+template <typename Platform>
+Ptr<EndpointChannel>
+EndpointChannelManager<Platform>::ChannelState::updateChannelForEndpoint(
+    const string& endpoint_id, Ptr<EndpointChannel> endpoint_channel) {
+  Ptr<EndpointChannel> previous_endpoint_channel;
+  Ptr<EndpointMetaData> endpoint_metadata;
+
+  typename EndpointIdToMetadataMap::iterator it =
+      endpoint_id_to_metadata_.find(endpoint_id);
+  if (it == endpoint_id_to_metadata_.end()) {
+    endpoint_metadata = MakePtr(new EndpointMetaData());
+  } else {
+    endpoint_metadata = it->second;
+    previous_endpoint_channel = endpoint_metadata->endpoint_channel;
+  }
+  // Avoid leaks.
+  ScopedPtr<Ptr<EndpointChannel> > scoped_previous_endpoint_channel(
+      previous_endpoint_channel);
+
+  // Upgrade endpoint_channel to be reference-counted before starting to track
+  // it (and make it clear that endpoint_channel no longer owns the raw
+  // pointer).
+  endpoint_metadata->endpoint_channel = MakeRefCountedPtr(&(*endpoint_channel));
+  endpoint_channel.clear();
+  endpoint_id_to_metadata_[endpoint_id] = endpoint_metadata;
+
+  return scoped_previous_endpoint_channel.release();
+}
+
+template <typename Platform>
+Ptr<securegcm::D2DConnectionContextV1> EndpointChannelManager<Platform>::
+    ChannelState::updateEncryptionContextForEndpoint(
+        const string& endpoint_id,
+        Ptr<securegcm::D2DConnectionContextV1> encryption_context) {
+  Ptr<securegcm::D2DConnectionContextV1> previous_encryption_context;
+  Ptr<EndpointMetaData> endpoint_metadata;
+
+  typename EndpointIdToMetadataMap::iterator it =
+      endpoint_id_to_metadata_.find(endpoint_id);
+  if (it == endpoint_id_to_metadata_.end()) {
+    endpoint_metadata = MakePtr(new EndpointMetaData());
+  } else {
+    endpoint_metadata = it->second;
+    previous_encryption_context = endpoint_metadata->encryption_context;
+  }
+  // Avoid leaks.
+  ScopedPtr<Ptr<securegcm::D2DConnectionContextV1> >
+      scoped_previous_encryption_context(previous_encryption_context);
+
+  endpoint_metadata->encryption_context = encryption_context;
+  endpoint_id_to_metadata_[endpoint_id] = endpoint_metadata;
+
+  return scoped_previous_encryption_context.release();
+}
+
+template <typename Platform>
+bool EndpointChannelManager<Platform>::ChannelState::removeEndpoint(
+    const string& endpoint_id, proto::connections::DisconnectionReason reason) {
+  typename EndpointIdToMetadataMap::iterator it =
+      endpoint_id_to_metadata_.find(endpoint_id);
+  if (it == endpoint_id_to_metadata_.end()) {
+    return false;
+  }
+
+  it->second->endpoint_channel->close(reason);
+  it->second.destroy();
+  endpoint_id_to_metadata_.erase(it);
+  return true;
+}
+
+template <typename Platform>
+Ptr<securegcm::D2DConnectionContextV1>
+EndpointChannelManager<Platform>::ChannelState::getEncryptionContextForEndpoint(
+    const string& endpoint_id) {
+  typename EndpointIdToMetadataMap::iterator it =
+      endpoint_id_to_metadata_.find(endpoint_id);
+  if (it == endpoint_id_to_metadata_.end()) {
+    return Ptr<securegcm::D2DConnectionContextV1>();
+  }
+
+  return it->second->encryption_context;
+}
+
+template <typename Platform>
+Ptr<EndpointChannel>
+EndpointChannelManager<Platform>::ChannelState::getChannelForEndpoint(
+    const string& endpoint_id) {
+  typename EndpointIdToMetadataMap::iterator it =
+      endpoint_id_to_metadata_.find(endpoint_id);
+  if (it == endpoint_id_to_metadata_.end()) {
+    return Ptr<EndpointChannel>();
+  }
+
+  return it->second->endpoint_channel;
+}
+
+template <typename Platform>
+bool EndpointChannelManager<Platform>::unregisterChannelForEndpoint(
+    const string& endpoint_id) {
+  Synchronized s(lock_.get());
+
+  if (!channel_state_->removeEndpoint(
+          endpoint_id,
+          proto::connections::DisconnectionReason::LOCAL_DISCONNECTION)) {
+    return false;
+  }
+
+  // TODO(tracyzhou): Add logging.
+
+  return true;
+}
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/endpoint_channel_manager.h

@@ -0,0 +1,143 @@
+#ifndef CORE_INTERNAL_ENDPOINT_CHANNEL_MANAGER_H_
+#define CORE_INTERNAL_ENDPOINT_CHANNEL_MANAGER_H_
+
+#include <map>
+
+#include "core/internal/client_proxy.h"
+#include "core/internal/endpoint_channel.h"
+#include "core/internal/medium_manager.h"
+#include "platform/api/ble.h"
+#include "platform/api/bluetooth_classic.h"
+#include "platform/api/lock.h"
+#include "platform/port/string.h"
+#include "platform/ptr.h"
+#include "securegcm/d2d_connection_context_v1.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+// Manages the communication channels to all the remote endpoints with which we
+// are interacting, including serving as a factory for creating said channels.
+//
+// The factory methods would be static, but for the fact that they need to use
+// the MediumManager.
+template <typename Platform>
+class EndpointChannelManager {
+ public:
+  explicit EndpointChannelManager(Ptr<MediumManager<Platform> > medium_manager);
+  ~EndpointChannelManager();
+
+  Ptr<EndpointChannel> createOutgoingBluetoothEndpointChannel(
+      const string& channel_name, Ptr<BluetoothSocket> bluetooth_socket);
+  Ptr<EndpointChannel> createIncomingBluetoothEndpointChannel(
+      const string& channel_name, Ptr<BluetoothSocket> bluetooth_socket);
+
+  Ptr<EndpointChannel> createOutgoingBLEEndpointChannel(
+      const string& channel_name, Ptr<BLESocket> ble_socket);
+  Ptr<EndpointChannel> createIncomingBLEEndpointChannel(
+      const string& channel_name, Ptr<BLESocket> ble_socket);
+
+  // Registers the initial EndpointChannel to be associated with an endpoint;
+  // if there already exists a previously-associated EndpointChannel, that will
+  // be closed before continuing the registration.
+  void registerChannelForEndpoint(Ptr<ClientProxy<Platform> > client_proxy,
+                                  const string& endpoint_id,
+                                  Ptr<EndpointChannel> endpoint_channel);
+
+#ifdef BANDWIDTH_UPGRADE_MANAGER_IMPLEMENTED
+  // Replaces the EndpointChannel to be associated with an endpoint from here on
+  // in, transferring the encryption context from the previous EndpointChannel
+  // to the newly-provided EndpointChannel.
+  //
+  // Returns the previous EndpointChannel, or null Ptr object if called out of
+  // order.
+  Ptr<EndpointChannel> replaceChannelForEndpoint(
+      Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_id,
+      Ptr<EndpointChannel> endpoint_channel);
+#endif
+
+  bool encryptChannelForEndpoint(
+      const string& endpoint_id,
+      Ptr<securegcm::D2DConnectionContextV1> encryption_context);
+
+  // The returned Ptr will be owned (and destroyed) by the caller.
+  Ptr<EndpointChannel> getChannelForEndpoint(const string& endpoint_id);
+
+  // Returns true if 'endpoint_id' actually had a registered EndpointChannel.
+  // IOW, a return of false signifies a no-op.
+  bool unregisterChannelForEndpoint(const string& endpoint_id);
+
+ private:
+  // Tracks channel state for all endpoints. This includes what EndpointChannel
+  // the endpoint is currently using and whether or not the EndpointChannel has
+  // been encrypted yet.
+  class ChannelState {
+   public:
+    ~ChannelState();
+
+    // True if we have an 'encryption_context' for the endpoint.
+    bool isEndpointEncrypted(const string& endpoint_id);
+
+    // Stores a new EndpointChannel for the endpoint, returning the previous
+    // one (if it existed).
+    Ptr<EndpointChannel> updateChannelForEndpoint(
+        const string& endpoint_id, Ptr<EndpointChannel> endpoint_channel);
+    // Stores a new D2DConnectionContextV1 for the endpoint, returning the
+    // previous one (if it existed).
+    Ptr<securegcm::D2DConnectionContextV1> updateEncryptionContextForEndpoint(
+        const string& endpoint_id,
+        Ptr<securegcm::D2DConnectionContextV1> encryption_context);
+
+    // Removes all knowledge of this endpoint, cleaning up as necessary.
+    // Returns false if the endpoint was not found.
+    bool removeEndpoint(const string& endpoint_id,
+                        proto::connections::DisconnectionReason reason);
+
+    // Gets the 'encryption_context' for the endpoint. Null if the endpoint was
+    // not found, or if there is no 'encryption_context' yet.
+    Ptr<securegcm::D2DConnectionContextV1> getEncryptionContextForEndpoint(
+        const string& endpoint_id);
+    // Gets the 'endpoint_channel' for the endpoint. Null if the endpoint was
+    // not found.
+    //
+    // The returned Ptr will be owned (and destroyed) by the caller.
+    Ptr<EndpointChannel> getChannelForEndpoint(const string& endpoint_id);
+
+   private:
+    struct EndpointMetaData {
+      ~EndpointMetaData() {
+        encryption_context.destroy();
+        endpoint_channel.destroy();
+      }
+
+      Ptr<EndpointChannel> endpoint_channel;
+      Ptr<securegcm::D2DConnectionContextV1> encryption_context;
+    };
+
+    // Endpoint ID -> EndpointMetadata. Contains everything we know about the
+    // endpoint.
+    typedef std::map<string, Ptr<EndpointMetaData> > EndpointIdToMetadataMap;
+    EndpointIdToMetadataMap endpoint_id_to_metadata_;
+  };
+
+  void setActiveEndpointChannel(Ptr<ClientProxy<Platform> > client_proxy,
+                                const string& endpoint_id,
+                                Ptr<EndpointChannel> endpoint_channel);
+  void encryptChannel(
+      const string& endpoint_id, Ptr<EndpointChannel> endpoint_channel,
+      Ptr<securegcm::D2DConnectionContextV1> encryption_context);
+
+  ScopedPtr<Ptr<Lock> > lock_;
+
+  Ptr<MediumManager<Platform> > medium_manager_;
+  Ptr<ChannelState> channel_state_;
+};
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#include "core/internal/endpoint_channel_manager.cc"
+
+#endif  // CORE_INTERNAL_ENDPOINT_CHANNEL_MANAGER_H_

cpp/core/internal/endpoint_manager.cc

@@ -0,0 +1,749 @@
+#include "core/internal/endpoint_manager.h"
+
+#include <utility>
+
+#include "core/internal/offline_frames.h"
+#include "proto/connections_enums.pb.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+namespace endpoint_manager {
+
+// A Runnable that continuously grabs the most recent EndpointChannel available
+// for an endpoint. Override
+// EndpointChannelLoopRunnable.execute(EndpointChannel) to interact with the
+// EndpointChannel.
+template <typename Platform>
+class EndpointChannelLoopRunnable : public Runnable {
+ public:
+  EndpointChannelLoopRunnable(Ptr<EndpointManager<Platform>> endpoint_manager,
+                              const string& runnable_name,
+                              Ptr<ClientProxy<Platform>> client_proxy,
+                              const string& endpoint_id)
+      : endpoint_manager_(endpoint_manager),
+        runnable_name_(runnable_name),
+        client_proxy_(client_proxy),
+        endpoint_id_(endpoint_id) {}
+  ~EndpointChannelLoopRunnable() override {}
+
+  void run() override {
+    // The implication of using the EndpointChannel's medium to identify it is
+    // that this loop will break if we ever allow creating multiple
+    // EndpointChannels to the same endpoint over the same medium.
+    proto::connections::Medium last_failed_endpoint_channel_medium =
+        proto::connections::UNKNOWN_MEDIUM;
+    while (true) {
+      // It's important to keep re-fetching the EndpointChannel for an endpoint
+      // because it can be changed out from under us (for example, when we
+      // upgrade from Bluetooth to Wifi).
+      ScopedPtr<Ptr<EndpointChannel>> scoped_endpoint_channel(
+          endpoint_manager_->endpoint_channel_manager_->getChannelForEndpoint(
+              endpoint_id_));
+      if (scoped_endpoint_channel.isNull()) {
+        // TODO(tracyzhou): Add logging.
+        break;
+      }
+
+      // If we're looping back around after a failure, and there's not a new
+      // EndpointChannel for this endpoint, there's nothing more to do here.
+      if ((last_failed_endpoint_channel_medium !=
+           proto::connections::UNKNOWN_MEDIUM) &&
+          (scoped_endpoint_channel->getMedium() ==
+           last_failed_endpoint_channel_medium)) {
+        // TODO(tracyzhou): Add logging.
+        break;
+      }
+
+      ExceptionOr<bool> keep_using_channel =
+          useHealthyEndpointChannel(scoped_endpoint_channel.get());
+
+      if (!keep_using_channel.ok()) {
+        Exception::Value exception = keep_using_channel.exception();
+        if (Exception::IO == exception) {
+          last_failed_endpoint_channel_medium =
+              scoped_endpoint_channel->getMedium();
+          // TODO(tracyzhou): Add logging.
+          continue;
+        }
+        if (Exception::INTERRUPTED == exception) {
+          // Thread.currentThread().interrupt();
+          // TODO(tracyzhou): Add logging.
+          break;
+        }
+      }
+
+      if (!keep_using_channel.result()) {
+        // TODO(tracyzhou): Add logging.
+        break;
+      }
+    }
+
+    // Always clear out all state related to this endpoint before terminating
+    // this thread.
+    endpoint_manager_->discardEndpoint(client_proxy_, endpoint_id_);
+  }
+
+  // Called whenever an EndpointChannel is available for endpointId.
+  // Implementations are expected to read/write freely to the EndpointChannel
+  // until an Exception::IO is thrown. Once an Exception::IO occurs, a check
+  // will be performed to see if another EndpointChannel is available for the
+  // given endpoint and, if so, useHealthyEndpointChannel(EndpointChannel) will
+  // be called again.
+  //
+  // <p>Return false to exit the loop.
+  virtual ExceptionOr<bool> useHealthyEndpointChannel(
+      Ptr<EndpointChannel> endpoint_channel) = 0;  // throws Exception::IO,
+                                                   // Exception::INTERRUPTED
+
+ protected:
+  Ptr<EndpointManager<Platform>> endpoint_manager_;
+  const string runnable_name_;
+  Ptr<ClientProxy<Platform>> client_proxy_;
+  const string endpoint_id_;
+};
+
+template <typename Platform>
+class ReaderRunnable : public EndpointChannelLoopRunnable<Platform> {
+ public:
+  ReaderRunnable(Ptr<EndpointManager<Platform>> endpoint_manager,
+                 Ptr<ClientProxy<Platform>> client_proxy,
+                 const string& endpoint_id)
+      : EndpointChannelLoopRunnable<Platform>(endpoint_manager, "Read",
+                                              client_proxy, endpoint_id) {}
+
+  // @EndpointManagerReaderThread
+  ExceptionOr<bool> useHealthyEndpointChannel(
+      Ptr<EndpointChannel> endpoint_channel) override {
+    // Read as much as we can from the healthy EndpointChannel - when it is no
+    // longer in good shape (i.e. our read from it throws an Exception), our
+    // super class will loop back around and try our luck in case there's been
+    // a replacement for this endpoint since we last checked with the
+    // EndpointChannelManager.
+    while (true) {
+      ExceptionOr<ConstPtr<ByteArray>> read_bytes = endpoint_channel->read();
+      if (!read_bytes.ok()) {
+        if (Exception::INVALID_PROTOCOL_BUFFER == read_bytes.exception()) {
+          // TODO(reznor): logger.atDebug().withCause(e).log("EndpointManager
+          // failed to decode message from endpoint %s on channel %s,
+          // discarding.", endpointId, endpointChannel.getType());
+          continue;
+        } else if (Exception::IO == read_bytes.exception()) {
+          return ExceptionOr<bool>(read_bytes.exception());
+        }
+      }
+      ScopedPtr<ConstPtr<ByteArray>> scoped_read_bytes(read_bytes.result());
+
+      ExceptionOr<ConstPtr<OfflineFrame>> offline_frame =
+          OfflineFrames::fromBytes(scoped_read_bytes.get());
+      if (!offline_frame.ok()) {
+        if (Exception::INVALID_PROTOCOL_BUFFER == offline_frame.exception()) {
+          // TODO(reznor): logger.atDebug().withCause(e).log("EndpointManager
+          // received an invalid OfflineFrame from endpoint %s on channel %s,
+          // discarding.", endpointId, endpointChannel.getType());
+          continue;
+        }
+      }
+      ScopedPtr<ConstPtr<OfflineFrame>> scoped_offline_frame(
+          offline_frame.result());
+
+      // Route the incoming offlineFrame to its registered processor.
+      V1Frame::FrameType frame_type =
+          OfflineFrames::getFrameType(scoped_offline_frame.get());
+      Ptr<typename EndpointManager<Platform>::IncomingOfflineFrameProcessor>
+          incoming_offline_frame_processor =
+              this->endpoint_manager_->getOfflineFrameProcessor(frame_type);
+      if (incoming_offline_frame_processor.isNull()) {
+        // TODO(tracyzhou): Add logging.
+        continue;
+      }
+
+      incoming_offline_frame_processor->processIncomingOfflineFrame(
+          scoped_offline_frame.release(), this->endpoint_id_,
+          this->client_proxy_, endpoint_channel->getMedium());
+    }
+  }
+};
+
+template <typename Platform>
+class KeepAliveManagerRunnable : public EndpointChannelLoopRunnable<Platform> {
+ public:
+  KeepAliveManagerRunnable(Ptr<EndpointManager<Platform>> endpoint_manager,
+                           Ptr<ClientProxy<Platform>> client_proxy,
+                           const string& endpoint_id)
+      : EndpointChannelLoopRunnable<Platform>(
+            endpoint_manager, "KeepAliveManager", client_proxy, endpoint_id) {}
+
+  // @EndpointManagerKeepAliveThread
+  ExceptionOr<bool> useHealthyEndpointChannel(
+      Ptr<EndpointChannel> endpoint_channel) override {
+    // Check if it has been too long since we received a frame from our
+    // endpoint.
+    if ((endpoint_channel->getLastReadTimestamp() != -1) &&
+        ((endpoint_channel->getLastReadTimestamp() +
+          EndpointManager<Platform>::kKeepAliveReadTimeoutMillis) <
+         this->endpoint_manager_->system_clock_->elapsedRealtime())) {
+      // TODO(tracyzhou): Add logging.
+      return ExceptionOr<bool>(false);
+    }
+
+    // Attempt to send the KeepAlive frame over the endpoint channel - if the
+    // write fails, our super class will loop back around and try our luck again
+    // in case there's been a replacement for this endpoint.
+    Exception::Value write_exception =
+        endpoint_channel->write(OfflineFrames::forKeepAlive());
+    if (Exception::NONE != write_exception) {
+      if (Exception::IO == write_exception) {
+        return ExceptionOr<bool>(write_exception);
+      }
+    }
+
+    // We sleep as the very last step because we want to minimize the caching of
+    // the EndpointChannel. If we do hold on to the EndpointChannel, and it's
+    // switched out from under us in BandwidthUpgradeManager, our write will
+    // trigger an erroneous write to the encryption context that will cascade
+    // into all our remote endpoint's future reads failing.
+    Exception::Value sleep_exception =
+        this->endpoint_manager_->thread_utils_->sleep(
+            EndpointManager<Platform>::kKeepAliveWriteIntervalMillis);
+    if (Exception::NONE != sleep_exception) {
+      if (Exception::INTERRUPTED == sleep_exception) {
+        return ExceptionOr<bool>(sleep_exception);
+      }
+    }
+
+    return ExceptionOr<bool>(true);
+  }
+};
+
+template <typename Platform>
+class RegisterIncomingOfflineFrameProcessorRunnable : public Runnable {
+ public:
+  RegisterIncomingOfflineFrameProcessorRunnable(
+      Ptr<EndpointManager<Platform>> endpoint_manager,
+      V1Frame::FrameType frame_type,
+      Ptr<typename EndpointManager<Platform>::IncomingOfflineFrameProcessor>
+          processor)
+      : endpoint_manager_(endpoint_manager),
+        frame_type_(frame_type),
+        processor_(processor) {}
+
+  void run() override {
+    typename EndpointManager<
+        Platform>::IncomingOfflineFrameProcessorsMap::iterator it =
+        endpoint_manager_->incoming_offline_frame_processors_.find(frame_type_);
+    if (it != endpoint_manager_->incoming_offline_frame_processors_.end()) {
+      // TODO(tracyzhou): Add logging.
+      it->second = processor_;
+    } else {
+      endpoint_manager_->incoming_offline_frame_processors_.insert(
+          std::make_pair(frame_type_, processor_));
+    }
+  }
+
+ private:
+  Ptr<EndpointManager<Platform>> endpoint_manager_;
+  const V1Frame::FrameType frame_type_;
+  Ptr<typename EndpointManager<Platform>::IncomingOfflineFrameProcessor>
+      processor_;
+};
+
+template <typename Platform>
+class UnregisterIncomingOfflineFrameProcessorRunnable : public Runnable {
+ public:
+  UnregisterIncomingOfflineFrameProcessorRunnable(
+      Ptr<EndpointManager<Platform>> endpoint_manager,
+      V1Frame::FrameType frame_type,
+      Ptr<typename EndpointManager<Platform>::IncomingOfflineFrameProcessor>
+          processor)
+      : endpoint_manager_(endpoint_manager),
+        frame_type_(frame_type),
+        processor_(processor) {}
+
+  void run() override {
+    typename EndpointManager<
+        Platform>::IncomingOfflineFrameProcessorsMap::iterator it =
+        endpoint_manager_->incoming_offline_frame_processors_.find(frame_type_);
+    if (it != endpoint_manager_->incoming_offline_frame_processors_.end()) {
+      if (it->second != processor_) {
+        // TODO(tracyzhou): Add logging.
+        return;
+      }
+
+      endpoint_manager_->incoming_offline_frame_processors_.erase(it);
+    }
+  }
+
+ private:
+  Ptr<EndpointManager<Platform>> endpoint_manager_;
+  const V1Frame::FrameType frame_type_;
+  Ptr<typename EndpointManager<Platform>::IncomingOfflineFrameProcessor>
+      processor_;
+};
+
+template <typename Platform>
+class RegisterEndpointRunnable : public Runnable {
+ public:
+  RegisterEndpointRunnable(
+      Ptr<EndpointManager<Platform>> endpoint_manager,
+      Ptr<ClientProxy<Platform>> client_proxy, const string& endpoint_id,
+      const string& endpoint_name, const string& authentication_token,
+      ConstPtr<ByteArray> raw_authentication_token, bool is_incoming,
+      Ptr<EndpointChannel> endpoint_channel,
+      Ptr<ConnectionLifecycleListener> connection_lifecycle_listener,
+      Ptr<CountDownLatch> latch)
+      : endpoint_manager_(endpoint_manager),
+        client_proxy_(client_proxy),
+        endpoint_id_(endpoint_id),
+        endpoint_name_(endpoint_name),
+        authentication_token_(authentication_token),
+        raw_authentication_token_(raw_authentication_token),
+        is_incoming_(is_incoming),
+        endpoint_channel_(endpoint_channel),
+        connection_lifecycle_listener_(connection_lifecycle_listener),
+        latch_(latch) {}
+
+  void run() override {
+    endpoint_manager_->endpoint_channel_manager_->registerChannelForEndpoint(
+        client_proxy_, endpoint_id_, endpoint_channel_);
+
+    // For every endpoint, there's one Reader instance running on the
+    // EndpointManagerReaderThread. This instance reads from the endpoint and
+    // delegates incoming frames to various IncomingOfflineFrameProcessors.
+    // Once the frame has been properly handled, it starts reading again for the
+    // next frame. If the Reader fails its read and no other EndpointChannels
+    // are available for this endpoint, a disconnection will be initiated.
+    endpoint_manager_->startEndpointReader(MakePtr(new ReaderRunnable<Platform>(
+        endpoint_manager_, client_proxy_, endpoint_id_)));
+
+    // For every endpoint, there's one KeepAliveManager instance running on the
+    // EndpointManagerKeepAliveThread. This instance will periodically
+    // send out a ping* to the endpoint while listening for an incoming pong**.
+    // If it fails to send the ping, or if no pong is heard within
+    // kKeepAliveReadTimeoutMillis milliseconds, it initiates a
+    // disconnection.
+    //
+    // (*) Bluetooth requires a constant outgoing stream of messages. If there's
+    // silence, Android will break the socket. This is why we ping.
+    // (**) Wifi Hotspots can fail to notice a connection has been lost, and
+    // they will happily keep writing to /dev/null. This is why we listen for
+    // the pong.
+    endpoint_manager_->startEndpointKeepAliveManager(
+        MakePtr(new KeepAliveManagerRunnable<Platform>(
+            endpoint_manager_, client_proxy_, endpoint_id_)));
+    // TODO(tracyzhou): Add logging.
+
+    // It's now time to let the client know of this new connection so that they
+    // can accept or reject it.
+    client_proxy_->onConnectionInitiated(
+        endpoint_id_, endpoint_name_, authentication_token_,
+        raw_authentication_token_.release(), is_incoming_,
+        connection_lifecycle_listener_.release());
+    latch_->countDown();
+  }
+
+ private:
+  Ptr<EndpointManager<Platform>> endpoint_manager_;
+  Ptr<ClientProxy<Platform>> client_proxy_;
+  const string endpoint_id_;
+  const string endpoint_name_;
+  const string authentication_token_;
+  ScopedPtr<ConstPtr<ByteArray>> raw_authentication_token_;
+  const bool is_incoming_;
+  Ptr<EndpointChannel> endpoint_channel_;
+  ScopedPtr<Ptr<ConnectionLifecycleListener>> connection_lifecycle_listener_;
+  Ptr<CountDownLatch> latch_;
+};
+
+template <typename Platform>
+class UnregisterEndpointRunnable : public Runnable {
+ public:
+  UnregisterEndpointRunnable(Ptr<EndpointManager<Platform>> endpoint_manager,
+                             Ptr<ClientProxy<Platform>> client_proxy,
+                             const string& endpoint_id,
+                             Ptr<CountDownLatch> latch)
+      : endpoint_manager_(endpoint_manager),
+        client_proxy_(client_proxy),
+        endpoint_id_(endpoint_id),
+        latch_(latch) {}
+
+  void run() override {
+    endpoint_manager_->removeEndpoint(
+        client_proxy_, endpoint_id_, /*send_disconnection_notification=*/false);
+
+    latch_->countDown();
+  }
+
+ private:
+  Ptr<EndpointManager<Platform>> endpoint_manager_;
+  Ptr<ClientProxy<Platform>> client_proxy_;
+  const string endpoint_id_;
+  Ptr<CountDownLatch> latch_;
+};
+
+template <typename Platform>
+class DiscardEndpointRunnable : public Runnable {
+ public:
+  DiscardEndpointRunnable(Ptr<EndpointManager<Platform>> endpoint_manager,
+                          Ptr<ClientProxy<Platform>> client_proxy,
+                          const string& endpoint_id)
+      : endpoint_manager_(endpoint_manager),
+        client_proxy_(client_proxy),
+        endpoint_id_(endpoint_id) {}
+
+  void run() override {
+    endpoint_manager_->removeEndpoint(
+        client_proxy_, endpoint_id_,
+        /*send_disconnection_notification=*/
+        client_proxy_->isConnectedToEndpoint(endpoint_id_));
+  }
+
+ private:
+  Ptr<EndpointManager<Platform>> endpoint_manager_;
+  Ptr<ClientProxy<Platform>> client_proxy_;
+  const string endpoint_id_;
+};
+
+template <typename Platform>
+class GetOfflineFrameProcessorCallable
+    : public Callable<Ptr<
+          typename EndpointManager<Platform>::IncomingOfflineFrameProcessor>> {
+ public:
+  typedef Ptr<typename EndpointManager<Platform>::IncomingOfflineFrameProcessor>
+      ReturnType;
+
+  GetOfflineFrameProcessorCallable(
+      Ptr<EndpointManager<Platform>> endpoint_manager,
+      V1Frame::FrameType frame_type)
+      : endpoint_manager_(endpoint_manager), frame_type_(frame_type) {}
+
+  ExceptionOr<ReturnType> call() override {
+    typename EndpointManager<
+        Platform>::IncomingOfflineFrameProcessorsMap::iterator it =
+        endpoint_manager_->incoming_offline_frame_processors_.find(frame_type_);
+    if (it == endpoint_manager_->incoming_offline_frame_processors_.end()) {
+      return ExceptionOr<ReturnType>(ReturnType());
+    }
+    return ExceptionOr<ReturnType>(it->second);
+  }
+
+ private:
+  Ptr<EndpointManager<Platform>> endpoint_manager_;
+  const V1Frame::FrameType frame_type_;
+};
+
+}  // namespace endpoint_manager
+
+template <typename Platform>
+bool EndpointManager<Platform>::IncomingOfflineFrameProcessor::operator==(
+    const EndpointManager<Platform>::IncomingOfflineFrameProcessor& rhs) {
+  // We're comparing addresses because these objects are callbacks which need to
+  // be matched by exact instances.
+  return this == &rhs;
+}
+
+template <typename Platform>
+bool EndpointManager<Platform>::IncomingOfflineFrameProcessor::operator<(
+    const EndpointManager<Platform>::IncomingOfflineFrameProcessor& rhs) {
+  // We're comparing addresses because these objects are callbacks which need to
+  // be matched by exact instances.
+  return this < &rhs;
+}
+
+template <typename Platform>
+const std::int32_t EndpointManager<Platform>::kKeepAliveWriteIntervalMillis =
+    5000;
+template <typename Platform>
+const std::int32_t EndpointManager<Platform>::kKeepAliveReadTimeoutMillis =
+    30000;
+template <typename Platform>
+const std::int32_t
+    EndpointManager<Platform>::kProcessEndpointDisconnectionTimeoutMillis =
+        2000;
+template <typename Platform>
+const std::int32_t EndpointManager<Platform>::kMaxConcurrentEndpoints = 50;
+
+template <typename Platform>
+EndpointManager<Platform>::EndpointManager(
+    Ptr<EndpointChannelManager<Platform>> endpoint_channel_manager)
+    : thread_utils_(Platform::createThreadUtils()),
+      system_clock_(Platform::createSystemClock()),
+      endpoint_channel_manager_(endpoint_channel_manager),
+      incoming_offline_frame_processors_(),
+      endpoint_keep_alive_manager_thread_pool_(
+          Platform::createMultiThreadExecutor(kMaxConcurrentEndpoints)),
+      endpoint_readers_thread_pool_(
+          Platform::createMultiThreadExecutor(kMaxConcurrentEndpoints)),
+      serial_executor_(Platform::createSingleThreadExecutor()) {}
+
+template <typename Platform>
+EndpointManager<Platform>::~EndpointManager() {
+  // TODO(tracyzhou): Add logging.
+  // Stop all the ongoing Runnables (as gracefully as possible).
+  serial_executor_->shutdown();
+  endpoint_readers_thread_pool_->shutdown();
+  endpoint_keep_alive_manager_thread_pool_->shutdown();
+
+  // 'incoming_offline_frame_processors' does not own the processors.
+  incoming_offline_frame_processors_.clear();
+  // TODO(tracyzhou): Add logging.
+}
+
+template <typename Platform>
+void EndpointManager<Platform>::registerIncomingOfflineFrameProcessor(
+    V1Frame::FrameType frame_type,
+    Ptr<typename EndpointManager<Platform>::IncomingOfflineFrameProcessor>
+        processor) {
+  runOnEndpointManagerThread(MakePtr(
+      new endpoint_manager::RegisterIncomingOfflineFrameProcessorRunnable<
+          Platform>(MakePtr(this), frame_type, processor)));
+}
+
+template <typename Platform>
+void EndpointManager<Platform>::unregisterIncomingOfflineFrameProcessor(
+    V1Frame::FrameType frame_type,
+    Ptr<typename EndpointManager<Platform>::IncomingOfflineFrameProcessor>
+        processor) {
+  runOnEndpointManagerThread(MakePtr(
+      new endpoint_manager::UnregisterIncomingOfflineFrameProcessorRunnable<
+          Platform>(MakePtr(this), frame_type, processor)));
+}
+
+template <typename Platform>
+Ptr<typename EndpointManager<Platform>::IncomingOfflineFrameProcessor>
+EndpointManager<Platform>::getOfflineFrameProcessor(
+    V1Frame::FrameType frame_type) {
+  typedef Ptr<typename EndpointManager<Platform>::IncomingOfflineFrameProcessor>
+      PtrIncomingOfflineFrameProcessor;
+  typedef Ptr<Future<PtrIncomingOfflineFrameProcessor>> ResultType;
+
+  ScopedPtr<ResultType> future_result(
+      runOnEndpointManagerThread<PtrIncomingOfflineFrameProcessor>(MakePtr(
+          new endpoint_manager::GetOfflineFrameProcessorCallable<Platform>(
+              MakePtr(this), frame_type))));
+
+  return waitForResult("getOfflineFrameProcessor", future_result.get());
+}
+
+template <typename Platform>
+void EndpointManager<Platform>::registerEndpoint(
+    Ptr<ClientProxy<Platform>> client_proxy, const string& endpoint_id,
+    const string& endpoint_name, const string& authentication_token,
+    ConstPtr<ByteArray> raw_authentication_token, bool is_incoming,
+    Ptr<EndpointChannel> endpoint_channel,
+    Ptr<ConnectionLifecycleListener> connection_lifecycle_listener) {
+  ScopedPtr<Ptr<CountDownLatch>> latch(Platform::createCountDownLatch(1));
+  runOnEndpointManagerThread(
+      MakePtr(new endpoint_manager::RegisterEndpointRunnable<Platform>(
+          MakePtr(this), client_proxy, endpoint_id, endpoint_name,
+          authentication_token, raw_authentication_token, is_incoming,
+          endpoint_channel, connection_lifecycle_listener, latch.get())));
+  waitForLatch("registerEndpoint", latch.get());
+}
+
+template <typename Platform>
+void EndpointManager<Platform>::unregisterEndpoint(
+    Ptr<ClientProxy<Platform>> client_proxy, const string& endpoint_id) {
+  ScopedPtr<Ptr<CountDownLatch>> latch(Platform::createCountDownLatch(1));
+  runOnEndpointManagerThread(
+      MakePtr(new endpoint_manager::UnregisterEndpointRunnable<Platform>(
+          MakePtr(this), client_proxy, endpoint_id, latch.get())));
+  waitForLatch("unregisterEndpoint", latch.get());
+}
+
+template <typename Platform>
+void EndpointManager<Platform>::discardEndpoint(
+    Ptr<ClientProxy<Platform>> client_proxy, const string& endpoint_id) {
+  runOnEndpointManagerThread(
+      MakePtr(new endpoint_manager::DiscardEndpointRunnable<Platform>(
+          MakePtr(this), client_proxy, endpoint_id)));
+}
+
+template <typename Platform>
+std::vector<string> EndpointManager<Platform>::sendPayloadChunk(
+    const PayloadTransferFrame::PayloadHeader& payload_header,
+    const PayloadTransferFrame::PayloadChunk& payload_chunk,
+    const std::vector<string>& endpoint_ids) {
+  ConstPtr<ByteArray> payload_transfer_frame_bytes =
+      OfflineFrames::forDataPayloadTransferFrame(payload_header, payload_chunk);
+
+  return sendTransferFrameBytes(endpoint_ids, payload_transfer_frame_bytes,
+                                payload_header.id(),
+                                /*offset=*/payload_chunk.offset(),
+                                /*packet_type=*/"DATA");
+}
+
+template <typename Platform>
+void EndpointManager<Platform>::sendControlMessage(
+    const PayloadTransferFrame::PayloadHeader& payload_header,
+    const PayloadTransferFrame::ControlMessage& control_message,
+    const std::vector<string>& endpoint_ids) {
+  ConstPtr<ByteArray> payload_transfer_frame_bytes =
+      OfflineFrames::forControlPayloadTransferFrame(payload_header,
+                                                    control_message);
+
+  sendTransferFrameBytes(endpoint_ids, payload_transfer_frame_bytes,
+                         payload_header.id(),
+                         /*offset=*/control_message.offset(),
+                         /*packet_type=*/"CONTROL");
+}
+
+template <typename Platform>
+void EndpointManager<Platform>::waitForLatch(const string& method_name,
+                                             Ptr<CountDownLatch> latch) {
+  Exception::Value await_exception = latch->await();
+  if (Exception::NONE != await_exception) {
+    if (Exception::INTERRUPTED == await_exception) {
+      // TODO(tracyzhou): Add logging.
+      // Thread.currentThread().interrupt();
+    }
+  }
+}
+
+template <typename Platform>
+void EndpointManager<Platform>::waitForLatch(const string& method_name,
+                                             Ptr<CountDownLatch> latch,
+                                             std::int32_t timeout_millis) {
+  ExceptionOr<bool> await_succeeded = latch->await(timeout_millis);
+
+  if (!await_succeeded.ok()) {
+    // TODO(tracyzhou): Add logging.
+    if (Exception::INTERRUPTED == await_succeeded.exception()) {
+      // TODO(tracyzhou): Add logging.
+      // Thread.currentThread().interrupt();
+      return;
+    }
+  }
+
+  if (!await_succeeded.result()) {
+    // TODO(tracyzhou): Add logging.
+  }
+}
+
+template <typename Platform>
+template <typename T>
+T EndpointManager<Platform>::waitForResult(const string& method_name,
+                                           Ptr<Future<T>> result_future) {
+  ExceptionOr<T> result = result_future->get();
+
+  if (!result.ok()) {
+    Exception::Value exception = result.exception();
+    if (Exception::INTERRUPTED == exception ||
+        Exception::EXECUTION == exception) {
+      // TODO(tracyzhou): Add logging.
+      if (Exception::INTERRUPTED == exception) {
+        // Thread.currentThread().interrupt();
+      }
+      return T();
+    }
+  }
+
+  return result.result();
+}
+
+// @EndpointManagerThread
+template <typename Platform>
+void EndpointManager<Platform>::removeEndpoint(
+    Ptr<ClientProxy<Platform>> client_proxy, const string& endpoint_id,
+    bool send_disconnection_notification) {
+  // Unregistering from endpoint_channel_manager_ will also serve to terminate
+  // the dedicated reader and KeepAlive threads we started when we registered
+  // this endpoint.
+  if (endpoint_channel_manager_->unregisterChannelForEndpoint(endpoint_id)) {
+    // Notify all frame processors of the disconnection immediately and wait
+    // for them to clean up state. Only once all processors are done cleaning
+    // up, we can remove the endpoint from ClientProxy after which there
+    // should be no further interactions with the endpoint.
+    // (See b/37352254 for history)
+    waitForEndpointDisconnectionProcessing(client_proxy, endpoint_id);
+
+    client_proxy->onDisconnected(endpoint_id, send_disconnection_notification);
+    // TODO(tracyzhou): Add logging.
+  }
+}
+
+// @EndpointManagerThread
+template <typename Platform>
+void EndpointManager<Platform>::waitForEndpointDisconnectionProcessing(
+    Ptr<ClientProxy<Platform>> client_proxy, const string& endpoint_id) {
+  ScopedPtr<Ptr<CountDownLatch>> process_disconnection_barrier(
+      Platform::createCountDownLatch(static_cast<std::int32_t>(
+          incoming_offline_frame_processors_.size())));
+
+  for (typename IncomingOfflineFrameProcessorsMap::iterator it =
+           incoming_offline_frame_processors_.begin();
+       it != incoming_offline_frame_processors_.end(); it++) {
+    it->second->processEndpointDisconnection(
+        client_proxy, endpoint_id, process_disconnection_barrier.get());
+  }
+
+  waitForLatch("waitForEndpointDisconnectionProcessing",
+               process_disconnection_barrier.get(),
+               kProcessEndpointDisconnectionTimeoutMillis);
+}
+
+template <typename Platform>
+std::vector<string> EndpointManager<Platform>::sendTransferFrameBytes(
+    const std::vector<string>& endpoint_ids,
+    ConstPtr<ByteArray> payload_transfer_frame_bytes, std::int64_t payload_id,
+    std::int64_t offset, const string& packet_type) {
+  ScopedPtr<ConstPtr<ByteArray>> scoped_payload_transfer_frame_bytes(
+      payload_transfer_frame_bytes);
+  std::vector<string> failed_endpoint_ids;
+  for (std::vector<string>::const_iterator it = endpoint_ids.begin();
+       it != endpoint_ids.end(); it++) {
+    const string& endpoint_id = *it;
+
+    ScopedPtr<Ptr<EndpointChannel>> scoped_endpoint_channel(
+        endpoint_channel_manager_->getChannelForEndpoint(endpoint_id));
+
+    if (scoped_endpoint_channel.isNull()) {
+      // We no longer know about this endpoint (it was either explicitly
+      // unregistered, or a read/write error made us unregister it internally).
+      // TODO(tracyzhou): Add logging.
+      failed_endpoint_ids.push_back(endpoint_id);
+      continue;
+    }
+
+    Exception::Value write_exception = scoped_endpoint_channel->write(
+        scoped_payload_transfer_frame_bytes.release());
+    if (Exception::NONE != write_exception) {
+      if (Exception::IO == write_exception) {
+        // TODO(tracyzhou): Add logging.
+        failed_endpoint_ids.push_back(endpoint_id);
+        continue;
+      }
+    }
+  }
+
+  return failed_endpoint_ids;
+}
+
+template <typename Platform>
+void EndpointManager<Platform>::startEndpointReader(Ptr<Runnable> runnable) {
+  endpoint_readers_thread_pool_->execute(runnable);
+}
+
+template <typename Platform>
+void EndpointManager<Platform>::startEndpointKeepAliveManager(
+    Ptr<Runnable> runnable) {
+  endpoint_keep_alive_manager_thread_pool_->execute(runnable);
+}
+
+template <typename Platform>
+void EndpointManager<Platform>::runOnEndpointManagerThread(
+    Ptr<Runnable> runnable) {
+  serial_executor_->execute(runnable);
+}
+
+template <typename Platform>
+template <typename T>
+Ptr<Future<T>> EndpointManager<Platform>::runOnEndpointManagerThread(
+    Ptr<Callable<T>> callable) {
+  return serial_executor_->submit(callable);
+}
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/endpoint_manager.h

@@ -0,0 +1,232 @@
+#ifndef CORE_INTERNAL_ENDPOINT_MANAGER_H_
+#define CORE_INTERNAL_ENDPOINT_MANAGER_H_
+
+#include <cstdint>
+
+#include "core/internal/client_proxy.h"
+#include "core/internal/endpoint_channel.h"
+#include "core/internal/endpoint_channel_manager.h"
+#include "proto/connections/offline_wire_formats.pb.h"
+#include "platform/api/count_down_latch.h"
+#include "platform/api/submittable_executor.h"
+#include "platform/api/system_clock.h"
+#include "platform/api/thread_utils.h"
+#include "platform/byte_array.h"
+#include "platform/port/string.h"
+#include "platform/ptr.h"
+#include "platform/runnable.h"
+#include "proto/connections_enums.pb.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+namespace endpoint_manager {
+
+template <typename>
+class ReaderRunnable;
+template <typename>
+class KeepAliveManagerRunnable;
+template <typename>
+class EndpointChannelLoopRunnable;
+template <typename>
+class RegisterIncomingOfflineFrameProcessorRunnable;
+template <typename>
+class UnregisterIncomingOfflineFrameProcessorRunnable;
+template <typename>
+class RegisterEndpointRunnable;
+template <typename>
+class UnregisterEndpointRunnable;
+template <typename>
+class DiscardEndpointRunnable;
+template <typename>
+class GetOfflineFrameProcessorCallable;
+
+}  // namespace endpoint_manager
+
+// Manages all operations related to the remote endpoints with which we are
+// interacting.
+//
+// <p>All processing of incoming and outgoing payloads is spread across this and
+// the PayloadManager as described below.
+//
+// <p>The sending of outgoing payloads originates in
+// PayloadManager.sendPayload() before control is transferred over to
+// EndpointManager.sendPayloadChunk(). This work happens on one of three
+// dedicated writer threads belonging to the PayloadManager. The writer thread
+// that is used depends on the PayloadType.
+//
+// <p>The EndpointManager has one dedicated reader thread for each registered
+// endpoint, and the receiving of every incoming payload (and its subsequent
+// chunks) originates on one of those threads before control is transferred over
+// to PayloadManager.processIncomingOfflineFrame() (still running on that
+// same dedicated reader thread).
+template <typename Platform>
+class EndpointManager {
+ public:
+  class IncomingOfflineFrameProcessor {
+   public:
+    virtual ~IncomingOfflineFrameProcessor() {}
+
+    // This function takes full ownership of offline_frame.
+    // @EndpointManagerReaderThread
+    virtual void processIncomingOfflineFrame(
+        ConstPtr<OfflineFrame> offline_frame, const string& from_endpoint_id,
+        Ptr<ClientProxy<Platform> > to_client_proxy,
+        proto::connections::Medium current_medium) = 0;
+
+    // Implementations must call process_disconnection_barrier.countDown() once
+    // they're done. This parallelizes the disconnection event across all frame
+    // processors.
+    //
+    // @EndpointManagerThread
+    virtual void processEndpointDisconnection(
+        Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_id,
+        Ptr<CountDownLatch> process_disconnection_barrier) = 0;
+
+    // Operator overloads when comparing Ptr<IncomingOfflineFrameProcessor>.
+    bool operator==(
+        const typename EndpointManager<Platform>::IncomingOfflineFrameProcessor&
+            rhs);
+    bool operator<(
+        const typename EndpointManager<Platform>::IncomingOfflineFrameProcessor&
+            rhs);
+  };
+
+  explicit EndpointManager(
+      Ptr<EndpointChannelManager<Platform> > endpoint_channel_manager);
+  ~EndpointManager();
+
+  // Invoked from the constructors of the various *Manager components that make
+  // up the OfflineServiceController implementation.
+  void registerIncomingOfflineFrameProcessor(
+      V1Frame::FrameType frame_type,
+      Ptr<IncomingOfflineFrameProcessor> processor);
+  void unregisterIncomingOfflineFrameProcessor(
+      V1Frame::FrameType frame_type,
+      Ptr<IncomingOfflineFrameProcessor> processor);
+
+  // Invoked from the different PCPHandler implementations (of which there can
+  // be only one at a time).
+  void registerEndpoint(
+      Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_id,
+      const string& endpoint_name, const string& authentication_token,
+      ConstPtr<ByteArray> raw_authentication_token, bool is_incoming,
+      Ptr<EndpointChannel> endpoint_channel,
+      Ptr<ConnectionLifecycleListener> connection_lifecycle_listener);
+  // Called when a client explicitly asks to disconnect from this endpoint. In
+  // this case, we do not notify the client of onDisconnected().
+  void unregisterEndpoint(Ptr<ClientProxy<Platform> > client_proxy,
+                          const string& endpoint_id);
+  // Called when we internally want to get rid of the endpoint, without the
+  // client directly telling us to. For example...
+  //    a) We failed to read from the endpoint in its dedicated reader thread.
+  //    b) We failed to write to the endpoint in PayloadManager.
+  //    c) The connection was rejected in PCPHandler.
+  //    d) The dedicated KeepAlive thread exceeded its period of inactivity.
+  // Or in the numerous other cases where a failure occurred and we no longer
+  // believe the endpoint is in a healthy state.
+  //
+  // Note: This must not block. Otherwise we can get into a deadlock where we
+  // ask everyone who's registered an IncomingOfflineFrameProcessor to
+  // processEndpointDisconnection() while the caller of discardEndpoint() is
+  // blocked here.
+  void discardEndpoint(Ptr<ClientProxy<Platform> > client_proxy,
+                       const string& endpoint_id);
+
+  Ptr<IncomingOfflineFrameProcessor> getOfflineFrameProcessor(
+      V1Frame::FrameType frame_type);
+
+  // Returns the list of endpoints to which sending this chunk failed.
+  //
+  // Invoked from the PayloadManager's sendPayload() method.
+  std::vector<string> sendPayloadChunk(
+      const PayloadTransferFrame::PayloadHeader& payload_header,
+      const PayloadTransferFrame::PayloadChunk& payload_chunk,
+      const std::vector<string>& endpoint_ids);
+  void sendControlMessage(
+      const PayloadTransferFrame::PayloadHeader& payload_header,
+      const PayloadTransferFrame::ControlMessage& control_message,
+      const std::vector<string>& endpoint_ids);
+
+ private:
+  template <typename>
+  friend class endpoint_manager::ReaderRunnable;
+  template <typename>
+  friend class endpoint_manager::KeepAliveManagerRunnable;
+  template <typename>
+  friend class endpoint_manager::EndpointChannelLoopRunnable;
+  template <typename>
+  friend class endpoint_manager::RegisterIncomingOfflineFrameProcessorRunnable;
+  template <typename>
+  friend class endpoint_manager::
+      UnregisterIncomingOfflineFrameProcessorRunnable;
+  template <typename>
+  friend class endpoint_manager::RegisterEndpointRunnable;
+  template <typename>
+  friend class endpoint_manager::UnregisterEndpointRunnable;
+  template <typename>
+  friend class endpoint_manager::DiscardEndpointRunnable;
+  template <typename>
+  friend class endpoint_manager::GetOfflineFrameProcessorCallable;
+
+  static void waitForLatch(const string& method_name,
+                           Ptr<CountDownLatch> latch);
+  static void waitForLatch(const string& method_name, Ptr<CountDownLatch> latch,
+                           std::int32_t timeout_millis);
+  template <typename T>
+  static T waitForResult(const string& method_name,
+                         Ptr<Future<T> > result_future);
+
+  static const std::int32_t kKeepAliveWriteIntervalMillis;
+  static const std::int32_t kKeepAliveReadTimeoutMillis;
+  static const std::int32_t kProcessEndpointDisconnectionTimeoutMillis;
+  static const std::int32_t kMaxConcurrentEndpoints;
+  static const std::int32_t kEndpointIdLength;
+
+  // It should be noted that this method may be called multiple times (because
+  // invoking this method closes the endpoint channel, which causes the
+  // dedicated reader and KeepAlive threads to terminate, which in turn leads to
+  // this method being called), but that's alright because the implementation of
+  // this method is idempotent.
+  void removeEndpoint(Ptr<ClientProxy<Platform> > client_proxy,
+                      const string& endpoint_id,
+                      bool send_disconnection_notification);
+
+  void waitForEndpointDisconnectionProcessing(
+      Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_id);
+
+  std::vector<string> sendTransferFrameBytes(
+      const std::vector<string>& endpoint_ids,
+      ConstPtr<ByteArray> payload_transfer_frame_bytes, std::int64_t payload_id,
+      std::int64_t offset, const string& packet_type);
+
+  void startEndpointReader(Ptr<Runnable> runnable);
+  void startEndpointKeepAliveManager(Ptr<Runnable> runnable);
+  void runOnEndpointManagerThread(Ptr<Runnable> runnable);
+  template <typename T>
+  Ptr<Future<T> > runOnEndpointManagerThread(Ptr<Callable<T> > callable);
+
+  ScopedPtr<Ptr<ThreadUtils> > thread_utils_;
+  ScopedPtr<Ptr<SystemClock> > system_clock_;
+
+  Ptr<EndpointChannelManager<Platform> > endpoint_channel_manager_;
+
+  typedef std::map<V1Frame::FrameType, Ptr<IncomingOfflineFrameProcessor> >
+      IncomingOfflineFrameProcessorsMap;
+  IncomingOfflineFrameProcessorsMap incoming_offline_frame_processors_;
+
+  ScopedPtr<Ptr<typename Platform::MultiThreadExecutorType> >
+      endpoint_keep_alive_manager_thread_pool_;
+  ScopedPtr<Ptr<typename Platform::MultiThreadExecutorType> >
+      endpoint_readers_thread_pool_;
+  ScopedPtr<Ptr<typename Platform::SingleThreadExecutorType> > serial_executor_;
+};
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#include "core/internal/endpoint_manager.cc"
+
+#endif  // CORE_INTERNAL_ENDPOINT_MANAGER_H_

cpp/core/internal/internal_payload.cc

@@ -0,0 +1,20 @@
+#include "core/internal/internal_payload.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+InternalPayload::InternalPayload(ConstPtr<Payload> payload)
+    : payload_(payload), payload_id_(payload_->getId()) {}
+
+InternalPayload::~InternalPayload() {}
+
+ConstPtr<Payload> InternalPayload::releasePayload() {
+  return payload_.release();
+}
+
+std::int64_t InternalPayload::getId() const { return payload_id_; }
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/internal_payload.h

@@ -0,0 +1,82 @@
+#ifndef CORE_INTERNAL_INTERNAL_PAYLOAD_H_
+#define CORE_INTERNAL_INTERNAL_PAYLOAD_H_
+
+#include <cstdint>
+
+#include "core/payload.h"
+#include "proto/connections/offline_wire_formats.pb.h"
+#include "platform/byte_array.h"
+#include "platform/exception.h"
+#include "platform/ptr.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+// Defines the operations layered atop a Payload, for use inside the
+// OfflineServiceController.
+//
+// <p>There will be an extension of this abstract base class per type of
+// Payload.
+class InternalPayload {
+ public:
+  explicit InternalPayload(ConstPtr<Payload> payload);
+  virtual ~InternalPayload();
+
+  ConstPtr<Payload> releasePayload();
+
+  std::int64_t getId() const;
+
+  // Returns the PayloadType of the Payload to which this object is bound.
+  //
+  // <p>Note that this is supposed to return the type from the OfflineFrame
+  // proto rather than what is already available via
+  // Payload::getType().
+  //
+  // @return The PayloadType.
+  virtual PayloadTransferFrame::PayloadHeader::PayloadType getType() const = 0;
+
+  // Deduces the total size of the Payload to which this object is bound.
+  //
+  // @return The total size, or -1 if it cannot be deduced (for example, when
+  // dealing with streaming data).
+  virtual std::int64_t getTotalSize() const = 0;
+
+  // Breaks off the next chunk from the Payload to which this object is bound.
+  //
+  // <p>Used when we have a complete Payload that we want to break into smaller
+  // byte blobs for sending across a hard boundary (like the other side of
+  // a Binder, or another device altogether).
+  //
+  // @return The next chunk from the Payload, or null if we've reached the end.
+  virtual ExceptionOr<ConstPtr<ByteArray> > detachNextChunk() = 0;
+
+  // Adds the next chunk that comprises the Payload to which this object is
+  // bound.
+  //
+  // <p>Used when we are trying to reconstruct a Payload that lives on the
+  // other side of a hard boundary (like the other side of a Binder, or another
+  // device altogether), one byte blob at a time.
+  //
+  // @param chunk The next chunk; this being null signals that this is the last
+  // chunk, which will typically be used as a trigger to perform whatever state
+  // cleanup may be required by the concrete implementation.
+  virtual Exception::Value attachNextChunk(ConstPtr<ByteArray> chunk) = 0;
+
+  // Cleans up any resources used by this Payload. Called when we're stopping
+  // early, e.g. after being cancelled or having no more recipients left.
+  virtual void close() {}
+
+ protected:
+  ScopedPtr<ConstPtr<Payload> > payload_;
+  // We're caching the payload ID here because the backing payload will be
+  // released to another owner during the lifetime of an incoming
+  // InternalPayload.
+  const std::int64_t payload_id_;
+};
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#endif  // CORE_INTERNAL_INTERNAL_PAYLOAD_H_

cpp/core/internal/internal_payload_factory.cc

@@ -0,0 +1,312 @@
+#include "core/internal/internal_payload_factory.h"
+
+#include <cstdint>
+
+#include "core/payload.h"
+#include "platform/api/condition_variable.h"
+#include "platform/api/lock.h"
+#include "platform/byte_array.h"
+#include "platform/exception.h"
+#include "platform/file_impl.h"
+#include "platform/pipe.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+namespace {
+
+class BytesInternalPayload : public InternalPayload {
+ public:
+  explicit BytesInternalPayload(ConstPtr<Payload> payload)
+      : InternalPayload(payload),
+        total_size_(payload_->asBytes()->size()),
+        detached_only_chunk_(false) {}
+
+  PayloadTransferFrame::PayloadHeader::PayloadType getType() const override {
+    return PayloadTransferFrame::PayloadHeader::BYTES;
+  }
+
+  std::int64_t getTotalSize() const override { return total_size_; }
+
+  ExceptionOr<ConstPtr<ByteArray> > detachNextChunk() override {
+    if (detached_only_chunk_) {
+      return ExceptionOr<ConstPtr<ByteArray> >(ConstPtr<ByteArray>());
+    }
+
+    detached_only_chunk_ = true;
+    return ExceptionOr<ConstPtr<ByteArray> >(payload_->releaseBytes());
+  }
+
+  Exception::Value attachNextChunk(ConstPtr<ByteArray> chunk) override {
+    // Avoid leaks.
+    ScopedPtr<ConstPtr<ByteArray> > scoped_chunk(chunk);
+
+    // Nothing to do - this method makes sense for other, more long-running
+    // InternalPayload concrete implementations.
+    return Exception::NONE;
+  }
+
+ private:
+  // We're caching the total size here because the backing payload will be
+  // released to another owner during the lifetime of an incoming
+  // InternalPayload.
+  const std::int64_t total_size_;
+  bool detached_only_chunk_;
+};
+
+template <typename Platform>
+class OutgoingStreamInternalPayload : public InternalPayload {
+ public:
+  explicit OutgoingStreamInternalPayload(ConstPtr<Payload> payload)
+      : InternalPayload(payload) {}
+
+  PayloadTransferFrame::PayloadHeader::PayloadType getType() const override {
+    return PayloadTransferFrame::PayloadHeader::STREAM;
+  }
+
+  std::int64_t getTotalSize() const override { return -1; }
+
+  ExceptionOr<ConstPtr<ByteArray> > detachNextChunk() override {
+    Ptr<InputStream> input_stream(payload_->asStream()->asInputStream());
+
+    ExceptionOr<ConstPtr<ByteArray> > bytes_read =
+        input_stream->read(kChunkSize);
+    if (!bytes_read.ok()) {
+      if (Exception::IO == bytes_read.exception()) {
+        // Ignore the potential Exception returned by close(), as a counterpart
+        // to Java's closeQuietly().
+        input_stream->close();
+        return bytes_read;
+      }
+    }
+
+    // Avoid leaks.
+    ScopedPtr<ConstPtr<ByteArray> > scoped_bytes_read(bytes_read.result());
+
+    if (scoped_bytes_read.isNull()) {
+      // TODO(reznor): logger.atVerbose().log("No more data for outgoing payload
+      // %s, closing InputStream.", this);
+
+      // Ignore the potential Exception returned by close(), as a counterpart
+      // to Java's closeQuietly().
+      input_stream->close();
+      return ExceptionOr<ConstPtr<ByteArray> >(ConstPtr<ByteArray>());
+    }
+
+    return ExceptionOr<ConstPtr<ByteArray> >(scoped_bytes_read.release());
+  }
+
+  Exception::Value attachNextChunk(ConstPtr<ByteArray> chunk) override {
+    return Exception::IO;
+  }
+
+  void close() override {
+    // Ignore the potential Exception returned by close(), as a counterpart
+    // to Java's closeQuietly().
+    payload_->asStream()->asInputStream()->close();
+  }
+
+ private:
+  static const std::int64_t kChunkSize = 64 * 1024;
+};
+
+template <typename Platform>
+class IncomingStreamInternalPayload : public InternalPayload {
+ public:
+  IncomingStreamInternalPayload(ConstPtr<Payload> payload,
+                                Ptr<OutputStream> output_stream)
+      : InternalPayload(payload), output_stream_(output_stream) {}
+
+  PayloadTransferFrame::PayloadHeader::PayloadType getType() const override {
+    return PayloadTransferFrame::PayloadHeader::STREAM;
+  }
+
+  std::int64_t getTotalSize() const override { return -1; }
+
+  ExceptionOr<ConstPtr<ByteArray> > detachNextChunk() override {
+    return ExceptionOr<ConstPtr<ByteArray> >(Exception::IO);
+  }
+
+  Exception::Value attachNextChunk(ConstPtr<ByteArray> chunk) override {
+    ScopedPtr<ConstPtr<ByteArray> > scoped_chunk(chunk);
+
+    if (scoped_chunk.isNull()) {
+      output_stream_->close();
+      return Exception::NONE;
+    }
+
+    return output_stream_->write(scoped_chunk.release());
+  }
+
+  void close() override {
+    output_stream_->close();
+  }
+
+ private:
+  ScopedPtr<Ptr<OutputStream> > output_stream_;
+};
+
+class OutgoingFileInternalPayload : public InternalPayload {
+ public:
+  explicit OutgoingFileInternalPayload(ConstPtr<Payload> payload)
+      : InternalPayload(std::move(payload)) {}
+
+  PayloadTransferFrame::PayloadHeader::PayloadType getType() const override {
+    return PayloadTransferFrame::PayloadHeader::FILE;
+  }
+
+  std::int64_t getTotalSize() const override {
+    return payload_->asFile()->asInputFile()->getTotalSize();
+  }
+
+  ExceptionOr<ConstPtr<ByteArray>> detachNextChunk() override {
+    Ptr<InputFile> input_file(payload_->asFile()->asInputFile());
+
+    ExceptionOr<ConstPtr<ByteArray>> bytes_read = input_file->read(kChunkSize);
+    if (!bytes_read.ok()) {
+      if (Exception::IO == bytes_read.exception()) {
+        input_file->close();
+        return bytes_read;
+      }
+    }
+
+    // Avoid leaks.
+    ScopedPtr<ConstPtr<ByteArray>> scoped_bytes_read(bytes_read.result());
+
+    if (scoped_bytes_read.isNull()) {
+      // No more data for outgoing payload.
+
+      input_file->close();
+      return ExceptionOr<ConstPtr<ByteArray>>(ConstPtr<ByteArray>());
+    }
+
+    return ExceptionOr<ConstPtr<ByteArray>>(scoped_bytes_read.release());
+  }
+
+  Exception::Value attachNextChunk(ConstPtr<ByteArray> chunk) override {
+    return Exception::IO;
+  }
+
+  void close() override { payload_->asFile()->asInputFile()->close(); }
+
+ private:
+  static const std::int64_t kChunkSize = 64 * 1024;
+};
+
+class IncomingFileInternalPayload : public InternalPayload {
+ public:
+  IncomingFileInternalPayload(ConstPtr<Payload> payload,
+                              const Ptr<OutputFile>& output_file,
+                              std::int64_t total_size)
+      : InternalPayload(std::move(payload)),
+        output_file_(output_file),
+        total_size_(total_size) {}
+
+  PayloadTransferFrame::PayloadHeader::PayloadType getType() const override {
+    return PayloadTransferFrame::PayloadHeader::FILE;
+  }
+
+  std::int64_t getTotalSize() const override { return total_size_; }
+
+  ExceptionOr<ConstPtr<ByteArray>> detachNextChunk() override {
+    return ExceptionOr<ConstPtr<ByteArray>>(Exception::IO);
+  }
+
+  Exception::Value attachNextChunk(ConstPtr<ByteArray> chunk) override {
+    ScopedPtr<ConstPtr<ByteArray>> scoped_chunk(chunk);
+
+    if (scoped_chunk.isNull()) {
+      // Received null last chunk for incoming payload.
+      output_file_->close();
+      return Exception::NONE;
+    }
+
+    return output_file_->write(scoped_chunk.release());
+  }
+
+  void close() override { output_file_->close(); }
+
+ private:
+  ScopedPtr<Ptr<OutputFile>> output_file_;
+  const std::int64_t total_size_;
+};
+
+}  // namespace
+
+template <typename Platform>
+Ptr<InternalPayload> InternalPayloadFactory<Platform>::createOutgoing(
+    ConstPtr<Payload> payload) {
+  // Avoid leaks.
+  ScopedPtr<ConstPtr<Payload> > scoped_payload(payload);
+
+  switch (scoped_payload->getType()) {
+    case Payload::Type::BYTES:
+      return MakePtr(new BytesInternalPayload(scoped_payload.release()));
+
+    case Payload::Type::FILE:
+      return MakePtr(new OutgoingFileInternalPayload(scoped_payload.release()));
+
+    case Payload::Type::STREAM:
+      return MakePtr(new OutgoingStreamInternalPayload<Platform>(
+          scoped_payload.release()));
+
+    default: {}
+      // Fall through
+  }
+
+  // This should never be reached since the ServiceControllerRouter has already
+  // checked whether or not we can work with this Payload type.
+  return Ptr<InternalPayload>();
+}
+
+template <typename Platform>
+Ptr<InternalPayload> InternalPayloadFactory<Platform>::createIncoming(
+    const PayloadTransferFrame& payload_transfer_frame) {
+  if (PayloadTransferFrame::DATA != payload_transfer_frame.packet_type()) {
+    return Ptr<InternalPayload>();
+  }
+
+  const int64_t payload_id = payload_transfer_frame.payload_header().id();
+  switch (payload_transfer_frame.payload_header().type()) {
+    case PayloadTransferFrame::PayloadHeader::BYTES: {
+      const string& body = payload_transfer_frame.payload_chunk().body();
+      return MakePtr(new BytesInternalPayload(MakeConstPtr(new Payload(
+          payload_id, MakeConstPtr(new ByteArray(body.data(), body.size()))))));
+    }
+
+    case PayloadTransferFrame::PayloadHeader::STREAM: {
+      // pipe will be auto-destroyed when it is no longer referenced.
+      auto pipe = MakeRefCountedPtr(new Pipe<Platform>());
+
+      return MakePtr(new IncomingStreamInternalPayload<Platform>(
+          MakeConstPtr(new Payload(
+              payload_id,
+              MakeConstPtr(new Payload::Stream(
+                  Pipe<Platform>::createInputStream(pipe))))),
+          Pipe<Platform>::createOutputStream(pipe)));
+    }
+
+    case PayloadTransferFrame::PayloadHeader::FILE: {
+      const std::string payload_path = Platform::getPayloadPath(payload_id);
+      Ptr<InputFile> input_file = MakePtr(new InputFileImpl(
+          payload_path, payload_transfer_frame.payload_header().total_size()));
+      Ptr<OutputFile> output_file = MakePtr(new OutputFileImpl(payload_path));
+      ConstPtr<Payload> payload = MakeConstPtr(
+          new Payload(payload_id, MakeConstPtr(new Payload::File(input_file))));
+      return MakePtr(new IncomingFileInternalPayload(
+          payload, output_file,
+          payload_transfer_frame.payload_header().total_size()));
+    }
+    default: {}
+      // Fall through.
+  }
+
+  // This should never be reached since the ServiceControllerRouter has
+  // already checked whether or not we can work with this Payload type.
+  return Ptr<InternalPayload>();
+}
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/internal_payload_factory.h

@@ -0,0 +1,34 @@
+#ifndef CORE_INTERNAL_INTERNAL_PAYLOAD_FACTORY_H_
+#define CORE_INTERNAL_INTERNAL_PAYLOAD_FACTORY_H_
+
+#include "core/internal/internal_payload.h"
+#include "core/payload.h"
+#include "proto/connections/offline_wire_formats.pb.h"
+#include "platform/ptr.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+template <typename Platform>
+class InternalPayloadFactory {
+ public:
+  // Creates an InternalPayload representing an outgoing Payload.
+  //
+  // The returned Ptr<InternalPayload> will take ownership of the passed-in
+  // 'payload'.
+  Ptr<InternalPayload> createOutgoing(ConstPtr<Payload> payload);
+
+  // Creates an InternalPayload representing an incoming Payload from a remote
+  // endpoint.
+  Ptr<InternalPayload> createIncoming(
+      const PayloadTransferFrame& payload_transfer_frame);
+};
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#include "core/internal/internal_payload_factory.cc"
+
+#endif  // CORE_INTERNAL_INTERNAL_PAYLOAD_FACTORY_H_

cpp/core/internal/loop_runner.cc

@@ -0,0 +1,54 @@
+#include "core/internal/loop_runner.h"
+
+#include "platform/exception.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+LoopRunner::LoopRunner(const std::string& name) : name_(name) {}
+
+bool LoopRunner::loop(Ptr<Callable<bool> > callable) {
+  ScopedPtr<Ptr<Callable<bool> > > scoped_callable(callable);
+
+  onEnterLoop();
+  while (true) {
+    onEnterIteration();
+    ExceptionOr<bool> should_continue = scoped_callable->call();
+    if (!should_continue.ok()) {
+      onExceptionExitLoop(should_continue.exception());
+      break;
+    }
+
+    onExitIteration();
+    if (!should_continue.result()) {
+      onExitLoop();
+      return true;
+    }
+  }
+  return false;
+}
+
+void LoopRunner::onEnterLoop() {
+  // TODO(tracyzhou): Add logging.
+}
+
+void LoopRunner::onEnterIteration() {
+  // TODO(tracyzhou): Add logging.
+}
+
+void LoopRunner::onExitIteration() {
+  // TODO(tracyzhou): Add logging.
+}
+
+void LoopRunner::onExitLoop() {
+  // TODO(tracyzhou): Add logging.
+}
+
+void LoopRunner::onExceptionExitLoop(Exception::Value exception) {
+  // TODO(tracyzhou): Add logging.
+}
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/loop_runner.h

@@ -0,0 +1,42 @@
+#ifndef CORE_INTERNAL_LOOP_RUNNER_H_
+#define CORE_INTERNAL_LOOP_RUNNER_H_
+
+#include "platform/callable.h"
+#include "platform/exception.h"
+#include "platform/port/string.h"
+#include "platform/ptr.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+// Construct to run a loop repeatedly. This class is useful to increase
+// testability for multi-threaded code that runs loops; it shouldn't be used for
+// general purpose loops unless tests require fine-grained control over the
+// looping procedure.
+class LoopRunner {
+ public:
+  explicit LoopRunner(const std::string& name);
+
+  // Runs the provided callable repeatedly until it returns false.
+  //
+  // @return true if the loop completed successfully, false if an exception was
+  // encountered.
+  bool loop(Ptr<Callable<bool> > callable);
+
+ protected:
+  void onEnterLoop();
+  void onEnterIteration();
+  void onExitIteration();
+  void onExitLoop();
+  void onExceptionExitLoop(Exception::Value exception);
+
+ private:
+  const std::string name_;
+};
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#endif  // CORE_INTERNAL_LOOP_RUNNER_H_

cpp/core/internal/medium_manager.cc

@@ -0,0 +1,361 @@
+#include "core/internal/medium_manager.h"
+
+#include "platform/synchronized.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+template <typename Platform>
+MediumManager<Platform>::MediumManager()
+    : mediums_(new Mediums<Platform>()),
+      bluetooth_classic_lock_(Platform::createLock()),
+      ble_lock_(Platform::createLock()) {}
+
+template <typename Platform>
+MediumManager<Platform>::~MediumManager() {
+  // TODO(reznor): log.atDebug().log("Initiating shutdown of MediumManager.");
+  Synchronized s1(bluetooth_classic_lock_.get());
+  Synchronized s2(ble_lock_.get());
+
+  mediums_.destroy();
+  // TODO(reznor): log.atDebug().log("MediumManager has shut down.");
+}
+
+// ~~~~~~~~~~~~~~~~~~~~~~~~ BLUETOOTH ~~~~~~~~~~~~~~~~~~~~~~~~
+
+template <typename Platform>
+bool MediumManager<Platform>::isBluetoothAvailable() {
+  Synchronized s(bluetooth_classic_lock_.get());
+
+  return mediums_->bluetoothClassic()->isAvailable();
+}
+
+template <typename Platform>
+bool MediumManager<Platform>::turnOnBluetoothDiscoverability(
+    const string& device_name) {
+  Synchronized s(bluetooth_classic_lock_.get());
+
+  return mediums_->bluetoothRadio()->enable() &&
+         mediums_->bluetoothClassic()->turnOnDiscoverability(device_name);
+}
+
+template <typename Platform>
+void MediumManager<Platform>::turnOffBluetoothDiscoverability() {
+  Synchronized s(bluetooth_classic_lock_.get());
+
+  mediums_->bluetoothClassic()->turnOffDiscoverability();
+}
+
+template <typename Platform>
+class DiscoveredDeviceCallback
+    : public BluetoothClassic<Platform>::DiscoveredDeviceCallback {
+ public:
+  typedef typename MediumManager<Platform>::FoundBluetoothDeviceProcessor
+      FoundBluetoothDeviceProcessor;
+
+  explicit DiscoveredDeviceCallback(
+      Ptr<FoundBluetoothDeviceProcessor> found_bluetooth_device_processor)
+      : found_bluetooth_device_processor_(found_bluetooth_device_processor) {}
+
+  void onDeviceDiscovered(Ptr<BluetoothDevice> device) override {
+    found_bluetooth_device_processor_->onFoundBluetoothDevice(device);
+  }
+
+  void onDeviceNameChanged(Ptr<BluetoothDevice> device) override {
+    found_bluetooth_device_processor_->onFoundBluetoothDevice(device);
+  }
+
+  void onDeviceLost(Ptr<BluetoothDevice> device) override {
+    found_bluetooth_device_processor_->onLostBluetoothDevice(device);
+  }
+
+ private:
+  ScopedPtr<Ptr<FoundBluetoothDeviceProcessor> >
+      found_bluetooth_device_processor_;
+};
+
+template <typename Platform>
+bool MediumManager<Platform>::startScanningForBluetoothDevices(
+    Ptr<FoundBluetoothDeviceProcessor> found_bluetooth_device_processor) {
+  Synchronized s(bluetooth_classic_lock_.get());
+
+  return mediums_->bluetoothRadio()->enable() &&
+         mediums_->bluetoothClassic()->startDiscovery(
+             MakePtr(new DiscoveredDeviceCallback<Platform>(
+                 found_bluetooth_device_processor)));
+}
+
+template <typename Platform>
+void MediumManager<Platform>::stopScanningForBluetoothDevices() {
+  Synchronized s(bluetooth_classic_lock_.get());
+
+  mediums_->bluetoothClassic()->stopDiscovery();
+}
+
+template <typename Platform>
+bool MediumManager<Platform>::isListeningForIncomingBluetoothConnections(
+    const string& service_name) {
+  Synchronized s(bluetooth_classic_lock_.get());
+
+  return mediums_->bluetoothClassic()->isAcceptingConnections(service_name);
+}
+
+template <typename Platform>
+class BluetoothAcceptedConnectionCallback
+    : public BluetoothClassic<Platform>::AcceptedConnectionCallback {
+ public:
+  typedef typename MediumManager<Platform>::IncomingBluetoothConnectionProcessor
+      IncomingBluetoothConnectionProcessor;
+
+  explicit BluetoothAcceptedConnectionCallback(
+      Ptr<IncomingBluetoothConnectionProcessor>
+          incoming_bluetooth_connection_processor)
+      : incoming_bluetooth_connection_processor_(
+            incoming_bluetooth_connection_processor) {}
+
+  void onConnectionAccepted(Ptr<BluetoothSocket> socket) override {
+    incoming_bluetooth_connection_processor_->onIncomingBluetoothConnection(
+        socket);
+  }
+
+ private:
+  ScopedPtr<Ptr<IncomingBluetoothConnectionProcessor> >
+      incoming_bluetooth_connection_processor_;
+};
+
+template <typename Platform>
+bool MediumManager<Platform>::startListeningForIncomingBluetoothConnections(
+    const string& service_name, Ptr<IncomingBluetoothConnectionProcessor>
+                                    incoming_bluetooth_connection_processor) {
+  Synchronized s(bluetooth_classic_lock_.get());
+
+  return mediums_->bluetoothRadio()->enable() &&
+         mediums_->bluetoothClassic()->startAcceptingConnections(
+             service_name,
+             MakePtr(new BluetoothAcceptedConnectionCallback<Platform>(
+                 incoming_bluetooth_connection_processor)));
+}
+
+template <typename Platform>
+void MediumManager<Platform>::stopListeningForIncomingBluetoothConnections(
+    const string& service_name) {
+  Synchronized s(bluetooth_classic_lock_.get());
+
+  mediums_->bluetoothClassic()->stopAcceptingConnections(service_name);
+}
+
+template <typename Platform>
+Ptr<BluetoothSocket> MediumManager<Platform>::connectToBluetoothDevice(
+    Ptr<BluetoothDevice> bluetooth_device, const string& service_name) {
+  Synchronized s(bluetooth_classic_lock_.get());
+
+  if (!mediums_->bluetoothRadio()->enable()) {
+    return Ptr<BluetoothSocket>();
+  }
+
+  return mediums_->bluetoothClassic()->connect(bluetooth_device, service_name);
+}
+
+// ~~~~~~~~~~~~~~~~~~~~~~~~ BLE ~~~~~~~~~~~~~~~~~~~~~~~~
+template <typename Platform>
+bool MediumManager<Platform>::isBleAvailable() {
+  Synchronized s(ble_lock_.get());
+
+#if BLE_V2_IMPLEMENTED
+  return mediums_->bleV2()->isAvailable();
+#else
+  return mediums_->ble()->isAvailable();
+#endif
+}
+
+// TODO(ahlee): Add nearbyNotificationsBeaconData for phase 2 of implementation.
+// TODO(ahlee): Add fast_advertisement_service_uuid and power_level to
+// AdvertisingOptions and pass it through.
+template <typename Platform>
+bool MediumManager<Platform>::startBleAdvertising(
+    const string& service_id, ConstPtr<ByteArray> advertisement_data) {
+  Synchronized s(ble_lock_.get());
+
+  return mediums_->bluetoothRadio()->enable() &&
+#if BLE_V2_IMPLEMENTED
+         mediums_->bleV2()->startAdvertising(
+             service_id, advertisement_data, BLEMediumV2::PowerMode::HIGH,
+             /* fast_advertisement_service_uuid= */ "");
+#else
+         mediums_->ble()->startAdvertising(service_id, advertisement_data);
+#endif
+}
+
+template <typename Platform>
+void MediumManager<Platform>::stopBleAdvertising(const string& service_id) {
+  Synchronized s(ble_lock_.get());
+
+#if BLE_V2_IMPLEMENTED
+  mediums_->bleV2()->stopAdvertising();
+#else
+  mediums_->ble()->stopAdvertising();
+#endif
+}
+
+#if BLE_V2_IMPLEMENTED
+template <typename Platform>
+class BLEAcceptedConnectionCallback
+    : public mediums::BLEV2<Platform>::AcceptedConnectionCallback {
+ public:
+  BLEAcceptedConnectionCallback() {}
+};
+#else
+template <typename Platform>
+class BLEAcceptedConnectionCallback
+    : public BLE<Platform>::AcceptedConnectionCallback {
+ public:
+  typedef typename MediumManager<Platform>::IncomingBleConnectionProcessor
+      IncomingBleConnectionProcessor;
+
+  explicit BLEAcceptedConnectionCallback(
+      Ptr<IncomingBleConnectionProcessor> incoming_ble_connection_processor)
+      : incoming_ble_connection_processor_(incoming_ble_connection_processor) {}
+
+  void onConnectionAccepted(Ptr<BLESocket> socket,
+                            const string& service_id) override {
+    incoming_ble_connection_processor_->onIncomingBleConnection(socket,
+                                                                service_id);
+  }
+
+ private:
+  ScopedPtr<Ptr<IncomingBleConnectionProcessor> >
+      incoming_ble_connection_processor_;
+};
+#endif
+
+template <typename Platform>
+bool MediumManager<Platform>::isListeningForIncomingBleConnections(
+    const string& service_id) {
+  Synchronized s(ble_lock_.get());
+
+#if BLE_V2_IMPLEMENTED
+  return mediums_->bleV2()->isAcceptingConnections();
+#else
+  return mediums_->ble()->isAcceptingConnections();
+#endif
+}
+
+template <typename Platform>
+bool MediumManager<Platform>::startListeningForIncomingBleConnections(
+    const string& service_id,
+    Ptr<IncomingBleConnectionProcessor> incoming_ble_connection_processor) {
+  Synchronized s(ble_lock_.get());
+
+  return mediums_->bluetoothRadio()->enable() &&
+#if BLE_V2_IMPLEMENTED
+         mediums_->bleV2()->startAcceptingConnections(
+             service_id,
+             MakePtr(new BLEAcceptedConnectionCallback<Platform>()));
+#else
+         mediums_->ble()->startAcceptingConnections(
+             service_id, MakePtr(new BLEAcceptedConnectionCallback<Platform>(
+                             incoming_ble_connection_processor)));
+#endif
+}
+
+template <typename Platform>
+void MediumManager<Platform>::stopListeningForIncomingBleConnections(
+    const string& service_id) {
+  Synchronized s(ble_lock_.get());
+
+#if BLE_V2_IMPLEMENTED
+  mediums_->bleV2()->stopAcceptingConnections();
+#else
+  mediums_->ble()->stopAcceptingConnections();
+#endif
+}
+
+template <typename Platform>
+class DiscoveredPeripheralCallback : public DISCOVERED_PERIPHERAL_CALLBACK {
+ public:
+  typedef typename MediumManager<Platform>::FoundBlePeripheralProcessor
+      FoundBlePeripheralProcessor;
+
+  explicit DiscoveredPeripheralCallback(
+      Ptr<FoundBlePeripheralProcessor> found_ble_peripheral_processor)
+      : found_ble_peripheral_processor_(found_ble_peripheral_processor) {}
+
+  void onPeripheralDiscovered(Ptr<BLE_PERIPHERAL> ble_peripheral,
+                              const string& service_id,
+#if BLE_V2_IMPLEMENTED
+                              ConstPtr<ByteArray> advertisement_data,
+                              // TODO(ahlee): Add is_fast_advertisement to
+                              // FoundBlePeripheralProcessor.
+                              bool is_fast_advertisement) override {
+#else
+                              ConstPtr<ByteArray> advertisement_data) {
+#endif
+    found_ble_peripheral_processor_->onFoundBlePeripheral(
+        ble_peripheral, service_id, advertisement_data);
+  }
+
+  void onPeripheralLost(Ptr<BLE_PERIPHERAL> ble_peripheral,
+                        const string& service_id) override {
+    found_ble_peripheral_processor_->onLostBlePeripheral(ble_peripheral,
+                                                         service_id);
+  }
+
+ private:
+  ScopedPtr<Ptr<FoundBlePeripheralProcessor> > found_ble_peripheral_processor_;
+};
+
+// TODO(ahlee): Add fast_advertisement_service_uuid and power_level to
+// DiscoveryOptions and pass it through.
+template <typename Platform>
+bool MediumManager<Platform>::startBleScanning(
+    const string& service_id,
+    Ptr<FoundBlePeripheralProcessor> found_ble_peripheral_processor) {
+  Synchronized s(ble_lock_.get());
+
+  return mediums_->bluetoothRadio()->enable() &&
+#if BLE_V2_IMPLEMENTED
+         mediums_->bleV2()->startScanning(
+             service_id,
+             MakePtr(new DiscoveredPeripheralCallback<Platform>(
+                 found_ble_peripheral_processor)),
+             BLEMediumV2::PowerMode::HIGH,
+             /* fast_advertisement_service_uuid= */ "");
+#else
+         mediums_->ble()->startScanning(
+             service_id, MakePtr(new DiscoveredPeripheralCallback<Platform>(
+                             found_ble_peripheral_processor)));
+#endif
+}
+
+template <typename Platform>
+void MediumManager<Platform>::stopBleScanning(const string& service_id) {
+  Synchronized s(ble_lock_.get());
+
+#if BLE_V2_IMPLEMENTED
+  mediums_->bleV2()->stopScanning();
+#else
+  mediums_->ble()->stopScanning();
+#endif
+}
+
+template <typename Platform>
+Ptr<BLESocket> MediumManager<Platform>::connectToBlePeripheral(
+    Ptr<BLE_PERIPHERAL> ble_peripheral, const string& service_id) {
+  Synchronized s(ble_lock_.get());
+
+  if (!mediums_->bluetoothRadio()->enable()) {
+    return Ptr<BLESocket>();
+  }
+
+#if BLE_V2_IMPLEMENTED
+  // TODO(ahlee): Replace when connecting logic is implemented.
+  return Ptr<BLESocket>();
+#else
+  return mediums_->ble()->connect(ble_peripheral, service_id);
+#endif
+}
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/medium_manager.h

@@ -0,0 +1,140 @@
+#ifndef CORE_INTERNAL_MEDIUM_MANAGER_H_
+#define CORE_INTERNAL_MEDIUM_MANAGER_H_
+
+#include "core/internal/ble_compat.h"
+#include "core/internal/mediums/mediums.h"
+#include "platform/api/bluetooth_classic.h"
+#include "platform/api/lock.h"
+#include "platform/port/string.h"
+#include "platform/ptr.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+/**
+ * Manages everything related to the mediums used by Nearby Connections, acting
+ * as a simplifying layer around the different APIs used for said management.
+ *
+ * <p>An overview of thread safety:
+ *
+ * <ul>
+ *   <li>Methods are synchronized at a per-medium level. For example, all
+ *       Bluetooth Classic calls are synchronized under the same
+ *       'bluetooth_classic_lock_'. This ensures work on a particular medium is
+ *       well-ordered without blocking other mediums from running. Nearby
+ *       Mediums as a whole is already threadsafe, which is why we don't need to
+ *       synchronize at a per-radio level.
+ *   <li>All calls are guarded by the flag 'mediums_are_available_', which
+ *       defaults to true and is set to false in shutdown(). This flag ensures
+ *       that no further work is done after shutdown() has been called.
+ *       Note: shutdown() is the one and only time we grab every
+ *       medium-specific lock, to ensure everything stops at once.
+ * </ul>
+ *
+ * <p>Note: For methods that start an action (eg. startAdvertising()), the radio
+ * is first enabled. This is a prerequisite before doing any work on a medium;
+ * they will otherwise fail if the radio is off. Calls that stop an action (eg.
+ * stopAdvertising()) do not attempt to enable the radio because, if the radio
+ * was off, there is no work for them to stop.
+ */
+template <typename Platform>
+class MediumManager {
+ public:
+  MediumManager();
+  ~MediumManager();
+
+  // ~~~~~~~~~~~~~~~~~~~~~~~~ BLUETOOTH ~~~~~~~~~~~~~~~~~~~~~~~~
+  bool isBluetoothAvailable();
+
+  bool turnOnBluetoothDiscoverability(const string& device_name);
+  void turnOffBluetoothDiscoverability();
+
+  class FoundBluetoothDeviceProcessor {
+   public:
+    virtual ~FoundBluetoothDeviceProcessor() {}
+
+    virtual void onFoundBluetoothDevice(
+        Ptr<BluetoothDevice> bluetooth_device) = 0;
+    virtual void onLostBluetoothDevice(
+        Ptr<BluetoothDevice> bluetooth_device) = 0;
+  };
+
+  bool startScanningForBluetoothDevices(
+      Ptr<FoundBluetoothDeviceProcessor> found_bluetooth_device_processor);
+  void stopScanningForBluetoothDevices();
+
+  class IncomingBluetoothConnectionProcessor {
+   public:
+    virtual ~IncomingBluetoothConnectionProcessor() {}
+
+    virtual void onIncomingBluetoothConnection(
+        Ptr<BluetoothSocket> bluetooth_socket) = 0;
+  };
+
+  bool isListeningForIncomingBluetoothConnections(const string& service_name);
+  bool startListeningForIncomingBluetoothConnections(
+      const string& service_name, Ptr<IncomingBluetoothConnectionProcessor>
+                                      incoming_bluetooth_connection_processor);
+  void stopListeningForIncomingBluetoothConnections(const string& service_name);
+
+  Ptr<BluetoothSocket> connectToBluetoothDevice(
+      Ptr<BluetoothDevice> bluetooth_device, const string& service_name);
+
+  // ~~~~~~~~~~~~~~~~~~~~~~~~ BLE ~~~~~~~~~~~~~~~~~~~~~~~~
+
+  bool isBleAvailable();
+
+  bool startBleAdvertising(const string& service_id,
+                           ConstPtr<ByteArray> advertisement_data);
+  void stopBleAdvertising(const string& service_id);
+
+  class IncomingBleConnectionProcessor {
+   public:
+    virtual ~IncomingBleConnectionProcessor() {}
+
+    virtual void onIncomingBleConnection(Ptr<BLESocket> ble_socket,
+                                         const string& service_id) = 0;
+  };
+
+  bool isListeningForIncomingBleConnections(const string& service_id);
+  bool startListeningForIncomingBleConnections(
+      const string& service_id,
+      Ptr<IncomingBleConnectionProcessor> incoming_ble_connection_processor);
+  void stopListeningForIncomingBleConnections(const string& service_id);
+
+  class FoundBlePeripheralProcessor {
+   public:
+    virtual ~FoundBlePeripheralProcessor() {}
+
+    virtual void onFoundBlePeripheral(
+        Ptr<BLE_PERIPHERAL> ble_peripheral, const string& service_id,
+        ConstPtr<ByteArray> advertisement_data) = 0;
+    virtual void onLostBlePeripheral(Ptr<BLE_PERIPHERAL> ble_peripheral,
+                                     const string& service_id) = 0;
+  };
+
+  bool startBleScanning(
+      const string& service_id,
+      Ptr<FoundBlePeripheralProcessor> found_ble_peripheral_processor);
+  void stopBleScanning(const string& service_id);
+
+  Ptr<BLESocket> connectToBlePeripheral(Ptr<BLE_PERIPHERAL> ble_peripheral,
+                                        const string& service_id);
+
+ private:
+  // The destructor for this needs to be manually invoked after the locks below
+  // are acquired, so it cannot be a ScopedPtr.
+  Ptr<Mediums<Platform> > mediums_;
+
+  ScopedPtr<Ptr<Lock> > bluetooth_classic_lock_;
+  ScopedPtr<Ptr<Lock> > ble_lock_;
+};
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#include "core/internal/medium_manager.cc"
+
+#endif  // CORE_INTERNAL_MEDIUM_MANAGER_H_

cpp/core/internal/mediums/BUILD

@@ -0,0 +1,107 @@
+cc_library(
+    name = "mediums",
+    srcs = [
+        "ble_advertisement.cc",
+        "ble_advertisement_header.cc",
+        "ble_packet.cc",
+        "ble_peripheral.cc",
+        "utils.cc",
+        "utils.h",
+    ],
+    hdrs = [
+        "advertisement_read_result.cc",
+        "advertisement_read_result.h",
+        "ble.cc",
+        "ble.h",
+        "ble_advertisement.h",
+        "ble_advertisement_header.h",
+        "ble_packet.h",
+        "ble_peripheral.h",
+        "ble_v2.cc",
+        "ble_v2.h",
+        "bloom_filter.cc",
+        "bloom_filter.h",
+        "bluetooth_classic.cc",
+        "bluetooth_classic.h",
+        "bluetooth_radio.cc",
+        "bluetooth_radio.h",
+        "discovered_peripheral_callback.h",
+        "discovered_peripheral_tracker.cc",
+        "discovered_peripheral_tracker.h",
+        "lost_entity_tracker.cc",
+        "lost_entity_tracker.h",
+        "mediums.cc",
+        "mediums.h",
+        "uuid.cc",
+        "uuid.h",
+    ],
+    visibility = ["//core/internal:__pkg__"],
+    deps = [
+        "//platform:logging",
+        "//platform:types",
+        "//platform:utils",
+        "//platform/api",
+        "//platform/port:string",
+        "//absl/numeric:int128",
+        "//absl/strings",
+        "//smhasher:libmurmur3",
+    ],
+)
+
+cc_test(
+    name = "advertisement_read_result_test",
+    srcs = ["advertisement_read_result_test.cc"],
+    deps = [
+        ":mediums",
+        "//platform/impl/default",
+        "//testing/base/public:gunit_main",
+        "//absl/time",
+    ],
+)
+
+cc_test(
+    name = "ble_advertisement_header_test",
+    srcs = ["ble_advertisement_header_test.cc"],
+    deps = [
+        ":mediums",
+        "//platform:utils",
+        "//testing/base/public:gunit_main",
+    ],
+)
+
+cc_test(
+    name = "ble_advertisement_test",
+    srcs = ["ble_advertisement_test.cc"],
+    deps = [
+        ":mediums",
+        "//testing/base/public:gunit_main",
+    ],
+)
+
+cc_test(
+    name = "ble_packet_test",
+    srcs = ["ble_packet_test.cc"],
+    deps = [
+        ":mediums",
+        "//testing/base/public:gunit_main",
+    ],
+)
+
+cc_test(
+    name = "bloom_filter_test",
+    srcs = ["bloom_filter_test.cc"],
+    deps = [
+        ":mediums",
+        "//testing/base/public:gunit_main",
+    ],
+)
+
+cc_test(
+    name = "lost_entity_tracker_test",
+    srcs = ["lost_entity_tracker_test.cc"],
+    deps = [
+        ":mediums",
+        "//platform/impl/default",
+        "//testing/base/public:gunit_main",
+    ],
+)

cpp/core/internal/mediums/advertisement_read_result.cc

@@ -0,0 +1,186 @@
+#include "core/internal/mediums/advertisement_read_result.h"
+
+#include <algorithm>
+
+#include "platform/synchronized.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+namespace mediums {
+
+namespace {
+
+template <typename K, typename V>
+void eraseOwnedPtrFromMap(std::map<K, ConstPtr<V> >& m, const K& k) {
+  typename std::map<K, ConstPtr<V> >::iterator it = m.find(k);
+  if (it != m.end()) {
+    it->second.destroy();
+    m.erase(it);
+  }
+}
+
+}  // namespace
+
+// How much to multiply the backoff duration by with every failure to read
+// from the advertisement GATT server. This should never be below 1!
+template <typename Platform>
+const float AdvertisementReadResult<Platform>::kAdvertisementBackoffMultiplier =
+    2.0;
+
+// The initial backoff duration when we fail to read from an advertisement
+// GATT server.
+template <typename Platform>
+const std::int64_t
+    AdvertisementReadResult<Platform>::kAdvertisementBaseBackoffDurationMillis =
+        1 * 1000;  // 1 second
+
+// The maximum backoff duration allowed between advertisement GATT server
+// reads.
+template <typename Platform>
+const std::int64_t
+    AdvertisementReadResult<Platform>::kAdvertisementMaxBackoffDurationMillis =
+        5 * 60 * 1000;  // 5 minutes
+
+template <typename Platform>
+AdvertisementReadResult<Platform>::AdvertisementReadResult()
+    : lock_(Platform::createLock()),
+      system_clock_(Platform::createSystemClock()),
+      advertisements_(),
+      backoff_duration_millis_(kAdvertisementBaseBackoffDurationMillis),
+      // We need a long enough duration such that we always trigger a read
+      // retry AND we always connect to it without delay. The former case
+      // helps us initialize an AdvertisementReadResult so that we
+      // unconditionally try reading on the first sighting. And the latter
+      // case helps us connect immediately when we initialize a dummy read
+      // result for fast advertisements (which don't use the GATT server).
+      last_read_timestamp_millis_(system_clock_->elapsedRealtime() -
+                                  kAdvertisementMaxBackoffDurationMillis),
+      result_(Result::Value::UNKNOWN) {}
+
+template <typename Platform>
+AdvertisementReadResult<Platform>::~AdvertisementReadResult() {
+  Synchronized s(lock_.get());
+
+  for (AdvertisementMap::iterator it = advertisements_.begin();
+       it != advertisements_.end(); ++it) {
+    it->second.destroy();
+  }
+  advertisements_.clear();
+}
+
+// Adds a successfully read advertisement for the specified slot to this read
+// result. This is fundamentally different from
+// {@link #recordLastReadStatus(boolean)} because we can report a read
+// failure, but still manage to read some advertisements.
+// Note: advertisement should be passed in as a RefCounted Ptr. It is not the
+// responsibility of AdvertisementReadResult to make it RefCounted.
+template <typename Platform>
+void AdvertisementReadResult<Platform>::addAdvertisement(
+    std::int32_t slot, /* RefCounted */ ConstPtr<ByteArray> advertisement) {
+  Synchronized s(lock_.get());
+
+  ScopedPtr<ConstPtr<ByteArray>> scoped_advertisement(advertisement);
+
+  // Blindly remove from the advertisements map to make sure any existing
+  // key-value pair is destroyed.
+  eraseOwnedPtrFromMap(advertisements_, slot);
+
+  advertisements_.insert(std::make_pair(slot, scoped_advertisement.release()));
+}
+
+// Determines whether or not an advertisement was successfully read at the
+// specified slot.
+template <typename Platform>
+bool AdvertisementReadResult<Platform>::hasAdvertisement(std::int32_t slot) {
+  Synchronized s(lock_.get());
+
+  return advertisements_.find(slot) != advertisements_.end();
+}
+
+// Retrieves all raw advertisements that were successfully read.
+template <typename Platform>
+std::set<ConstPtr<ByteArray>>
+AdvertisementReadResult<Platform>::getAdvertisements() {
+  Synchronized s(lock_.get());
+
+  std::set<ConstPtr<ByteArray>> all_advertisements;
+  for (AdvertisementMap::iterator it = advertisements_.begin();
+       it != advertisements_.end(); ++it) {
+    all_advertisements.insert(it->second);
+  }
+
+  return all_advertisements;
+}
+
+// Determines what stage we're in for retrying a read from an advertisement
+// GATT server.
+template <typename Platform>
+typename AdvertisementReadResult<Platform>::RetryStatus::Value
+AdvertisementReadResult<Platform>::evaluateRetryStatus() {
+  Synchronized s(lock_.get());
+
+  // Check if we have already succeeded reading this advertisement.
+  if (result_ == Result::SUCCESS) {
+    return RetryStatus::PREVIOUSLY_SUCCEEDED;
+  }
+
+  // Check if we have recently failed to read this advertisement.
+  if (getDurationSinceReadMillis() < backoff_duration_millis_) {
+    return RetryStatus::TOO_SOON;
+  }
+
+  return RetryStatus::RETRY;
+}
+
+// Records the status of the latest read, and updates the next backoff
+// duration for subsequent reads. Be sure to also call
+// {@link #addAdvertisement(int, byte[])} if any advertisements were read.
+template <typename Platform>
+void AdvertisementReadResult<Platform>::recordLastReadStatus(bool is_success) {
+  Synchronized s(lock_.get());
+
+  // Update the last read timestamp.
+  last_read_timestamp_millis_ = system_clock_->elapsedRealtime();
+
+  // Update the backoff duration.
+  if (is_success) {
+    // Reset the backoff duration now that we had a successful read.
+    backoff_duration_millis_ = kAdvertisementBaseBackoffDurationMillis;
+  } else {
+    // Determine whether or not we were already failing before. If we were, we
+    // should increase the backoff duration.
+    if (result_ == Result::FAILURE) {
+      // Use exponential backoff to determine the next backoff duration. This
+      // simply involves multiplying our current backoff duration by some
+      // multiplier.
+      std::int64_t next_backoff_duration =
+          kAdvertisementBackoffMultiplier * backoff_duration_millis_;
+      // Update the backoff duration, making sure not to blow past the
+      // ceiling.
+      backoff_duration_millis_ = std::min(
+          next_backoff_duration, kAdvertisementMaxBackoffDurationMillis);
+    } else {
+      // This is our first time failing, so we should only backoff for the
+      // initial duration.
+      backoff_duration_millis_ = kAdvertisementBaseBackoffDurationMillis;
+    }
+  }
+
+  // Update the internal result.
+  result_ = is_success ? Result::SUCCESS : Result::FAILURE;
+}
+
+// Returns how much time has passed since we last tried reading from an
+// advertisement GATT server.
+template <typename Platform>
+std::int64_t AdvertisementReadResult<Platform>::getDurationSinceReadMillis() {
+  Synchronized s(lock_.get());
+
+  return system_clock_->elapsedRealtime() - last_read_timestamp_millis_;
+}
+
+}  // namespace mediums
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/mediums/advertisement_read_result.h

@@ -0,0 +1,73 @@
+#ifndef CORE_INTERNAL_MEDIUMS_ADVERTISEMENT_READ_RESULT_H_
+#define CORE_INTERNAL_MEDIUMS_ADVERTISEMENT_READ_RESULT_H_
+
+#include <cstdint>
+#include <map>
+#include <set>
+
+#include "platform/api/lock.h"
+#include "platform/api/system_clock.h"
+#include "platform/byte_array.h"
+#include "platform/ptr.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+namespace mediums {
+
+// Representation of a GATT advertisement read result. This object helps us
+// determine whether or not we need to retry GATT reads.
+template <typename Platform>
+class AdvertisementReadResult {
+ public:
+  AdvertisementReadResult();
+  ~AdvertisementReadResult();
+
+  struct RetryStatus {
+    enum Value {
+      UNKNOWN = 0,
+      RETRY = 1,
+      PREVIOUSLY_SUCCEEDED = 2,
+      TOO_SOON = 3,
+    };
+  };
+
+  void addAdvertisement(std::int32_t slot, ConstPtr<ByteArray> advertisement);
+  bool hasAdvertisement(std::int32_t slot);
+  std::set<ConstPtr<ByteArray>> getAdvertisements();
+  typename RetryStatus::Value evaluateRetryStatus();
+  void recordLastReadStatus(bool is_success);
+  std::int64_t getDurationSinceReadMillis();
+
+ private:
+  struct Result {
+    enum Value { UNKNOWN = 0, SUCCESS = 1, FAILURE = 2 };
+  };
+
+  static const float kAdvertisementBackoffMultiplier;
+  static const std::int64_t kAdvertisementBaseBackoffDurationMillis;
+  static const std::int64_t kAdvertisementMaxBackoffDurationMillis;
+
+  // ------------ GENERAL ------------
+  ScopedPtr<Ptr<Lock>> lock_;
+  ScopedPtr<Ptr<SystemClock>> system_clock_;
+
+  // ------ ADVERTISEMENTREADRESULT STATE ------
+  // Maps slot numbers to the GATT advertisement found in that slot.
+  typedef std::map<std::int32_t, /* RefCounted */ ConstPtr<ByteArray>>
+      AdvertisementMap;
+  AdvertisementMap advertisements_;
+
+  std::int64_t backoff_duration_millis_;
+  std::int64_t last_read_timestamp_millis_;
+  typename Result::Value result_;
+};
+
+}  // namespace mediums
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#include "core/internal/mediums/advertisement_read_result.cc"
+
+#endif  // CORE_INTERNAL_MEDIUMS_ADVERTISEMENT_READ_RESULT_H_

cpp/core/internal/mediums/advertisement_read_result_test.cc

@@ -0,0 +1,148 @@
+#include "core/internal/mediums/advertisement_read_result.h"
+
+#include "platform/impl/default/default_platform.h"
+#include "gtest/gtest.h"
+#include "absl/time/clock.h"
+#include "absl/time/time.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+namespace mediums {
+
+namespace {
+
+class SampleSystemClock : public SystemClock {
+ public:
+  SampleSystemClock() {}
+  ~SampleSystemClock() override {}
+
+  std::int64_t elapsedRealtime() override {
+    return absl::ToUnixMillis(absl::Now());
+  }
+};
+
+class SamplePlatform {
+ public:
+  static Ptr<Lock> createLock() { return DefaultPlatform::createLock(); }
+  static Ptr<SystemClock> createSystemClock() {
+    return MakePtr(new SampleSystemClock());
+  }
+};
+
+// We keep a copy of these constants because this is an old-school test (so we
+// can't delare it as a friend class of AdvertisementReadResult).
+const absl::Duration kAdvertisementBaseBackoffDuration =
+    absl::Milliseconds(1000);  // 1 second
+const absl::Duration kAdvertisementMaxBackoffDuration =
+    absl::Milliseconds(6000);  // 6 seconds
+const char kAdvertisementBytes[] = {0x0A, 0x0B, 0x0C};
+
+TEST(AdvertisementReadResultTest, AdvertisementExists) {
+  AdvertisementReadResult<SamplePlatform> advertisement_read_result;
+  advertisement_read_result.recordLastReadStatus(/* is_success= */ true);
+
+  std::int32_t slot = 6;
+  advertisement_read_result.addAdvertisement(
+      slot,
+      MakeConstPtr(new ByteArray(kAdvertisementBytes,
+                                 sizeof(kAdvertisementBytes) / sizeof(char))));
+
+  ASSERT_TRUE(advertisement_read_result.hasAdvertisement(slot));
+}
+
+TEST(AdvertisementReadResultTest, AdvertisementNonExistent) {
+  AdvertisementReadResult<SamplePlatform> advertisement_read_result;
+  advertisement_read_result.recordLastReadStatus(/* is_success= */ true);
+
+  std::int32_t slot = 6;
+
+  ASSERT_FALSE(advertisement_read_result.hasAdvertisement(slot));
+}
+
+TEST(AdvertisementReadResultTest, EvaluateRetryStatusInitialized) {
+  AdvertisementReadResult<SamplePlatform> advertisement_read_result;
+
+  ASSERT_EQ(advertisement_read_result.evaluateRetryStatus(),
+            AdvertisementReadResult<SamplePlatform>::RetryStatus::RETRY);
+}
+
+TEST(AdvertisementReadResultTest, EvaluateRetryStatusSuccess) {
+  AdvertisementReadResult<SamplePlatform> advertisement_read_result;
+  advertisement_read_result.recordLastReadStatus(/* is_success= */ true);
+
+  ASSERT_EQ(advertisement_read_result.evaluateRetryStatus(),
+            AdvertisementReadResult<
+                SamplePlatform>::RetryStatus::PREVIOUSLY_SUCCEEDED);
+}
+
+TEST(AdvertisementReadResultTest, EvaluateRetryStatusTooSoon) {
+  AdvertisementReadResult<SamplePlatform> advertisement_read_result;
+  advertisement_read_result.recordLastReadStatus(/* is_success= */ false);
+
+  // Sleep for some time, but not long enough to warrant a retry.
+  absl::SleepFor(absl::Milliseconds(
+      absl::ToInt64Milliseconds(kAdvertisementBaseBackoffDuration) / 2));
+
+  ASSERT_EQ(advertisement_read_result.evaluateRetryStatus(),
+            AdvertisementReadResult<SamplePlatform>::RetryStatus::TOO_SOON);
+}
+
+TEST(AdvertisementReadResultTest, EvaluateRetryStatusRetry) {
+  AdvertisementReadResult<SamplePlatform> advertisement_read_result;
+  advertisement_read_result.recordLastReadStatus(/* is_success= */ false);
+
+  // Sleep long enough to warrant a retry.
+  absl::SleepFor(kAdvertisementBaseBackoffDuration);
+
+  ASSERT_EQ(advertisement_read_result.evaluateRetryStatus(),
+            AdvertisementReadResult<SamplePlatform>::RetryStatus::RETRY);
+}
+
+TEST(AdvertisementReadResultTest, ReportStatusExponentialBackoff) {
+  AdvertisementReadResult<SamplePlatform> advertisement_read_result;
+  advertisement_read_result.recordLastReadStatus(/* is_success= */ false);
+
+  // Record an additional failure so our backoff duration increases.
+  advertisement_read_result.recordLastReadStatus(/* is_success= */ false);
+
+  // Sleep for the backoff duration. We shouldn't trigger a retry because the
+  // backoff should have increased from failing a second time.
+  absl::SleepFor(kAdvertisementBaseBackoffDuration);
+
+  ASSERT_EQ(advertisement_read_result.evaluateRetryStatus(),
+            AdvertisementReadResult<SamplePlatform>::RetryStatus::TOO_SOON);
+}
+
+TEST(AdvertisementReadResultTest, ReportStatusExponentialBackoffMax) {
+  AdvertisementReadResult<SamplePlatform> advertisement_read_result;
+  advertisement_read_result.recordLastReadStatus(/* is_success= */ false);
+
+  // Record an absurd amount of failures so we hit the maximum backoff duration.
+  for (std::int32_t i = 0; i < 1000; i++) {
+    advertisement_read_result.recordLastReadStatus(/* is_success= */ false);
+  }
+
+  // Sleep for the maximum backoff duration. This should be enough to warrant a
+  // retry.
+  absl::SleepFor(kAdvertisementMaxBackoffDuration);
+
+  ASSERT_EQ(advertisement_read_result.evaluateRetryStatus(),
+            AdvertisementReadResult<SamplePlatform>::RetryStatus::RETRY);
+}
+
+TEST(AdvertisementReadResultTest, GetDurationSinceRead) {
+  AdvertisementReadResult<SamplePlatform> advertisement_read_result;
+  advertisement_read_result.recordLastReadStatus(/* is_success= */ true);
+
+  std::int64_t sleepTime = 420;
+  absl::SleepFor(absl::Milliseconds(sleepTime));
+
+  ASSERT_GE(advertisement_read_result.getDurationSinceReadMillis(), sleepTime);
+}
+
+}  // namespace
+}  // namespace mediums
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/mediums/ble.cc

@@ -0,0 +1,281 @@
+#include "core/internal/mediums/ble.h"
+
+#include "platform/synchronized.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+template <typename Platform>
+const std::int32_t BLE<Platform>::kMaxAdvertisementLength = 512;
+
+template <typename Platform>
+BLE<Platform>::BLE(Ptr<BluetoothRadio<Platform>> bluetooth_radio)
+    : lock_(Platform::createLock()),
+      bluetooth_radio_(bluetooth_radio),
+      bluetooth_adapter_(Platform::createBluetoothAdapter()),
+      ble_medium_(Platform::createBLEMedium()),
+      scanning_info_(),
+      advertising_info_(),
+      accepting_connections_info_() {}
+
+template <typename Platform>
+BLE<Platform>::~BLE() {
+  stopAdvertising();
+  stopAcceptingConnections();
+  stopScanning();
+}
+
+template <typename Platform>
+bool BLE<Platform>::isAvailable() {
+  Synchronized s(lock_.get());
+
+  return !ble_medium_.isNull() && !bluetooth_adapter_.isNull();
+}
+
+// TODO(ahlee): Add fastPairData for phase 2 of C++ implementation.
+template <typename Platform>
+bool BLE<Platform>::startAdvertising(const string& service_id,
+                                     ConstPtr<ByteArray> advertisement) {
+  Synchronized s(lock_.get());
+
+  // Avoid leaks.
+  ScopedPtr<ConstPtr<ByteArray>> scoped_advertisement(advertisement);
+  if (scoped_advertisement.isNull() || service_id.empty()) {
+    // TODO(ahlee): logger.atSevere().log("Refusing to start BLE advertising
+    // because a null parameter was passed in.");
+    return false;
+  }
+
+  if (scoped_advertisement->size() > kMaxAdvertisementLength) {
+    // TODO(ahlee): logger.atSevere().log("Refusing to start BLE advertising
+    // because the advertisement was too long. Expected at most %d bytes but
+    // received %d.", kMaxAdvertisementLength, advertisement->size());
+    return false;
+  }
+
+  if (isAdvertising()) {
+    // TODO(ahlee): logger.atSevere().log("Failed to BLE advertise because we're
+    // already advertising.");
+    return false;
+  }
+
+  if (!bluetooth_radio_->isEnabled()) {
+    // TODO(ahlee): logger.atSevere().log("Can't start BLE advertising because
+    // Bluetooth isn't enabled.");
+    return false;
+  }
+
+  if (!isAvailable()) {
+    // TODO(ahlee): logger.atSevere().log("Can't start BLE advertising because
+    // BLE isn't enabled.");
+    return false;
+  }
+
+  if (!ble_medium_->startAdvertising(service_id,
+                                     scoped_advertisement.release())) {
+    // TODO(ahlee) logger.atSevere().log("Failed to start BLE advertising");
+    return false;
+  }
+
+  advertising_info_ = MakePtr(new AdvertisingInfo(service_id));
+  return true;
+}
+
+template <typename Platform>
+void BLE<Platform>::stopAdvertising() {
+  Synchronized s(lock_.get());
+
+  if (!isAdvertising()) {
+    // TODO(ahlee): logger.atDebug().log("Can't turn off BLE advertising because
+    // it never started.");
+    return;
+  }
+
+  ble_medium_->stopAdvertising(advertising_info_->service_id);
+  // Reset our bundle of advertising state to mark that we're no longer
+  // advertising.
+  advertising_info_.destroy();
+
+  // TODO(ahlee): logger.atVerbose().log("Turned BLE advertising off");
+}
+
+template <typename Platform>
+bool BLE<Platform>::isAdvertising() {
+  Synchronized s(lock_.get());
+
+  return !advertising_info_.isNull();
+}
+
+template <typename Platform>
+bool BLE<Platform>::startScanning(
+    const string& service_id,
+    Ptr<DiscoveredPeripheralCallback> discovered_peripheral_callback) {
+  Synchronized s(lock_.get());
+
+  // Avoid leaks.
+  ScopedPtr<Ptr<DiscoveredPeripheralCallback>>
+      scoped_discovered_peripheral_callback(discovered_peripheral_callback);
+  if (scoped_discovered_peripheral_callback.isNull() || service_id.empty()) {
+    // TODO(ahlee): logger.atSevere().log("Refusing to start BLE scanning
+    // because a null parameter was passed in.");
+    return false;
+  }
+
+  if (isScanning()) {
+    // TODO(ahlee): logger.atSevere().log("Refusing to start BLE scanning
+    // because we are already scanning.");
+    return false;
+  }
+
+  if (!bluetooth_radio_->isEnabled()) {
+    // TODO(ahlee): logger.atSevere().log("Can't start BLE scanning because
+    // Bluetooth was never turned on");
+    return false;
+  }
+
+  if (!isAvailable()) {
+    // TODO(ahlee): logger.atSevere().log("Can't start BLE scanning because
+    // BLE isn't available.");
+    return false;
+  }
+
+  // Avoid leaks.
+  ScopedPtr<Ptr<BLEDiscoveredPeripheralCallback>>
+      scoped_ble_discovered_peripheral_callback(
+          new BLEDiscoveredPeripheralCallback(
+              scoped_discovered_peripheral_callback.release()));
+  if (!ble_medium_->startScanning(
+          service_id, scoped_ble_discovered_peripheral_callback.get())) {
+    // TODO(ahlee): logger.atSevere().log("Failed to start BLE scanning.");
+    return false;
+  }
+
+  scanning_info_ = MakePtr(new ScanningInfo(
+      service_id, scoped_ble_discovered_peripheral_callback.release()));
+  return true;
+}
+
+template <typename Platform>
+void BLE<Platform>::stopScanning() {
+  Synchronized s(lock_.get());
+
+  if (!isScanning()) {
+    // TODO(ahlee): logger.atDebug().log("Can't turn off BLE scanning because we
+    // never started scanning.");
+    return;
+  }
+
+  ble_medium_->stopScanning(scanning_info_->service_id);
+  // Reset our bundle of scanning state to mark that we're no longer scanning.
+  scanning_info_.destroy();
+}
+
+template <typename Platform>
+bool BLE<Platform>::isScanning() {
+  Synchronized s(lock_.get());
+
+  return !scanning_info_.isNull();
+}
+
+template <typename Platform>
+bool BLE<Platform>::startAcceptingConnections(
+    const string& service_id,
+    Ptr<AcceptedConnectionCallback> accepted_connection_callback) {
+  Synchronized s(lock_.get());
+
+  // Avoid leaks.
+  ScopedPtr<Ptr<AcceptedConnectionCallback>>
+      scoped_accepted_connection_callback(accepted_connection_callback);
+  if (scoped_accepted_connection_callback.isNull() || service_id.empty()) {
+    // TODO(ahlee): logger.atSevere().log("Refusing to start accepting BLE
+    // connections because a null parameter was passed in.");
+    return false;
+  }
+
+  if (isAcceptingConnections()) {
+    // TODO(ahlee): logger.atSevere().log("Refusing to start accepting BLE
+    // connections for %s because another BLE server socket is already
+    // in-progress.", service_id);
+    return false;
+  }
+
+  if (!bluetooth_radio_->isEnabled()) {
+    // TODO(ahlee): logger.atSevere().log("Can't start accepting BLE connections
+    // for %s because Bluetooth isn't enabled.", serviceId);
+    return false;
+  }
+
+  if (!isAvailable()) {
+    // TODO(ahlee): logger.atSevere().log("Can't start accepting BLE connections
+    // for %s because BLE isn't available.", serviceId);
+    return false;
+  }
+
+  // Avoid leaks.
+  ScopedPtr<Ptr<BLEAcceptedConnectionCallback>>
+      scoped_ble_accepted_connection_callback(new BLEAcceptedConnectionCallback(
+          scoped_accepted_connection_callback.release()));
+  if (!ble_medium_->startAcceptingConnections(
+          service_id, scoped_ble_accepted_connection_callback.get())) {
+    return false;
+  }
+
+  accepting_connections_info_ = MakePtr(new AcceptingConnectionsInfo(
+      service_id, scoped_ble_accepted_connection_callback.release()));
+  return true;
+}
+
+template <typename Platform>
+void BLE<Platform>::stopAcceptingConnections() {
+  Synchronized s(lock_.get());
+
+  if (!isAcceptingConnections()) {
+    // TODO(ahlee): logger.atDebug().log("Can't stop accepting BLE connections
+    // because it was never started.");
+    return;
+  }
+
+  ble_medium_->stopAcceptingConnections(
+      accepting_connections_info_->service_id);
+  // Reset our bundle of accepting connections state to mark that we're no
+  // longer accepting connections.
+  accepting_connections_info_.destroy();
+}
+
+template <typename Platform>
+bool BLE<Platform>::isAcceptingConnections() {
+  Synchronized s(lock_.get());
+
+  return !accepting_connections_info_.isNull();
+}
+
+template <typename Platform>
+Ptr<BLESocket> BLE<Platform>::connect(Ptr<BLEPeripheral> ble_peripheral,
+                                      const string& service_id) {
+  Synchronized s(lock_.get());
+
+  if (ble_peripheral.isNull() || service_id.empty()) {
+    // TODO(ahlee): logger.atSevere().log("Refusing to create client BLE socket
+    // because at least one of blePeripheral or serviceId is null.");
+    return Ptr<BLESocket>();
+  }
+
+  if (!bluetooth_radio_->isEnabled()) {
+    // TODO(ahlee): logger.atSevere().log("Can't create client BLE socket to %s
+    // because Bluetooth isn't enabled.", blePeripheral);
+    return Ptr<BLESocket>();
+  }
+
+  if (!isAvailable()) {
+    // TODO(ahlee): logger.atSevere().log("Can't create client BLE socket to %s
+    // because BLE isn't available.", blePeripheral);
+    return Ptr<BLESocket>();
+  }
+
+  return ble_medium_->connect(ble_peripheral, service_id);
+}
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/mediums/ble.h

@@ -0,0 +1,197 @@
+#ifndef CORE_INTERNAL_MEDIUMS_BLE_H_
+#define CORE_INTERNAL_MEDIUMS_BLE_H_
+
+#include <cstdint>
+
+#include "core/internal/mediums/bluetooth_radio.h"
+#include "platform/api/ble.h"
+#include "platform/api/bluetooth_adapter.h"
+#include "platform/api/lock.h"
+#include "platform/byte_array.h"
+#include "platform/port/string.h"
+#include "platform/ptr.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+template <typename Platform>
+class BLE {
+ public:
+  explicit BLE(Ptr<BluetoothRadio<Platform>> bluetooth_radio);
+  ~BLE();
+
+  bool isAvailable();
+
+  bool startAdvertising(const string& service_id,
+                        ConstPtr<ByteArray> advertisement);
+  void stopAdvertising();
+
+  class DiscoveredPeripheralCallback {
+   public:
+    virtual ~DiscoveredPeripheralCallback() {}
+
+    virtual void onPeripheralDiscovered(Ptr<BLEPeripheral> ble_peripheral,
+                                        const string& service_id,
+                                        ConstPtr<ByteArray> advertisement) = 0;
+    virtual void onPeripheralLost(Ptr<BLEPeripheral> ble_peripheral,
+                                  const string& service_id) = 0;
+  };
+
+  bool startScanning(
+      const string& service_id,
+      Ptr<DiscoveredPeripheralCallback> discovered_peripheral_callback);
+  void stopScanning();
+
+  class AcceptedConnectionCallback {
+   public:
+    virtual ~AcceptedConnectionCallback() {}
+
+    virtual void onConnectionAccepted(Ptr<BLESocket> socket,
+                                      const string& service_id) = 0;
+  };
+
+  bool startAcceptingConnections(
+      const string& service_id,
+      Ptr<AcceptedConnectionCallback> accepted_connection_callback);
+  void stopAcceptingConnections();
+  bool isAcceptingConnections();
+
+  Ptr<BLESocket> connect(Ptr<BLEPeripheral> ble_peripheral,
+                         const string& service_id);
+
+ private:
+  // TODO(ahlee): Rename to DiscoveredPeripheralCallbackBridge
+  class BLEDiscoveredPeripheralCallback
+      : public BLEMedium::DiscoveredPeripheralCallback {
+   public:
+    explicit BLEDiscoveredPeripheralCallback(
+        Ptr<BLE::DiscoveredPeripheralCallback> discovered_peripheral_callback)
+        : discovered_peripheral_callback_(discovered_peripheral_callback) {}
+    ~BLEDiscoveredPeripheralCallback() override {
+      // Nothing to do.
+    }
+
+    void onPeripheralDiscovered(Ptr<BLEPeripheral> ble_peripheral,
+                                const string& service_id,
+                                ConstPtr<ByteArray> advertisement) override {
+      discovered_peripheral_callback_->onPeripheralDiscovered(
+          ble_peripheral, service_id, advertisement);
+    }
+    void onPeripheralLost(Ptr<BLEPeripheral> ble_peripheral,
+                          const string& service_id) override {
+      discovered_peripheral_callback_->onPeripheralLost(ble_peripheral,
+                                                        service_id);
+    }
+
+   private:
+    ScopedPtr<Ptr<BLE::DiscoveredPeripheralCallback>>
+        discovered_peripheral_callback_;
+  };
+
+  // TODO(ahlee): Rename to AcceptedConnectionCallbackBridge
+  class BLEAcceptedConnectionCallback
+      : public BLEMedium::AcceptedConnectionCallback {
+   public:
+    explicit BLEAcceptedConnectionCallback(
+        Ptr<BLE::AcceptedConnectionCallback> accepted_connection_callback)
+        : accepted_connection_callback_(accepted_connection_callback) {}
+    ~BLEAcceptedConnectionCallback() override {
+      // Nothing to do.
+    }
+
+    void onConnectionAccepted(Ptr<BLESocket> ble_socket,
+                              const string& service_id) override {
+      accepted_connection_callback_->onConnectionAccepted(ble_socket,
+                                                          service_id);
+    }
+
+   private:
+    ScopedPtr<Ptr<BLE::AcceptedConnectionCallback>>
+        accepted_connection_callback_;
+  };
+
+  struct ScanningInfo {
+    ScanningInfo(
+        const string& service_id,
+        Ptr<BLEDiscoveredPeripheralCallback> ble_discovered_peripheral_callback)
+        : service_id(service_id),
+          ble_discovered_peripheral_callback(
+              ble_discovered_peripheral_callback) {}
+    ~ScanningInfo() {
+      // Nothing to do (the ScopedPtr members take care of themselves).
+    }
+
+    const string service_id;
+    ScopedPtr<Ptr<BLEDiscoveredPeripheralCallback>>
+        ble_discovered_peripheral_callback;
+  };
+
+  struct AdvertisingInfo {
+    explicit AdvertisingInfo(const string& service_id)
+        : service_id(service_id) {}
+    ~AdvertisingInfo() {}
+
+    const string service_id;
+  };
+
+  struct AcceptingConnectionsInfo {
+    AcceptingConnectionsInfo(
+        const string& service_id,
+        Ptr<BLEAcceptedConnectionCallback> ble_accepted_connection_callback)
+        : service_id(service_id),
+          ble_accepted_connection_callback(ble_accepted_connection_callback) {}
+    ~AcceptingConnectionsInfo() {
+      // Nothing to do (the ScopedPtr members take care of themselves).
+    }
+
+    const string service_id;
+    ScopedPtr<Ptr<BLEAcceptedConnectionCallback>>
+        ble_accepted_connection_callback;
+  };
+
+  static const std::int32_t kMaxAdvertisementLength;
+
+  bool isAdvertising();
+  bool isScanning();
+
+  // ------------ GENERAL ------------
+
+  ScopedPtr<Ptr<Lock>> lock_;
+
+  // ------------ CORE BLE ------------
+
+  Ptr<BluetoothRadio<Platform>> bluetooth_radio_;
+  ScopedPtr<Ptr<BluetoothAdapter>> bluetooth_adapter_;
+  // The underlying, per-platform implementation.
+  ScopedPtr<Ptr<BLEMedium>> ble_medium_;
+
+  // ------------ DISCOVERY ------------
+
+  // A bundle of state required to start/stop BLE scanning. When non-null,
+  // we are currently performing a BLE scan.
+  // In the Java code this maps to the bleListener and
+  // bleScanningMediumOperation.
+  Ptr<ScanningInfo> scanning_info_;
+
+  // ------------ ADVERTISING ------------
+
+  // A bundle of state required to start/stop BLE advertising. When non-null,
+  // we are currently advertising over BLE.
+  // In the Java code this maps to bleAdvertiser, advertiseCallback, and
+  // bleAdvertisingMediumOperation.
+  Ptr<AdvertisingInfo> advertising_info_;
+
+  // A bundle of state required to start/stop accepting BLE connections. When
+  // non-null, we are currently accepting BLE connections.
+  // In the Java code this maps to the bleServerSocket.
+  Ptr<AcceptingConnectionsInfo> accepting_connections_info_;
+};
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#include "core/internal/mediums/ble.cc"
+
+#endif  // CORE_INTERNAL_MEDIUMS_BLE_H_

cpp/core/internal/mediums/ble_advertisement.cc

@@ -0,0 +1,288 @@
+#include "core/internal/mediums/ble_advertisement.h"
+
+#include "platform/logging.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+namespace mediums {
+
+const std::uint32_t BLEAdvertisement::kServiceIdHashLength = 3;
+
+const std::uint32_t BLEAdvertisement::kVersionLength = 1;
+// Length of one int. Be sure to re-evaluate how we compute data size in this
+// class if this constant ever changes!
+const std::uint32_t BLEAdvertisement::kDataSizeLength = 4;
+const std::uint32_t BLEAdvertisement::kMinAdvertisementLength =
+    kVersionLength + kServiceIdHashLength + kDataSizeLength;
+// The maximum length for a GATT characteristic value is 512 bytes, so make sure
+// the entire advertisement is less than that. The data can take up whatever
+// space is remaining after the bytes preceding it.
+const std::uint32_t BLEAdvertisement::kMaxDataSize =
+    512 - kMinAdvertisementLength;
+const std::uint16_t BLEAdvertisement::kVersionBitmask = 0x0E0;
+const std::uint16_t BLEAdvertisement::kSocketVersionBitmask = 0x01C;
+
+ConstPtr<BLEAdvertisement> BLEAdvertisement::fromBytes(
+    ConstPtr<ByteArray> ble_advertisement_bytes) {
+  if (ble_advertisement_bytes.isNull()) {
+    NEARBY_LOG(INFO,
+               "Cannot deserialize BLEAdvertisement: null bytes passed in");
+    return ConstPtr<BLEAdvertisement>();
+  }
+
+  if (ble_advertisement_bytes->size() < kMinAdvertisementLength) {
+    NEARBY_LOG(INFO,
+               "Cannot deserialize BLEAdvertisement: expecting min %u raw "
+               "bytes, got %zu",
+               kMinAdvertisementLength, ble_advertisement_bytes->size());
+    return ConstPtr<BLEAdvertisement>();
+  }
+
+  // Now, time to read the bytes!
+  const char *ble_advertisement_bytes_read_ptr =
+      ble_advertisement_bytes->getData();
+
+  // 1. Version.
+  Version::Value version = parseVersionFromByte(
+      static_cast<std::uint16_t>(*ble_advertisement_bytes_read_ptr));
+  if (!isSupportedVersion(version)) {
+    NEARBY_LOG(INFO,
+               "Cannot deserialize BLEAdvertisement: unsupported Version %u",
+               version);
+    return ConstPtr<BLEAdvertisement>();
+  }
+
+  // 2. Socket Version.
+  SocketVersion::Value socket_version = parseSocketVersionFromByte(
+      static_cast<std::uint16_t>(*ble_advertisement_bytes_read_ptr));
+  if (!isSupportedSocketVersion(socket_version)) {
+    NEARBY_LOG(
+        INFO,
+        "Cannot deserialize BLEAdvertisement: unsupported SocketVersion %u",
+        socket_version);
+    return ConstPtr<BLEAdvertisement>();
+  }
+  ble_advertisement_bytes_read_ptr += kVersionLength;
+
+  // 3. Service ID hash.
+  ScopedPtr<ConstPtr<ByteArray> > scoped_service_id_hash(MakeConstPtr(
+      new ByteArray(ble_advertisement_bytes_read_ptr, kServiceIdHashLength)));
+  ble_advertisement_bytes_read_ptr += kServiceIdHashLength;
+
+  // 4.1. Data size.
+  size_t expected_data_size =
+      deserializeDataSize(ble_advertisement_bytes_read_ptr);
+  if (expected_data_size < 0) {
+    NEARBY_LOG(INFO,
+               "Cannot deserialize BLEAdvertisement: negative data size %zu",
+               expected_data_size);
+    return ConstPtr<BLEAdvertisement>();
+  }
+  ble_advertisement_bytes_read_ptr += kDataSizeLength;
+
+  // Check that the stated data size is the same as what we received.
+  size_t actual_data_size = computeDataSize(ble_advertisement_bytes);
+  if (actual_data_size < expected_data_size) {
+    NEARBY_LOG(INFO,
+               "Cannot deserialize BLEAdvertisement: expected data to be %zu "
+               "bytes, got %zu bytes",
+               expected_data_size, actual_data_size);
+    return ConstPtr<BLEAdvertisement>();
+  }
+
+  // 4.2. Data.
+  ScopedPtr<ConstPtr<ByteArray> > scoped_data(MakeConstPtr(
+      new ByteArray(ble_advertisement_bytes_read_ptr, expected_data_size)));
+  ble_advertisement_bytes_read_ptr += expected_data_size;
+
+  return MakeRefCountedConstPtr(new BLEAdvertisement(
+      version, socket_version, scoped_service_id_hash.release(),
+      scoped_data.release()));
+}
+
+ConstPtr<ByteArray> BLEAdvertisement::toBytes(
+    Version::Value version, SocketVersion::Value socket_version,
+    ConstPtr<ByteArray> service_id_hash, ConstPtr<ByteArray> data) {
+  // Check that the given input is valid.
+  if (!isSupportedVersion(version)) {
+    NEARBY_LOG(INFO,
+               "Cannot serialize BLEAdvertisement: unsupported Version %u",
+               version);
+    return ConstPtr<ByteArray>();
+  }
+
+  if (!isSupportedSocketVersion(socket_version)) {
+    NEARBY_LOG(
+        INFO, "Cannot serialize BLEAdvertisement: unsupported SocketVersion %u",
+        socket_version);
+    return ConstPtr<ByteArray>();
+  }
+
+  if (service_id_hash->size() != kServiceIdHashLength) {
+    NEARBY_LOG(INFO,
+               "Cannot serialize BLEAdvertisement: expected a service_id_hash "
+               "of %u bytes, but got %zu",
+               kServiceIdHashLength, service_id_hash->size());
+    return ConstPtr<ByteArray>();
+  }
+
+  if (data->size() > kMaxDataSize) {
+    NEARBY_LOG(INFO,
+               "Cannot serialize BLEAdvertisement: expected data of at most %u "
+               "bytes, but got %zu",
+               kMaxDataSize, data->size());
+    return ConstPtr<ByteArray>();
+  }
+
+  // Initialize the bytes.
+  size_t advertisement_length = computeAdvertisementLength(data);
+  Ptr<ByteArray> advertisement_bytes{new ByteArray{advertisement_length}};
+  char *advertisement_bytes_write_ptr = advertisement_bytes->getData();
+
+  // 1. Version.
+  serializeVersionByte(advertisement_bytes_write_ptr, version);
+
+  // 2. SocketVersion.
+  serializeSocketVersionByte(advertisement_bytes_write_ptr, socket_version);
+  advertisement_bytes_write_ptr += kVersionLength;
+
+  // 3. Service ID hash.
+  memcpy(advertisement_bytes_write_ptr, service_id_hash->getData(),
+         kServiceIdHashLength);
+  advertisement_bytes_write_ptr += kServiceIdHashLength;
+
+  // 4.1. Data length.
+  serializeDataSize(advertisement_bytes_write_ptr, data->size());
+  advertisement_bytes_write_ptr += kDataSizeLength;
+
+  // 4.2. Data.
+  memcpy(advertisement_bytes_write_ptr, data->getData(), data->size());
+  advertisement_bytes_write_ptr += data->size();
+
+  return ConstifyPtr(advertisement_bytes);
+}
+
+bool BLEAdvertisement::isSupportedVersion(Version::Value version) {
+  return version >= Version::V1 && version <= Version::V2;
+}
+
+bool BLEAdvertisement::isSupportedSocketVersion(
+    SocketVersion::Value socket_version) {
+  return socket_version >= SocketVersion::V1 &&
+         socket_version <= SocketVersion::V2;
+}
+
+BLEAdvertisement::Version::Value BLEAdvertisement::parseVersionFromByte(
+    std::uint16_t byte) {
+  return static_cast<BLEAdvertisement::Version::Value>(
+      (byte & kVersionBitmask) >> 5);
+}
+
+BLEAdvertisement::SocketVersion::Value
+BLEAdvertisement::parseSocketVersionFromByte(std::uint16_t byte) {
+  return static_cast<SocketVersion::Value>((byte & kSocketVersionBitmask) >> 2);
+}
+
+size_t BLEAdvertisement::deserializeDataSize(
+    const char *data_size_bytes_read_ptr) {
+  // Allocate a chunk of memory to store our deserialized size.
+  char data_size_bytes[kDataSizeLength];
+
+  // Assign the bits of our size from the given raw bytes, keeping in mind that
+  // we need to convert from Big Endian to Little Endian in the process.
+  for (int i = 0; i < kDataSizeLength; ++i) {
+    data_size_bytes[i] = data_size_bytes_read_ptr[kDataSizeLength - i - 1];
+  }
+
+  // Interpret the char array as a single int.
+  return static_cast<size_t>(
+      *(reinterpret_cast<std::uint32_t *>(&data_size_bytes)));
+}
+
+size_t BLEAdvertisement::computeDataSize(
+    ConstPtr<ByteArray> ble_advertisement_bytes) {
+  return ble_advertisement_bytes->size() - kMinAdvertisementLength;
+}
+
+size_t BLEAdvertisement::computeAdvertisementLength(ConstPtr<ByteArray> data) {
+  // The advertisement length is the minimum length + the length of the data.
+  return kMinAdvertisementLength + data->size();
+}
+
+void BLEAdvertisement::serializeVersionByte(char *version_byte_write_ptr,
+                                            Version::Value version) {
+  *version_byte_write_ptr |=
+      static_cast<char>((version << 5) & kVersionBitmask);
+}
+
+void BLEAdvertisement::serializeSocketVersionByte(
+    char *socket_version_byte_write_ptr, SocketVersion::Value socket_version) {
+  *socket_version_byte_write_ptr |=
+      static_cast<char>((socket_version << 2) & kSocketVersionBitmask);
+}
+
+void BLEAdvertisement::serializeDataSize(char *data_size_bytes_write_ptr,
+                                         size_t data_size) {
+  // Get a raw representation of the data size bytes in memory.
+  char *data_size_bytes = reinterpret_cast<char *>(&data_size);
+
+  // Append these raw bytes to advertisement bytes, keeping in mind that we need
+  // to convert from Little Endian to Big Endian in the process.
+  for (int i = 0; i < kDataSizeLength; ++i) {
+    data_size_bytes_write_ptr[i] = data_size_bytes[kDataSizeLength - i - 1];
+  }
+}
+
+BLEAdvertisement::BLEAdvertisement(Version::Value version,
+                                   SocketVersion::Value socket_version,
+                                   ConstPtr<ByteArray> service_id_hash,
+                                   ConstPtr<ByteArray> data)
+    : version_(version),
+      socket_version_(socket_version),
+      service_id_hash_(service_id_hash),
+      data_(data) {}
+
+BLEAdvertisement::~BLEAdvertisement() {
+  // Nothing to do.
+}
+
+BLEAdvertisement::Version::Value BLEAdvertisement::getVersion() const {
+  return version_;
+}
+
+BLEAdvertisement::SocketVersion::Value BLEAdvertisement::getSocketVersion()
+    const {
+  return socket_version_;
+}
+
+ConstPtr<ByteArray> BLEAdvertisement::getServiceIdHash() const {
+  return service_id_hash_.get();
+}
+
+ConstPtr<ByteArray> BLEAdvertisement::getData() const { return data_.get(); }
+
+bool BLEAdvertisement::operator==(const BLEAdvertisement &rhs) const {
+  return this->getVersion() == rhs.getVersion() &&
+         this->getSocketVersion() == rhs.getSocketVersion() &&
+         *(this->getServiceIdHash()) == *(rhs.getServiceIdHash()) &&
+         *(this->getData()) == *(rhs.getData());
+}
+
+bool BLEAdvertisement::operator<(const BLEAdvertisement &rhs) const {
+  if (this->getVersion() != rhs.getVersion()) {
+    return this->getVersion() < rhs.getVersion();
+  }
+  if (this->getSocketVersion() != rhs.getSocketVersion()) {
+    return this->getSocketVersion() < rhs.getSocketVersion();
+  }
+  if (*(this->getServiceIdHash()) != *(rhs.getServiceIdHash())) {
+    return *(this->getServiceIdHash()) < *(rhs.getServiceIdHash());
+  }
+  return *(this->getData()) < *(rhs.getData());
+}
+
+}  // namespace mediums
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/mediums/ble_advertisement.h

@@ -0,0 +1,100 @@
+#ifndef CORE_INTERNAL_MEDIUMS_BLE_ADVERTISEMENT_H_
+#define CORE_INTERNAL_MEDIUMS_BLE_ADVERTISEMENT_H_
+
+#include "platform/byte_array.h"
+#include "platform/ptr.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+namespace mediums {
+
+// Represents the format of the Mediums BLE Advertisement used in advertising
+// and discovery.
+//
+// [VERSION][SOCKET_VERSION][2_RESERVED_BITS][SERVICE_ID_HASH][DATA_SIZE][DATA]
+//
+// See go/nearby-ble-design for more information.
+class BLEAdvertisement {
+ public:
+  // Versions of the BLEAdvertisement.
+  struct Version {
+    enum Value {
+      UNKNOWN = 0,
+      V1 = 1,
+      V2 = 2,
+      // Version is only allocated 3 bits in the BLEAdvertisement, so this can
+      // never go beyond V7.
+    };
+  };
+
+  // Versions of the BLESocket.
+  struct SocketVersion {
+    enum Value {
+      UNKNOWN = 0,
+      V1 = 1,
+      V2 = 2,
+      // SocketVersion is only allocated 3 bits in the BLEAdvertisement, so this
+      // can never go beyond V7.
+    };
+  };
+
+  static ConstPtr<BLEAdvertisement> fromBytes(
+      ConstPtr<ByteArray> ble_advertisement_bytes);
+
+  static ConstPtr<ByteArray> toBytes(Version::Value version,
+                                     SocketVersion::Value socket_version,
+                                     ConstPtr<ByteArray> service_id_hash,
+                                     ConstPtr<ByteArray> data);
+
+  static const std::uint32_t kServiceIdHashLength;
+
+  ~BLEAdvertisement();
+
+  Version::Value getVersion() const;
+  SocketVersion::Value getSocketVersion() const;
+  ConstPtr<ByteArray> getServiceIdHash() const;
+  ConstPtr<ByteArray> getData() const;
+
+  // Operator overloads when comparing ConstPtr<BLEAdvertisement>.
+  bool operator==(const BLEAdvertisement &rhs) const;
+  bool operator<(const BLEAdvertisement &rhs) const;
+
+ private:
+  static bool isSupportedVersion(Version::Value version);
+  static bool isSupportedSocketVersion(SocketVersion::Value socket_version);
+  static Version::Value parseVersionFromByte(std::uint16_t byte);
+  static SocketVersion::Value parseSocketVersionFromByte(std::uint16_t byte);
+  static size_t deserializeDataSize(const char *data_size_bytes_read_ptr);
+  static size_t computeDataSize(ConstPtr<ByteArray> ble_advertisement_bytes);
+  static size_t computeAdvertisementLength(ConstPtr<ByteArray> data);
+  static void serializeVersionByte(char *version_byte_write_ptr,
+                                   Version::Value version);
+  static void serializeSocketVersionByte(char *socket_version_byte_write_ptr,
+                                         SocketVersion::Value socket_version);
+  static void serializeDataSize(char *data_size_bytes_write_ptr,
+                                size_t data_size);
+
+  static const std::uint32_t kVersionLength;
+  static const std::uint32_t kDataSizeLength;
+  static const std::uint32_t kMinAdvertisementLength;
+  static const std::uint32_t kMaxDataSize;
+  static const std::uint16_t kVersionBitmask;
+  static const std::uint16_t kSocketVersionBitmask;
+
+  BLEAdvertisement(Version::Value version, SocketVersion::Value socket_version,
+                   ConstPtr<ByteArray> service_id_hash,
+                   ConstPtr<ByteArray> data);
+
+  const Version::Value version_;
+  const SocketVersion::Value socket_version_;
+  ScopedPtr<ConstPtr<ByteArray> > service_id_hash_;
+  ScopedPtr<ConstPtr<ByteArray> > data_;
+};
+
+}  // namespace mediums
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#endif  // CORE_INTERNAL_MEDIUMS_BLE_ADVERTISEMENT_H_

cpp/core/internal/mediums/ble_advertisement_header.cc

@@ -0,0 +1,208 @@
+#include "core/internal/mediums/ble_advertisement_header.h"
+
+#include "platform/base64_utils.h"
+#include "platform/byte_array.h"
+#include "platform/logging.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+namespace mediums {
+
+// The following IfThisThenThat is for BloomFilter length in
+// ble_v2.createAdvertisementHeader
+// LINT.IfChange
+const std::uint32_t BLEAdvertisementHeader::kServiceIdBloomFilterLength = 10;
+// LINT.ThenChange(//depot/google3/core/internal/\
+//     mediums/ble_v2.h)
+const std::uint32_t BLEAdvertisementHeader::kAdvertisementHashLength = 4;
+
+const std::uint32_t BLEAdvertisementHeader::kVersionAndNumSlotsLength = 1;
+const std::uint32_t BLEAdvertisementHeader::kMinAdvertisementHeaderLength =
+    kVersionAndNumSlotsLength + kServiceIdBloomFilterLength +
+    kAdvertisementHashLength;
+const std::uint16_t BLEAdvertisementHeader::kVersionBitmask = 0x0E0;
+const std::uint16_t BLEAdvertisementHeader::kNumSlotsBitmask = 0x01F;
+
+ConstPtr<BLEAdvertisementHeader> BLEAdvertisementHeader::fromString(
+    const std::string &ble_advertisement_header_string) {
+  ScopedPtr<Ptr<ByteArray> > scoped_ble_advertisement_header_bytes(
+      Base64Utils::decode(ble_advertisement_header_string));
+  if (scoped_ble_advertisement_header_bytes.isNull()) {
+    NEARBY_LOG(
+        INFO,
+        "Cannot deserialize BLEAdvertisementHeader: failed Base64 decoding");
+    return ConstPtr<BLEAdvertisementHeader>();
+  }
+
+  if (scoped_ble_advertisement_header_bytes->size() <
+      kMinAdvertisementHeaderLength) {
+    NEARBY_LOG(INFO,
+               "Cannot deserialize BLEAdvertisementHeader: expecting min %u "
+               "raw bytes, got %zu instead",
+               kMinAdvertisementHeaderLength,
+               scoped_ble_advertisement_header_bytes->size());
+    return ConstPtr<BLEAdvertisementHeader>();
+  }
+
+  // Now, time to read the bytes!
+  const char *ble_advertisement_header_read_ptr =
+      scoped_ble_advertisement_header_bytes->getData();
+
+  // 1. Version.
+  // The first 3 bits of the first byte represent the version.
+  Version::Value version = parseVersionFromByte(
+      static_cast<std::uint16_t>(*ble_advertisement_header_read_ptr));
+  if (version != Version::V2) {
+    NEARBY_LOG(
+        INFO,
+        "Cannot deserialize BLEAdvertisementHeader, unsupported version %u",
+        version);
+    return ConstPtr<BLEAdvertisementHeader>();
+  }
+
+  // 2. Number of slots.
+  // The last 5 bits of the first byte represent the number of slots.
+  std::uint32_t num_slots = parseNumSlotsFromByte(
+      static_cast<std::uint16_t>(*ble_advertisement_header_read_ptr));
+  ble_advertisement_header_read_ptr += kVersionAndNumSlotsLength;
+
+  // 3. Service ID bloom filter.
+  ScopedPtr<ConstPtr<ByteArray> > scoped_service_id_bloom_filter(
+      MakeConstPtr(new ByteArray(ble_advertisement_header_read_ptr,
+                                 kServiceIdBloomFilterLength)));
+  ble_advertisement_header_read_ptr += kServiceIdBloomFilterLength;
+
+  // 4. Advertisement hash.
+  ScopedPtr<ConstPtr<ByteArray> > scoped_advertisement_hash(
+      MakeConstPtr(new ByteArray(ble_advertisement_header_read_ptr,
+                                 kAdvertisementHashLength)));
+  ble_advertisement_header_read_ptr += kAdvertisementHashLength;
+
+  return MakeRefCountedConstPtr(new BLEAdvertisementHeader(
+      version, num_slots, scoped_service_id_bloom_filter.release(),
+      scoped_advertisement_hash.release()));
+}
+
+std::string BLEAdvertisementHeader::asString(
+    Version::Value version, std::uint32_t num_slots,
+    ConstPtr<ByteArray> service_id_bloom_filter,
+    ConstPtr<ByteArray> advertisement_hash) {
+  // Check that the given input is valid.
+  if (version != Version::V2) {
+    NEARBY_LOG(
+        INFO, "Cannot serialize BLEAdvertisementHeader: unsupported Version %u",
+        version);
+    return "";
+  }
+
+  if (service_id_bloom_filter->size() != kServiceIdBloomFilterLength) {
+    NEARBY_LOG(INFO,
+               "Cannot serialize BLEAdvertisementHeader: expected "
+               "service_id_bloom_filter of %u bytes, but got %zu",
+               kServiceIdBloomFilterLength, service_id_bloom_filter->size());
+    return "";
+  }
+
+  if (advertisement_hash->size() != kAdvertisementHashLength) {
+    NEARBY_LOG(INFO,
+               "Cannot serialize BLEAdvertisementHeader: expected "
+               "advertisement_hash of %u bytes, but got %zu",
+               kAdvertisementHashLength, advertisement_hash->size());
+    return "";
+  }
+
+  // Initialize the bytes.
+  ByteArray advertisement_header_bytes{kMinAdvertisementHeaderLength};
+  char *advertisement_header_bytes_write_ptr =
+      advertisement_header_bytes.getData();
+
+  // 1. Version.
+  serializeVersionByte(advertisement_header_bytes_write_ptr, version);
+
+  // 2. Number of slots.
+  serializeNumSlots(advertisement_header_bytes_write_ptr, num_slots);
+  advertisement_header_bytes_write_ptr += kVersionAndNumSlotsLength;
+
+  // 3. Service ID bloom filter.
+  memcpy(advertisement_header_bytes_write_ptr,
+         service_id_bloom_filter->getData(), kServiceIdBloomFilterLength);
+  advertisement_header_bytes_write_ptr += kServiceIdBloomFilterLength;
+
+  // 4. Advertisement hash.
+  memcpy(advertisement_header_bytes_write_ptr, advertisement_hash->getData(),
+         kAdvertisementHashLength);
+  advertisement_header_bytes_write_ptr += kAdvertisementHashLength;
+
+  // Header needs to be binary safe, so apply a Base64 encoding.
+  return Base64Utils::encode(advertisement_header_bytes);
+}
+
+BLEAdvertisementHeader::Version::Value
+BLEAdvertisementHeader::parseVersionFromByte(std::uint16_t byte) {
+  return static_cast<Version::Value>((byte & kVersionBitmask) >> 5);
+}
+
+std::uint32_t BLEAdvertisementHeader::parseNumSlotsFromByte(
+    std::uint16_t byte) {
+  return static_cast<std::uint32_t>((byte & kNumSlotsBitmask));
+}
+
+void BLEAdvertisementHeader::serializeVersionByte(char *version_byte_write_ptr,
+                                                  Version::Value version) {
+  *version_byte_write_ptr |=
+      static_cast<char>((version << 5) & kVersionBitmask);
+}
+
+void BLEAdvertisementHeader::serializeNumSlots(char *num_slots_byte_write_ptr,
+                                               std::uint32_t num_slots) {
+  *num_slots_byte_write_ptr |= static_cast<char>(num_slots & kNumSlotsBitmask);
+}
+
+BLEAdvertisementHeader::BLEAdvertisementHeader(
+    BLEAdvertisementHeader::Version::Value version, std::uint32_t num_slots,
+    ConstPtr<ByteArray> service_id_bloom_filter,
+    ConstPtr<ByteArray> advertisement_hash)
+    : version_(version),
+      num_slots_(num_slots),
+      service_id_bloom_filter_(service_id_bloom_filter),
+      advertisement_hash_(advertisement_hash) {}
+
+BLEAdvertisementHeader::~BLEAdvertisementHeader() {
+  // Nothing to do.
+}
+
+BLEAdvertisementHeader::Version::Value BLEAdvertisementHeader::getVersion()
+    const {
+  return version_;
+}
+
+std::uint32_t BLEAdvertisementHeader::getNumSlots() const { return num_slots_; }
+
+ConstPtr<ByteArray> BLEAdvertisementHeader::getServiceIdBloomFilter() const {
+  return service_id_bloom_filter_.get();
+}
+
+ConstPtr<ByteArray> BLEAdvertisementHeader::getAdvertisementHash() const {
+  return advertisement_hash_.get();
+}
+
+bool BLEAdvertisementHeader::operator<(
+    const BLEAdvertisementHeader &rhs) const {
+  if (this->getVersion() != rhs.getVersion()) {
+    return this->getVersion() < rhs.getVersion();
+  }
+  if (this->getNumSlots() != rhs.getNumSlots()) {
+    return this->getNumSlots() < rhs.getNumSlots();
+  }
+  if (*(this->getServiceIdBloomFilter()) != *(rhs.getServiceIdBloomFilter())) {
+    return *(this->getServiceIdBloomFilter()) <
+           *(rhs.getServiceIdBloomFilter());
+  }
+  return *(this->getAdvertisementHash()) < *(rhs.getAdvertisementHash());
+}
+
+}  // namespace mediums
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/mediums/ble_advertisement_header.h

@@ -0,0 +1,91 @@
+#ifndef CORE_INTERNAL_MEDIUMS_BLE_ADVERTISEMENT_HEADER_H_
+#define CORE_INTERNAL_MEDIUMS_BLE_ADVERTISEMENT_HEADER_H_
+
+#include "platform/byte_array.h"
+#include "platform/ptr.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+namespace mediums {
+
+// Represents the format of the Mediums BLE Advertisement Header used in
+// Advertising + Discovery.
+//
+// [VERSION][NUM_SLOTS][SERVICE_ID_BLOOM_FILTER][ADVERTISEMENT_HASH]
+//
+// See go/nearby-ble-design for more information.
+class BLEAdvertisementHeader {
+ public:
+  // Versions of the BLEAdvertisementHeader.
+  struct Version {
+    enum Value {
+      V2 = 2,
+      // Version is only allocated 3 bits in the BLEAdvertisementHeader, so this
+      // can never go beyond V7.
+      //
+      // V1 is not present because it's an old format used in Nearby Connections
+      // before this logic was pushed down into Nearby Mediums. V1 put
+      // everything in the service data, while V2 puts the data inside a GATT
+      // characteristic so the two are not compatible.
+    };
+  };
+
+  static ConstPtr<BLEAdvertisementHeader> fromString(
+      const std::string &ble_advertisement_header_string);
+
+  static std::string asString(Version::Value version, std::uint32_t num_slots,
+                              ConstPtr<ByteArray> service_id_bloom_filter,
+                              ConstPtr<ByteArray> advertisement_hash);
+
+  static const std::uint32_t kServiceIdBloomFilterLength;
+  static const std::uint32_t kAdvertisementHashLength;
+
+  ~BLEAdvertisementHeader();
+
+  Version::Value getVersion() const;
+  std::uint32_t getNumSlots() const;
+  ConstPtr<ByteArray> getServiceIdBloomFilter() const;
+  ConstPtr<ByteArray> getAdvertisementHash() const;
+
+  // Operator overloads when comparing ConstPtr<BLEAdvertisementHeader>.
+  bool operator<(const BLEAdvertisementHeader &rhs) const;
+
+ private:
+  // DiscoveredPeripheralTracker needs to be a friend of this class because it
+  // directly calls the constructor (the Java code keeps the constructor package
+  // private).
+  // Calling the constuctor directly allows us to avoid the unnessary extra
+  // calls to parse and decode to get the BLEAdvertisementHeader.
+  template <typename>
+  friend class DiscoveredPeripheralTracker;
+
+  static Version::Value parseVersionFromByte(std::uint16_t byte);
+  static std::uint32_t parseNumSlotsFromByte(std::uint16_t byte);
+
+  static const std::uint32_t kVersionAndNumSlotsLength;
+  static const std::uint32_t kMinAdvertisementHeaderLength;
+  static const std::uint16_t kVersionBitmask;
+  static const std::uint16_t kNumSlotsBitmask;
+
+  BLEAdvertisementHeader(Version::Value version, std::uint32_t num_slots,
+                         ConstPtr<ByteArray> service_id_bloom_filter,
+                         ConstPtr<ByteArray> advertisement_hash);
+
+  static void serializeVersionByte(char *version_byte_write_ptr,
+                                   Version::Value version);
+  static void serializeNumSlots(char *num_slots_byte_write_ptr,
+                                std::uint32_t num_slots);
+
+  const Version::Value version_;
+  const uint32_t num_slots_;
+  ScopedPtr<ConstPtr<ByteArray> > service_id_bloom_filter_;
+  ScopedPtr<ConstPtr<ByteArray> > advertisement_hash_;
+};
+
+}  // namespace mediums
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#endif  // CORE_INTERNAL_MEDIUMS_BLE_ADVERTISEMENT_HEADER_H_

cpp/core/internal/mediums/ble_advertisement_header_test.cc

@@ -0,0 +1,221 @@
+#include "core/internal/mediums/ble_advertisement_header.h"
+
+#include "platform/base64_utils.h"
+#include "gtest/gtest.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+namespace mediums {
+
+const BLEAdvertisementHeader::Version::Value kVersion =
+    BLEAdvertisementHeader::Version::V2;
+const std::uint32_t kNumSlots = 2;
+const char kServiceIDBloomFilter[] = {0x01, 0x02, 0x03, 0x04, 0x05,
+                                      0x06, 0x07, 0x08, 0x09, 0x0A};
+const char kAdvertisementHash[] = {0x0A, 0x0B, 0x0C, 0x0D};
+const size_t kAdvertisementHeaderLength = 15;
+const size_t kLongAdvertisementHeaderLength = kAdvertisementHeaderLength + 1;
+const size_t kShortAdvertisementHeaderLength = kAdvertisementHeaderLength - 1;
+
+TEST(BLEAdvertisementHeader, SerializationDeserializationWorks) {
+  ScopedPtr<ConstPtr<ByteArray> > scoped_service_id_bloom_filter(MakeConstPtr(
+      new ByteArray(kServiceIDBloomFilter,
+                    sizeof(kServiceIDBloomFilter) / sizeof(char))));
+  ScopedPtr<ConstPtr<ByteArray> > scoped_advertisement_hash(
+      MakeConstPtr(new ByteArray(kAdvertisementHash,
+                                 sizeof(kAdvertisementHash) / sizeof(char))));
+
+  std::string ble_advertisement_header_string(BLEAdvertisementHeader::asString(
+      kVersion, kNumSlots, scoped_service_id_bloom_filter.get(),
+      scoped_advertisement_hash.get()));
+  ScopedPtr<ConstPtr<BLEAdvertisementHeader> > scoped_ble_advertisement_header(
+      BLEAdvertisementHeader::fromString(ble_advertisement_header_string));
+
+  ASSERT_EQ(kVersion, scoped_ble_advertisement_header->getVersion());
+  ASSERT_EQ(kNumSlots, scoped_ble_advertisement_header->getNumSlots());
+  ASSERT_EQ(
+      0,
+      memcmp(
+          kServiceIDBloomFilter,
+          scoped_ble_advertisement_header->getServiceIdBloomFilter()->getData(),
+          scoped_ble_advertisement_header->getServiceIdBloomFilter()->size()));
+  ASSERT_EQ(
+      0,
+      memcmp(kAdvertisementHash,
+             scoped_ble_advertisement_header->getAdvertisementHash()->getData(),
+             scoped_ble_advertisement_header->getAdvertisementHash()->size()));
+}
+
+TEST(BLEAdvertisementHeader, SerializationFailsWithBadVersion) {
+  BLEAdvertisementHeader::Version::Value bad_version =
+      static_cast<BLEAdvertisementHeader::Version::Value>(666);
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_service_id_bloom_filter(MakeConstPtr(
+      new ByteArray(kServiceIDBloomFilter,
+                    sizeof(kServiceIDBloomFilter) / sizeof(char))));
+  ScopedPtr<ConstPtr<ByteArray> > scoped_advertisement_hash(
+      MakeConstPtr(new ByteArray(kAdvertisementHash,
+                                 sizeof(kAdvertisementHash) / sizeof(char))));
+
+  std::string ble_advertisement_header_string(BLEAdvertisementHeader::asString(
+      bad_version, kNumSlots, scoped_service_id_bloom_filter.get(),
+      scoped_advertisement_hash.get()));
+
+  ASSERT_EQ("", ble_advertisement_header_string);
+}
+
+TEST(BLEAdvertisementHeader, SerializationFailsWithShortServiceIdBloomFilter) {
+  char short_service_id_bloom_filter[] = {0x01, 0x02, 0x03, 0x04, 0x05,
+                                          0x06, 0x07, 0x08, 0x09};
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_service_id_bloom_filter(MakeConstPtr(
+      new ByteArray(short_service_id_bloom_filter,
+                    sizeof(short_service_id_bloom_filter) / sizeof(char))));
+  ScopedPtr<ConstPtr<ByteArray> > scoped_advertisement_hash(
+      MakeConstPtr(new ByteArray(kAdvertisementHash,
+                                 sizeof(kAdvertisementHash) / sizeof(char))));
+
+  std::string ble_advertisement_header_string(BLEAdvertisementHeader::asString(
+      kVersion, kNumSlots, scoped_service_id_bloom_filter.get(),
+      scoped_advertisement_hash.get()));
+
+  ASSERT_EQ("", ble_advertisement_header_string);
+}
+
+TEST(BLEAdvertisementHeader, SerializationFailsWithLongServiceIdBloomFilter) {
+  char long_service_id_bloom_filter[] = {0x01, 0x02, 0x03, 0x04, 0x05, 0x06,
+                                         0x07, 0x08, 0x09, 0x0A, 0x0B};
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_service_id_bloom_filter(MakeConstPtr(
+      new ByteArray(long_service_id_bloom_filter,
+                    sizeof(long_service_id_bloom_filter) / sizeof(char))));
+  ScopedPtr<ConstPtr<ByteArray> > scoped_advertisement_hash(
+      MakeConstPtr(new ByteArray(kAdvertisementHash,
+                                 sizeof(kAdvertisementHash) / sizeof(char))));
+
+  std::string ble_advertisement_header_string(BLEAdvertisementHeader::asString(
+      kVersion, kNumSlots, scoped_service_id_bloom_filter.get(),
+      scoped_advertisement_hash.get()));
+
+  ASSERT_EQ("", ble_advertisement_header_string);
+}
+
+TEST(BLEAdvertisementHeader, SerializationFailsWithShortAdvertisementHash) {
+  char short_advertisement_hash[] = {0x0A, 0x0B, 0x0C};
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_service_id_bloom_filter(MakeConstPtr(
+      new ByteArray(kServiceIDBloomFilter,
+                    sizeof(kServiceIDBloomFilter) / sizeof(char))));
+  ScopedPtr<ConstPtr<ByteArray> > scoped_advertisement_hash(MakeConstPtr(
+      new ByteArray(short_advertisement_hash,
+                    sizeof(short_advertisement_hash) / sizeof(char))));
+
+  std::string ble_advertisement_header_string(BLEAdvertisementHeader::asString(
+      kVersion, kNumSlots, scoped_service_id_bloom_filter.get(),
+      scoped_advertisement_hash.get()));
+
+  ASSERT_EQ("", ble_advertisement_header_string);
+}
+
+TEST(BLEAdvertisementHeader, SerializationFailsWithLongAdvertisementHash) {
+  char long_advertisement_hash[] = {0x0A, 0x0B, 0x0C, 0x0D, 0x0E};
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_service_id_bloom_filter(MakeConstPtr(
+      new ByteArray(kServiceIDBloomFilter,
+                    sizeof(kServiceIDBloomFilter) / sizeof(char))));
+  ScopedPtr<ConstPtr<ByteArray> > scoped_advertisement_hash(MakeConstPtr(
+      new ByteArray(long_advertisement_hash,
+                    sizeof(long_advertisement_hash) / sizeof(char))));
+
+  std::string ble_advertisement_header_string(BLEAdvertisementHeader::asString(
+      kVersion, kNumSlots, scoped_service_id_bloom_filter.get(),
+      scoped_advertisement_hash.get()));
+
+  ASSERT_EQ("", ble_advertisement_header_string);
+}
+
+TEST(BLEAdvertisementHeader, DeserializationWorksWithExtraBytes) {
+  ScopedPtr<ConstPtr<ByteArray> > scoped_service_id_bloom_filter(MakeConstPtr(
+      new ByteArray(kServiceIDBloomFilter,
+                    sizeof(kServiceIDBloomFilter) / sizeof(char))));
+  ScopedPtr<ConstPtr<ByteArray> > scoped_advertisement_hash(
+      MakeConstPtr(new ByteArray(kAdvertisementHash,
+                                 sizeof(kAdvertisementHash) / sizeof(char))));
+  std::string ble_advertisement_header_string =
+      BLEAdvertisementHeader::asString(kVersion, kNumSlots,
+                                       scoped_service_id_bloom_filter.get(),
+                                       scoped_advertisement_hash.get());
+
+  // Base64 decode the string, add a character, and then re-encode it. We must
+  // explicitly define how long our array is because we can't use variable
+  // length arrays.
+  ScopedPtr<Ptr<ByteArray> > scoped_ble_advertisement_header_bytes(
+      Base64Utils::decode(ble_advertisement_header_string));
+  char raw_long_ble_advertisement_header_bytes[kLongAdvertisementHeaderLength];
+  memcpy(raw_long_ble_advertisement_header_bytes,
+         scoped_ble_advertisement_header_bytes->getData(),
+         kLongAdvertisementHeaderLength);
+  ScopedPtr<ConstPtr<ByteArray> > scoped_long_ble_advertisement_header_bytes(
+      MakeConstPtr(new ByteArray(raw_long_ble_advertisement_header_bytes,
+                                 kLongAdvertisementHeaderLength)));
+  std::string long_ble_advertisement_header_string =
+      Base64Utils::encode(scoped_long_ble_advertisement_header_bytes.get());
+
+  ScopedPtr<ConstPtr<BLEAdvertisementHeader> > scoped_ble_advertisement_header(
+      BLEAdvertisementHeader::fromString(long_ble_advertisement_header_string));
+
+  ASSERT_EQ(kVersion, scoped_ble_advertisement_header->getVersion());
+  ASSERT_EQ(kNumSlots, scoped_ble_advertisement_header->getNumSlots());
+  ASSERT_EQ(
+      0,
+      memcmp(
+          kServiceIDBloomFilter,
+          scoped_ble_advertisement_header->getServiceIdBloomFilter()->getData(),
+          scoped_ble_advertisement_header->getServiceIdBloomFilter()->size()));
+  ASSERT_EQ(
+      0,
+      memcmp(kAdvertisementHash,
+             scoped_ble_advertisement_header->getAdvertisementHash()->getData(),
+             scoped_ble_advertisement_header->getAdvertisementHash()->size()));
+}
+
+TEST(BLEAdvertisementHeader, DeserializationFailsWithShortLength) {
+  ScopedPtr<ConstPtr<ByteArray> > scoped_service_id_bloom_filter(MakeConstPtr(
+      new ByteArray(kServiceIDBloomFilter,
+                    sizeof(kServiceIDBloomFilter) / sizeof(char))));
+  ScopedPtr<ConstPtr<ByteArray> > scoped_advertisement_hash(
+      MakeConstPtr(new ByteArray(kAdvertisementHash,
+                                 sizeof(kAdvertisementHash) / sizeof(char))));
+  std::string ble_advertisement_header_string =
+      BLEAdvertisementHeader::asString(kVersion, kNumSlots,
+                                       scoped_service_id_bloom_filter.get(),
+                                       scoped_advertisement_hash.get());
+
+  // Base64 decode the string, remove a character, and then re-encode it. We
+  // must explicitly define how long our array is because we can't use variable
+  // length arrays.
+  ScopedPtr<Ptr<ByteArray> > scoped_ble_advertisement_header_bytes(
+      Base64Utils::decode(ble_advertisement_header_string));
+  char
+      raw_short_ble_advertisement_header_bytes[kShortAdvertisementHeaderLength];
+  memcpy(raw_short_ble_advertisement_header_bytes,
+         scoped_ble_advertisement_header_bytes->getData(),
+         kShortAdvertisementHeaderLength);
+  ScopedPtr<ConstPtr<ByteArray> > scoped_short_ble_advertisement_header_bytes(
+      MakeConstPtr(new ByteArray(raw_short_ble_advertisement_header_bytes,
+                                 kShortAdvertisementHeaderLength)));
+  std::string short_ble_advertisement_header_string =
+      Base64Utils::encode(scoped_short_ble_advertisement_header_bytes.get());
+
+  ScopedPtr<ConstPtr<BLEAdvertisementHeader> > scoped_ble_advertisement_header(
+      BLEAdvertisementHeader::fromString(
+          short_ble_advertisement_header_string));
+
+  ASSERT_TRUE(scoped_ble_advertisement_header.isNull());
+}
+
+}  // namespace mediums
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/mediums/ble_advertisement_test.cc

@@ -0,0 +1,319 @@
+#include "core/internal/mediums/ble_advertisement.h"
+
+#include "gtest/gtest.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+namespace mediums {
+namespace {
+
+const BLEAdvertisement::Version::Value kVersion = BLEAdvertisement::Version::V2;
+const BLEAdvertisement::SocketVersion::Value kSocketVersion =
+    BLEAdvertisement::SocketVersion::V2;
+const char kServiceIDHashBytes[] = {0x0A, 0x0B, 0x0C};
+const char kData[] =
+    "How much wood can a woodchuck chuck if a wood chuck would chuck wood?";
+// This corresponds to the length of a specific BLEAdvertisement packed with the
+// kData given above. Be sure to update this if kData ever changes.
+const size_t kAdvertisementLength = 77;
+const size_t kLongAdvertisementLength = kAdvertisementLength + 1000;
+
+TEST(BLEAdvertisementTest, SerializationDeserializationWorksV1) {
+  ScopedPtr<ConstPtr<ByteArray> > scoped_service_id_hash(
+      MakeConstPtr(new ByteArray(kServiceIDHashBytes,
+                                 sizeof(kServiceIDHashBytes) / sizeof(char))));
+  ScopedPtr<ConstPtr<ByteArray> > scoped_data(
+      MakeConstPtr(new ByteArray(kData, sizeof(kData) / sizeof(char))));
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_ble_advertisement_bytes(
+      BLEAdvertisement::toBytes(
+          BLEAdvertisement::Version::V1, BLEAdvertisement::SocketVersion::V1,
+          scoped_service_id_hash.get(), scoped_data.get()));
+  ScopedPtr<ConstPtr<BLEAdvertisement> > scoped_ble_advertisement(
+      BLEAdvertisement::fromBytes(scoped_ble_advertisement_bytes.get()));
+
+  ASSERT_EQ(BLEAdvertisement::Version::V1,
+            scoped_ble_advertisement->getVersion());
+  ASSERT_EQ(BLEAdvertisement::SocketVersion::V1,
+            scoped_ble_advertisement->getSocketVersion());
+  ASSERT_EQ(scoped_service_id_hash->size(),
+            scoped_ble_advertisement->getServiceIdHash()->size());
+  ASSERT_EQ(0, memcmp(kServiceIDHashBytes,
+                      scoped_ble_advertisement->getServiceIdHash()->getData(),
+                      scoped_ble_advertisement->getServiceIdHash()->size()));
+  ASSERT_EQ(scoped_data->size(), scoped_ble_advertisement->getData()->size());
+  ASSERT_EQ(0, memcmp(kData, scoped_ble_advertisement->getData()->getData(),
+                      scoped_ble_advertisement->getData()->size()));
+}
+
+TEST(BLEAdvertisementTest, SerializationDeserializationWorks) {
+  ScopedPtr<ConstPtr<ByteArray> > scoped_service_id_hash(
+      MakeConstPtr(new ByteArray(kServiceIDHashBytes,
+                                 sizeof(kServiceIDHashBytes) / sizeof(char))));
+  ScopedPtr<ConstPtr<ByteArray> > scoped_data(
+      MakeConstPtr(new ByteArray(kData, sizeof(kData) / sizeof(char))));
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_ble_advertisement_bytes(
+      BLEAdvertisement::toBytes(kVersion, kSocketVersion,
+                                scoped_service_id_hash.get(),
+                                scoped_data.get()));
+  ScopedPtr<ConstPtr<BLEAdvertisement> > scoped_ble_advertisement(
+      BLEAdvertisement::fromBytes(scoped_ble_advertisement_bytes.get()));
+
+  ASSERT_EQ(kVersion, scoped_ble_advertisement->getVersion());
+  ASSERT_EQ(kSocketVersion, scoped_ble_advertisement->getSocketVersion());
+  ASSERT_EQ(scoped_service_id_hash->size(),
+            scoped_ble_advertisement->getServiceIdHash()->size());
+  ASSERT_EQ(0, memcmp(kServiceIDHashBytes,
+                      scoped_ble_advertisement->getServiceIdHash()->getData(),
+                      scoped_ble_advertisement->getServiceIdHash()->size()));
+  ASSERT_EQ(scoped_data->size(), scoped_ble_advertisement->getData()->size());
+  ASSERT_EQ(0, memcmp(kData, scoped_ble_advertisement->getData()->getData(),
+                      scoped_ble_advertisement->getData()->size()));
+}
+
+TEST(BLEAdvertisementTest, SerializationDeserializationWorksWithEmptyData) {
+  char empty_data[0];
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_service_id_hash(
+      MakeConstPtr(new ByteArray(kServiceIDHashBytes,
+                                 sizeof(kServiceIDHashBytes) / sizeof(char))));
+  ScopedPtr<ConstPtr<ByteArray> > scoped_data(MakeConstPtr(
+      new ByteArray(empty_data, sizeof(empty_data) / sizeof(char))));
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_ble_advertisement_bytes(
+      BLEAdvertisement::toBytes(kVersion, kSocketVersion,
+                                scoped_service_id_hash.get(),
+                                scoped_data.get()));
+  ScopedPtr<ConstPtr<BLEAdvertisement> > scoped_ble_advertisement(
+      BLEAdvertisement::fromBytes(scoped_ble_advertisement_bytes.get()));
+
+  ASSERT_EQ(kVersion, scoped_ble_advertisement->getVersion());
+  ASSERT_EQ(kSocketVersion, scoped_ble_advertisement->getSocketVersion());
+  ASSERT_EQ(scoped_service_id_hash->size(),
+            scoped_ble_advertisement->getServiceIdHash()->size());
+  ASSERT_EQ(0, memcmp(kServiceIDHashBytes,
+                      scoped_ble_advertisement->getServiceIdHash()->getData(),
+                      scoped_ble_advertisement->getServiceIdHash()->size()));
+  ASSERT_EQ(scoped_data->size(), scoped_ble_advertisement->getData()->size());
+  ASSERT_EQ(0, memcmp(kData, scoped_ble_advertisement->getData()->getData(),
+                      scoped_ble_advertisement->getData()->size()));
+}
+
+TEST(BLEAdvertisementTest, SerializationDeserializationFailsWithLargeData) {
+  // Create data that's larger than the allowed size.
+  char large_data[513];
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_service_id_hash(
+      MakeConstPtr(new ByteArray(kServiceIDHashBytes,
+                                 sizeof(kServiceIDHashBytes) / sizeof(char))));
+  ScopedPtr<ConstPtr<ByteArray> > scoped_data(MakeConstPtr(
+      new ByteArray(large_data, sizeof(large_data) / sizeof(char))));
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_ble_advertisement_bytes(
+      BLEAdvertisement::toBytes(kVersion, kSocketVersion,
+                                scoped_service_id_hash.get(),
+                                scoped_data.get()));
+  ScopedPtr<ConstPtr<BLEAdvertisement> > scoped_ble_advertisement(
+      BLEAdvertisement::fromBytes(scoped_ble_advertisement_bytes.get()));
+
+  ASSERT_TRUE(scoped_ble_advertisement.isNull());
+}
+
+TEST(BLEAdvertisementTest, SerializationFailsWithBadVersion) {
+  BLEAdvertisement::Version::Value bad_version =
+      static_cast<BLEAdvertisement::Version::Value>(666);
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_service_id_hash(
+      MakeConstPtr(new ByteArray(kServiceIDHashBytes,
+                                 sizeof(kServiceIDHashBytes) / sizeof(char))));
+  ScopedPtr<ConstPtr<ByteArray> > scoped_data(
+      MakeConstPtr(new ByteArray(kData, sizeof(kData) / sizeof(char))));
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_ble_advertisement_bytes(
+      BLEAdvertisement::toBytes(bad_version, kSocketVersion,
+                                scoped_service_id_hash.get(),
+                                scoped_data.get()));
+
+  ASSERT_TRUE(scoped_ble_advertisement_bytes.isNull());
+}
+
+TEST(BLEAdvertisementTest, SerializationFailsWithBadSocketVersion) {
+  BLEAdvertisement::SocketVersion::Value bad_socket_version =
+      static_cast<BLEAdvertisement::SocketVersion::Value>(666);
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_service_id_hash(
+      MakeConstPtr(new ByteArray(kServiceIDHashBytes,
+                                 sizeof(kServiceIDHashBytes) / sizeof(char))));
+  ScopedPtr<ConstPtr<ByteArray> > scoped_data(
+      MakeConstPtr(new ByteArray(kData, sizeof(kData) / sizeof(char))));
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_ble_advertisement_bytes(
+      BLEAdvertisement::toBytes(kVersion, bad_socket_version,
+                                scoped_service_id_hash.get(),
+                                scoped_data.get()));
+
+  ASSERT_TRUE(scoped_ble_advertisement_bytes.isNull());
+}
+
+TEST(BLEAdvertisementTest, SerializationFailsWithShortServiceIdHash) {
+  char short_service_id_hash_bytes[] = {0x0A, 0x0B};
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_service_id_hash(MakeConstPtr(
+      new ByteArray(short_service_id_hash_bytes,
+                    sizeof(short_service_id_hash_bytes) / sizeof(char))));
+  ScopedPtr<ConstPtr<ByteArray> > scoped_data(
+      MakeConstPtr(new ByteArray(kData, sizeof(kData) / sizeof(char))));
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_ble_advertisement_bytes(
+      BLEAdvertisement::toBytes(kVersion, kSocketVersion,
+                                scoped_service_id_hash.get(),
+                                scoped_data.get()));
+
+  ASSERT_TRUE(scoped_ble_advertisement_bytes.isNull());
+}
+
+TEST(BLEAdvertisementTest, SerializationFailsWithLongServiceIdHash) {
+  char long_service_id_hash_bytes[] = {0x0A, 0x0B, 0x0C, 0x0D};
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_service_id_hash(MakeConstPtr(
+      new ByteArray(long_service_id_hash_bytes,
+                    sizeof(long_service_id_hash_bytes) / sizeof(char))));
+  ScopedPtr<ConstPtr<ByteArray> > scoped_data(
+      MakeConstPtr(new ByteArray(kData, sizeof(kData) / sizeof(char))));
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_ble_advertisement_bytes(
+      BLEAdvertisement::toBytes(kVersion, kSocketVersion,
+                                scoped_service_id_hash.get(),
+                                scoped_data.get()));
+
+  ASSERT_TRUE(scoped_ble_advertisement_bytes.isNull());
+}
+
+TEST(BLEAdvertisementTest, SerializationFailsWithLongData) {
+  // BLEAdvertisement shouldn't be able to support data with the max GATT
+  // attribute length because it needs some room for the preceding fields.
+  char long_data[512];
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_service_id_hash(
+      MakeConstPtr(new ByteArray(kServiceIDHashBytes,
+                                 sizeof(kServiceIDHashBytes) / sizeof(char))));
+  ScopedPtr<ConstPtr<ByteArray> > scoped_data(
+      MakeConstPtr(new ByteArray(long_data, sizeof(long_data) / sizeof(char))));
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_ble_advertisement_bytes(
+      BLEAdvertisement::toBytes(kVersion, kSocketVersion,
+                                scoped_service_id_hash.get(),
+                                scoped_data.get()));
+
+  ASSERT_TRUE(scoped_ble_advertisement_bytes.isNull());
+}
+
+TEST(BLEAdvertisementTest, DeserializationWorksWithExtraBytes) {
+  ScopedPtr<ConstPtr<ByteArray> > scoped_service_id_hash(
+      MakeConstPtr(new ByteArray(kServiceIDHashBytes,
+                                 sizeof(kServiceIDHashBytes) / sizeof(char))));
+  ScopedPtr<ConstPtr<ByteArray> > scoped_data(
+      MakeConstPtr(new ByteArray(kData, sizeof(kData) / sizeof(char))));
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_ble_advertisement_bytes(
+      BLEAdvertisement::toBytes(kVersion, kSocketVersion,
+                                scoped_service_id_hash.get(),
+                                scoped_data.get()));
+
+  // Copy the bytes into a new array with extra bytes. We must explicitly
+  // define how long our array is because we can't use variable length arrays.
+  char raw_ble_advertisement_bytes[kLongAdvertisementLength];
+  memcpy(raw_ble_advertisement_bytes, scoped_ble_advertisement_bytes->getData(),
+         kLongAdvertisementLength);
+
+  // Re-parse the BLE advertisement using our extra long advertisement bytes.
+  ScopedPtr<ConstPtr<ByteArray> > scoped_long_ble_advertisement_bytes(
+      MakeConstPtr(new ByteArray(raw_ble_advertisement_bytes,
+                                 kLongAdvertisementLength)));
+  ScopedPtr<ConstPtr<BLEAdvertisement> > scoped_long_ble_advertisement(
+      BLEAdvertisement::fromBytes(scoped_long_ble_advertisement_bytes.get()));
+
+  ASSERT_EQ(kVersion, scoped_long_ble_advertisement->getVersion());
+  ASSERT_EQ(kSocketVersion, scoped_long_ble_advertisement->getSocketVersion());
+  ASSERT_EQ(scoped_service_id_hash->size(),
+            scoped_long_ble_advertisement->getServiceIdHash()->size());
+  ASSERT_EQ(0,
+            memcmp(kServiceIDHashBytes,
+                   scoped_long_ble_advertisement->getServiceIdHash()->getData(),
+                   scoped_long_ble_advertisement->getServiceIdHash()->size()));
+  ASSERT_EQ(scoped_data->size(),
+            scoped_long_ble_advertisement->getData()->size());
+  ASSERT_EQ(0,
+            memcmp(kData, scoped_long_ble_advertisement->getData()->getData(),
+                   scoped_long_ble_advertisement->getData()->size()));
+}
+
+TEST(BLEAdvertisementTest, DeserializationFailsWithNullBytes) {
+  ScopedPtr<ConstPtr<BLEAdvertisement> > scoped_ble_advertisement(
+      BLEAdvertisement::fromBytes(ConstPtr<ByteArray>()));
+
+  ASSERT_TRUE(scoped_ble_advertisement.isNull());
+}
+
+TEST(BLEAdvertisementTest, DeserializationFailsWithShortLength) {
+  ScopedPtr<ConstPtr<ByteArray> > scoped_service_id_hash(
+      MakeConstPtr(new ByteArray(kServiceIDHashBytes,
+                                 sizeof(kServiceIDHashBytes) / sizeof(char))));
+  ScopedPtr<ConstPtr<ByteArray> > scoped_data(
+      MakeConstPtr(new ByteArray(kData, sizeof(kData) / sizeof(char))));
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_ble_advertisement_bytes(
+      BLEAdvertisement::toBytes(kVersion, kSocketVersion,
+                                scoped_service_id_hash.get(),
+                                scoped_data.get()));
+
+  // Cut off the advertisement so that it's too short.
+  ScopedPtr<ConstPtr<ByteArray> > scoped_short_ble_advertisement_bytes(
+      MakeConstPtr(
+          new ByteArray(scoped_ble_advertisement_bytes->getData(), 7)));
+  ScopedPtr<ConstPtr<BLEAdvertisement> > scoped_ble_advertisement(
+      BLEAdvertisement::fromBytes(scoped_short_ble_advertisement_bytes.get()));
+
+  ASSERT_TRUE(scoped_ble_advertisement.isNull());
+}
+
+TEST(BLEAdvertisementTest, DeserializationFailsWithInvalidDataLength) {
+  ScopedPtr<ConstPtr<ByteArray> > scoped_service_id_hash(
+      MakeConstPtr(new ByteArray(kServiceIDHashBytes,
+                                 sizeof(kServiceIDHashBytes) / sizeof(char))));
+  ScopedPtr<ConstPtr<ByteArray> > scoped_data(
+      MakeConstPtr(new ByteArray(kData, sizeof(kData) / sizeof(char))));
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_ble_advertisement_bytes(
+      BLEAdvertisement::toBytes(kVersion, kSocketVersion,
+                                scoped_service_id_hash.get(),
+                                scoped_data.get()));
+
+  // Corrupt the DATA_SIZE bits. Start by making a raw copy of the BLE
+  // advertisement bytes so we can modify it. We must explicitly define how long
+  // our array is because we can't use variable length arrays.
+  char raw_ble_advertisement_bytes[kAdvertisementLength];
+  memcpy(raw_ble_advertisement_bytes, scoped_ble_advertisement_bytes->getData(),
+         kAdvertisementLength);
+
+  // The data size field lives in indices 4-7. Corrupt it.
+  memset(raw_ble_advertisement_bytes + 4, 0xFF, 4);
+
+  // Try to parse the BLE advertisement using our corrupted advertisement bytes.
+  ScopedPtr<ConstPtr<ByteArray> > scoped_corrupted_ble_advertisement_bytes(
+      MakeConstPtr(
+          new ByteArray(raw_ble_advertisement_bytes, kAdvertisementLength)));
+  ScopedPtr<ConstPtr<BLEAdvertisement> > scoped_ble_advertisement(
+      BLEAdvertisement::fromBytes(
+          scoped_corrupted_ble_advertisement_bytes.get()));
+
+  ASSERT_TRUE(scoped_ble_advertisement.isNull());
+}
+
+}  // namespace
+}  // namespace mediums
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/mediums/ble_packet.cc

@@ -0,0 +1,112 @@
+#include "core/internal/mediums/ble_packet.h"
+
+#include <limits>
+
+#include "platform/logging.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+namespace mediums {
+
+const std::uint32_t BLEPacket::kServiceIdHashLength = 3;
+
+const std::uint32_t BLEPacket::kMinPacketLength = kServiceIdHashLength;
+const std::uint32_t BLEPacket::kMaxDataSize =
+    std::numeric_limits<int32_t>::max() - kMinPacketLength;
+
+ConstPtr<BLEPacket> BLEPacket::fromBytes(ConstPtr<ByteArray> ble_packet_bytes) {
+  if (ble_packet_bytes.isNull()) {
+    NEARBY_LOG(INFO, "Cannot deserialize BLEPacket: null bytes passed in");
+    return ConstPtr<BLEPacket>();
+  }
+
+  if (ble_packet_bytes->size() < kMinPacketLength) {
+    NEARBY_LOG(
+        INFO,
+        "Cannot deserialize BLEPacket: expecting min %u raw bytes, got %zu",
+        kMinPacketLength, ble_packet_bytes->size());
+    return ConstPtr<BLEPacket>();
+  }
+
+  // Now, time to read the bytes!
+  const char *ble_packet_bytes_read_ptr = ble_packet_bytes->getData();
+
+  // 1. Service ID hash.
+  ScopedPtr<ConstPtr<ByteArray> > scoped_service_id_hash(MakeConstPtr(
+      new ByteArray(ble_packet_bytes_read_ptr, kServiceIdHashLength)));
+  ble_packet_bytes_read_ptr += kServiceIdHashLength;
+
+  // 2. Data.
+  size_t data_size = computeDataSize(ble_packet_bytes);
+  ScopedPtr<ConstPtr<ByteArray> > scoped_data(
+      MakeConstPtr(new ByteArray(ble_packet_bytes_read_ptr, data_size)));
+  ble_packet_bytes_read_ptr += data_size;
+
+  return MakeConstPtr(
+      new BLEPacket(scoped_service_id_hash.release(), scoped_data.release()));
+}
+
+ConstPtr<ByteArray> BLEPacket::toBytes(ConstPtr<ByteArray> service_id_hash,
+                                       ConstPtr<ByteArray> data) {
+  if (service_id_hash->size() != kServiceIdHashLength) {
+    NEARBY_LOG(
+        INFO,
+        "Cannot serialize BLEPacket: expected a service_id_hash of %u bytes, "
+        "but got %zu",
+        kServiceIdHashLength, service_id_hash->size());
+    return ConstPtr<ByteArray>();
+  }
+
+  if (data->size() > kMaxDataSize) {
+    NEARBY_LOG(INFO,
+               "Cannot serialize BLEPacket: expected data of at most %u bytes, "
+               "but got %zu",
+               kMaxDataSize, data->size());
+    return ConstPtr<ByteArray>();
+  }
+
+  // Initialize the bytes.
+  size_t packet_length = computePacketLength(data);
+  Ptr<ByteArray> packet_bytes{new ByteArray{packet_length}};
+  char *packet_bytes_write_ptr = packet_bytes->getData();
+
+  // 1. Service ID hash.
+  memcpy(packet_bytes_write_ptr, service_id_hash->getData(),
+         kServiceIdHashLength);
+  packet_bytes_write_ptr += kServiceIdHashLength;
+
+  // 2. Data.
+  memcpy(packet_bytes_write_ptr, data->getData(), data->size());
+  packet_bytes_write_ptr += data->size();
+
+  return ConstifyPtr(packet_bytes);
+}
+
+size_t BLEPacket::computeDataSize(ConstPtr<ByteArray> ble_packet_bytes) {
+  return ble_packet_bytes->size() - kMinPacketLength;
+}
+
+size_t BLEPacket::computePacketLength(ConstPtr<ByteArray> data) {
+  // The packet length is the minimum length + the length of the data.
+  return kMinPacketLength + data->size();
+}
+
+BLEPacket::BLEPacket(ConstPtr<ByteArray> service_id_hash,
+                     ConstPtr<ByteArray> data)
+    : service_id_hash_(service_id_hash), data_(data) {}
+
+BLEPacket::~BLEPacket() {
+  // Nothing to do.
+}
+
+ConstPtr<ByteArray> BLEPacket::getServiceIdHash() const {
+  return service_id_hash_.get();
+}
+
+ConstPtr<ByteArray> BLEPacket::getData() const { return data_.get(); }
+
+}  // namespace mediums
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/mediums/ble_packet.h

@@ -0,0 +1,49 @@
+#ifndef CORE_INTERNAL_MEDIUMS_BLE_PACKET_H_
+#define CORE_INTERNAL_MEDIUMS_BLE_PACKET_H_
+
+#include "platform/byte_array.h"
+#include "platform/ptr.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+namespace mediums {
+
+// Represents the format of data sent over BLE sockets.
+//
+// [SERVICE_ID_HASH][DATA]
+//
+// See go/nearby-ble-design for more information.
+class BLEPacket {
+ public:
+  static ConstPtr<BLEPacket> fromBytes(ConstPtr<ByteArray> ble_packet_bytes);
+
+  static ConstPtr<ByteArray> toBytes(ConstPtr<ByteArray> service_id_hash,
+                                     ConstPtr<ByteArray> data);
+
+  static const std::uint32_t kServiceIdHashLength;
+
+  ~BLEPacket();
+
+  ConstPtr<ByteArray> getServiceIdHash() const;
+  ConstPtr<ByteArray> getData() const;
+
+ private:
+  static size_t computeDataSize(ConstPtr<ByteArray> ble_packet_bytes);
+  static size_t computePacketLength(ConstPtr<ByteArray> data);
+
+  static const std::uint32_t kMinPacketLength;
+  static const std::uint32_t kMaxDataSize;
+
+  BLEPacket(ConstPtr<ByteArray> service_id_hash, ConstPtr<ByteArray> data);
+
+  ScopedPtr<ConstPtr<ByteArray> > service_id_hash_;
+  ScopedPtr<ConstPtr<ByteArray> > data_;
+};
+
+}  // namespace mediums
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#endif  // CORE_INTERNAL_MEDIUMS_BLE_PACKET_H_

cpp/core/internal/mediums/ble_packet_test.cc

@@ -0,0 +1,108 @@
+#include "core/internal/mediums/ble_packet.h"
+
+#include "gtest/gtest.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+namespace mediums {
+
+const char kServiceIDHash[] = {0x0A, 0x0B, 0x0C};
+const char kData[] = {0x00, 0x01, 0x02, 0x03, 0x04};
+
+TEST(BLEPacket, SerializationDeserializationWorks) {
+  ScopedPtr<ConstPtr<ByteArray> > scoped_service_id_hash(MakeConstPtr(
+      new ByteArray(kServiceIDHash, sizeof(kServiceIDHash) / sizeof(char))));
+  ScopedPtr<ConstPtr<ByteArray> > scoped_data(
+      MakeConstPtr(new ByteArray(kData, sizeof(kData) / sizeof(char))));
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_ble_packet_bytes(
+      BLEPacket::toBytes(scoped_service_id_hash.get(), scoped_data.get()));
+  ScopedPtr<ConstPtr<BLEPacket> > scoped_ble_packet(
+      BLEPacket::fromBytes(scoped_ble_packet_bytes.get()));
+
+  ASSERT_EQ(0, memcmp(kServiceIDHash,
+                      scoped_ble_packet->getServiceIdHash()->getData(),
+                      scoped_ble_packet->getServiceIdHash()->size()));
+  ASSERT_EQ(0, memcmp(kData, scoped_ble_packet->getData()->getData(),
+                      scoped_ble_packet->getData()->size()));
+}
+
+TEST(BLEPacket, SerializationDeserializationWorksWithEmptyData) {
+  char empty_data[] = {};
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_service_id_hash(MakeConstPtr(
+      new ByteArray(kServiceIDHash, sizeof(kServiceIDHash) / sizeof(char))));
+  ScopedPtr<ConstPtr<ByteArray> > scoped_data(MakeConstPtr(
+      new ByteArray(empty_data, sizeof(empty_data) / sizeof(char))));
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_ble_packet_bytes(
+      BLEPacket::toBytes(scoped_service_id_hash.get(), scoped_data.get()));
+  ScopedPtr<ConstPtr<BLEPacket> > scoped_ble_packet(
+      BLEPacket::fromBytes(scoped_ble_packet_bytes.get()));
+
+  ASSERT_EQ(0, memcmp(kServiceIDHash,
+                      scoped_ble_packet->getServiceIdHash()->getData(),
+                      scoped_ble_packet->getServiceIdHash()->size()));
+  ASSERT_EQ(0, memcmp(empty_data, scoped_ble_packet->getData()->getData(),
+                      scoped_ble_packet->getData()->size()));
+}
+
+TEST(BLEPacket, SerializationFailsWithShortServiceIdHash) {
+  char short_service_id_hash[] = {0x0A, 0x0B};
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_service_id_hash(MakeConstPtr(
+      new ByteArray(short_service_id_hash,
+                    sizeof(short_service_id_hash) / sizeof(char))));
+  ScopedPtr<ConstPtr<ByteArray> > scoped_data(
+      MakeConstPtr(new ByteArray(kData, sizeof(kData) / sizeof(char))));
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_ble_packet_bytes(
+      BLEPacket::toBytes(scoped_service_id_hash.get(), scoped_data.get()));
+
+  ASSERT_TRUE(scoped_ble_packet_bytes.isNull());
+}
+
+TEST(BLEPacket, SerializationFailsWithLongServiceIdHash) {
+  char long_service_id_hash[]{0x0A, 0x0B, 0x0C, 0x0D};
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_service_id_hash(
+      MakeConstPtr(new ByteArray(long_service_id_hash,
+                                 sizeof(long_service_id_hash) / sizeof(char))));
+  ScopedPtr<ConstPtr<ByteArray> > scoped_data(
+      MakeConstPtr(new ByteArray(kData, sizeof(kData) / sizeof(char))));
+
+  ScopedPtr<ConstPtr<ByteArray> > scoped_ble_packet_bytes(
+      BLEPacket::toBytes(scoped_service_id_hash.get(), scoped_data.get()));
+
+  ASSERT_TRUE(scoped_ble_packet_bytes.isNull());
+}
+
+TEST(BLEPacket, DeserializationFailsWithNullBytes) {
+  ScopedPtr<ConstPtr<BLEPacket> > scoped_ble_packet(
+      BLEPacket::fromBytes(ConstPtr<ByteArray>()));
+
+  ASSERT_TRUE(scoped_ble_packet.isNull());
+}
+
+TEST(BLEPacket, DeserializationFailsWithShortLength) {
+  ScopedPtr<ConstPtr<ByteArray> > scoped_service_id_hash(MakeConstPtr(
+      new ByteArray(kServiceIDHash, sizeof(kServiceIDHash) / sizeof(char))));
+  ScopedPtr<ConstPtr<ByteArray> > scoped_data(
+      MakeConstPtr(new ByteArray(kData, sizeof(kData) / sizeof(char))));
+  ScopedPtr<ConstPtr<ByteArray> > scoped_ble_packet_bytes(
+      BLEPacket::toBytes(scoped_service_id_hash.get(), scoped_data.get()));
+
+  // Cut off the packet so that it's too short
+  ScopedPtr<ConstPtr<ByteArray> > scoped_short_ble_packet_bytes(
+      MakeConstPtr(new ByteArray(scoped_ble_packet_bytes->getData(), 2)));
+  ScopedPtr<ConstPtr<BLEPacket> > scoped_ble_packet(
+      BLEPacket::fromBytes(scoped_short_ble_packet_bytes.get()));
+
+  ASSERT_TRUE(scoped_ble_packet.isNull());
+}
+
+}  // namespace mediums
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/mediums/ble_peripheral.cc

@@ -0,0 +1,19 @@
+#include "core/internal/mediums/ble_peripheral.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+namespace mediums {
+
+BLEPeripheral::BLEPeripheral(ConstPtr<ByteArray> id) : id_(id) {}
+
+BLEPeripheral::~BLEPeripheral() {
+  // Nothing to do.
+}
+
+ConstPtr<ByteArray> BLEPeripheral::getId() const { return id_.get(); }
+
+}  // namespace mediums
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/mediums/ble_peripheral.h

@@ -0,0 +1,30 @@
+#ifndef CORE_INTERNAL_MEDIUMS_BLE_PERIPHERAL_H_
+#define CORE_INTERNAL_MEDIUMS_BLE_PERIPHERAL_H_
+
+#include "platform/byte_array.h"
+#include "platform/ptr.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+namespace mediums {
+
+class BLEPeripheral {
+ public:
+  explicit BLEPeripheral(ConstPtr<ByteArray> id);
+  ~BLEPeripheral();
+
+  ConstPtr<ByteArray> getId() const;
+
+ private:
+  // A unique identifier for this peripheral. It can be the BLE advertisement it
+  // was found on, or even simply the BLE MAC address.
+  ScopedPtr<ConstPtr<ByteArray>> id_;
+};
+
+}  // namespace mediums
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#endif  // CORE_INTERNAL_MEDIUMS_BLE_PERIPHERAL_H_

cpp/core/internal/mediums/ble_v2.cc

@@ -0,0 +1,831 @@
+#include "core/internal/mediums/ble.h"
+#include "core/internal/mediums/ble_advertisement_header.h"
+#include "core/internal/mediums/bloom_filter.h"
+#include "core/internal/mediums/utils.h"
+#include "core/internal/mediums/uuid.h"
+#include "platform/synchronized.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+namespace mediums {
+
+namespace ble_v2 {
+
+template <typename Platform>
+class ProcessOnLostRunnable : public Runnable {
+ public:
+  explicit ProcessOnLostRunnable(Ptr<BLEV2<Platform>> ble_v2)
+      : ble_v2_(ble_v2) {}
+
+  void run() override { ble_v2_->processOnLostTimeout(); }
+
+ private:
+  Ptr<BLEV2<Platform>> ble_v2_;
+};
+
+template <typename Platform>
+class OnAdvertisementFoundRunnable : public Runnable {
+ public:
+  OnAdvertisementFoundRunnable(
+      Ptr<BLEV2<Platform>> ble_v2, Ptr<BLEPeripheralV2> peripheral,
+      ConstPtr<BLEAdvertisementData> advertisement_data)
+      : ble_v2_(ble_v2),
+        peripheral_(peripheral),
+        advertisement_data_(advertisement_data) {}
+
+  // This method is synchronized because it affects class state, but is called
+  // from a separate thread that fires whenever a BLE advertisement is seen.
+  void run() override {
+    Synchronized s(ble_v2_->lock_.get());
+
+    ble_v2_->discovered_peripheral_tracker_->processFoundBleAdvertisement(
+        peripheral_, advertisement_data_.release(),
+        MakePtr(new typename BLEV2<Platform>::GATTAdvertisementFetcherFacade(
+            ble_v2_)));
+  }
+
+ private:
+  Ptr<BLEV2<Platform>> ble_v2_;
+  Ptr<BLEPeripheralV2> peripheral_;
+  ScopedPtr<ConstPtr<BLEAdvertisementData>> advertisement_data_;
+};
+
+}  // namespace ble_v2
+
+template <typename Platform>
+const std::int32_t BLEV2<Platform>::kNumAdvertisementSlots = 2;
+
+template <typename Platform>
+const std::int32_t BLEV2<Platform>::kMaxAdvertisementLength = 512;
+
+template <typename Platform>
+const std::int32_t BLEV2<Platform>::kDummyServiceIdLength = 512;
+
+template <typename Platform>
+const char* BLEV2<Platform>::kCopresenceServiceUuid =
+    "0000FEF3-0000-1000-8000-00805F9B34FB";
+
+template <typename Platform>
+const std::int64_t BLEV2<Platform>::kOnLostTimeoutMillis = 15000;
+
+template <typename Platform>
+const std::int64_t BLEV2<Platform>::kGattAdvertisementOperationTimeoutMillis =
+    5000;
+
+template <typename Platform>
+const std::int64_t
+    BLEV2<Platform>::kMinConnectionAttemptRecoveryDurationMillis = 1000;
+
+template <typename Platform>
+const std::int32_t
+    BLEV2<Platform>::kMaxConnectionAttemptRecoveryFuzzDurationMillis = 10000;
+
+template <typename Platform>
+const std::uint32_t BLEV2<Platform>::kDefaultMtu = 512;
+
+// These two values make up the base UUID we use when advertising a slot. The
+// base is an all zero Version-3 name-based UUID. To turn this into an
+// advertisement slot UUID, we simply OR the least significant bits with the
+// slot number.
+//
+// More info about the format can be found here:
+// https://en.wikipedia.org/wiki/Universally_unique_identifier#Versions_3_and_5_(namespace_name-based)
+template <typename Platform>
+const std::int64_t BLEV2<Platform>::kAdvertisementUuidMsb = 0x0000000000003000;
+
+template <typename Platform>
+const std::int64_t BLEV2<Platform>::kAdvertisementUuidLsb = 0x8000000000000000;
+
+template <typename Platform>
+BLEV2<Platform>::BLEV2(Ptr<BluetoothRadio<Platform>> bluetooth_radio)
+    : lock_(Platform::createLock()),
+      platform_thread_offloader_(Platform::createSingleThreadExecutor()),
+      prng_(MakePtr(new Prng())),
+      hash_utils_(Platform::createHashUtils()),
+      bluetooth_radio_(bluetooth_radio),
+      bluetooth_adapter_(Platform::createBluetoothAdapter()),
+      ble_medium_(Platform::createBLEMediumV2()),
+      scanning_info_(),
+      discovered_peripheral_tracker_(
+          new DiscoveredPeripheralTracker<Platform>()),
+      on_lost_executor_(Platform::createScheduledExecutor()),
+      advertising_info_(),
+      gatt_server_info_(),
+      accepting_connections_info_() {}
+
+template <typename Platform>
+BLEV2<Platform>::~BLEV2() {
+  Synchronized s(lock_.get());
+
+  on_lost_executor_->shutdown();
+  platform_thread_offloader_->shutdown();
+  stopAdvertising();
+  stopAdvertisementGattServer();
+  stopAcceptingConnections();
+  stopScanning();
+  // discovered_peripheral_tracker is a ScopedPtr member and will take care of
+  // itself.
+}
+
+template <typename Platform>
+bool BLEV2<Platform>::isAvailable() {
+  // This is purposefully left un-synchronized like its java counterpart.
+  // Callers should be able to query this without waiting for other operations
+  // to complete first and this should be safe to call after shutdown. We would
+  // have made it static, but it relies on variables from the constructor (like
+  // ble_medium_ and bluetooth_adapter_).
+  return !ble_medium_.isNull() && !bluetooth_adapter_.isNull();
+}
+
+// Returns true if currently scanning for BLE advertisements.
+template <typename Platform>
+bool BLEV2<Platform>::isAdvertising() {
+  Synchronized s(lock_.get());
+
+  return !advertising_info_.isNull();
+}
+
+// Starts BLE advertising, delivering additional information through a GATT
+// server.
+template <typename Platform>
+bool BLEV2<Platform>::startAdvertising(
+    const string& service_id, ConstPtr<ByteArray> advertisement_bytes,
+    BLEMediumV2::PowerMode::Value power_mode,
+    const string& fast_advertisement_service_uuid) {
+  Synchronized s(lock_.get());
+
+  // Avoid leaks.
+  ScopedPtr<ConstPtr<ByteArray>> scoped_advertisement_bytes(
+      advertisement_bytes);
+
+  if (service_id.empty() || scoped_advertisement_bytes.isNull()) {
+    // logger.atSevere().log("Refusing to start BLE advertising because a null
+    // parameter was passed in.");
+    return false;
+  }
+
+  if (scoped_advertisement_bytes->size() > kMaxAdvertisementLength) {
+    // logger.atSevere().log("Refusing to start BLE advertising because the
+    // advertisement was too long. Expected at most %d bytes but received %d.",
+    // kMaxAdvertisementLength, scoped_advertisement_bytes->size());
+    return false;
+  }
+
+  // Note: We don't include logic checking/using the fast_pair_model_id because
+  // that is a java-only concept for now.
+
+  if (isAdvertising()) {
+    // logger.atSevere().log("Failed to BLE advertise because we're already
+    // advertising.");
+    return false;
+  }
+
+  if (!bluetooth_radio_->isEnabled()) {
+    // logger.atSevere().log("Can't start BLE advertising because Bluetooth
+    // isn't enabled.");
+    return false;
+  }
+
+  if (!isAvailable()) {
+    // logger.atSevere().log("Can't start BLE advertising because BLE is not
+    // available.");
+    return false;
+  }
+
+  // TODO(ahlee): Remove this check here and in the java code (redundant)
+  // Stop any existing advertisement GATT servers. We don't stop it in
+  // stopAdvertising() to avoid GATT issues with BLE sockets.
+  if (isAdvertisementGattServerRunning()) {
+    stopAdvertisementGattServer();
+  }
+
+  // Start a GATT server to deliver the full advertisement data. If we fail to
+  // advertise the header, we must shut this down before the method returns.
+  bool is_fast_advertisement = !fast_advertisement_service_uuid.empty();
+  if (!is_fast_advertisement) {
+    if (!startAdvertisementGattServer(service_id,
+                                      scoped_advertisement_bytes.get())) {
+      // logger.atSevere().log("Failed to to BLE advertise because the
+      // advertisement GATT server failed to start");
+      return false;
+    }
+  }
+
+  ScopedPtr<ConstPtr<ByteArray>> advertisement_header_bytes(
+      createAdvertisementHeader(service_id, scoped_advertisement_bytes.get(),
+                                is_fast_advertisement));
+  if (advertisement_header_bytes.isNull()) {
+    // logger.atSevere().log("Failed to to BLE advertise because we could not
+    // create an advertisement header");
+    // We failed to start BLE advertising, so stop the advertisement GATT
+    // server.
+    stopAdvertisementGattServer();
+    return false;
+  }
+
+  ScopedPtr<Ptr<BLEAdvertisementData>> advertisement(
+      new BLEAdvertisementData());
+  advertisement->is_connectable = true;
+  advertisement->tx_power_level =
+      BLEAdvertisementData::UNSPECIFIED_TX_POWER_LEVEL;
+
+  ScopedPtr<Ptr<BLEAdvertisementData>> scan_response(
+      new BLEAdvertisementData());
+  scan_response->is_connectable = true;
+  scan_response->tx_power_level =
+      BLEAdvertisementData::UNSPECIFIED_TX_POWER_LEVEL;
+  scan_response->service_uuids.insert(kCopresenceServiceUuid);
+  scan_response->service_data.insert(std::make_pair(
+      kCopresenceServiceUuid, advertisement_header_bytes.release()));
+
+  // Note: We don't use fast pair data because that is java-only for now.
+
+  // TODO(ahlee): Fix this if check in the java code.
+  if (is_fast_advertisement) {
+    ScopedPtr<ConstPtr<ByteArray>> service_id_hash(
+        generateServiceIdHash(BLEAdvertisement::Version::V2, service_id));
+    ScopedPtr<ConstPtr<ByteArray>> fast_advertisement_bytes(
+        BLEAdvertisement::toBytes(
+            BLEAdvertisement::Version::V2, BLEAdvertisement::SocketVersion::V2,
+            service_id_hash.get(), scoped_advertisement_bytes.get()));
+    if (fast_advertisement_bytes.isNull()) {
+      // logger.atSevere().log("Failed to BLE advertise because we could not
+      // create a fast advertisement for service UUID %s.",
+      // fast_advertisement_service_uuid);
+
+      // We shouldn't have started an advertisement GATT server in the first
+      // place if we are using fast advertisements. However, to avoid careless
+      // leaks, try shutting down the server anyway.
+      stopAdvertisementGattServer();
+      return false;
+    }
+    advertisement->service_data.insert(std::make_pair(
+        fast_advertisement_service_uuid, fast_advertisement_bytes.release()));
+    scan_response->service_uuids.insert(fast_advertisement_service_uuid);
+  }
+
+  if (!ble_medium_->startAdvertising(ConstifyPtr(advertisement.release()),
+                                     ConstifyPtr(scan_response.release()),
+                                     power_mode)) {
+    // If BLE advertising was not successful, stop the advertisement GATT
+    // server.
+    stopAdvertisementGattServer();
+    return false;
+  }
+
+  // logger.atVerbose().flog("Started BLE advertising with advertisement %s for
+  // serviceID %s.", advertisement_header, service_id);
+  advertising_info_ = MakePtr(new AdvertisingInfo(service_id));
+  return true;
+}
+
+template <typename Platform>
+ConstPtr<ByteArray> BLEV2<Platform>::createAdvertisementHeader(
+    const string& service_id, ConstPtr<ByteArray> advertisement_bytes,
+    bool is_fast_advertisement) {
+  // Create a randomized dummy service ID to anonymize our header with.
+  string dummy_service_id;
+  dummy_service_id.reserve(kDummyServiceIdLength);
+  for (int i = 0; i < kDummyServiceIdLength; i++) {
+    dummy_service_id[i] = static_cast<char>(prng_->nextInt32() & 0x000000FF);
+  }
+
+  // Put the service ID along with the dummy service ID into our bloom filter
+  // Note: BloomFilter length should always match
+  // BLEAdvertisementHeader::kServiceIdBloomFilterLength
+  ScopedPtr<Ptr<BloomFilter<10>>> bloom_filter(new BloomFilter<10>());
+  bloom_filter->add(dummy_service_id);
+
+  // Only add the service ID to our bloom filter if it's not a fast
+  // advertisement. Fast advertisements want discoverers to avoid reading our
+  // GATT advertisement.
+  if (!is_fast_advertisement) {
+    bloom_filter->add(service_id);
+  }
+
+  // Create a hash seeded from dummy_service_id + advertisementBytes
+  //
+  // First, populate advertisement_bodies with the dummy_service_id and
+  // advertisement_bytes.
+  string advertisement_bodies;
+  advertisement_bodies.reserve(dummy_service_id.size() +
+                               advertisement_bytes->size());
+  advertisement_bodies.append(dummy_service_id.data(), dummy_service_id.size());
+  advertisement_bodies.append(advertisement_bytes->getData(),
+                              advertisement_bytes->size());
+
+  // Then, generate the advertisement hash from the populated
+  // advertisement_bodies string.
+  ScopedPtr<ConstPtr<ByteArray>> advertisement_bodies_byte_array(MakeConstPtr(
+      new ByteArray(advertisement_bodies.data(), advertisement_bodies.size())));
+  ScopedPtr<ConstPtr<ByteArray>> advertisement_hash(
+      generateAdvertisementHash(advertisement_bodies_byte_array.get()));
+
+  ScopedPtr<ConstPtr<ByteArray>> bloom_filter_bytes(bloom_filter->asBytes());
+  string ble_advertisement_header_string = BLEAdvertisementHeader::asString(
+      BLEAdvertisementHeader::Version::V2, kNumAdvertisementSlots,
+      bloom_filter_bytes.get(), advertisement_hash.get());
+
+  return MakeConstPtr(new ByteArray(ble_advertisement_header_string.data(),
+                                    ble_advertisement_header_string.size()));
+}
+
+// Stops BLE advertising.
+template <typename Platform>
+void BLEV2<Platform>::stopAdvertising() {
+  Synchronized s(lock_.get());
+
+  if (!isAdvertising()) {
+    // logger.atDebug().log("Can't turn off BLE advertising because it never
+    // started.");
+    return;
+  }
+
+  ble_medium_->stopAdvertising();
+  // Reset advertising_info_to mark that we're no longer advertising.
+  advertising_info_.destroy();
+
+  // Do NOT stop the advertisement GATT server here. Doing so will cause any
+  // other existing GATT connections to stop receiving callbacks. This affects
+  // our BLE sockets. Therefore, we only stop it in shutdown() and
+  // startAdvertising(), where it is safe to do so. At those two points, we
+  // shouldn't expect any BLE sockets to be connected.
+
+  // logger.atVerbose().log("Turned BLE advertising off");
+}
+
+// Returns true if currently scanning for BLE advertisements.
+template <typename Platform>
+bool BLEV2<Platform>::isScanning() {
+  Synchronized s(lock_.get());
+
+  return !scanning_info_.isNull();
+}
+
+// Starts scanning for BLE advertisements (if it is possible for the device).
+template <typename Platform>
+bool BLEV2<Platform>::startScanning(
+    const string& service_id,
+    Ptr<DiscoveredPeripheralCallback> discovered_peripheral_callback,
+    BLEMediumV2::PowerMode::Value power_mode,
+    const string& fast_advertisement_service_uuid) {
+  Synchronized s(lock_.get());
+
+  // Avoid leaks.
+  ScopedPtr<Ptr<DiscoveredPeripheralCallback>>
+      scoped_discovered_peripheral_callback(discovered_peripheral_callback);
+
+  if (service_id.empty() || scoped_discovered_peripheral_callback.isNull()) {
+    // logger.atSevere().log("Refusing to start BLE scanning because at least
+    // one of workSource, serviceId, or discoveredPeripheralCallback is null.");
+    return false;
+  }
+
+  if (isScanning()) {
+    // logger.atSevere().log("Refusing to start BLE scanning because we are
+    // already scanning.");
+    return false;
+  }
+
+  if (!bluetooth_radio_->isEnabled()) {
+    // logger.atSevere().log("Can't start BLE scanning because Bluetooth was
+    // never turned on");
+    return false;
+  }
+
+  if (!isAvailable()) {
+    // logger.atSevere().log("Can't start BLE scanning because BLE is not
+    // available.");
+    return false;
+  }
+
+  discovered_peripheral_tracker_->startTracking(
+      service_id, scoped_discovered_peripheral_callback.release(),
+      fast_advertisement_service_uuid);
+  // Avoid leaks.
+  ScopedPtr<Ptr<ScanCallbackFacade>> scan_callback_facade(
+      new ScanCallbackFacade(MakePtr(this)));
+  std::set<string> service_uuids;
+  service_uuids.insert(kCopresenceServiceUuid);
+  if (!ble_medium_->startScanning(service_uuids, power_mode,
+                                  scan_callback_facade.get())) {
+    discovered_peripheral_tracker_->stopTracking(service_id);
+    return false;
+  }
+
+  // logger.atVerbose().log("Started BLE scanning for serviceID %s.",
+  // service_id);
+  scanning_info_ = MakePtr(new ScanningInfo(
+      service_id, scan_callback_facade.release(), createOnLostAlarm()));
+  return true;
+}
+
+template <typename Platform>
+void BLEV2<Platform>::onAdvertisementFoundImpl(
+    Ptr<BLEPeripheralV2> ble_peripheral,
+    ConstPtr<BLEAdvertisementData> advertisement_data) {
+  offloadFromPlatformThread(
+      MakePtr(new ble_v2::OnAdvertisementFoundRunnable<Platform>(
+          MakePtr(this), ble_peripheral, advertisement_data)));
+}
+
+// This method is synchronized because it affects class state, but is called
+// from a separate thread that has a recurring alarm running on it.
+template <typename Platform>
+void BLEV2<Platform>::processOnLostTimeout() {
+  Synchronized s(lock_.get());
+
+  discovered_peripheral_tracker_->processLostGattAdvertisements();
+}
+
+// Stops scanning for BLE advertisements.
+template <typename Platform>
+void BLEV2<Platform>::stopScanning() {
+  Synchronized s(lock_.get());
+
+  if (!isScanning()) {
+    // logger.atDebug().log("Can't turn off BLE scanning because we never
+    // started scanning.");
+    return;
+  }
+
+  scanning_info_->on_lost_alarm->cancel();
+
+  ble_medium_->stopScanning();
+  discovered_peripheral_tracker_->stopTracking(scanning_info_->service_id);
+  // Reset our bundle of scanning state to mark that we're no longer scanning.
+  scanning_info_.destroy();
+}
+
+// TODO(b/112199086) Change to RecurringCancelableAlarm
+template <typename Platform>
+Ptr<CancelableAlarm<Platform>> BLEV2<Platform>::createOnLostAlarm() {
+  // return MakePtr(new CancelableAlarm<Platform>(
+  //             "BluetoothLowEnergy.startScanning() onLost",
+  //             MakePtr(new
+  //             ble_v2::ProcessOnLostRunnable<Platform>(MakePtr(this))),
+  //             kOnLostTimeoutMillis, on_lost_executor_.get()));
+  return Ptr<CancelableAlarm<Platform>>();
+}
+
+// Returns true if the device is currently accepting incoming BLE socket
+// connections.
+template <typename Platform>
+bool BLEV2<Platform>::isAcceptingConnections() {
+  Synchronized s(lock_.get());
+
+  return !accepting_connections_info_.isNull();
+}
+
+// Starts accepting incoming BLE socket connections.
+template <typename Platform>
+bool BLEV2<Platform>::startAcceptingConnections(
+    const string& service_id,
+    Ptr<AcceptedConnectionCallback> accepted_connection_callback) {
+  Synchronized s(lock_.get());
+
+  // Avoid leaks.
+  ScopedPtr<Ptr<AcceptedConnectionCallback>>
+      scoped_accepted_connection_callback(accepted_connection_callback);
+  if (service_id.empty() || scoped_accepted_connection_callback.isNull()) {
+    // logger.atSevere().log("Refusing to start accepting BLE connections
+    // because at least one of serviceId or acceptedConnectionCallback is
+    // null.");
+    return false;
+  }
+
+  if (isAcceptingConnections()) {
+    // logger.atSevere().log("Refusing to start accepting BLE connections for %s
+    // because another BLE server socket is already in-progress.", service_id);
+    return false;
+  }
+
+  if (!bluetooth_radio_->isEnabled()) {
+    // logger.atSevere().log("Can't start accepting BLE connections for %s
+    // because Bluetooth isn't enabled.", service_id);
+    return false;
+  }
+
+  if (!isAvailable()) {
+    // logger.atSevere().log("Can't start accepting BLE connections for %s
+    // because BLE is not available.", service_id);
+    return false;
+  }
+
+  // TODO(ahlee): Implement w/ the rest of the connecting logic.
+  // Default to returning true and creating accepting_connections_info_ so we
+  // can test the advertising and discovery flow fully.
+  accepting_connections_info_ =
+      MakePtr(new AcceptingConnectionsInfo(service_id));
+  return true;
+}
+
+// Stops accepting incoming BLE socket connections.
+template <typename Platform>
+void BLEV2<Platform>::stopAcceptingConnections() {
+  Synchronized s(lock_.get());
+
+  if (!isAcceptingConnections()) {
+    // logger.atDebug().log("Can't stop accepting BLE connections because it was
+    // never started.");
+    return;
+  }
+
+  ble_medium_->stopListeningForIncomingBLESockets();
+
+  // Reset our bundle of accepting connections state to mark that we're no
+  // longer accepting connections.
+  accepting_connections_info_.destroy();
+}
+
+// Note: getGattConnectionBackoffPeriodMillis is only used in the java version
+// of reliablyConnect() for now.
+
+// Returns true if the advertisement GATT server is currently running.
+template <typename Platform>
+bool BLEV2<Platform>::isAdvertisementGattServerRunning() {
+  return !gatt_server_info_.isNull();
+}
+
+// Starts a GATT server to deliver additional advertisement data. Returns true
+// if the server was started successfully.
+template <typename Platform>
+bool BLEV2<Platform>::startAdvertisementGattServer(
+    const string& service_id, ConstPtr<ByteArray> advertisement) {
+  // advertisement is not being wrapped in a ScopedPtr because ownership is not
+  // passed on from startAdvertising().
+
+  if (isAdvertisementGattServerRunning()) {
+    // logger.atSevere().log("Refusing to start an advertisement GATT server
+    // because one is already running.");
+    return false;
+  }
+
+  // Create a BleAdvertisement to wrap over the passed in advertisement.
+  ScopedPtr<ConstPtr<ByteArray>> legacy_service_id_hash(
+      generateServiceIdHash(BLEAdvertisement::Version::V1, service_id));
+  ScopedPtr<ConstPtr<ByteArray>> legacy_ble_advertisement_bytes(
+      BLEAdvertisement::toBytes(BLEAdvertisement::Version::V1,
+                                BLEAdvertisement::SocketVersion::V1,
+                                legacy_service_id_hash.get(), advertisement));
+  if (legacy_ble_advertisement_bytes.isNull()) {
+    // logger.atSevere().log("Refusing to start an advertisement GATT server
+    // because creating a legacy BleAdvertisement with service ID %s failed.",
+    // service_id);
+    return false;
+  }
+
+  ScopedPtr<ConstPtr<ByteArray>> service_id_hash(
+      generateServiceIdHash(BLEAdvertisement::Version::V2, service_id));
+  ScopedPtr<ConstPtr<ByteArray>> ble_advertisement_bytes(
+      BLEAdvertisement::toBytes(BLEAdvertisement::Version::V2,
+                                BLEAdvertisement::SocketVersion::V2,
+                                service_id_hash.get(), advertisement));
+  if (ble_advertisement_bytes.isNull()) {
+    // logger.atSevere().log("Refusing to start an advertisement GATT server
+    // because creating a BleAdvertisement with service ID %s failed.",
+    // service_id);
+    return false;
+  }
+
+  return internalStartAdvertisementGattServer(
+      legacy_ble_advertisement_bytes.release(),
+      ble_advertisement_bytes.release());
+}
+
+template <typename Platform>
+bool BLEV2<Platform>::internalStartAdvertisementGattServer(
+    ConstPtr<ByteArray> legacy_ble_advertisement_bytes,
+    ConstPtr<ByteArray> ble_advertisement_bytes) {
+  // Avoid leaks.
+  ScopedPtr<ConstPtr<ByteArray>> scoped_legacy_ble_advertisement_bytes(
+      legacy_ble_advertisement_bytes);
+  ScopedPtr<ConstPtr<ByteArray>> scoped_ble_advertisement_bytes(
+      ble_advertisement_bytes);
+
+  ScopedPtr<Ptr<ServerGATTConnectionLifecycleCallbackFacade>>
+      connection_lifecycle_callback(
+          new ServerGATTConnectionLifecycleCallbackFacade(MakePtr(this)));
+  ScopedPtr<Ptr<GATTServer>> gatt_server(
+      ble_medium_->startGATTServer(connection_lifecycle_callback.get()));
+  if (gatt_server.isNull()) {
+    // logger.atSevere().withCause(e).log("Unable to start an advertisement GATT
+    // server.");
+    return false;
+  }
+
+  if (!generateAdvertisementCharacteristic(
+          /* slot= */ 0, scoped_legacy_ble_advertisement_bytes.release(),
+          gatt_server.get())) {
+    gatt_server->stop();
+    return false;
+  }
+
+  if (!generateAdvertisementCharacteristic(
+          /* slot= */ 1, scoped_ble_advertisement_bytes.release(),
+          gatt_server.get())) {
+    gatt_server->stop();
+    return false;
+  }
+
+  // GattCharacteristic is not included in GATTServerInfo because we don't need
+  // it after it's been updated.
+  gatt_server_info_ = MakePtr(new GATTServerInfo(
+      gatt_server.release(), connection_lifecycle_callback.release()));
+  return true;
+}
+
+template <typename Platform>
+bool BLEV2<Platform>::generateAdvertisementCharacteristic(
+    std::int32_t slot, ConstPtr<ByteArray> advertisement,
+    Ptr<GATTServer> gatt_server) {
+  // Avoid leaks.
+  ScopedPtr<ConstPtr<ByteArray>> scoped_advertisement(advertisement);
+
+  std::set<GATTCharacteristic::Permission::Value> permissions;
+  permissions.insert(GATTCharacteristic::Permission::READ);
+  std::set<GATTCharacteristic::Property::Value> properties;
+  properties.insert(GATTCharacteristic::Property::READ);
+  Ptr<GATTCharacteristic> gatt_characteristic(gatt_server->createCharacteristic(
+      kCopresenceServiceUuid, generateAdvertisementUuid(slot), permissions,
+      properties));
+
+  if (gatt_characteristic.isNull()) {
+    // logger.atSevere().withCause(e).log("Unable to create and add a
+    // characterstic to the gatt server for the advertisement.");
+    return false;
+  }
+
+  if (!gatt_server->updateCharacteristic(gatt_characteristic,
+                                         scoped_advertisement.release())) {
+    // logger.atSevere().withCause(e).log("Unable to write a value to the GATT
+    // characteristic.");
+    return false;
+  }
+
+  return true;
+}
+
+// Note: In the java counterpart this in a utils class.
+// Generates a characteristic UUID for an advertisement at the given slot.
+template <typename Platform>
+string BLEV2<Platform>::generateAdvertisementUuid(std::int32_t slot) {
+  return UUID<Platform>(kAdvertisementUuidMsb, kAdvertisementUuidLsb | slot)
+      .str();
+}
+
+// Stops a GATT server used for additional advertisement data.
+template <typename Platform>
+void BLEV2<Platform>::stopAdvertisementGattServer() {
+  Synchronized s(lock_.get());
+
+  if (!isAdvertisementGattServerRunning()) {
+    // logger.atSevere().log("Unable to stop the advertisement GATT server
+    // because it's not running.");
+    return;
+  }
+
+  gatt_server_info_->gatt_server->stop();
+  gatt_server_info_.destroy();
+}
+
+// Connects to a GATT server, reads advertisement data, and then disconnects
+// from the GATT server. This method blocks until all advertisements are read,
+// or a connection error occurs.
+template <typename Platform>
+Ptr<AdvertisementReadResult<Platform>>
+BLEV2<Platform>::processFetchGattAdvertisementsRequest(
+    Ptr<BLEPeripheralV2> peripheral, std::int32_t num_slots,
+    Ptr<AdvertisementReadResult<Platform>> advertisement_read_result) {
+  Synchronized s(lock_.get());
+
+  if (advertisement_read_result.isNull()) {
+    advertisement_read_result =
+        MakeRefCountedPtr(new AdvertisementReadResult<Platform>());
+  }
+
+  if (peripheral.isNull()) {
+    // logger.atSevere().log("Can't read from an advertisement GATT server
+    // because ble peripheral is null.");
+    return advertisement_read_result;
+  }
+
+  if (!bluetooth_radio_->isEnabled()) {
+    // logger.atSevere().log("Can't read from an advertisement GATT server
+    // because Bluetooth was never turned on.");
+    return advertisement_read_result;
+  }
+
+  if (!isAvailable()) {
+    // logger.atSevere().log("Can't read from an advertisement GATT server
+    // because BLE is not available.");
+    return advertisement_read_result;
+  }
+
+  return internalReadFromAdvertisementGattServer(peripheral, num_slots,
+                                                 advertisement_read_result);
+}
+
+template <typename Platform>
+Ptr<AdvertisementReadResult<Platform>>
+BLEV2<Platform>::internalReadFromAdvertisementGattServer(
+    Ptr<BLEPeripheralV2> peripheral, std::int32_t num_slots,
+    Ptr<AdvertisementReadResult<Platform>> advertisement_read_result) {
+  // Attempt to connect and read some GATT characteristics.
+  bool read_success = true;
+
+  ScopedPtr<Ptr<ClientGATTConnectionLifecycleCallbackFacade>>
+      connection_lifecycle_callback(
+          new ClientGATTConnectionLifecycleCallbackFacade(MakePtr(this)));
+  ScopedPtr<Ptr<ClientGATTConnection>> gatt_connection(
+      ble_medium_->connectToGATTServer(peripheral, kDefaultMtu,
+                                       BLEMediumV2::PowerMode::HIGH,
+                                       connection_lifecycle_callback.get()));
+  if (!gatt_connection.isNull() && gatt_connection->discoverServices()) {
+    // Read all advertisements from all slots that we haven't read from yet.
+    for (std::int32_t slot = 0; slot < num_slots; ++slot) {
+      // Make sure we haven't already read this advertisement before.
+      if (advertisement_read_result->hasAdvertisement(slot)) {
+        continue;
+      }
+
+      // Make sure the characteristic even exists for this slot number. If the
+      // characteristic doesn't exist, we shouldn't count the fetch as a
+      // failure because there's nothing we could've done about a non-existent
+      // characteristic.
+      Ptr<GATTCharacteristic> gatt_characteristic(
+          gatt_connection->getCharacteristic(kCopresenceServiceUuid,
+                                             generateAdvertisementUuid(slot)));
+      if (/* !advertisementSlotExists()= */ gatt_characteristic.isNull()) {
+        continue;
+      }
+
+      // Read advertisement data from the characteristic associated with this
+      // slot.
+      ScopedPtr<ConstPtr<ByteArray>> characteristic_value(
+          gatt_connection->readCharacteristic(gatt_characteristic));
+      if (!characteristic_value.isNull()) {
+        advertisement_read_result->addAdvertisement(
+            slot, characteristic_value.release());
+        // logger.atVerbose().log("Successfully read advertisement at slot %d
+        // on peripheral %s.", slot, peripheral);
+      } else {
+        // logger.atWarning().withCause(characteristicReadException).log("Can't
+        // read advertisement for slot %d on peripheral %s.", slot,
+        // peripheral);
+        read_success = false;
+      }
+      // Whether or not we succeeded with this slot, we should try reading the
+      // other slots to get as many advertisements as possible before
+      // returning a success or failure.
+    }
+
+    gatt_connection->disconnect();
+  } else {
+    // logger.atWarning().withCause(connectException).log("Can't connect to an
+    // advertisement GATT server for peripheral %s.", peripheral);
+    read_success = false;
+  }
+
+  advertisement_read_result->recordLastReadStatus(read_success);
+  return advertisement_read_result;
+}
+
+template <typename Platform>
+void BLEV2<Platform>::offloadFromPlatformThread(Ptr<Runnable> runnable) {
+  platform_thread_offloader_->execute(runnable);
+}
+
+template <typename Platform>
+ConstPtr<ByteArray> BLEV2<Platform>::generateAdvertisementHash(
+    ConstPtr<ByteArray> advertisement_bytes) {
+  return Utils::sha256Hash(hash_utils_.get(), advertisement_bytes,
+                           BLEAdvertisementHeader::kAdvertisementHashLength);
+}
+
+template <typename Platform>
+ConstPtr<ByteArray> BLEV2<Platform>::generateServiceIdHash(
+    BLEAdvertisement::Version::Value version, const string& service_id) {
+  ScopedPtr<ConstPtr<ByteArray>> service_id_bytes(
+      MakeConstPtr(new ByteArray(service_id.data(), service_id.size())));
+  switch (version) {
+    case BLEAdvertisement::Version::V1:
+      return Utils::legacySha256HashOnlyForPrinting(
+          hash_utils_.get(), service_id_bytes.get(),
+          BLEAdvertisement::kServiceIdHashLength);
+    case BLEAdvertisement::Version::V2:
+      // Fall through.
+    case BLEAdvertisement::Version::UNKNOWN:
+      // Fall through.
+    default:
+      // Use the latest known hashing scheme.
+      return Utils::sha256Hash(hash_utils_.get(), service_id_bytes.get(),
+                               BLEAdvertisement::kServiceIdHashLength);
+  }
+}
+
+}  // namespace mediums
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/mediums/ble_v2.h

@@ -0,0 +1,312 @@
+#ifndef CORE_INTERNAL_MEDIUMS_BLE_V2_H_
+#define CORE_INTERNAL_MEDIUMS_BLE_V2_H_
+
+#include <cstdint>
+
+#include "core/internal/mediums/advertisement_read_result.h"
+#include "core/internal/mediums/ble_advertisement.h"
+#include "core/internal/mediums/bluetooth_radio.h"
+#include "core/internal/mediums/discovered_peripheral_callback.h"
+#include "core/internal/mediums/discovered_peripheral_tracker.h"
+#include "platform/api/ble_v2.h"
+#include "platform/api/bluetooth_adapter.h"
+#include "platform/api/hash_utils.h"
+#include "platform/api/lock.h"
+#include "platform/byte_array.h"
+#include "platform/cancelable_alarm.h"
+#include "platform/port/string.h"
+#include "platform/prng.h"
+#include "platform/ptr.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+namespace mediums {
+
+namespace ble_v2 {
+
+template <typename>
+class ProcessOnLostRunnable;
+
+template <typename>
+class OnAdvertisementFoundRunnable;
+
+}  // namespace ble_v2
+
+template <typename Platform>
+class BLEV2 {
+ public:
+  explicit BLEV2(Ptr<BluetoothRadio<Platform>> bluetooth_radio);
+  ~BLEV2();
+
+  bool isAvailable();
+  // While the start* functions for each action (advertising, scanning,
+  // accepting connections) take in a service_id, the stop* and is* functions do
+  // not. This is because the service_id isn't used. In the java code, shutdown
+  // calls all the stop* functions w/ a null service_id. The service_id is just
+  // passed through to the corresponding is* function, which ignores it.
+  // service_id should be added back in when C++ supports multi-client.
+  bool startAdvertising(const string& service_id,
+                        ConstPtr<ByteArray> advertisement,
+                        BLEMediumV2::PowerMode::Value power_mode,
+                        const string& fast_advertisement_service_uuid);
+  void stopAdvertising();
+
+  bool startScanning(
+      const string& service_id,
+      Ptr<DiscoveredPeripheralCallback> discovered_peripheral_callback,
+      BLEMediumV2::PowerMode::Value power_mode,
+      const string& fast_advertisement_service_uuid);
+  void stopScanning();
+
+  class AcceptedConnectionCallback {
+   public:
+    virtual ~AcceptedConnectionCallback() {}
+
+    // TODO(ahlee): Add in connecting logic.
+  };
+
+  bool isAcceptingConnections();
+  bool startAcceptingConnections(
+      const string& service_id,
+      Ptr<AcceptedConnectionCallback> accepted_connection_callback);
+  void stopAcceptingConnections();
+
+ private:
+  template <typename>
+  friend class ble_v2::ProcessOnLostRunnable;
+  template <typename>
+  friend class ble_v2::OnAdvertisementFoundRunnable;
+
+  class GATTAdvertisementFetcherFacade
+      : public DiscoveredPeripheralTracker<Platform>::GattAdvertisementFetcher {
+   public:
+    explicit GATTAdvertisementFetcherFacade(Ptr<BLEV2<Platform>> impl)
+        : impl_(impl) {}
+    ~GATTAdvertisementFetcherFacade() override {}
+
+    Ptr<AdvertisementReadResult<Platform>> fetchGattAdvertisements(
+        Ptr<BLEPeripheralV2> ble_peripheral, std::int32_t num_slots,
+        Ptr<AdvertisementReadResult<Platform>> advertisement_read_result)
+        override {
+      return impl_->processFetchGattAdvertisementsRequest(
+          ble_peripheral, num_slots, advertisement_read_result);
+    }
+
+   private:
+    Ptr<BLEV2<Platform>> impl_;
+  };
+
+  class ScanCallbackFacade : public BLEMediumV2::ScanCallback {
+   public:
+    explicit ScanCallbackFacade(Ptr<BLEV2<Platform>> impl) : impl_(impl) {}
+    ~ScanCallbackFacade() override {}
+
+    void onAdvertisementFound(
+        Ptr<BLEPeripheralV2> peripheral,
+        ConstPtr<BLEAdvertisementData> advertisement_data) override {
+      impl_->onAdvertisementFoundImpl(peripheral, advertisement_data);
+    }
+
+   private:
+    Ptr<BLEV2<Platform>> impl_;
+  };
+
+  class ClientGATTConnectionLifecycleCallbackFacade
+      : public ClientGATTConnectionLifecycleCallback {
+   public:
+    explicit ClientGATTConnectionLifecycleCallbackFacade(
+        Ptr<BLEV2<Platform>> impl)
+        : impl_(impl) {}
+    ~ClientGATTConnectionLifecycleCallbackFacade() override {}
+
+    void onDisconnected(Ptr<ClientGATTConnection> connection) override {
+      // Avoid leaks.
+      ScopedPtr<Ptr<ClientGATTConnection>> scoped_connection(connection);
+
+      // Nothing else to do for now.
+    }
+
+   private:
+    Ptr<BLEV2<Platform>> impl_;
+  };
+
+  class ServerGATTConnectionLifecycleCallbackFacade
+      : public ServerGATTConnectionLifecycleCallback {
+   public:
+    explicit ServerGATTConnectionLifecycleCallbackFacade(
+        Ptr<BLEV2<Platform>> impl)
+        : impl_(impl) {}
+    ~ServerGATTConnectionLifecycleCallbackFacade() override {}
+
+    void onCharacteristicSubscription(
+        Ptr<ServerGATTConnection> connection,
+        Ptr<GATTCharacteristic> characteristic) override {
+      // Avoid leaks. Do not scope the characteristic because it is ref counted
+      // by the per-platform ble_v2 implementation.
+      ScopedPtr<Ptr<ServerGATTConnection>> scoped_connection(connection);
+
+      // Nothing else to do for now.
+    }
+
+    void onCharacteristicUnsubscription(
+        Ptr<ServerGATTConnection> connection,
+        Ptr<GATTCharacteristic> characteristic) override {
+      // Avoid leaks. Do not scope the characteristic because it is ref counted
+      // by the per-platform ble_v2 implementation.
+      ScopedPtr<Ptr<ServerGATTConnection>> scoped_connection(connection);
+
+      // Nothing else to do for now.
+    }
+
+   private:
+    Ptr<BLEV2<Platform>> impl_;
+  };
+
+  struct ScanningInfo {
+    ScanningInfo(const string& service_id,
+                 Ptr<ScanCallbackFacade> scan_callback_facade,
+                 Ptr<CancelableAlarm<Platform>> on_lost_alarm)
+        : service_id(service_id),
+          scan_callback_facade(scan_callback_facade),
+          on_lost_alarm(on_lost_alarm) {}
+    ~ScanningInfo() {
+      // Nothing to do (the ScopedPtr members take care of themselves).
+    }
+
+    const string service_id;
+    ScopedPtr<Ptr<ScanCallbackFacade>> scan_callback_facade;
+    // TODO(ahlee): Change to recurring cancelable alarm
+    ScopedPtr<Ptr<CancelableAlarm<Platform>>> on_lost_alarm;
+  };
+
+  struct AdvertisingInfo {
+    explicit AdvertisingInfo(const string& service_id)
+        : service_id(service_id) {}
+    ~AdvertisingInfo() {}
+
+    const string service_id;
+  };
+
+  struct GATTServerInfo {
+    GATTServerInfo(Ptr<GATTServer> gatt_server,
+                   Ptr<ServerGATTConnectionLifecycleCallbackFacade>
+                       connection_lifecycle_callback)
+        : gatt_server(gatt_server),
+          connection_lifecycle_callback(connection_lifecycle_callback) {}
+    ~GATTServerInfo() {
+      // Nothing to do (the ScopedPtr members take care of themselves).
+    }
+
+    ScopedPtr<Ptr<GATTServer>> gatt_server;
+    ScopedPtr<Ptr<ServerGATTConnectionLifecycleCallbackFacade>>
+        connection_lifecycle_callback;
+  };
+
+  struct AcceptingConnectionsInfo {
+    explicit AcceptingConnectionsInfo(const string& service_id)
+        : service_id(service_id) {}
+    ~AcceptingConnectionsInfo() {
+      // Nothing to do (the ScopedPtr members take care of themselves).
+    }
+
+    const string service_id;
+    // TODO(ahlee): Fill in.
+  };
+
+  static const std::int32_t kNumAdvertisementSlots;
+  static const std::int32_t kMaxAdvertisementLength;
+  static const std::int32_t kDummyServiceIdLength;
+  static const char* kCopresenceServiceUuid;
+  static const std::int64_t kOnLostTimeoutMillis;
+  static const std::int64_t kGattAdvertisementOperationTimeoutMillis;
+  static const std::int64_t kMinConnectionAttemptRecoveryDurationMillis;
+  static const std::int32_t kMaxConnectionAttemptRecoveryFuzzDurationMillis;
+  static const std::uint32_t kDefaultMtu;
+  static const std::int64_t kAdvertisementUuidMsb;
+  static const std::int64_t kAdvertisementUuidLsb;
+
+  bool isAdvertising();
+  ConstPtr<ByteArray> createAdvertisementHeader(
+      const string& service_id, ConstPtr<ByteArray> advertisement_bytes,
+      bool is_fast_advertisement);
+
+  bool isScanning();
+  void onAdvertisementFoundImpl(
+      Ptr<BLEPeripheralV2> ble_peripheral,
+      ConstPtr<BLEAdvertisementData> advertisement_data);
+  void processOnLostTimeout();
+  Ptr<CancelableAlarm<Platform>> createOnLostAlarm();
+
+  bool isAdvertisementGattServerRunning();
+  bool startAdvertisementGattServer(const string& service_id,
+                                    ConstPtr<ByteArray> advertisement);
+  bool internalStartAdvertisementGattServer(
+      ConstPtr<ByteArray> legacy_ble_advertisement_bytes,
+      ConstPtr<ByteArray> ble_advertisement_bytes);
+  bool generateAdvertisementCharacteristic(
+    std::int32_t slot, ConstPtr<ByteArray> advertisement,
+    Ptr<GATTServer> gatt_server);
+  void stopAdvertisementGattServer();
+
+  Ptr<AdvertisementReadResult<Platform>> processFetchGattAdvertisementsRequest(
+      Ptr<BLEPeripheralV2> peripheral, std::int32_t num_slots,
+      Ptr<AdvertisementReadResult<Platform>> advertisement_read_result);
+  Ptr<AdvertisementReadResult<Platform>>
+  internalReadFromAdvertisementGattServer(
+      Ptr<BLEPeripheralV2> ble_peripheral, std::int32_t num_slots,
+      Ptr<AdvertisementReadResult<Platform>> advertisement_read_result);
+
+  void offloadFromPlatformThread(Ptr<Runnable> runnable);
+  // TODO(ahlee): Move these out to utils (also used by
+  // DiscoveredPeripheralTracker).
+  ConstPtr<ByteArray> generateAdvertisementHash(
+      ConstPtr<ByteArray> advertisement_bytes);
+  ConstPtr<ByteArray> generateServiceIdHash(
+      BLEAdvertisement::Version::Value version, const string& service_id);
+
+  // This maps to a helper function found in bluetoothlowenergy/Utils.java. In
+  // the C++ code we moved it because it's only used here.
+  string generateAdvertisementUuid(std::int32_t slot);
+
+  // ------------ GENERAL ------------
+
+  ScopedPtr<Ptr<Lock>> lock_;
+  // Where we throw potentially blocking work off of the platform thread.
+  ScopedPtr<Ptr<typename Platform::SingleThreadExecutorType>>
+      platform_thread_offloader_;
+  ScopedPtr<Ptr<Prng>> prng_;
+  ScopedPtr<Ptr<HashUtils>> hash_utils_;
+
+  // ------------ CORE BLE ------------
+
+  Ptr<BluetoothRadio<Platform>> bluetooth_radio_;
+  ScopedPtr<Ptr<BluetoothAdapter>> bluetooth_adapter_;
+  // The underlying, per-platform implementation.
+  ScopedPtr<Ptr<BLEMediumV2>> ble_medium_;
+
+  // ------------ DISCOVERY ------------
+
+  // scanning_info_ is not scoped because it's nullable.
+  Ptr<ScanningInfo> scanning_info_;
+  ScopedPtr<Ptr<DiscoveredPeripheralTracker<Platform>>>
+      discovered_peripheral_tracker_;
+  ScopedPtr<Ptr<typename Platform::ScheduledExecutorType>> on_lost_executor_;
+
+  // ------------ ADVERTISING ------------
+
+  // advertising_info_, gatt_server_info_, and accepting_connections_info_ are
+  // not scoped because they are nullable.
+  Ptr<AdvertisingInfo> advertising_info_;
+  Ptr<GATTServerInfo> gatt_server_info_;
+  Ptr<AcceptingConnectionsInfo> accepting_connections_info_;
+};
+
+}  // namespace mediums
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#include "core/internal/mediums/ble_v2.cc"
+
+#endif  // CORE_INTERNAL_MEDIUMS_BLE_V2_H_

cpp/core/internal/mediums/bloom_filter.cc

@@ -0,0 +1,109 @@
+#include "core/internal/mediums/bloom_filter.h"
+
+#include "absl/numeric/int128.h"
+#include "absl/strings/numbers.h"
+#include "smhasher/MurmurHash3.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+namespace mediums {
+
+template <size_t CapacityInBytes>
+const std::int32_t BloomFilter<CapacityInBytes>::kHasherNumberOfRepetitions = 5;
+
+template <size_t CapacityInBytes>
+BloomFilter<CapacityInBytes>::BloomFilter() : bits_() {}
+
+template <size_t CapacityInBytes>
+BloomFilter<CapacityInBytes>::BloomFilter(ConstPtr<ByteArray> bytes) : bits_() {
+  const char* bytes_read_ptr = bytes->getData();
+  for (size_t byte_index = 0; byte_index < bytes->size(); byte_index++) {
+    for (size_t bit_index = 0; bit_index < 8; bit_index++) {
+      bits_.set((byte_index * 8) + bit_index,
+                (*bytes_read_ptr >> bit_index) & 0x01);
+    }
+    bytes_read_ptr++;
+  }
+}
+
+template <size_t CapacityInBytes>
+BloomFilter<CapacityInBytes>::~BloomFilter() {
+  // Nothing to do.
+}
+
+template <size_t CapacityInBytes>
+ConstPtr<ByteArray> BloomFilter<CapacityInBytes>::asBytes() {
+  // Gets a binary string representation of the bitset where the leftmost
+  // character corresponds to bitset position (total size) - 1.
+  //
+  // If the bitset's internal representation is:
+  //     [position 0]     0 0 1 1 0 0 0 1 0 1 0 1     [position 11]
+  // The string representation will be outputted like this:
+  //                     "1 0 1 0 1 0 0 0 1 1 0 0"
+  std::string bitset_binary_string = bits_.to_string();
+
+  Ptr<ByteArray> result_bytes{new ByteArray{CapacityInBytes}};
+  char* result_bytes_write_ptr = result_bytes->getData();
+  // We go through the string backwards because the rightmost character
+  // corresponds to position 0 in the bitset.
+  for (size_t i = bits_.size(); i > 0; i -= 8) {
+    std::string byte_binary_string = bitset_binary_string.substr(i - 8, 8);
+    std::uint32_t byte_value;
+    absl::numbers_internal::safe_strtou32_base(byte_binary_string, &byte_value,
+                                               /* base= */ 2);
+    *result_bytes_write_ptr = static_cast<char>(byte_value & 0x000000FF);
+    result_bytes_write_ptr++;
+  }
+  return ConstifyPtr(result_bytes);
+}
+
+template <size_t CapacityInBytes>
+void BloomFilter<CapacityInBytes>::add(const std::string& s) {
+  std::vector<std::int32_t> hashes = getHashes(s);
+  for (std::vector<std::int32_t>::iterator it = hashes.begin();
+       it != hashes.end(); ++it) {
+    size_t position = static_cast<size_t>(*it) % bits_.size();
+    bits_.set(position);
+  }
+}
+
+template <size_t CapacityInBytes>
+bool BloomFilter<CapacityInBytes>::possiblyContains(const std::string& s) {
+  std::vector<std::int32_t> hashes = getHashes(s);
+  for (std::vector<std::int32_t>::iterator i = hashes.begin();
+       i != hashes.end(); ++i) {
+    size_t position = static_cast<size_t>(*i) % bits_.size();
+    if (!bits_.test(position)) {
+      return false;
+    }
+  }
+  return true;
+}
+
+template <size_t CapacityInBytes>
+std::vector<std::int32_t> BloomFilter<CapacityInBytes>::getHashes(
+    const std::string& s) {
+  std::vector<std::int32_t> hashes(kHasherNumberOfRepetitions, 0);
+
+  absl::uint128 hash128;
+  MurmurHash3_x64_128(s.data(), s.size(), 0, &hash128);
+  std::uint64_t hash64 =
+      absl::Uint128Low64(hash128);  // the lower 64 bits of the 128-bit hash
+  std::int32_t hash1 = static_cast<std::int32_t>(
+      hash64 & 0x00000000FFFFFFFF);  // the lower 32 bits of the 64-bit hash
+  std::int32_t hash2 = static_cast<std::int32_t>(
+      (hash64 >> 32) & 0x0FFFFFFFF);  // the upper 32 bits of the 64-bit hash
+  for (size_t i = 1; i <= kHasherNumberOfRepetitions; i++) {
+    std::int32_t combinedHash = static_cast<std::int32_t>(hash1 + (i * hash2));
+    // Flip all the bits if it's negative (guaranteed positive number)
+    if (combinedHash < 0) combinedHash = ~combinedHash;
+    hashes[i - 1] = combinedHash;
+  }
+  return hashes;
+}
+
+}  // namespace mediums
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/mediums/bloom_filter.h

@@ -0,0 +1,54 @@
+#ifndef CORE_INTERNAL_MEDIUMS_BLOOM_FILTER_H_
+#define CORE_INTERNAL_MEDIUMS_BLOOM_FILTER_H_
+
+#include <bitset>
+#include <cstdint>
+#include <vector>
+
+#include "platform/byte_array.h"
+#include "platform/port/string.h"
+#include "platform/ptr.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+namespace mediums {
+
+/**
+ * A bloom filter that gives access to the underlying BitSet. The implementation
+ * is copied from our Java version of Bloom filter, which in turn copies from
+ * Guava's BloomFilter.
+ *
+ * BloomFilter is templatized on the size of the byte array and not the size of
+ * the bit set to ensure the bit set's length is a multiple of 8 (and can
+ * neatly be returned as a ByteArray).
+ */
+template <size_t CapacityInBytes>
+class BloomFilter {
+ public:
+  BloomFilter();
+  explicit BloomFilter(ConstPtr<ByteArray> bytes);
+  ~BloomFilter();
+
+  ConstPtr<ByteArray> asBytes();
+
+  void add(const std::string& s);
+
+  bool possiblyContains(const std::string& s);
+
+ private:
+  static const std::int32_t kHasherNumberOfRepetitions;
+
+  std::vector<std::int32_t> getHashes(const std::string& s);
+
+  std::bitset<CapacityInBytes * 8> bits_;
+};
+
+}  // namespace mediums
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#include "core/internal/mediums/bloom_filter.cc"
+
+#endif  // CORE_INTERNAL_MEDIUMS_BLOOM_FILTER_H_

cpp/core/internal/mediums/bloom_filter_test.cc

@@ -0,0 +1,162 @@
+#include "core/internal/mediums/bloom_filter.h"
+
+#include <algorithm>
+
+#include "gtest/gtest.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+namespace mediums {
+namespace {
+
+const size_t kByteArrayLength = 100;
+
+TEST(BloomFilterTest, EmptyFilterReturnsEmptyArray) {
+  ScopedPtr<Ptr<BloomFilter<kByteArrayLength>>> scoped_bloom_filter(
+      new BloomFilter<kByteArrayLength>());
+
+  ScopedPtr<ConstPtr<ByteArray>> scoped_bloom_filter_bytes(
+      scoped_bloom_filter->asBytes());
+  std::string empty_string(kByteArrayLength, '\0');
+  ASSERT_EQ(0, memcmp(scoped_bloom_filter_bytes->getData(), empty_string.data(),
+                      empty_string.size()));
+}
+
+TEST(BloomFilterTest, EmptyFilterNeverContains) {
+  ScopedPtr<Ptr<BloomFilter<kByteArrayLength>>> scoped_bloom_filter(
+      new BloomFilter<kByteArrayLength>());
+
+  ASSERT_FALSE(scoped_bloom_filter->possiblyContains("ELEMENT_1"));
+  ASSERT_FALSE(scoped_bloom_filter->possiblyContains("ELEMENT_2"));
+  ASSERT_FALSE(scoped_bloom_filter->possiblyContains("ELEMENT_3"));
+}
+
+TEST(BloomFilterTest, AddSuccess) {
+  ScopedPtr<Ptr<BloomFilter<kByteArrayLength>>> scoped_bloom_filter(
+      new BloomFilter<kByteArrayLength>());
+  ASSERT_FALSE(scoped_bloom_filter->possiblyContains("ELEMENT_1"));
+
+  scoped_bloom_filter->add("ELEMENT_1");
+  ASSERT_TRUE(scoped_bloom_filter->possiblyContains("ELEMENT_1"));
+}
+
+TEST(BloomFilterTest, AddOnlyGivenArg) {
+  ScopedPtr<Ptr<BloomFilter<kByteArrayLength>>> scoped_bloom_filter(
+      new BloomFilter<kByteArrayLength>());
+  scoped_bloom_filter->add("ELEMENT_1");
+
+  ASSERT_TRUE(scoped_bloom_filter->possiblyContains("ELEMENT_1"));
+  ASSERT_FALSE(scoped_bloom_filter->possiblyContains("ELEMENT_2"));
+  ASSERT_FALSE(scoped_bloom_filter->possiblyContains("ELEMENT_3"));
+}
+
+TEST(BloomFilterTest, AddMultipleArgs) {
+  ScopedPtr<Ptr<BloomFilter<kByteArrayLength>>> scoped_bloom_filter(
+      new BloomFilter<kByteArrayLength>());
+  scoped_bloom_filter->add("ELEMENT_1");
+  scoped_bloom_filter->add("ELEMENT_2");
+
+  ASSERT_TRUE(scoped_bloom_filter->possiblyContains("ELEMENT_1"));
+  ASSERT_TRUE(scoped_bloom_filter->possiblyContains("ELEMENT_2"));
+  ASSERT_FALSE(scoped_bloom_filter->possiblyContains("ELEMENT_3"));
+}
+
+TEST(BloomFilterTest, AddMultipleArgsReturnsNonemptyArray) {
+  ScopedPtr<Ptr<BloomFilter<10>>> scoped_bloom_filter(new BloomFilter<10>());
+  scoped_bloom_filter->add("ELEMENT_1");
+  scoped_bloom_filter->add("ELEMENT_2");
+  scoped_bloom_filter->add("ELEMENT_3");
+
+  ScopedPtr<ConstPtr<ByteArray>> scoped_bloom_filter_bytes(
+      scoped_bloom_filter->asBytes());
+  std::string empty_string(kByteArrayLength, '\0');
+  ASSERT_NE(0, memcmp(scoped_bloom_filter_bytes->getData(), empty_string.data(),
+                      empty_string.size()));
+}
+
+/**
+ * This test was added because of a bug where the BloomFilter doesn't utilize
+ * all bits given. Functionally, the filter still works, but we just have a much
+ * higher false positive rate. The bug was caused by confusing bit length and
+ * byte length, which made our BloomFilter only set bits on the first byteLength
+ * (bitLength / 8) bits rather than the whole bitLength bits.
+ *
+ * <p>Here, we're verifying that the bits set are somewhat scattered. So instead
+ * of something like [ 0, 1, 1, 0, 0, 0, 0, ..., 0 ], we should be getting
+ * something like [ 0, 1, 0, 0, 1, 1, 0, 0, 0, 1, ..., 1, 0].
+ */
+TEST(BloomFilterTest, RandomnessNoEndBias) {
+  ScopedPtr<Ptr<BloomFilter<kByteArrayLength>>> scoped_bloom_filter(
+      new BloomFilter<kByteArrayLength>());
+  // Add one element to our BloomFilter.
+  scoped_bloom_filter->add("ELEMENT_1");
+
+  std::int32_t non_zero_count = 0;
+  std::int32_t longest_zero_streak = 0;
+  std::int32_t current_zero_streak = 0;
+
+  // Record the amount of non-zero bytes and the longest streak of zero bytes in
+  // the resulting BloomFilter. This is an approximation of reasonable
+  // distribution since we're recording by bytes instead of bits.
+  ScopedPtr<ConstPtr<ByteArray>> scoped_bloom_filter_bytes(
+      scoped_bloom_filter->asBytes());
+  const char* bloom_filter_bytes_read_ptr =
+      scoped_bloom_filter_bytes->getData();
+  for (int i = 0; i < scoped_bloom_filter_bytes->size(); i++) {
+    if (*bloom_filter_bytes_read_ptr == '\0') {
+      current_zero_streak++;
+    } else {
+      // Increment the number of non-zero bytes we've seen, update the longest
+      // zero streak, and then reset the current zero streak.
+      non_zero_count++;
+      longest_zero_streak = std::max(longest_zero_streak, current_zero_streak);
+      current_zero_streak = 0;
+    }
+    bloom_filter_bytes_read_ptr++;
+  }
+  // Update the longest zero streak again for the tail case.
+  longest_zero_streak = std::min(longest_zero_streak, current_zero_streak);
+
+  // Since randomness is hard to measure within one unit test, we instead do a
+  // sanity check. All non-zero bytes should not be packed into one end of the
+  // array.
+  //
+  // In this case, the size of one end is approximated to be:
+  //     kByteArrayLength / nonZeroCount.
+  // Therefore, the longest zero streak should be less than:
+  //     kByteArrayLength - one end of the array.
+  std::int32_t longest_acceptable_zero_streak =
+      kByteArrayLength - (kByteArrayLength / non_zero_count);
+  ASSERT_TRUE(longest_zero_streak <= longest_acceptable_zero_streak);
+}
+
+TEST(BloomFilterTest, RandomnessFalsePositiveRate) {
+  ScopedPtr<Ptr<BloomFilter<10>>> scoped_bloom_filter(new BloomFilter<10>());
+  // Add 5 distinct elements to the BloomFilter.
+  scoped_bloom_filter->add("ELEMENT_1");
+  scoped_bloom_filter->add("ELEMENT_2");
+  scoped_bloom_filter->add("ELEMENT_3");
+  scoped_bloom_filter->add("ELEMENT_4");
+  scoped_bloom_filter->add("ELEMENT_5");
+
+  std::int32_t false_positives = 0;
+  // Now test 100 other elements and record the number of false positives.
+  for (int i = 5; i < 105; i++) {
+    false_positives +=
+        scoped_bloom_filter->possiblyContains("ELEMENT_" + std::to_string(i))
+            ? 1
+            : 0;
+  }
+
+  // We expect the false positive rate to be 3% with 5 elements in a 10 byte
+  // filter. Thus, we give a little leeway and verify that the false positive
+  // rate is no more than 5%.
+  ASSERT_LE(false_positives, 5);
+}
+
+}  // namespace
+}  // namespace mediums
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/mediums/bluetooth_classic.cc

@@ -0,0 +1,468 @@
+#include "core/internal/mediums/bluetooth_classic.h"
+
+#include <utility>
+
+#include "core/internal/mediums/uuid.h"
+#include "platform/synchronized.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+template <typename Platform>
+const std::int32_t BluetoothClassic<Platform>::kMaxConcurrentAcceptLoops = 5;
+
+template <typename Platform>
+BluetoothClassic<Platform>::BluetoothClassic(
+    Ptr<BluetoothRadio<Platform>> bluetooth_radio)
+    : lock_(Platform::createLock()),
+      bluetooth_radio_(bluetooth_radio),
+      bluetooth_adapter_(Platform::createBluetoothAdapter()),
+      bluetooth_classic_medium_(Platform::createBluetoothClassicMedium()),
+      scan_info_(),
+      original_scan_mode_(BluetoothAdapter::ScanMode::UNKNOWN),
+      original_device_name_(),
+      accept_loops_thread_pool_(
+          Platform::createMultiThreadExecutor(kMaxConcurrentAcceptLoops)),
+      bluetooth_server_sockets_() {}
+
+template <typename Platform>
+BluetoothClassic<Platform>::~BluetoothClassic() {
+  stopDiscovery();
+  for (BluetoothServerSocketMap::iterator it =
+           bluetooth_server_sockets_.begin();
+       it != bluetooth_server_sockets_.end(); ++it) {
+    stopAcceptingConnections(it->first);
+  }
+  turnOffDiscoverability();
+
+  // All the AcceptLoopRunnable objects in here should already have gotten an
+  // opportunity to shut themselves down cleanly in the calls to
+  // stopAcceptingConnections() above.
+  accept_loops_thread_pool_->shutdown();
+
+  original_device_name_.destroy();
+  scan_info_.destroy();
+}
+
+template <typename Platform>
+bool BluetoothClassic<Platform>::isAvailable() {
+  Synchronized s(lock_.get());
+
+  return !bluetooth_classic_medium_.isNull() && !bluetooth_adapter_.isNull();
+}
+
+template <typename Platform>
+bool BluetoothClassic<Platform>::turnOnDiscoverability(
+    const string& device_name) {
+  Synchronized s(lock_.get());
+
+  if (device_name.empty()) {
+    // TODO(ahlee): logger.atSevere().log("Refusing to turn on Bluetooth
+    // discoverability because a null deviceName was passed in.");
+    return false;
+  }
+
+  if (!bluetooth_radio_->isEnabled()) {
+    // TODO(reznor): log.atSevere().log("Can't turn on Bluetooth discoverability
+    // because Bluetooth isn't enabled.");
+    return false;
+  }
+
+  if (!isAvailable()) {
+    // TODO(reznor): log.atSevere().log("Can't turn on Bluetooth discoverability
+    // because Bluetooth isn't available.");
+    return false;
+  }
+
+  if (isDiscoverable()) {
+    // TODO(reznor): log.atSevere().log("Refusing to turn on Bluetooth
+    // discoverability with device name %s because we're already discoverable
+    // with device name %s.", deviceName, bluetoothAdapter.getName());
+    return false;
+  }
+
+  if (!modifyDeviceName(device_name)) {
+    // TODO(reznor): log.atSevere().log("Failed to turn on Bluetooth
+    // discoverability because we couldn't set the device name to %s",
+    // deviceName);
+    return false;
+  }
+
+  if (!modifyScanMode(BluetoothAdapter::ScanMode::CONNECTABLE_DISCOVERABLE)) {
+    // TODO(reznor): log.atSevere().log("Failed to turn on Bluetooth
+    // discoverability because we couldn't set the scan mode to %d",
+    // BluetoothAdapter.SCAN_MODE_CONNECTABLE_DISCOVERABLE);
+
+    // Don't forget to perform this rollback of the partial state changes we've
+    // made til now.
+    restoreDeviceName();
+    return false;
+  }
+
+  // TODO(reznor): log.atVerbose().log("Turned on Bluetooth discoverability with
+  // deviceName %s", deviceName);
+  return true;
+}
+
+template <typename Platform>
+void BluetoothClassic<Platform>::turnOffDiscoverability() {
+  Synchronized s(lock_.get());
+
+  if (!isDiscoverable()) {
+    // TODO(reznor): log.atDebug().log("Can't turn off Bluetooth discoverability
+    // because it was never turned on.");
+    return;
+  }
+
+  restoreScanMode();
+  restoreDeviceName();
+
+  // TODO(reznor): log.atVerbose().log("Turned Bluetooth discoverability off");
+}
+
+template <typename Platform>
+bool BluetoothClassic<Platform>::isDiscoverable() const {
+  return ((!original_device_name_.isNull()) &&
+          (BluetoothAdapter::ScanMode::CONNECTABLE_DISCOVERABLE ==
+           bluetooth_adapter_->getScanMode()));
+}
+
+template <typename Platform>
+bool BluetoothClassic<Platform>::modifyDeviceName(const string& device_name) {
+  original_device_name_ = bluetooth_adapter_->getName();
+
+  if (!bluetooth_adapter_->setName(device_name)) {
+    original_device_name_.destroy();
+    return false;
+  }
+
+  return true;
+}
+
+template <typename Platform>
+bool BluetoothClassic<Platform>::modifyScanMode(
+    BluetoothAdapter::ScanMode::Value scan_mode) {
+  original_scan_mode_ = bluetooth_adapter_->getScanMode();
+
+  if (!bluetooth_adapter_->setScanMode(scan_mode)) {
+    original_scan_mode_ = BluetoothAdapter::ScanMode::UNKNOWN;
+    return false;
+  }
+
+  return true;
+}
+
+template <typename Platform>
+void BluetoothClassic<Platform>::restoreScanMode() {
+  if (!bluetooth_adapter_->setScanMode(original_scan_mode_)) {
+    // TODO(reznor): log.atWarning().log("Failed to restore original Bluetooth
+    // scan mode to %d", originalScanMode);
+  }
+
+  // Regardless of whether or not we could actually restore the Bluetooth scan
+  // mode, reset our relevant state.
+  original_scan_mode_ = BluetoothAdapter::ScanMode::UNKNOWN;
+}
+
+template <typename Platform>
+void BluetoothClassic<Platform>::restoreDeviceName() {
+  if (!bluetooth_adapter_->setName(*original_device_name_)) {
+    // TODO(reznor): log.atWarning().log("Failed to restore original Bluetooth
+    // device name to %s", originalDeviceName);
+  }
+
+  // Regardless of whether or not we could actually restore the Bluetooth device
+  // name, reset the marker that opens us up for business for the next time
+  // 'round.
+  original_device_name_.destroy();
+}
+
+template <typename Platform>
+bool BluetoothClassic<Platform>::startDiscovery(
+    Ptr<DiscoveredDeviceCallback> discovered_device_callback) {
+  Synchronized s(lock_.get());
+
+  if (discovered_device_callback.isNull()) {
+    // TODO(reznor): log.atSevere().log("Refusing to start discovery of
+    // Bluetooth devices because a null discoveredDeviceCallback was passed
+    // in.");
+    return false;
+  }
+  // Avoid leaks.
+  ScopedPtr<Ptr<DiscoveredDeviceCallback>> scoped_discovered_device_callback(
+      discovered_device_callback);
+
+  if (!bluetooth_radio_->isEnabled()) {
+    // TODO(reznor): log.atSevere().log("Can't discover Bluetooth devices
+    // because Bluetooth isn't enabled.");
+    return false;
+  }
+
+  if (!isAvailable()) {
+    // TODO(reznor): log.atSevere().log("Can't discover Bluetooth devices
+    // because Bluetooth isn't available.");
+    return false;
+  }
+
+  if (isDiscovering()) {
+    // TODO(reznor): log.atSevere().log("Refusing to start discovery of
+    // Bluetooth devices because another discovery is already in-progress.");
+    return false;
+  }
+
+  // Avoid leaks.
+  ScopedPtr<Ptr<BluetoothDiscoveryCallback>>
+      scoped_bluetooth_discovery_callback(new BluetoothDiscoveryCallback(
+          scoped_discovered_device_callback.get()));
+
+  if (!bluetooth_classic_medium_->startDiscovery(
+          scoped_bluetooth_discovery_callback.get())) {
+    // TODO(reznor): log.atSevere().log("Failed to start discovery of Bluetooth
+    // devices.");
+    return false;
+  }
+
+  // Mark the fact that we're currently performing a Bluetooth scan.
+  scan_info_ =
+      MakePtr(new ScanInfo(scoped_discovered_device_callback.release(),
+                           scoped_bluetooth_discovery_callback.release()));
+  return true;
+}
+
+template <typename Platform>
+void BluetoothClassic<Platform>::stopDiscovery() {
+  Synchronized s(lock_.get());
+
+  if (!isDiscovering()) {
+    // TODO(reznor): log.atDebug().log("Can't stop discovery of Bluetooth
+    // devices because it never started.");
+    return;
+  }
+
+  if (!bluetooth_classic_medium_->stopDiscovery()) {
+    // TODO(reznor): log.atWarning().log("Failed to stop discovery of Bluetooth
+    // devices.");
+  }
+  // Regardless of whether or not stopDiscovery() succeeded, destroy scan_info_
+  // to:
+  //
+  // a) Avoid a leak.
+  // b) Mark the fact that we're no longer performing a Bluetooth discovery.
+  scan_info_.destroy();
+}
+
+template <typename Platform>
+bool BluetoothClassic<Platform>::isDiscovering() const {
+  return !scan_info_.isNull();
+}
+
+template <typename Platform>
+class AcceptLoopRunnable : public Runnable {
+ public:
+  AcceptLoopRunnable(
+      Ptr<typename BluetoothClassic<Platform>::AcceptedConnectionCallback>
+          accepted_connection_callback,
+      Ptr<BluetoothServerSocket> listening_socket, const string& service_name)
+      : accepted_connection_callback_(accepted_connection_callback),
+        listening_socket_(listening_socket),
+        service_name_(service_name) {}
+
+  void run() override {
+    while (true) {
+      ExceptionOr<Ptr<BluetoothSocket>> bluetooth_socket =
+          listening_socket_->accept();
+      if (!bluetooth_socket.ok()) {
+        if (Exception::IO == bluetooth_socket.exception()) {
+          Utils::closeSocket(listening_socket_, "Bluetooth", service_name_);
+        }
+        break;
+      }
+
+      accepted_connection_callback_->onConnectionAccepted(
+          bluetooth_socket.result());
+    }
+  }
+
+ private:
+  ScopedPtr<
+      Ptr<typename BluetoothClassic<Platform>::AcceptedConnectionCallback>>
+      accepted_connection_callback_;
+  Ptr<BluetoothServerSocket> listening_socket_;
+  const string service_name_;
+};
+
+template <typename Platform>
+bool BluetoothClassic<Platform>::startAcceptingConnections(
+    const string& service_name,
+    Ptr<AcceptedConnectionCallback> accepted_connection_callback) {
+  Synchronized s(lock_.get());
+
+  // Avoid leaks.
+  ScopedPtr<Ptr<AcceptedConnectionCallback>>
+      scoped_accepted_connection_callback(accepted_connection_callback);
+  if (scoped_accepted_connection_callback.isNull() || service_name.empty()) {
+    // TODO(reznor): log.atSevere().log("Refusing to start accepting Bluetooth
+    // connections because at least one of serviceName or
+    // acceptedConnectionCallback is null.");
+    return false;
+  }
+
+  if (!bluetooth_radio_->isEnabled()) {
+    // TODO(reznor): log.atSevere().log("Can't create Bluetooth server socket
+    // for %s because Bluetooth isn't enabled.", serviceName);
+    return false;
+  }
+
+  if (!isAvailable()) {
+    // TODO(reznor): log.atSevere().log("Can't start accepting BLuetooth
+    // connections for %s because Bluetooth isn't available.", serviceName);
+    return false;
+  }
+
+  if (isAcceptingConnections(service_name)) {
+    // TODO(reznor): log.atSevere().log("Refusing to start accepting Bluetooth
+    // connections for %s because a Bluetooth server is already in-progress for
+    // that service name.", serviceName);
+    return false;
+  }
+
+  ExceptionOr<Ptr<BluetoothServerSocket>> listening_socket =
+      bluetooth_classic_medium_->listenForService(
+          service_name, generateUUIDFromString(service_name));
+  if (!listening_socket.ok()) {
+    if (Exception::IO == listening_socket.exception()) {
+      // TODO(reznor): log.atSevere().withCause(e).log("Failed to start
+      // accepting Bluetooth connections for %s.", serviceName);
+      return false;
+    }
+  }
+
+  // Start the accept loop on a dedicated thread - this stays alive and
+  // listening for new incoming connections until stopAcceptingConnections() is
+  // invoked.
+  accept_loops_thread_pool_->execute(MakePtr(new AcceptLoopRunnable<Platform>(
+      scoped_accepted_connection_callback.release(), listening_socket.result(),
+      service_name)));
+
+  // Mark the fact that there's an in-progress Bluetooth server accepting
+  // connections.
+  bluetooth_server_sockets_.insert(
+      std::make_pair(service_name, listening_socket.result()));
+  return true;
+}
+
+template <typename Platform>
+bool BluetoothClassic<Platform>::isAcceptingConnections(
+    const string& service_name) {
+  Synchronized s(lock_.get());
+
+  return bluetooth_server_sockets_.find(service_name) !=
+         bluetooth_server_sockets_.end();
+}
+
+template <typename Platform>
+void BluetoothClassic<Platform>::stopAcceptingConnections(
+    const string& service_name) {
+  Synchronized s(lock_.get());
+
+  if (service_name.empty()) {
+    // TODO(ahlee): logger.atSevere().log("Unable to stop accepting Bluetooth
+    // connections because the serviceName is empty.");
+    return;
+  }
+
+  if (!isAcceptingConnections(service_name)) {
+    // TODO(reznor): log.atDebug().log("Can't stop accepting Bluetooth
+    // connections for %s because it was never started.", serviceName);
+    return;
+  }
+
+  // Closing the BluetoothServerSocket will kick off the suicide of the thread
+  // in accept_loops_thread_pool_ that blocks on BluetoothServerSocket.accept().
+  // That may take some time to complete, but there's no particular reason to
+  // wait around for it.
+  BluetoothServerSocketMap::iterator listening_socket_iter =
+      bluetooth_server_sockets_.find(service_name);
+
+  // Store a handle to the BluetoothServerSocket, so we can use it after
+  // removing the entry from bluetooth_server_sockets_; making it scoped
+  // is a bonus that takes care of deallocation before we leave this method.
+  ScopedPtr<Ptr<BluetoothServerSocket>> scoped_listening_socket(
+      listening_socket_iter->second);
+
+  // Regardless of whether or not we fail to close the existing
+  // BluetoothServerSocket, remove it from bluetooth_server_sockets_ so that it
+  // frees up this service for another round.
+  bluetooth_server_sockets_.erase(listening_socket_iter);
+
+  // Finally, close the BluetoothServerSocket.
+  Exception::Value e = scoped_listening_socket->close();
+  if (Exception::NONE != e) {
+    if (Exception::IO == e) {
+      // TODO(reznor): log.atSevere().withCause(e).log("Failed to close
+      // Bluetooth server socket for %s.", serviceName);
+    }
+  }
+}
+
+template <typename Platform>
+Ptr<BluetoothSocket> BluetoothClassic<Platform>::connect(
+    Ptr<BluetoothDevice> bluetooth_device, const string& service_name) {
+  Synchronized s(lock_.get());
+
+  if (bluetooth_device.isNull() || service_name.empty()) {
+    // TODO(reznor): log.atSevere().log("Refusing to create client Bluetooth
+    // socket because at least one of bluetoothDevice or serviceName is null.");
+    return Ptr<BluetoothSocket>();
+  }
+
+  if (!bluetooth_radio_->isEnabled()) {
+    // TODO(reznor): log.atSevere().log("Can't create client Bluetooth socket to
+    // %s because Bluetooth isn't enabled.", bluetoothSocketName);
+    return Ptr<BluetoothSocket>();
+  }
+
+  if (!isAvailable()) {
+    // TODO(reznor): log.atSevere().log("Can't create client Bluetooth socket to
+    // %s because Bluetooth isn't available.", bluetoothSocketName);
+    return Ptr<BluetoothSocket>();
+  }
+
+  //                      WARNING WARNING WARNING
+  //
+  // This block deviates from the corresponding Java code.
+  //
+  // In Java, we pause an in-progress discovery before attempting this
+  // connection, and then resume it after, but the memory management of the
+  // DiscoveredDeviceCallback is complicated in C++, and would need a severe
+  // deviation from the Java code, so we're choosing the lesser of 2 evils, and
+  // introducing this (simplifying) deviation instead -- also, this deviation is
+  // fairly inconsequential since we don't yet have a use-case that needs a
+  // device that:
+  //
+  // a) uses the C++ code,
+  // b) has Bluetooth Classic support, and
+  // c) plays the role of Discoverer.
+  ExceptionOr<Ptr<BluetoothSocket>> bluetooth_socket =
+      bluetooth_classic_medium_->connectToService(
+          bluetooth_device, generateUUIDFromString(service_name));
+  if (!bluetooth_socket.ok()) {
+    if (Exception::IO == bluetooth_socket.exception()) {
+      // TODO(reznor): log.atSevere().log("Failed to connect via Bluetooth
+      // socket to %s.", bluetoothSocketName);
+    }
+    return Ptr<BluetoothSocket>();
+  }
+
+  return bluetooth_socket.result();
+}
+
+template <typename Platform>
+string BluetoothClassic<Platform>::generateUUIDFromString(const string& data) {
+  return UUID<Platform>(data).str();
+}
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/mediums/bluetooth_classic.h

@@ -0,0 +1,169 @@
+#ifndef CORE_INTERNAL_MEDIUMS_BLUETOOTH_CLASSIC_H_
+#define CORE_INTERNAL_MEDIUMS_BLUETOOTH_CLASSIC_H_
+
+#include <cstdint>
+#include <map>
+
+#include "core/internal/mediums/bluetooth_radio.h"
+#include "core/internal/mediums/utils.h"
+#include "platform/api/bluetooth_adapter.h"
+#include "platform/api/bluetooth_classic.h"
+#include "platform/api/lock.h"
+#include "platform/api/multi_thread_executor.h"
+#include "platform/byte_array.h"
+#include "platform/port/string.h"
+#include "platform/ptr.h"
+#include "platform/runnable.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+template <typename Platform>
+class BluetoothClassic {
+ public:
+  explicit BluetoothClassic(Ptr<BluetoothRadio<Platform>> bluetooth_radio);
+  ~BluetoothClassic();
+
+  bool isAvailable();
+
+  bool turnOnDiscoverability(const string& device_name);
+  void turnOffDiscoverability();
+
+  // Callback that is invoked when a nearby Bluetooth device is discovered.
+  class DiscoveredDeviceCallback {
+   public:
+    virtual ~DiscoveredDeviceCallback() {}
+
+    virtual void onDeviceDiscovered(Ptr<BluetoothDevice> device) = 0;
+    virtual void onDeviceNameChanged(Ptr<BluetoothDevice> device) = 0;
+    virtual void onDeviceLost(Ptr<BluetoothDevice> device) = 0;
+  };
+
+  bool startDiscovery(Ptr<DiscoveredDeviceCallback> discovered_device_callback);
+  void stopDiscovery();
+
+  // Callback that is invoked when a new connection is accepted.
+  class AcceptedConnectionCallback {
+   public:
+    virtual ~AcceptedConnectionCallback() {}
+
+    virtual void onConnectionAccepted(Ptr<BluetoothSocket> socket) = 0;
+  };
+
+  bool startAcceptingConnections(
+      const string& service_name,
+      Ptr<AcceptedConnectionCallback> accepted_connection_callback);
+  bool isAcceptingConnections(const string& service_name);
+  void stopAcceptingConnections(const string& service_name);
+
+  Ptr<BluetoothSocket> connect(Ptr<BluetoothDevice> bluetooth_device,
+                               const string& service_name);
+
+ private:
+  class BluetoothDiscoveryCallback
+      : public BluetoothClassicMedium::DiscoveryCallback {
+   public:
+    explicit BluetoothDiscoveryCallback(
+        Ptr<DiscoveredDeviceCallback> discovered_device_callback)
+        : discovered_device_callback_(discovered_device_callback) {}
+    ~BluetoothDiscoveryCallback() override {
+      // Nothing to do.
+    }
+
+    void onDeviceDiscovered(Ptr<BluetoothDevice> bluetooth_device) override {
+      discovered_device_callback_->onDeviceDiscovered(bluetooth_device);
+    }
+    void onDeviceNameChanged(Ptr<BluetoothDevice> bluetooth_device) override {
+      discovered_device_callback_->onDeviceNameChanged(bluetooth_device);
+    }
+    void onDeviceLost(Ptr<BluetoothDevice> bluetooth_device) override {
+      discovered_device_callback_->onDeviceLost(bluetooth_device);
+    }
+
+   private:
+    // This could well have been a ScopedPtr, with BluetoothDiscoveryCallback in
+    // turn being owned by ScanInfo (and it would have been cleaner overall,
+    // since the chain of wrapped callbacks starting from
+    // BluetoothDiscoveryCallback would then destruct like a stack of dominoes
+    // falling, triggered by the destruction of ScanInfo), but we instead give
+    // ownership of this DiscoveredDeviceCallback *and*
+    // BluetoothDiscoveryCallback to ScanInfo, to maintain compatibility with
+    // the Java code.
+    Ptr<DiscoveredDeviceCallback> discovered_device_callback_;
+  };
+
+  struct ScanInfo {
+    ScanInfo(Ptr<DiscoveredDeviceCallback> discovered_device_callback,
+             Ptr<BluetoothDiscoveryCallback> bluetooth_discovery_callback)
+        : discovered_device_callback(discovered_device_callback),
+          bluetooth_discovery_callback(bluetooth_discovery_callback) {}
+    ~ScanInfo() {
+      // Nothing to do (the ScopedPtr members take care of themselves).
+    }
+
+    // Stores the DiscoveredDeviceCallback passed in to startDiscovery() by
+    // clients so that we can internally stop and start Bluetooth scans
+    // transparently as needed (for example, when a call to connect() is
+    // invoked).
+    ScopedPtr<Ptr<DiscoveredDeviceCallback>> discovered_device_callback;
+    // The ordering of bluetooth_discovery_callback_ coming after
+    // discovered_device_callback_ is very deliberate --
+    // bluetooth_discovery_callback_ contains a reference to
+    // discovered_device_callback_, so it should be destroyed first.
+    ScopedPtr<Ptr<BluetoothDiscoveryCallback>> bluetooth_discovery_callback;
+  };
+
+  static string generateUUIDFromString(const string& data);
+
+  static const std::int32_t kMaxConcurrentAcceptLoops;
+
+  bool isDiscoverable() const;
+  bool modifyDeviceName(const string& device_name);
+  bool modifyScanMode(BluetoothAdapter::ScanMode::Value scan_mode);
+  void restoreScanMode();
+  void restoreDeviceName();
+  bool isDiscovering() const;
+
+  // ------------ GENERAL ------------
+
+  ScopedPtr<Ptr<Lock>> lock_;
+
+  // ------------ CORE BLUETOOTH ------------
+
+  Ptr<BluetoothRadio<Platform>> bluetooth_radio_;
+  ScopedPtr<Ptr<BluetoothAdapter>> bluetooth_adapter_;
+  // The underlying, per-platform implementation.
+  ScopedPtr<Ptr<BluetoothClassicMedium>> bluetooth_classic_medium_;
+
+  // ------------ DISCOVERY ------------
+
+  // A bundle of state required to do a Bluetooth Classic scan. When non-null,
+  // we are currently performing a Bluetooth scan.
+  Ptr<ScanInfo> scan_info_;
+
+  // ------------ ADVERTISING ------------
+
+  // The original scan mode (that controls visibility to scanners) of the device
+  // before we modified it. Restored when we stop advertising.
+  BluetoothAdapter::ScanMode::Value original_scan_mode_;
+  // The original Bluetooth device name, before we modified it. If non-null, we
+  // are currently Bluetooth discoverable. Restored when we stop advertising.
+  Ptr<string> original_device_name_;
+  // A thread pool dedicated to running all the accept loops from
+  // startAcceptingConnections().
+  ScopedPtr<Ptr<typename Platform::MultiThreadExecutorType>>
+      accept_loops_thread_pool_;
+  // A map of service name -> ServerSocket. While this map is non-empty, we
+  // are currently listening for incoming connections.
+  typedef std::map<string, Ptr<BluetoothServerSocket>> BluetoothServerSocketMap;
+  BluetoothServerSocketMap bluetooth_server_sockets_;
+};
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#include "core/internal/mediums/bluetooth_classic.cc"
+
+#endif  // CORE_INTERNAL_MEDIUMS_BLUETOOTH_CLASSIC_H_

cpp/core/internal/mediums/bluetooth_radio.cc

@@ -0,0 +1,122 @@
+#include "core/internal/mediums/bluetooth_radio.h"
+
+#include "platform/exception.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+template <typename Platform>
+std::int64_t BluetoothRadio<Platform>::kPauseBetweenToggleDurationMillis = 3000;
+
+template <typename Platform>
+BluetoothRadio<Platform>::BluetoothRadio()
+    : bluetooth_adapter_(Platform::createBluetoothAdapter()),
+      thread_utils_(Platform::createThreadUtils()),
+      originally_enabled_() {
+  if (bluetooth_adapter_.isNull()) {
+    // TODO(reznor): log.atSevere().log("Failed to retrieve default
+    // BluetoothAdapter, Bluetooth is unsupported.");
+  }
+}
+
+template <typename Platform>
+BluetoothRadio<Platform>::~BluetoothRadio() {
+  // We never enabled Bluetooth, nothing to do.
+  if (originally_enabled_.isNull()) {
+    return;
+  }
+
+  // Make sure we cleanup the one non-ScopedPtr member before we leave the
+  // destructor.
+  ScopedPtr<Ptr<AtomicBoolean> > scoped_originally_enabled(originally_enabled_);
+
+  // Toggle Bluetooth regardless of our original state. Some devices/chips can
+  // start to freak out after some time (e.g. b/37775337), and this helps to
+  // ensure BT resets properly.
+  toggle();
+
+  if (!setBluetoothState(originally_enabled_->get())) {
+    // TODO(reznor): log.atWarning().log("Failed to turn Bluetooth back to its
+    // original state.");
+  }
+}
+
+template <typename Platform>
+bool BluetoothRadio<Platform>::enable() {
+  if (!saveOriginalState()) {
+    return false;
+  }
+
+  return setBluetoothState(true);
+}
+
+template <typename Platform>
+bool BluetoothRadio<Platform>::disable() {
+  if (!saveOriginalState()) {
+    return false;
+  }
+
+  return setBluetoothState(false);
+}
+
+template <typename Platform>
+bool BluetoothRadio<Platform>::isEnabled() {
+  return !bluetooth_adapter_.isNull() && isInDesiredState(true);
+}
+
+template <typename Platform>
+void BluetoothRadio<Platform>::toggle() {
+  if (!saveOriginalState()) {
+    return;
+  }
+
+  if (!setBluetoothState(false)) {
+    // TODO(reznor): log.atWarning().log("Failed to turn Bluetooth off while
+    // toggling state.");
+  }
+
+  if (Exception::INTERRUPTED ==
+      thread_utils_->sleep(kPauseBetweenToggleDurationMillis)) {
+    // TODO(reznor): log.atSevere().withCause(e).log("Interrupted while waiting
+    // in between a Bluetooth toggle.");
+    return;
+  }
+
+  if (!setBluetoothState(true)) {
+    // TODO(reznor): log.atWarning().log("Failed to turn Bluetooth on while
+    // toggling state.");
+  }
+}
+
+template <typename Platform>
+bool BluetoothRadio<Platform>::setBluetoothState(bool enable) {
+  return bluetooth_adapter_->setStatus(
+      enable ? BluetoothAdapter::Status::ENABLED
+             : BluetoothAdapter::Status::DISABLED);
+}
+
+template <typename Platform>
+bool BluetoothRadio<Platform>::isInDesiredState(bool should_be_enabled) const {
+  return ((should_be_enabled && bluetooth_adapter_->isEnabled()) ||
+          (!should_be_enabled && !bluetooth_adapter_->isEnabled()));
+}
+
+template <typename Platform>
+bool BluetoothRadio<Platform>::saveOriginalState() {
+  if (bluetooth_adapter_.isNull()) {
+    return false;
+  }
+
+  // If we haven't saved the original state of the radio, save it.
+  if (originally_enabled_.isNull()) {
+    originally_enabled_ =
+        Platform::createAtomicBoolean(bluetooth_adapter_->isEnabled());
+  }
+
+  return true;
+}
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/mediums/bluetooth_radio.h

@@ -0,0 +1,69 @@
+#ifndef CORE_INTERNAL_MEDIUMS_BLUETOOTH_RADIO_H_
+#define CORE_INTERNAL_MEDIUMS_BLUETOOTH_RADIO_H_
+
+#include <cstdint>
+
+#include "platform/api/atomic_boolean.h"
+#include "platform/api/bluetooth_adapter.h"
+#include "platform/api/thread_utils.h"
+#include "platform/ptr.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+// Provides the operations that can be performed on the Bluetooth radio.
+template <typename Platform>
+class BluetoothRadio {
+ public:
+  BluetoothRadio();
+  // Reverts the Bluetooth radio to its original state.
+  ~BluetoothRadio();
+
+  // Enables Bluetooth.
+  //
+  // This must be called before attempting to invoke any other methods of
+  // this class.
+  //
+  // Returns true if enabled successfully.
+  bool enable();
+  // Disables Bluetooth.
+  //
+  // Returns true if disabled successfully.
+  bool disable();
+  // Returns true if the Bluetooth radio is currently enabled.
+  bool isEnabled();
+
+  void toggle();
+
+ private:
+  static std::int64_t kPauseBetweenToggleDurationMillis;
+
+  bool setBluetoothState(bool enable);
+  bool isInDesiredState(bool should_be_enabled) const;
+  // To be called in enable(), disable(), and toggle(). This will remember the
+  // original state of the radio before any radio state has been modified.
+  // Returns false if Bluetooth doesn't exist on the device and the state cannot
+  // be obtained.
+  bool saveOriginalState();
+
+  // Null if the device does not support Bluetooth.
+  ScopedPtr<Ptr<BluetoothAdapter>> bluetooth_adapter_;
+  ScopedPtr<Ptr<ThreadUtils>> thread_utils_;
+  // The Bluetooth radio's original state, before we modified it. True if
+  // originally enabled, false if originally disabled, null if we never modified
+  // the radio state. We restore the radio to its original state in the
+  // destructor.
+  //
+  // This is a Ptr instead of a ScopedPtr because it's lazily initialized
+  // (and ScopedPtr doesn't support re-assignment).
+  Ptr<AtomicBoolean> originally_enabled_;
+};
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#include "core/internal/mediums/bluetooth_radio.cc"
+
+#endif  // CORE_INTERNAL_MEDIUMS_BLUETOOTH_RADIO_H_

cpp/core/internal/mediums/discovered_peripheral_callback.h

@@ -0,0 +1,32 @@
+#ifndef CORE_INTERNAL_MEDIUMS_DISCOVERED_PERIPHERAL_CALLBACK_H_
+#define CORE_INTERNAL_MEDIUMS_DISCOVERED_PERIPHERAL_CALLBACK_H_
+
+#include "core/internal/mediums/ble_peripheral.h"
+#include "platform/byte_array.h"
+#include "platform/port/string.h"
+#include "platform/ptr.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+namespace mediums {
+
+/** Callback that is invoked when a {@link BLEPeripheral} is discovered. */
+class DiscoveredPeripheralCallback {
+ public:
+  virtual ~DiscoveredPeripheralCallback() {}
+
+  virtual void onPeripheralDiscovered(Ptr<BLEPeripheral> ble_peripheral,
+                                      const string& service_id,
+                                      ConstPtr<ByteArray> advertisement,
+                                      bool is_fast_advertisement) = 0;
+  virtual void onPeripheralLost(Ptr<BLEPeripheral> ble_peripheral,
+                                const string& service_id);
+};
+
+}  // namespace mediums
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#endif  // CORE_INTERNAL_MEDIUMS_DISCOVERED_PERIPHERAL_CALLBACK_H_

cpp/core/internal/mediums/discovered_peripheral_tracker.cc

@@ -0,0 +1,744 @@
+#include "core/internal/mediums/discovered_peripheral_tracker.h"
+
+#include "core/internal/mediums/ble_packet.h"
+#include "core/internal/mediums/bloom_filter.h"
+#include "core/internal/mediums/utils.h"
+#include "platform/synchronized.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+namespace mediums {
+
+namespace dpt {
+
+template <typename K, typename V>
+void eraseOwnedPtrFromMap(std::map<K, V>& m, const K& k) {
+  typename std::map<K, V>::iterator it = m.find(k);
+  if (it != m.end()) {
+    it->second.destroy();
+    m.erase(it);
+  }
+}
+
+template <typename K, typename V>
+void eraseAllOwnedPtrsFromMap(std::map<K, Ptr<V>>& m) {
+  for (typename std::map<K, Ptr<V>>::iterator it = m.begin(); it != m.end();
+       ++it) {
+    it->second.destroy();
+  }
+  m.clear();
+}
+
+template <typename K, typename V>
+V removeOwnedPtrFromMap(std::map<K, V>& m, const K& k) {
+  V removed_ptr;
+  typename std::map<K, V>::iterator it = m.find(k);
+  if (it != m.end()) {
+    removed_ptr = it->second;
+    m.erase(it);
+  }
+  return removed_ptr;
+}
+
+}  // namespace dpt
+
+// The maximum number of advertisement slots to assume if we don't know the
+// exact number.
+template <typename Platform>
+const std::int32_t DiscoveredPeripheralTracker<Platform>::kMaxSlots = 10;
+
+// Amount of time to wait before attempting a connection. This is needed to
+// prevent the GATT server from operation overload if we just came from a GATT
+// discovery.
+template <typename Platform>
+const std::int64_t
+    DiscoveredPeripheralTracker<Platform>::kMinConnectionDelayMillis =
+        5 * 1000;  // 5 seconds
+
+template <typename Platform>
+const char* DiscoveredPeripheralTracker<Platform>::kCopresenceServiceUuid =
+    "0000FEF3-0000-1000-8000-00805F9B34FB";
+
+template <typename Platform>
+DiscoveredPeripheralTracker<Platform>::DiscoveredPeripheralTracker()
+    : lock_(Platform::createLock()),
+      thread_utils_(Platform::createThreadUtils()),
+      system_clock_(Platform::createSystemClock()),
+      hash_utils_(Platform::createHashUtils()),
+      discovered_peripheral_callbacks_(),
+      lost_entity_trackers_(),
+      fast_advertisement_service_uuids_(),
+      advertisement_read_results_(),
+      gatt_advertisements_(),
+      advertisement_service_ids_(),
+      advertisement_headers_(),
+      mac_addresses_() {}
+
+template <typename Platform>
+DiscoveredPeripheralTracker<Platform>::~DiscoveredPeripheralTracker() {
+  Synchronized s(lock_.get());
+
+  mac_addresses_.clear();
+  advertisement_headers_.clear();
+  advertisement_service_ids_.clear();
+  // gatt_advertisements_ maps a string to a Ptr to a set of ConstPtrs. We do
+  // not go and iterate through every set because those values are RefCounted.
+  dpt::eraseAllOwnedPtrsFromMap(gatt_advertisements_);
+  dpt::eraseAllOwnedPtrsFromMap(advertisement_read_results_);
+  fast_advertisement_service_uuids_.clear();
+  dpt::eraseAllOwnedPtrsFromMap(lost_entity_trackers_);
+  dpt::eraseAllOwnedPtrsFromMap(discovered_peripheral_callbacks_);
+}
+
+// Starts tracking discoveries for a particular service ID.
+template <typename Platform>
+void DiscoveredPeripheralTracker<Platform>::startTracking(
+    const string& service_id,
+    Ptr<DiscoveredPeripheralCallback> discovered_peripheral_callback,
+    const string& fast_advertisement_service_uuid) {
+  Synchronized s(lock_.get());
+
+  dpt::eraseOwnedPtrFromMap(discovered_peripheral_callbacks_, service_id);
+  discovered_peripheral_callbacks_.insert(
+      std::make_pair(service_id, discovered_peripheral_callback));
+
+  // We create a new LostEntityTracker because any pre-existing ones only
+  // contain stale advertisements. LostEntityTracker also doesn't provide a
+  // reset method, so creating a new one is the right way to go.
+  dpt::eraseOwnedPtrFromMap(lost_entity_trackers_, service_id);
+  lost_entity_trackers_.insert(std::make_pair(
+      service_id,
+      MakePtr(new LostEntityTracker<Platform, BLEAdvertisement>())));
+
+  if (!fast_advertisement_service_uuid.empty()) {
+    fast_advertisement_service_uuids_.erase(service_id);
+    fast_advertisement_service_uuids_.insert(
+        std::make_pair(service_id, fast_advertisement_service_uuid));
+  }
+
+  // Clear all of the GATT read results. With this cleared, we will now attempt
+  // to reconnect to every peripheral we see, giving us a chance to search for
+  // the new service we're now tracking.
+  // See the documentation of advertisementReadResults for more information.
+  dpt::eraseAllOwnedPtrsFromMap(advertisement_read_results_);
+
+  // Remove stale data from any previous sessions.
+  clearDataForServiceId(service_id);
+}
+
+// Stops tracking discoveries for a particular service ID.
+template <typename Platform>
+void DiscoveredPeripheralTracker<Platform>::stopTracking(
+    const string& service_id) {
+  Synchronized s(lock_.get());
+
+  fast_advertisement_service_uuids_.erase(service_id);
+  dpt::eraseOwnedPtrFromMap(lost_entity_trackers_, service_id);
+  dpt::eraseOwnedPtrFromMap(discovered_peripheral_callbacks_, service_id);
+}
+
+// Processes a found BLE advertisement.
+template <typename Platform>
+void DiscoveredPeripheralTracker<Platform>::processFoundBleAdvertisement(
+    Ptr<BLEPeripheralV2> ble_peripheral,
+    ConstPtr<BLEAdvertisementData> advertisement_data,
+    Ptr<GattAdvertisementFetcher> gatt_advertisement_fetcher) {
+  Synchronized s(lock_.get());
+
+  // Avoid leaks.
+  ScopedPtr<ConstPtr<BLEAdvertisementData>> scoped_advertisement_data(
+      advertisement_data);
+  ScopedPtr<Ptr<GattAdvertisementFetcher>> scoped_gatt_advertisement_fetcher(
+      gatt_advertisement_fetcher);
+
+  if (getTrackedServiceIds().empty()) {
+    // TODO(ahlee) logger.atVerbose().log("Ignoring BLE advertisement header
+    // because we are not tracking any service IDs.");
+    return;
+  }
+
+  if (ble_peripheral.isNull() || scoped_advertisement_data.isNull()) {
+    // TODO(ahlee) logger.atVerbose().log("Ignoring BLE advertisement header
+    // because the given BleSighting is null or incomplete.");
+    return;
+  }
+
+  handleFastAdvertisement(ble_peripheral, scoped_advertisement_data.get());
+  handleAdvertisementHeader(ble_peripheral, scoped_advertisement_data.get(),
+                            scoped_gatt_advertisement_fetcher.get());
+}
+
+// Processes the set of lost GATT advertisements and notifies the client of any
+// lost peripherals.
+template <typename Platform>
+void DiscoveredPeripheralTracker<Platform>::processLostGattAdvertisements() {
+  Synchronized s(lock_.get());
+
+  std::set<string> tracked_service_ids = getTrackedServiceIds();
+  for (typename std::set<string>::iterator tsi_it = tracked_service_ids.begin();
+       tsi_it != tracked_service_ids.end(); ++tsi_it) {
+    BLEAdvertisementSet lost_gatt_advertisements =
+        lost_entity_trackers_.find(*tsi_it)->second->computeLostEntities();
+
+    // Clear the map state for each lost GATT advertisement and report it to the
+    // client.
+    for (BLEAdvertisementSet::iterator lga_it =
+             lost_gatt_advertisements.begin();
+         lga_it != lost_gatt_advertisements.end(); ++lga_it) {
+      clearGattAdvertisement(*lga_it);
+      discovered_peripheral_callbacks_.find(*tsi_it)->second->onPeripheralLost(
+          generateBlePeripheral(*lga_it), *tsi_it);
+    }
+  }
+}
+
+template <typename Platform>
+Ptr<BLEPeripheral> DiscoveredPeripheralTracker<Platform>::generateBlePeripheral(
+    ConstPtr<BLEAdvertisement> gatt_advertisement) {
+  // TODO(ahlee): Reminder to port over deviceToken change.
+  return MakePtr(new BLEPeripheral(BLEAdvertisement::toBytes(
+      gatt_advertisement->getVersion(), gatt_advertisement->getSocketVersion(),
+      gatt_advertisement->getServiceIdHash(), gatt_advertisement->getData())));
+}
+
+template <typename Platform>
+std::set<string> DiscoveredPeripheralTracker<Platform>::getTrackedServiceIds() {
+  std::set<string> tracked_service_ids;
+  for (DiscoveredPeripheralCallbackMap::iterator dpc_it =
+           discovered_peripheral_callbacks_.begin();
+       dpc_it != discovered_peripheral_callbacks_.end(); ++dpc_it) {
+    tracked_service_ids.insert(dpc_it->first);
+  }
+  return tracked_service_ids;
+}
+
+// Note: There is no C++ equivalent for getTrackedGattAdvertisements() because
+// we make a copy of the subset of the keys in directly in
+// clearDataForServiceId().
+
+template <typename Platform>
+void DiscoveredPeripheralTracker<Platform>::clearDataForServiceId(
+    const string& service_id) {
+  BLEAdvertisementSet gatt_advertisements_to_clear;
+  for (AdvertisementServiceIdMap::iterator it =
+           advertisement_service_ids_.begin();
+       it != advertisement_service_ids_.end(); ++it) {
+    if (it->second != service_id) {
+      continue;
+    }
+    gatt_advertisements_to_clear.insert(it->first);
+  }
+
+  for (BLEAdvertisementSet::iterator it = gatt_advertisements_to_clear.begin();
+       it != gatt_advertisements_to_clear.end(); ++it) {
+    clearGattAdvertisement(*it);
+  }
+}
+
+// Clears out all data related to the provided GATT advertisement. This
+// includes:
+//   1. Removing the GATT advertisement from GATT advertisement keyed maps. This
+//      includes advertisementServiceIds, AdvertisementHeaders, and
+//      macAddresses.
+//   2. Removing the corresponding advertisement header from
+//      advertisementReadResults.
+//   3. Removing the corresponding advertisement header from gattAdvertisements,
+//      only if there are no remaining GATT advertisements related to that
+//      header.
+template <typename Platform>
+void DiscoveredPeripheralTracker<Platform>::clearGattAdvertisement(
+    ConstPtr<BLEAdvertisement> gatt_advertisement) {
+  // BLEAdvertisement is RefCounted, so it does not need to be scoped.
+  advertisement_service_ids_.erase(gatt_advertisement);
+  mac_addresses_.erase(gatt_advertisement);
+
+  ConstPtr<BLEAdvertisementHeader> advertisement_header =
+      dpt::removeOwnedPtrFromMap(advertisement_headers_, gatt_advertisement);
+  typename GattAdvertisementMap::iterator ga_it =
+      gatt_advertisements_.find(advertisement_header);
+  if (ga_it != gatt_advertisements_.end()) {
+    // Remove the GATT advertisement from the advertisement header it's
+    // associated with.
+    Ptr<BLEAdvertisementSet> header_gatt_advertisements = ga_it->second;
+    header_gatt_advertisements->erase(gatt_advertisement);
+
+    // Unconditionally remove the header from advertisementReadResults so we
+    // can attempt to reread the GATT advertisement if they return.
+    dpt::eraseOwnedPtrFromMap(advertisement_read_results_,
+                              advertisement_header);
+
+    // If there are no more tracked GATT advertisements under this header, go
+    // ahead and remove it from gattAdvertisements.
+    if (header_gatt_advertisements->empty()) {
+      dpt::eraseOwnedPtrFromMap(gatt_advertisements_, advertisement_header);
+    }
+  }
+}
+
+template <typename Platform>
+void DiscoveredPeripheralTracker<Platform>::handleFastAdvertisement(
+    Ptr<BLEPeripheralV2> ble_peripheral,
+    ConstPtr<BLEAdvertisementData> advertisement_data) {
+  // Extract the fast advertisement bytes, if any.
+  ScopedPtr<ConstPtr<ByteArray>> fast_advertisement_bytes(
+      extractFastAdvertisementBytes(advertisement_data));
+  if (fast_advertisement_bytes.isNull()) {
+    return;
+  }
+
+  // Create a header tied to this fast advertisement. This helps us track the
+  // advertisement when reporting it as lost or connecting.
+  /* RefCounted */ ConstPtr<BLEAdvertisementHeader> fast_advertisement_header =
+      createFastAdvertisementHeader(fast_advertisement_bytes.get());
+
+  // Process the fast advertisement like we would a GATT advertisement and
+  // insert a placeholder AdvertisementReadResult.
+  dpt::eraseOwnedPtrFromMap(advertisement_read_results_,
+                            fast_advertisement_header);
+  advertisement_read_results_.insert(
+      std::make_pair(fast_advertisement_header,
+                     MakePtr(new AdvertisementReadResult<Platform>())));
+
+  std::set<ConstPtr<ByteArray>> fast_advertisement_bytes_set;
+  fast_advertisement_bytes_set.insert(fast_advertisement_bytes.get());
+  handleRawGattAdvertisements(fast_advertisement_header,
+                              fast_advertisement_bytes_set,
+                              /* are_fast_advertisements= */ true);
+  updateCommonStateForFoundBleAdvertisement(fast_advertisement_header,
+                                            ble_peripheral->getId());
+}
+
+template <typename Platform>
+void DiscoveredPeripheralTracker<Platform>::handleAdvertisementHeader(
+    Ptr<BLEPeripheralV2> ble_peripheral,
+    ConstPtr<BLEAdvertisementData> advertisement_data,
+    Ptr<GattAdvertisementFetcher> gatt_advertisement_fetcher) {
+  // Attempt to parse the advertisement header.
+  /* RefCounted */ ConstPtr<BLEAdvertisementHeader> advertisement_header =
+      BLEAdvertisementHeader::fromString(
+          extractAdvertisementHeaderBytes(ble_peripheral, advertisement_data));
+  if (advertisement_header.isNull()) {
+    // TODO(ahlee) logger.atVerbose().log("Failed to deserialize BLE
+    // advertisement header %s. Ignoring.",
+    // bytesToString(advertisementHeaderBytes));
+    return;
+  }
+
+  // Check if the advertisement header contains a service ID we're tracking.
+  if (!isInterestingAdvertisementHeader(advertisement_header)) {
+    // TODO(ahlee) logger.atVerbose().log("Ignoring BLE advertisement header %s
+    // because it does not contain any service IDs we're interested in.",
+    // advertisementHeader);
+    return;
+  }
+
+  // Determine whether or not we need to read a fresh GATT advertisement.
+  if (shouldReadFromAdvertisementGattServer(advertisement_header)) {
+    // Determine whether or not we need to read a fresh GATT advertisement.
+    std::set<ConstPtr<ByteArray>> raw_gatt_advertisements =
+        fetchRawGattAdvertisements(ble_peripheral, advertisement_header,
+                                   gatt_advertisement_fetcher);
+    if (!raw_gatt_advertisements.empty()) {
+      handleRawGattAdvertisements(advertisement_header, raw_gatt_advertisements,
+                                  /* are_fast_advertisements= */ false);
+    }
+  }
+
+  // Regardless of whether or not we read a new GATT advertisement, the maps
+  // should now be up-to-date. With this information, do some general
+  // housekeeping.
+  updateCommonStateForFoundBleAdvertisement(
+      advertisement_header, /* mac_address= */ ble_peripheral->getId());
+}
+
+template <typename Platform>
+string DiscoveredPeripheralTracker<Platform>::extractAdvertisementHeaderBytes(
+    Ptr<BLEPeripheralV2> ble_peripheral,
+    ConstPtr<BLEAdvertisementData> advertisement_data) {
+  ConstPtr<ByteArray> service_data;
+  std::map<string, ConstPtr<ByteArray>>::const_iterator sd_it =
+      advertisement_data->service_data.find(kCopresenceServiceUuid);
+  if (sd_it != advertisement_data->service_data.end()) {
+    service_data = sd_it->second;
+  }
+  const string& local_name = advertisement_data->local_name;  // alias
+
+  // A valid advertisement header lives in either the local name (iOS) or the
+  // service data (Android).
+  if (!service_data.isNull()) {
+    // TODO(ahlee) logger.atVerbose().log("Service data found on possible
+    // Android BLE peripheral at address %s",
+    // bleSighting.getDevice().getAddress());
+    return string(service_data->getData(), service_data->size());
+  } else if (!local_name.empty()) {
+    // TODO(ahlee) logger.atVerbose().log("Local name found on possible iOS BLE
+    // peripheral at address %s", bleSighting.getDevice().getAddress());
+    return local_name;
+  } else {
+    // iOS peripherals have a bug where the local name sometimes doesn't appear.
+    // In that case, we should still take a look at the advertisement in case
+    // there's something valuable on the peripheral's GATT server.
+
+    // TODO(ahlee) logger.atVerbose().log("BLE advertisement found with no
+    // service data or local name from BLE peripheral at address %s (could be a
+    // buggy iOS peripheral with a missing local name).",
+    // bleSighting.getDevice().getAddress());
+
+    // Create a phony BloomFilter that always contains the service ID we're
+    // looking for.
+    return createDummyAdvertisementHeaderBytes(ble_peripheral);
+  }
+}
+
+template <typename Platform>
+ConstPtr<ByteArray>
+DiscoveredPeripheralTracker<Platform>::extractFastAdvertisementBytes(
+    ConstPtr<BLEAdvertisementData> advertisement_data) {
+  ConstPtr<ByteArray> fast_advertisement_bytes;
+  // Iterate through all tracked service IDs to see if any of their fast
+  // advertisements are contained within this BLE advertisement.
+  std::set<string> tracked_service_ids = getTrackedServiceIds();
+  for (typename std::set<string>::iterator tsi_it = tracked_service_ids.begin();
+       tsi_it != tracked_service_ids.end(); ++tsi_it) {
+    // First, check if a service UUID is tied to this service ID.
+    typename FastAdvertisementServiceUUIDMap::iterator fasu_it =
+        fast_advertisement_service_uuids_.find(*tsi_it);
+    if (fasu_it != fast_advertisement_service_uuids_.end()) {
+      const string& fast_advertisement_service_uuid = fasu_it->second;  // alias
+
+      // Then, check if there's service data for this fast advertisement
+      // service UUID. If so, we can short-circuit since all BLE
+      // advertisements can contain at most ONE fast advertisement.
+      typename std::map<string, ConstPtr<ByteArray>>::const_iterator sd_it =
+          advertisement_data->service_data.find(
+              fast_advertisement_service_uuid);
+      if (sd_it != advertisement_data->service_data.end()) {
+        // TODO(b/117432693): Remove this copy once Ptr is fully RefCounted.
+        fast_advertisement_bytes = MakeConstPtr(
+            new ByteArray(sd_it->second->getData(), sd_it->second->size()));
+        break;
+      }
+    }
+  }
+  return fast_advertisement_bytes;
+}
+
+// Creates an advertisement header that's purely a hash of the fast
+// advertisement, since they come with no header.
+template <typename Platform>
+/* RefCounted */ ConstPtr<BLEAdvertisementHeader>
+DiscoveredPeripheralTracker<Platform>::createFastAdvertisementHeader(
+    ConstPtr<ByteArray> fast_advertisement_bytes) {
+  // Our end goal is to have a fully zeroed-out byte array of the correct length
+  // representing an empty bloom filter.
+  // TODO(b/149938110): remove ScopedPtr.
+  ScopedPtr<ConstPtr<ByteArray>> bloom_filter_bytes{ConstPtr<ByteArray>{
+      new ByteArray{BLEAdvertisementHeader::kServiceIdBloomFilterLength}}};
+
+  ScopedPtr<ConstPtr<ByteArray>> advertisement_hash(
+      generateAdvertisementHash(fast_advertisement_bytes));
+  return MakeRefCountedConstPtr(new BLEAdvertisementHeader(
+      BLEAdvertisementHeader::Version::V2, /* num_slots= */ 1,
+      bloom_filter_bytes.get(), advertisement_hash.get()));
+}
+
+// Creates a dummy advertisement header that possibly contains all tracked
+// service IDs.
+template <typename Platform>
+string
+DiscoveredPeripheralTracker<Platform>::createDummyAdvertisementHeaderBytes(
+    Ptr<BLEPeripheralV2> ble_peripheral) {
+  // Put the service ID along with the dummy service ID into our bloom filter
+  // Note: BloomFilter length should always match
+  // BLEAdvertisementHeader::kServiceIdBloomFilterLength
+  ScopedPtr<Ptr<BloomFilter<10>>> bloom_filter(new BloomFilter<10>());
+
+  std::set<string> tracked_service_ids = getTrackedServiceIds();
+  for (typename std::set<string>::iterator tsi_it = tracked_service_ids.begin();
+       tsi_it != tracked_service_ids.end(); ++tsi_it) {
+    bloom_filter->add(*tsi_it);
+  }
+
+  const string& ble_peripheral_id = ble_peripheral->getId();  // alias
+  ScopedPtr<ConstPtr<ByteArray>> ble_peripheral_id_bytes(MakeConstPtr(
+      new ByteArray(ble_peripheral_id.data(), ble_peripheral_id.size())));
+  ScopedPtr<ConstPtr<ByteArray>> advertisement_hash(
+      generateAdvertisementHash(ble_peripheral_id_bytes.get()));
+  return BLEAdvertisementHeader::asString(BLEAdvertisementHeader::Version::V2,
+                                          kMaxSlots, bloom_filter->asBytes(),
+                                          advertisement_hash.get());
+}
+
+template <typename Platform>
+bool DiscoveredPeripheralTracker<Platform>::isInterestingAdvertisementHeader(
+    /* RefCounted */ ConstPtr<BLEAdvertisementHeader> advertisement_header) {
+  ScopedPtr<Ptr<BloomFilter<10>>> bloom_filter(
+      new BloomFilter<10>(advertisement_header->getServiceIdBloomFilter()));
+  std::set<string> tracked_service_ids = getTrackedServiceIds();
+  for (typename std::set<string>::iterator tsi_it = tracked_service_ids.begin();
+       tsi_it != tracked_service_ids.end(); ++tsi_it) {
+    if (bloom_filter->possiblyContains(*tsi_it)) {
+      return true;
+    }
+  }
+  return false;
+}
+
+template <typename Platform>
+bool DiscoveredPeripheralTracker<Platform>::
+    shouldReadFromAdvertisementGattServer(
+        /* RefCounted */ ConstPtr<BLEAdvertisementHeader>
+            advertisement_header) {
+  // Check if we have never seen this header. New headers should always be read.
+  typename AdvertisementReadResultMap::iterator arr_it =
+      advertisement_read_results_.find(advertisement_header);
+  if (arr_it == advertisement_read_results_.end()) {
+    // TODO(ahlee) logger.atDebug().log("Received advertisement header %s, but
+    // we have never seen it before. Will try reading its GATT advertisement.",
+    // advertisementHeader);
+    return true;
+  }
+
+  // Extract the last read result for this particular header.
+  Ptr<AdvertisementReadResult<Platform>> advertisement_read_result =
+      arr_it->second;  // alias
+
+  // Now evaluate if we should retry reading.
+  switch (advertisement_read_result->evaluateRetryStatus()) {
+    case AdvertisementReadResult<Platform>::RetryStatus::RETRY:
+      // TODO(ahlee) logger.atDebug().log("Received advertisement header %s.
+      // Will retry reading its GATT advertisement.", advertisementHeader);
+      return true;
+    case AdvertisementReadResult<Platform>::RetryStatus::PREVIOUSLY_SUCCEEDED:
+      // TODO(ahlee) logger.atVerbose().log("Received advertisement header %s,
+      // but we have already read its GATT advertisement.",
+      // advertisementHeader);
+      return false;
+    case AdvertisementReadResult<Platform>::RetryStatus::TOO_SOON:
+      // TODO(ahlee) logger.atDebug().log("Received advertisement header %s, but
+      // we have recently failed to read its GATT advertisement.",
+      // advertisementHeader);
+      return false;
+    case AdvertisementReadResult<Platform>::RetryStatus::UNKNOWN:
+      // Fall through.
+      break;
+  }
+
+  // TODO(ahlee) logger.atDebug().log("Received advertisement header %s, but we
+  // do not know whether or not to retry reading its GATT advertisement. Will
+  // retry to be safe.", advertisementHeader);
+  return true;
+}
+
+template <typename Platform>
+std::set<ConstPtr<ByteArray>>
+DiscoveredPeripheralTracker<Platform>::fetchRawGattAdvertisements(
+    Ptr<BLEPeripheralV2> ble_peripheral,
+    /* RefCounted */ ConstPtr<BLEAdvertisementHeader> advertisement_header,
+    Ptr<GattAdvertisementFetcher> gatt_advertisement_fetcher) {
+  Ptr<AdvertisementReadResult<Platform>> old_advertisement_read_result;
+  typename AdvertisementReadResultMap::iterator arr_it =
+      advertisement_read_results_.find(advertisement_header);
+  if (arr_it != advertisement_read_results_.end()) {
+    old_advertisement_read_result = arr_it->second;  // alias
+  }
+
+  /* RefCounted */ Ptr<AdvertisementReadResult<Platform>>
+      advertisement_read_result =
+          gatt_advertisement_fetcher->fetchGattAdvertisements(
+              ble_peripheral, advertisement_header->getNumSlots(),
+              old_advertisement_read_result);
+
+  dpt::eraseOwnedPtrFromMap(advertisement_read_results_, advertisement_header);
+  arr_it = advertisement_read_results_
+               .insert(std::make_pair(advertisement_header,
+                                      advertisement_read_result))
+               .first;
+
+  return arr_it->second->getAdvertisements();
+}
+
+template <typename Platform>
+void DiscoveredPeripheralTracker<Platform>::handleRawGattAdvertisements(
+    /* RefCounted */ ConstPtr<BLEAdvertisementHeader> advertisement_header,
+    const std::set<ConstPtr<ByteArray>>& raw_gatt_advertisements,
+    bool are_fast_advertisements) {
+  typedef std::map<string, ConstPtr<BLEAdvertisement>> BLEAdvertisementMap;
+  // Parse the raw GATT advertisements. The output of this method is a mapping
+  // of service ID -> GATT advertisement.
+  BLEAdvertisementMap parsed_gatt_advertisements =
+      parseRawGattAdvertisements(raw_gatt_advertisements);
+  ScopedPtr<Ptr<BLEAdvertisementSet>> parsed_gatt_advertisement_values(
+      new BLEAdvertisementSet());
+
+  // Update state for each GATT advertisement.
+  for (BLEAdvertisementMap::iterator pga_it =
+           parsed_gatt_advertisements.begin();
+       pga_it != parsed_gatt_advertisements.end(); ++pga_it) {
+    const string& service_id = pga_it->first;                        // alias
+    ConstPtr<BLEAdvertisement> gatt_advertisement = pga_it->second;  // alias
+    parsed_gatt_advertisement_values->insert(gatt_advertisement);
+
+    // TODO(ahlee): Update the java code to create old_advertisement_header
+    // within the if/else block.
+    AdvertisementHeaderMap::iterator ah_it =
+        advertisement_headers_.find(gatt_advertisement);
+    if (ah_it == advertisement_headers_.end()) {
+      discovered_peripheral_callbacks_.find(service_id)
+          ->second->onPeripheralDiscovered(
+              generateBlePeripheral(gatt_advertisement), service_id,
+              gatt_advertisement->getData(), are_fast_advertisements);
+    } else {
+      ConstPtr<BLEAdvertisementHeader> old_advertisement_header =
+          ah_it->second;  // alias
+      dpt::eraseOwnedPtrFromMap(advertisement_read_results_,
+                                old_advertisement_header);
+      dpt::eraseOwnedPtrFromMap(gatt_advertisements_, old_advertisement_header);
+    }
+
+    dpt::eraseOwnedPtrFromMap(advertisement_headers_, gatt_advertisement);
+    advertisement_headers_.insert(
+        std::make_pair(gatt_advertisement, advertisement_header));
+
+    advertisement_service_ids_.erase(gatt_advertisement);
+    advertisement_service_ids_.insert(
+        std::make_pair(gatt_advertisement, service_id));
+  }
+
+  // Insert the list of read GATT advertisements for this advertisement header.
+  dpt::eraseOwnedPtrFromMap(gatt_advertisements_, advertisement_header);
+  gatt_advertisements_.insert(std::make_pair(
+      advertisement_header, parsed_gatt_advertisement_values.release()));
+}
+
+// Returns a map of service IDs to GATT advertisements who belong to a tracked
+// service ID.
+template <typename Platform>
+std::map<string, ConstPtr<BLEAdvertisement>>
+DiscoveredPeripheralTracker<Platform>::parseRawGattAdvertisements(
+    const std::set<ConstPtr<ByteArray>>& raw_gatt_advertisements) {
+  std::set<string> tracked_service_ids = getTrackedServiceIds();
+  typedef std::map<string, ConstPtr<BLEAdvertisement>> BLEAdvertisementMap;
+  BLEAdvertisementMap parsed_gatt_advertisements;
+  for (std::set<ConstPtr<ByteArray>>::iterator rga_it =
+           raw_gatt_advertisements.begin();
+       rga_it != raw_gatt_advertisements.end(); ++rga_it) {
+    /* RefCounted */ ConstPtr<BLEAdvertisement> gatt_advertisement =
+        BLEAdvertisement::fromBytes(*rga_it);
+    if (gatt_advertisement.isNull()) {
+      // logger.atDebug().log("Unable to parse raw GATT advertisement %s",
+      // *rga_it);
+      continue;
+    }
+
+    // Make sure the advertisement belongs to a service ID we're tracking.
+    for (typename std::set<string>::iterator tsi_it =
+             tracked_service_ids.begin();
+         tsi_it != tracked_service_ids.end(); ++tsi_it) {
+      // If we already found a higher version advertisement for this service ID,
+      // there's no point in comparing this advertisement against it.
+      BLEAdvertisementMap::iterator pga_it =
+          parsed_gatt_advertisements.find(*tsi_it);
+      if (pga_it != parsed_gatt_advertisements.end()) {
+        if (pga_it->second->getVersion() > gatt_advertisement->getVersion()) {
+          continue;
+        }
+      }
+
+      // Map the service ID to the advertisement if the service ID hashes match.
+      ScopedPtr<ConstPtr<ByteArray>> service_id_hash(
+          generateServiceIdHash(gatt_advertisement->getVersion(), *tsi_it));
+      if (*service_id_hash == *(gatt_advertisement->getServiceIdHash())) {
+        // logger.atDebug().log("Matched service ID %s to GATT advertisement
+        // %s.", serviceId, gattAdvertisement);
+        parsed_gatt_advertisements.insert(
+            std::make_pair(*tsi_it, gatt_advertisement));
+        break;
+      }
+    }
+  }
+
+  return parsed_gatt_advertisements;
+}
+
+template <typename Platform>
+void DiscoveredPeripheralTracker<Platform>::
+    updateCommonStateForFoundBleAdvertisement(
+        /* RefCounted */ ConstPtr<BLEAdvertisementHeader> advertisement_header,
+        const string& mac_address) {
+  typename GattAdvertisementMap::iterator ga_it =
+      gatt_advertisements_.find(advertisement_header);
+  if (ga_it == gatt_advertisements_.end()) {
+    // logger.atDebug().log("No GATT advertisements found for advertisement
+    // header %s.", advertisementHeader);
+    return;
+  }
+
+  Ptr<BLEAdvertisementSet> saved_gatt_advertisements = ga_it->second;  // alias
+  for (BLEAdvertisementSet::iterator sga_it =
+           saved_gatt_advertisements->begin();
+       sga_it != saved_gatt_advertisements->end(); ++sga_it) {
+    ConstPtr<BLEAdvertisement> gatt_advertisement = *sga_it;  // alias
+
+    AdvertisementServiceIdMap::iterator asi_it =
+        advertisement_service_ids_.find(gatt_advertisement);
+    if (asi_it == advertisement_service_ids_.end()) {
+      continue;
+    }
+    const string& service_id = asi_it->second;  // alias
+
+    // Make sure the stored GATT advertisement is still being tracked.
+    std::set<string> tracked_service_ids = getTrackedServiceIds();
+    if (tracked_service_ids.find(service_id) == tracked_service_ids.end()) {
+      continue;
+    }
+
+    // The iterator returned from find() is guaranteed to be valid because it's
+    // tied to discovered_peripheral_callbacks_, whose keyset is checked through
+    // getTrackedServiceIds() above.
+    lost_entity_trackers_.find(service_id)
+        ->second->recordFoundEntity(gatt_advertisement);
+
+    // The iterator returned from find() is guaranteed to be valid because it's
+    // tied to advertisement_service_ids_ which is checked at the beginning of
+    // the for loop.
+    mac_addresses_.erase(gatt_advertisement);
+    mac_addresses_.insert(std::make_pair(gatt_advertisement, mac_address));
+  }
+}
+
+template <typename Platform>
+ConstPtr<ByteArray>
+DiscoveredPeripheralTracker<Platform>::generateAdvertisementHash(
+    ConstPtr<ByteArray> advertisement_bytes) {
+  return Utils::sha256Hash(hash_utils_.get(), advertisement_bytes,
+                           BLEAdvertisementHeader::kAdvertisementHashLength);
+}
+
+template <typename Platform>
+ConstPtr<ByteArray>
+DiscoveredPeripheralTracker<Platform>::generateServiceIdHash(
+    BLEAdvertisement::Version::Value version, const string& service_id) {
+  ScopedPtr<ConstPtr<ByteArray>> service_id_bytes(
+      MakeConstPtr(new ByteArray(service_id.data(), service_id.size())));
+  switch (version) {
+    case BLEAdvertisement::Version::V1:
+      return Utils::legacySha256HashOnlyForPrinting(
+          hash_utils_.get(), service_id_bytes.get(),
+          BLEPacket::kServiceIdHashLength);
+    case BLEAdvertisement::Version::V2:
+      // Fall through.
+    case BLEAdvertisement::Version::UNKNOWN:
+      // Fall through.
+    default:
+      // Use the latest known hashing scheme.
+      return Utils::sha256Hash(hash_utils_.get(), service_id_bytes.get(),
+                               BLEPacket::kServiceIdHashLength);
+  }
+}
+
+}  // namespace mediums
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/mediums/discovered_peripheral_tracker.h

@@ -0,0 +1,218 @@
+#ifndef CORE_INTERNAL_MEDIUMS_DISCOVERED_PERIPHERAL_TRACKER_H_
+#define CORE_INTERNAL_MEDIUMS_DISCOVERED_PERIPHERAL_TRACKER_H_
+
+#include <cstdint>
+#include <map>
+#include <set>
+
+#include "core/internal/mediums/advertisement_read_result.h"
+#include "core/internal/mediums/ble_advertisement.h"
+#include "core/internal/mediums/ble_advertisement_header.h"
+#include "core/internal/mediums/ble_peripheral.h"
+#include "core/internal/mediums/discovered_peripheral_callback.h"
+#include "core/internal/mediums/lost_entity_tracker.h"
+#include "platform/api/ble_v2.h"
+#include "platform/api/hash_utils.h"
+#include "platform/api/lock.h"
+#include "platform/api/system_clock.h"
+#include "platform/api/thread_utils.h"
+#include "platform/byte_array.h"
+#include "platform/port/string.h"
+#include "platform/ptr.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+namespace mediums {
+
+// Manages all discovered peripheral logic for {@link BluetoothLowEnergy}. This
+// includes tracking found peripherals, lost peripherals, and MAC addresses
+// associated with those peripherals.
+//
+// See go/ble-on-lost for more information. It includes the algorithms used to
+// compute found and lost peripherals.
+template <typename Platform>
+class DiscoveredPeripheralTracker {
+ public:
+  DiscoveredPeripheralTracker();
+  ~DiscoveredPeripheralTracker();
+
+  void startTracking(
+      const string& service_id,
+      Ptr<DiscoveredPeripheralCallback> discovered_peripheral_callback,
+      const string& fast_advertisement_service_uuid);
+  void stopTracking(const string& service_id);
+
+  // GATT advertisement fetcher.
+  class GattAdvertisementFetcher {
+   public:
+    virtual ~GattAdvertisementFetcher() {}
+
+    // Fetches relevant GATT advertisements for the peripheral found in {@link
+    // DiscoveredPeripheralTracker#processFoundBleAdvertisement(BleSighting,
+    // GattAdvertisementFetcher)}.
+    virtual Ptr<AdvertisementReadResult<Platform>> fetchGattAdvertisements(
+        Ptr<BLEPeripheralV2> ble_peripheral, std::int32_t num_slots,
+        Ptr<AdvertisementReadResult<Platform>> advertisement_read_result) = 0;
+  };
+  void processFoundBleAdvertisement(
+      Ptr<BLEPeripheralV2> ble_peripheral,
+      ConstPtr<BLEAdvertisementData> advertisement_data,
+      Ptr<GattAdvertisementFetcher> gatt_advertisement_fetcher);
+  void processLostGattAdvertisements();
+
+  // TODO(ahlee): Add connecting logic.
+
+ private:
+  static Ptr<BLEPeripheral> generateBlePeripheral(
+      ConstPtr<BLEAdvertisement> gatt_advertisement);
+
+  static const std::int32_t kMaxSlots;
+  static const std::int64_t kMinConnectionDelayMillis;
+  static const char* kCopresenceServiceUuid;
+
+  std::set<string> getTrackedServiceIds();
+  void clearDataForServiceId(const string& service_id);
+  void clearGattAdvertisement(ConstPtr<BLEAdvertisement> gatt_advertisement);
+  void handleFastAdvertisement(
+      Ptr<BLEPeripheralV2> ble_peripheral,
+      ConstPtr<BLEAdvertisementData> advertisement_data);
+  void handleAdvertisementHeader(
+      Ptr<BLEPeripheralV2> ble_peripheral,
+      ConstPtr<BLEAdvertisementData> advertisement_data,
+      Ptr<GattAdvertisementFetcher> gatt_advertisement_fetcher);
+  string extractAdvertisementHeaderBytes(
+      Ptr<BLEPeripheralV2> ble_peripheral,
+      ConstPtr<BLEAdvertisementData> advertisement_data);
+  ConstPtr<ByteArray> extractFastAdvertisementBytes(
+      ConstPtr<BLEAdvertisementData> advertisement_data);
+  /*RefCounted */ ConstPtr<BLEAdvertisementHeader>
+  createFastAdvertisementHeader(ConstPtr<ByteArray> fast_advertisement_bytes);
+  string createDummyAdvertisementHeaderBytes(
+      Ptr<BLEPeripheralV2> ble_peripheral);
+  bool isInterestingAdvertisementHeader(
+      /* RefCounted */ ConstPtr<BLEAdvertisementHeader> advertisement_header);
+  bool shouldReadFromAdvertisementGattServer(
+      /* RefCounted */ ConstPtr<BLEAdvertisementHeader> advertisement_header);
+  std::set<ConstPtr<ByteArray>> fetchRawGattAdvertisements(
+      Ptr<BLEPeripheralV2> ble_peripheral,
+      /* RefCounted */ ConstPtr<BLEAdvertisementHeader> advertisement_header,
+      Ptr<GattAdvertisementFetcher> gatt_advertisement_fetcher);
+  void handleRawGattAdvertisements(
+      /* RefCounted */ ConstPtr<BLEAdvertisementHeader> advertisement_header,
+      const std::set<ConstPtr<ByteArray>>& raw_gatt_advertisements,
+      bool are_fast_advertisements);
+  std::map<string, ConstPtr<BLEAdvertisement>> parseRawGattAdvertisements(
+      const std::set<ConstPtr<ByteArray>>& raw_gatt_advertisements);
+  void updateCommonStateForFoundBleAdvertisement(
+      /* RefCounted */ ConstPtr<BLEAdvertisementHeader> advertisement_header,
+      const string& mac_address);
+
+  // TODO(ahlee): Add in connecting logic.
+
+  // TODO(ahlee): Move these out to utils (also used by BLE V2).
+  ConstPtr<ByteArray> generateAdvertisementHash(
+      ConstPtr<ByteArray> advertisement_bytes);
+  ConstPtr<ByteArray> generateServiceIdHash(
+      BLEAdvertisement::Version::Value version, const string& service_id);
+
+  // ------------ GENERAL ------------
+  ScopedPtr<Ptr<Lock>> lock_;
+  ScopedPtr<Ptr<ThreadUtils>> thread_utils_;
+  ScopedPtr<Ptr<SystemClock>> system_clock_;
+  ScopedPtr<Ptr<HashUtils>> hash_utils_;
+
+  // ------------ SERVICE ID MAPS ------------
+  // Entries in these maps all follow the same lifecycle. Entries are added in
+  // startTracking, and removed in stopTracking.
+
+  // Maps service IDs to DiscoveredPeripheralCallbacks. Tracks what service IDs
+  // are currently active and gives us client callbacks to call.
+  typedef std::map<string, Ptr<DiscoveredPeripheralCallback>>
+      DiscoveredPeripheralCallbackMap;
+  DiscoveredPeripheralCallbackMap discovered_peripheral_callbacks_;
+
+  // Maps service IDs to LostEntityTrackers. Used to periodically compute lost
+  // GATT advertisements, grouped by service ID.
+  typedef std::map<string, Ptr<LostEntityTracker<Platform, BLEAdvertisement>>>
+      LostEntityTrackerMap;
+  LostEntityTrackerMap lost_entity_trackers_;
+
+  // Maps service IDs to BLE service UUIDs. Used to check for fast
+  // advertisements delivered through BLE advertisement service data, under the
+  // given UUID.
+  // UUIDs are represented as strings in this map because they are coming from
+  // AdvertisingOptions and our UUID class is an internal concept that we don't
+  // want to expose to clients.
+  typedef std::map<string, string> FastAdvertisementServiceUUIDMap;
+  FastAdvertisementServiceUUIDMap fast_advertisement_service_uuids_;
+
+  // ------------ ADVERTISEMENT HEADER MAPS ------------
+
+  // Maps advertisement headers to AdvertisementReadResults. Tells us when to
+  // retry reading a GATT advertisement. If no entry exists for a particular
+  // header, we should try reading a GATT advertisement. Entries are added
+  // whenever a GATT advertisement read is attempted, and removed when GATT
+  // advertisements are lost. Entries are also removed whenever
+  // gattAdvertisements removes its entry.
+  //
+  // The map is also cleared whenever startTracking is called, due to client
+  // changes. For example, say clients A and B start scanning and discover
+  // advertisements A and B (for both clients) on advertisement header 1. Then,
+  // A restarts scanning, causing us to clear stale advertisement A. However,
+  // since B was still scanning, we don't remove advertisement header 1 from the
+  // map. This causes us to never re-read advertisement A.
+  typedef std::map</* RefCounted */ ConstPtr<BLEAdvertisementHeader>,
+                   Ptr<AdvertisementReadResult<Platform>>>
+      AdvertisementReadResultMap;
+  AdvertisementReadResultMap advertisement_read_results_;
+
+  // Maps advertisement headers to a set of GATT advertisements from a single
+  // peripheral. Used to retrieve GATT advertisements that we need to reprocess
+  // every time a header is seen. Entries are added when GATT advertisements are
+  // read, removed when all associated GATT advertisements are lost or become
+  // stale, and replaced when the advertisement header is updated for a single
+  // remote peripheral.
+  typedef std::set</* RefCounted */ ConstPtr<BLEAdvertisement>>
+      BLEAdvertisementSet;
+  typedef std::map</* RefCounted */ ConstPtr<BLEAdvertisementHeader>,
+                   Ptr<BLEAdvertisementSet>>
+      GattAdvertisementMap;
+  GattAdvertisementMap gatt_advertisements_;
+
+  // ------------ GATT ADVERTISEMENT MAPS ------------
+  // Entries in these maps all follow the same lifecycle. Entries are added when
+  // GATT advertisements are read, and removed when GATT advertisements are lost
+  // or become stale.
+
+  // Maps GATT advertisements to the service ID it's associated with. Tracks
+  // what GATT advertisements are currently active. Used to determine which
+  // LostEntityTracker to invoke when advertisements are rediscovered.
+  typedef std::map</* RefCounted */ ConstPtr<BLEAdvertisement>, string>
+      AdvertisementServiceIdMap;
+  AdvertisementServiceIdMap advertisement_service_ids_;
+
+  // Maps GATT advertisements to advertisement headers. Used to efficiently find
+  // advertisement headers to delete when GATT advertisements are updated. This
+  // is a reverse map of gatt_advertisements_.
+  typedef std::map</* RefCounted */ ConstPtr<BLEAdvertisement>,
+                   /* RefCounted */ ConstPtr<BLEAdvertisementHeader>>
+      AdvertisementHeaderMap;
+  AdvertisementHeaderMap advertisement_headers_;
+
+  // Maps GATT advertisements to MAC addresses. Used when we need to make a
+  // socket connection based off of the GATT advertisement alone. Entries are
+  // modified every time a GATT advertisement's advertisement header is seen.
+  typedef std::map</* RefCounted */ ConstPtr<BLEAdvertisement>, string>
+      MacAddressMap;
+  MacAddressMap mac_addresses_;
+};
+
+}  // namespace mediums
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#include "core/internal/mediums/discovered_peripheral_tracker.cc"
+
+#endif  // CORE_INTERNAL_MEDIUMS_DISCOVERED_PERIPHERAL_TRACKER_H_

cpp/core/internal/mediums/lost_entity_tracker.cc

@@ -0,0 +1,56 @@
+#include "core/internal/mediums/lost_entity_tracker.h"
+
+#include "platform/synchronized.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+namespace mediums {
+
+template <typename Platform, typename Entity>
+LostEntityTracker<Platform, Entity>::LostEntityTracker()
+    : lock_(Platform::createLock()),
+      current_entities_(),
+      previously_found_entities_() {}
+
+template <typename Platform, typename Entity>
+LostEntityTracker<Platform, Entity>::~LostEntityTracker() {
+  previously_found_entities_.clear();
+  current_entities_.clear();
+}
+
+template <typename Platform, typename Entity>
+void LostEntityTracker<Platform, Entity>::recordFoundEntity(
+    ConstPtr<Entity> entity) {
+  Synchronized s(lock_.get());
+
+  current_entities_.insert(entity);
+}
+
+template <typename Platform, typename Entity>
+typename LostEntityTracker<Platform, Entity>::EntitySet
+LostEntityTracker<Platform, Entity>::computeLostEntities() {
+  Synchronized s(lock_.get());
+
+  // The set of lost entities is the previously found set MINUS the currently
+  // found set.
+  for (typename EntitySet::iterator it = current_entities_.begin();
+       it != current_entities_.end(); ++it) {
+    previously_found_entities_.erase(*it);
+  }
+  EntitySet lost_entities(previously_found_entities_.begin(),
+                          previously_found_entities_.end());
+
+  // Update our previous and current sets.
+  previously_found_entities_.clear();
+  previously_found_entities_.insert(current_entities_.begin(),
+                                    current_entities_.end());
+  current_entities_.clear();
+
+  return lost_entities;
+}
+
+}  // namespace mediums
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/mediums/lost_entity_tracker.h

@@ -0,0 +1,49 @@
+#ifndef CORE_INTERNAL_MEDIUMS_LOST_ENTITY_TRACKER_H_
+#define CORE_INTERNAL_MEDIUMS_LOST_ENTITY_TRACKER_H_
+
+#include <set>
+
+#include "platform/api/lock.h"
+#include "platform/ptr.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+namespace mediums {
+
+// Tracks "lost" entities based on a manual update/compute model. Used by
+// mediums that only report found devices. Lost entities are computed based off
+// of whether a specific entity was rediscovered since the last call to
+// computeLostEntities.
+//
+// Note: Entity must overload the < and == operators.
+template <typename Platform, typename Entity>
+class LostEntityTracker {
+ public:
+  typedef std::set<ConstPtr<Entity> > EntitySet;
+
+  LostEntityTracker();
+  ~LostEntityTracker();
+
+  // Records the given entity as being recently found, whether or not this is
+  // our first time discovering the entity.
+  void recordFoundEntity(ConstPtr<Entity> entity);
+
+  // Computes and returns the set of entities considered lost since the last
+  // time this method was called.
+  EntitySet computeLostEntities();
+
+ private:
+  ScopedPtr<Ptr<Lock> > lock_;
+  EntitySet current_entities_;
+  EntitySet previously_found_entities_;
+};
+
+}  // namespace mediums
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#include "core/internal/mediums/lost_entity_tracker.cc"
+
+#endif  // CORE_INTERNAL_MEDIUMS_LOST_ENTITY_TRACKER_H_

cpp/core/internal/mediums/lost_entity_tracker_test.cc

@@ -0,0 +1,121 @@
+#include "core/internal/mediums/lost_entity_tracker.h"
+
+#include "platform/impl/default/default_platform.h"
+#include "gtest/gtest.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+namespace mediums {
+namespace {
+
+struct TestEntity {
+  int id;
+
+  explicit TestEntity(int givenId) : id(givenId) {}
+
+  bool operator<(const TestEntity &other) const { return id < other.id; }
+};
+
+TEST(LostEntityTracker, NoEntitiesLost) {
+  LostEntityTracker<DefaultPlatform, TestEntity> lost_entity_tracker;
+  ScopedPtr<ConstPtr<TestEntity> > entity_1(MakeConstPtr(new TestEntity(1)));
+  ScopedPtr<ConstPtr<TestEntity> > entity_2(MakeConstPtr(new TestEntity(2)));
+  ScopedPtr<ConstPtr<TestEntity> > entity_3(MakeConstPtr(new TestEntity(3)));
+
+  // Discover some entities.
+  lost_entity_tracker.recordFoundEntity(entity_1.get());
+  lost_entity_tracker.recordFoundEntity(entity_2.get());
+  lost_entity_tracker.recordFoundEntity(entity_3.get());
+
+  // Make sure none are lost on the first round.
+  ASSERT_TRUE(lost_entity_tracker.computeLostEntities().empty());
+
+  // Rediscover the same entities.
+  lost_entity_tracker.recordFoundEntity(entity_1.get());
+  lost_entity_tracker.recordFoundEntity(entity_2.get());
+  lost_entity_tracker.recordFoundEntity(entity_3.get());
+
+  // Make sure we still didn't lose any entities.
+  ASSERT_TRUE(lost_entity_tracker.computeLostEntities().empty());
+}
+
+TEST(LostEntityTracker, AllEntitiesLost) {
+  LostEntityTracker<DefaultPlatform, TestEntity> lost_entity_tracker;
+  ScopedPtr<ConstPtr<TestEntity> > entity_1(MakeConstPtr(new TestEntity(1)));
+  ScopedPtr<ConstPtr<TestEntity> > entity_2(MakeConstPtr(new TestEntity(2)));
+  ScopedPtr<ConstPtr<TestEntity> > entity_3(MakeConstPtr(new TestEntity(3)));
+
+  // Discover some entities.
+  lost_entity_tracker.recordFoundEntity(entity_1.get());
+  lost_entity_tracker.recordFoundEntity(entity_2.get());
+  lost_entity_tracker.recordFoundEntity(entity_3.get());
+
+  // Make sure none are lost on the first round.
+  ASSERT_TRUE(lost_entity_tracker.computeLostEntities().empty());
+
+  // Go through a round without rediscovering any entities.
+  typename LostEntityTracker<DefaultPlatform, TestEntity>::EntitySet
+      lost_entities = lost_entity_tracker.computeLostEntities();
+  ASSERT_TRUE(lost_entities.find(entity_1.get()) != lost_entities.end());
+  ASSERT_TRUE(lost_entities.find(entity_2.get()) != lost_entities.end());
+  ASSERT_TRUE(lost_entities.find(entity_3.get()) != lost_entities.end());
+}
+
+TEST(LostEntityTracker, SomeEntitiesLost) {
+  LostEntityTracker<DefaultPlatform, TestEntity> lost_entity_tracker;
+  ScopedPtr<ConstPtr<TestEntity> > entity_1(MakeConstPtr(new TestEntity(1)));
+  ScopedPtr<ConstPtr<TestEntity> > entity_2(MakeConstPtr(new TestEntity(2)));
+  ScopedPtr<ConstPtr<TestEntity> > entity_3(MakeConstPtr(new TestEntity(3)));
+
+  // Discover some entities.
+  lost_entity_tracker.recordFoundEntity(entity_1.get());
+  lost_entity_tracker.recordFoundEntity(entity_2.get());
+
+  // Make sure none are lost on the first round.
+  ASSERT_TRUE(lost_entity_tracker.computeLostEntities().empty());
+
+  // Go through the next round only rediscovering one of our entities and
+  // discovering an additional entity as well. Then, verify that only one entity
+  // was lost after the check.
+  lost_entity_tracker.recordFoundEntity(entity_1.get());
+  lost_entity_tracker.recordFoundEntity(entity_3.get());
+  typename LostEntityTracker<DefaultPlatform, TestEntity>::EntitySet
+      lost_entities = lost_entity_tracker.computeLostEntities();
+  ASSERT_TRUE(lost_entities.find(entity_1.get()) == lost_entities.end());
+  ASSERT_TRUE(lost_entities.find(entity_2.get()) != lost_entities.end());
+  ASSERT_TRUE(lost_entities.find(entity_3.get()) == lost_entities.end());
+}
+
+TEST(LostEntityTracker, SameEntityMultipleCopies) {
+  LostEntityTracker<DefaultPlatform, TestEntity> lost_entity_tracker;
+  ScopedPtr<ConstPtr<TestEntity> > entity_1(MakeConstPtr(new TestEntity(1)));
+  ScopedPtr<ConstPtr<TestEntity> > entity_1_copy(
+      MakeConstPtr(new TestEntity(1)));
+
+  // Discover an entity.
+  lost_entity_tracker.recordFoundEntity(entity_1.get());
+
+  // Make sure none are lost on the first round.
+  ASSERT_TRUE(lost_entity_tracker.computeLostEntities().empty());
+
+  // Rediscover the same entity, but through a copy of it.
+  lost_entity_tracker.recordFoundEntity(entity_1_copy.get());
+
+  // Make sure none are lost on the second round.
+  ASSERT_TRUE(lost_entity_tracker.computeLostEntities().empty());
+
+  // Go through a round without rediscovering any entities and verify that we
+  // lost an entity equivalent to both copies of it.
+  typename LostEntityTracker<DefaultPlatform, TestEntity>::EntitySet
+      lost_entities = lost_entity_tracker.computeLostEntities();
+  ASSERT_EQ(lost_entities.size(), 1);
+  ASSERT_TRUE(lost_entities.find(entity_1.get()) != lost_entities.end());
+  ASSERT_TRUE(lost_entities.find(entity_1_copy.get()) != lost_entities.end());
+}
+
+}  // namespace
+}  // namespace mediums
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/mediums/mediums.cc

@@ -0,0 +1,42 @@
+#include "core/internal/mediums/mediums.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+template <typename Platform>
+Mediums<Platform>::Mediums()
+    : bluetooth_radio_(new BluetoothRadio<Platform>()),
+      bluetooth_classic_(
+          new BluetoothClassic<Platform>(bluetooth_radio_.get())),
+      ble_(new BLE<Platform>(bluetooth_radio_.get())),
+      ble_v2_(new mediums::BLEV2<Platform>(bluetooth_radio_.get())) {}
+
+template <typename Platform>
+Mediums<Platform>::~Mediums() {
+  // Nothing to do.
+}
+
+template <typename Platform>
+Ptr<BluetoothRadio<Platform> > Mediums<Platform>::bluetoothRadio() const {
+  return bluetooth_radio_.get();
+}
+
+template <typename Platform>
+Ptr<BluetoothClassic<Platform> > Mediums<Platform>::bluetoothClassic() const {
+  return bluetooth_classic_.get();
+}
+
+template <typename Platform>
+Ptr<BLE<Platform> > Mediums<Platform>::ble() const {
+  return ble_.get();
+}
+
+template <typename Platform>
+Ptr<mediums::BLEV2<Platform> > Mediums<Platform>::bleV2() const {
+  return ble_v2_.get();
+}
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/mediums/mediums.h

@@ -0,0 +1,52 @@
+#ifndef CORE_INTERNAL_MEDIUMS_MEDIUMS_H_
+#define CORE_INTERNAL_MEDIUMS_MEDIUMS_H_
+
+#include "core/internal/mediums/ble.h"
+#include "core/internal/mediums/ble_v2.h"
+#include "core/internal/mediums/bluetooth_classic.h"
+#include "core/internal/mediums/bluetooth_radio.h"
+#include "platform/ptr.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+// Facilitates convenient and reliable usage of various wireless mediums.
+template <typename Platform>
+class Mediums {
+ public:
+  Mediums();
+  // Reverts all the mediums to their original state.
+  ~Mediums();
+
+  // Returns a handle to the Bluetooth radio.
+  Ptr<BluetoothRadio<Platform> > bluetoothRadio() const;
+  // Returns a handle to the Bluetooth Classic medium.
+  Ptr<BluetoothClassic<Platform> > bluetoothClassic() const;
+  // Returns a handle to the Bluetooth Low Energy (BLE) medium.
+  Ptr<BLE<Platform> > ble() const;
+  // Returns a handle to V2 of the Bluetooth Low Energy (BLE) medium.
+  Ptr<mediums::BLEV2<Platform> > bleV2() const;
+
+ private:
+  // The order of declaration is critical for both construction and
+  // destruction.
+  //
+  // 1) Construction: The individual mediums have a dependency on the
+  // corresponding radio, so the radio must be initialized first.
+  //
+  // 2) Destruction: The individual mediums should be shut down before the
+  // corresponding radio.
+  ScopedPtr<Ptr<BluetoothRadio<Platform> > > bluetooth_radio_;
+  ScopedPtr<Ptr<BluetoothClassic<Platform> > > bluetooth_classic_;
+  ScopedPtr<Ptr<BLE<Platform> > > ble_;
+  ScopedPtr<Ptr<mediums::BLEV2<Platform> > > ble_v2_;
+};
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#include "core/internal/mediums/mediums.cc"
+
+#endif  // CORE_INTERNAL_MEDIUMS_MEDIUMS_H_

cpp/core/internal/mediums/utils.cc

@@ -0,0 +1,73 @@
+#include "core/internal/mediums/utils.h"
+
+#include <sstream>
+
+#include "platform/exception.h"
+#include "absl/strings/escaping.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+void Utils::closeSocket(Ptr<BluetoothServerSocket> socket,
+                        const std::string& type, const std::string& name) {
+  if (!socket.isNull()) {
+    Exception::Value e = socket->close();
+    if (Exception::NONE != e) {
+      if (Exception::IO == e) {
+        // TODO(reznor): log.atWarning().withCause(e).log("Failed to close
+        // %sSocket %s", type, name);
+      }
+      return;
+    }
+    // TODO(reznor): log.atVerbose().log("Closed %sSocket %s", type, name);
+  }
+}
+
+ConstPtr<ByteArray> Utils::sha256Hash(Ptr<HashUtils> hash_utils,
+                                      ConstPtr<ByteArray> source,
+                                      size_t length) {
+  if (source.isNull()) {
+    return ConstPtr<ByteArray>();
+  }
+
+  ScopedPtr<ConstPtr<ByteArray>> full_hash(
+      hash_utils->sha256(std::string(source->getData(), source->size())));
+  return MakeConstPtr(new ByteArray(full_hash->getData(), length));
+}
+
+ConstPtr<ByteArray> Utils::legacySha256HashOnlyForPrinting(
+    Ptr<HashUtils> hash_utils, ConstPtr<ByteArray> source, size_t length) {
+  if (source.isNull()) {
+    return ConstPtr<ByteArray>();
+  }
+
+  std::string formatted_hex_string = Utils::bytesToPrintableHexString(source);
+  ScopedPtr<ConstPtr<ByteArray>> formatted_hex_byte_array(MakeConstPtr(
+      new ByteArray(formatted_hex_string.data(), formatted_hex_string.size())));
+  return Utils::sha256Hash(hash_utils, formatted_hex_byte_array.get(), length);
+}
+
+std::string Utils::bytesToPrintableHexString(ConstPtr<ByteArray> bytes) {
+  std::string hex_string(
+      absl::BytesToHexString(std::string(bytes->getData(), bytes->size())));
+
+  // Print out the byte array as a space separated listing of hex bytes.
+  std::ostringstream formatted_hex_string_stream;
+  formatted_hex_string_stream << "[ ";
+  for (int i = 0; i < hex_string.size(); i += 2) {
+    formatted_hex_string_stream << "0x";
+    // This is safe because we have the guarantee that hex_string is of even
+    // length (because a hex encoding will always be double the size of its
+    // input).
+    formatted_hex_string_stream << hex_string[i] << hex_string[i + 1];
+    formatted_hex_string_stream << " ";
+  }
+  formatted_hex_string_stream << "]";
+
+  return formatted_hex_string_stream.str();
+}
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/mediums/utils.h

@@ -0,0 +1,32 @@
+#ifndef CORE_INTERNAL_MEDIUMS_UTILS_H_
+#define CORE_INTERNAL_MEDIUMS_UTILS_H_
+
+#include "platform/api/bluetooth_classic.h"
+#include "platform/api/hash_utils.h"
+#include "platform/byte_array.h"
+#include "platform/port/string.h"
+#include "platform/ptr.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+class Utils {
+ public:
+  static void closeSocket(Ptr<BluetoothServerSocket> socket,
+                          const std::string& type, const std::string& name);
+  static ConstPtr<ByteArray> sha256Hash(Ptr<HashUtils> hash_utils,
+                                        ConstPtr<ByteArray> source,
+                                        size_t length);
+  static ConstPtr<ByteArray> legacySha256HashOnlyForPrinting(
+      Ptr<HashUtils> hash_utils, ConstPtr<ByteArray> source, size_t length);
+
+ private:
+  static std::string bytesToPrintableHexString(ConstPtr<ByteArray> bytes);
+};
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#endif  // CORE_INTERNAL_MEDIUMS_UTILS_H_

cpp/core/internal/mediums/uuid.cc

@@ -0,0 +1,100 @@
+#include "core/internal/mediums/uuid.h"
+
+#include <iomanip>
+#include <sstream>
+
+#include "platform/api/hash_utils.h"
+#include "platform/ptr.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+template <typename Platform>
+UUID<Platform>::UUID(const string& data) {
+  // Based on the Java counterpart at
+  // http://androidxref.com/8.0.0_r4/xref/libcore/ojluni/src/main/java/java/util/UUID.java#162.
+  ScopedPtr<Ptr<HashUtils> > scoped_hash_utils(Platform::createHashUtils());
+  ScopedPtr<ConstPtr<ByteArray> > scoped_md5_bytes(
+      scoped_hash_utils->md5(data));
+  data_.assign(scoped_md5_bytes->getData(), scoped_md5_bytes->size());
+
+  data_[6] &= 0x0f;  // Clear version.
+  data_[6] |= 0x30;  // Set to version 3.
+  data_[8] &= 0x3f;  // Clear variant.
+  data_[8] |= 0x80;  // Set to IETF variant.
+}
+
+template <typename Platform>
+UUID<Platform>::UUID(std::int64_t most_sig_bits, std::int64_t least_sig_bits) {
+  // Base on the Java counterpart at
+  // http://androidxref.com/8.0.0_r4/xref/libcore/ojluni/src/main/java/java/util/UUID.java#104.
+  data_.reserve(sizeof(most_sig_bits) + sizeof(least_sig_bits));
+
+  data_[0] = static_cast<char>((most_sig_bits >> 56) & 0x0ff);
+  data_[1] = static_cast<char>((most_sig_bits >> 48) & 0x0ff);
+  data_[2] = static_cast<char>((most_sig_bits >> 40) & 0x0ff);
+  data_[3] = static_cast<char>((most_sig_bits >> 32) & 0x0ff);
+  data_[4] = static_cast<char>((most_sig_bits >> 24) & 0x0ff);
+  data_[5] = static_cast<char>((most_sig_bits >> 16) & 0x0ff);
+  data_[6] = static_cast<char>((most_sig_bits >> 8) & 0x0ff);
+  data_[7] = static_cast<char>((most_sig_bits >> 0) & 0x0ff);
+
+  data_[8] = static_cast<char>((least_sig_bits >> 56) & 0x0ff);
+  data_[9] = static_cast<char>((least_sig_bits >> 48) & 0x0ff);
+  data_[10] = static_cast<char>((least_sig_bits >> 40) & 0x0ff);
+  data_[11] = static_cast<char>((least_sig_bits >> 32) & 0x0ff);
+  data_[12] = static_cast<char>((least_sig_bits >> 24) & 0x0ff);
+  data_[13] = static_cast<char>((least_sig_bits >> 16) & 0x0ff);
+  data_[14] = static_cast<char>((least_sig_bits >> 8) & 0x0ff);
+  data_[15] = static_cast<char>((least_sig_bits >> 0) & 0x0ff);
+}
+
+template <typename Platform>
+UUID<Platform>::~UUID() {}
+
+template <typename Platform>
+string UUID<Platform>::str() {
+  // Based on the Java counterpart at
+  // http://androidxref.com/8.0.0_r4/xref/libcore/ojluni/src/main/java/java/util/UUID.java#375.
+
+  // The masking with 0x0ff is essential because we're taking 8-bit bytes and
+  // casting them to integers (which, depending on the platform, are 16- or
+  // 32-bits wide); without that, we get a leading FF (16-bit) or FFFFFF
+  // (32-bit) when the MSB of the 8-bit byte is 1.
+  //
+  // And the cast to an integer is required because std::hex only takes effect
+  // on integral types (and no, uint8_t doesn't activate it).
+#define BYTE_TO_HEX(b)                          \
+  std::setfill('0') << std::setw(2) << std::hex \
+                    << (static_cast<unsigned int>(b) & 0x0ff)
+
+  std::ostringstream md5_hex;
+
+  md5_hex << BYTE_TO_HEX(data_[0]);
+  md5_hex << BYTE_TO_HEX(data_[1]);
+  md5_hex << BYTE_TO_HEX(data_[2]);
+  md5_hex << BYTE_TO_HEX(data_[3]);
+  md5_hex << "-";
+  md5_hex << BYTE_TO_HEX(data_[4]);
+  md5_hex << BYTE_TO_HEX(data_[5]);
+  md5_hex << "-";
+  md5_hex << BYTE_TO_HEX(data_[6]);
+  md5_hex << BYTE_TO_HEX(data_[7]);
+  md5_hex << "-";
+  md5_hex << BYTE_TO_HEX(data_[8]);
+  md5_hex << BYTE_TO_HEX(data_[9]);
+  md5_hex << "-";
+  md5_hex << BYTE_TO_HEX(data_[10]);
+  md5_hex << BYTE_TO_HEX(data_[11]);
+  md5_hex << BYTE_TO_HEX(data_[12]);
+  md5_hex << BYTE_TO_HEX(data_[13]);
+  md5_hex << BYTE_TO_HEX(data_[14]);
+  md5_hex << BYTE_TO_HEX(data_[15]);
+
+  return md5_hex.str();
+}
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/mediums/uuid.h

@@ -0,0 +1,39 @@
+#ifndef CORE_INTERNAL_MEDIUMS_UUID_H_
+#define CORE_INTERNAL_MEDIUMS_UUID_H_
+
+#include <cstdint>
+
+#include "platform/port/string.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+// A type 3 name-based
+// (https://en.wikipedia.org/wiki/Universally_unique_identifier#Versions_3_and_5_(namespace_name-based))
+// UUID.
+//
+// https://developer.android.com/reference/java/util/UUID.html
+template <typename Platform>
+class UUID {
+ public:
+  explicit UUID(const string& data);
+  UUID(std::int64_t most_sig_bits, std::int64_t least_sig_bits);
+  ~UUID();
+
+  // Returns the canonical textual representation
+  // (https://en.wikipedia.org/wiki/Universally_unique_identifier#Format) of the
+  // UUID.
+  string str();
+
+ private:
+  string data_;
+};
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#include "core/internal/mediums/uuid.cc"
+
+#endif  // CORE_INTERNAL_MEDIUMS_UUID_H_

cpp/core/internal/offline_frames.cc

@@ -0,0 +1,268 @@
+#include "core/internal/offline_frames.h"
+
+#include "platform/port/down_cast.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+namespace {
+
+template <typename T>
+T *downcastToRaw(Ptr<proto_ns::MessageLite> message) {
+  return DOWN_CAST<T *>(message.operator->());
+}
+
+// This method takes ownership of the passed-in 'message'.
+//
+// This can be implemented more efficiently by taking in a reference to an
+// OfflineFrame object created on the caller's stack, but we instead create it
+// on the heap and return a Ptr to it for the sake of consistency.
+ConstPtr<OfflineFrame> newOfflineFrame(V1Frame::FrameType frame_type,
+                                       Ptr<proto_ns::MessageLite> message) {
+  V1Frame *v1_frame = new V1Frame();
+  v1_frame->set_type(frame_type);
+
+  switch (frame_type) {
+    case V1Frame::CONNECTION_REQUEST:
+      v1_frame->set_allocated_connection_request(
+          downcastToRaw<ConnectionRequestFrame>(message));
+      break;
+    case V1Frame::CONNECTION_RESPONSE:
+      v1_frame->set_allocated_connection_response(
+          downcastToRaw<ConnectionResponseFrame>(message));
+      break;
+    case V1Frame::PAYLOAD_TRANSFER:
+      v1_frame->set_allocated_payload_transfer(
+          downcastToRaw<PayloadTransferFrame>(message));
+      break;
+    case V1Frame::BANDWIDTH_UPGRADE_NEGOTIATION:
+      v1_frame->set_allocated_bandwidth_upgrade_negotiation(
+          downcastToRaw<BandwidthUpgradeNegotiationFrame>(message));
+      break;
+    case V1Frame::KEEP_ALIVE:
+      v1_frame->set_allocated_keep_alive(
+          downcastToRaw<KeepAliveFrame>(message));
+      break;
+    default:
+      break;
+  }
+
+  Ptr<OfflineFrame> offline_frame(new OfflineFrame());
+  offline_frame->set_version(OfflineFrame::V1);
+  offline_frame->set_allocated_v1(v1_frame);
+  return ConstifyPtr(offline_frame);
+}
+
+// This method takes ownership of the passed-in 'offline_frame' and destroys it
+// before returning.
+ConstPtr<ByteArray> toBytes(ConstPtr<OfflineFrame> offline_frame) {
+  ScopedPtr<ConstPtr<OfflineFrame> > scoped_offline_frame(offline_frame);
+
+  size_t serialized_size = offline_frame->ByteSizeLong();
+  Ptr<ByteArray> bytes{new ByteArray{serialized_size}};
+
+  offline_frame->SerializeToArray(bytes->getData(), serialized_size);
+  return ConstifyPtr(bytes);
+}
+
+}  // namespace
+
+ExceptionOr<ConstPtr<OfflineFrame> > OfflineFrames::fromBytes(
+    ConstPtr<ByteArray> offline_frame_bytes) {
+  ScopedPtr<Ptr<OfflineFrame> > offline_frame(new OfflineFrame());
+
+  if (!offline_frame->ParseFromArray(offline_frame_bytes->getData(),
+                                     offline_frame_bytes->size())) {
+    return ExceptionOr<ConstPtr<OfflineFrame> >(
+        Exception::INVALID_PROTOCOL_BUFFER);
+  }
+
+  return ExceptionOr<ConstPtr<OfflineFrame> >(
+      ConstifyPtr(offline_frame.release()));
+}
+
+V1Frame::FrameType OfflineFrames::getFrameType(
+    ConstPtr<OfflineFrame> offline_frame) {
+  if ((offline_frame->version() == OfflineFrame::V1) &&
+      offline_frame->has_v1()) {
+    return offline_frame->v1().type();
+  }
+
+  return V1Frame::UNKNOWN_FRAME_TYPE;
+}
+
+ConstPtr<ByteArray> OfflineFrames::forConnectionRequest(
+    const std::string &endpoint_id, const std::string &endpoint_name,
+    std::int32_t nonce,
+    const std::vector<proto::connections::Medium> &mediums) {
+  Ptr<ConnectionRequestFrame> connection_request(new ConnectionRequestFrame());
+  connection_request->set_endpoint_id(endpoint_id);
+  connection_request->set_endpoint_name(endpoint_name);
+  connection_request->set_nonce(nonce);
+
+  for (std::vector<proto::connections::Medium>::const_iterator it =
+           mediums.begin();
+       it != mediums.end(); it++) {
+    connection_request->add_mediums(mediumToConnectionRequestMedium(*it));
+  }
+
+  return toBytes(
+      newOfflineFrame(V1Frame::CONNECTION_REQUEST, connection_request));
+}
+
+ConstPtr<ByteArray> OfflineFrames::forConnectionResponse(std::int32_t status) {
+  Ptr<ConnectionResponseFrame> connection_response(
+      new ConnectionResponseFrame());
+  connection_response->set_status(status);
+
+  return toBytes(
+      newOfflineFrame(V1Frame::CONNECTION_RESPONSE, connection_response));
+}
+
+ConstPtr<ByteArray> OfflineFrames::forDataPayloadTransferFrame(
+    const PayloadTransferFrame::PayloadHeader &header,
+    const PayloadTransferFrame::PayloadChunk &chunk) {
+  Ptr<PayloadTransferFrame> payload_transfer(new PayloadTransferFrame());
+  payload_transfer->set_packet_type(PayloadTransferFrame::DATA);
+  *payload_transfer->mutable_payload_header() = header;
+  *payload_transfer->mutable_payload_chunk() = chunk;
+
+  return toBytes(newOfflineFrame(V1Frame::PAYLOAD_TRANSFER, payload_transfer));
+}
+
+ConstPtr<ByteArray> OfflineFrames::forControlPayloadTransferFrame(
+    const PayloadTransferFrame::PayloadHeader &header,
+    const PayloadTransferFrame::ControlMessage &control) {
+  Ptr<PayloadTransferFrame> payload_transfer(new PayloadTransferFrame());
+  payload_transfer->set_packet_type(PayloadTransferFrame::CONTROL);
+  *payload_transfer->mutable_payload_header() = header;
+  *payload_transfer->mutable_control_message() = control;
+
+  return toBytes(newOfflineFrame(V1Frame::PAYLOAD_TRANSFER, payload_transfer));
+}
+
+ConstPtr<ByteArray> OfflineFrames::
+    forWifiHotspotUpgradePathAvailableBandwidthUpgradeNegotiationEvent(
+        const std::string &ssid, const std::string &password,
+        std::int32_t port) {
+  BandwidthUpgradeNegotiationFrame::UpgradePathInfo::WifiHotspotCredentials
+      *wifi_hotspot_credentials = new BandwidthUpgradeNegotiationFrame::
+          UpgradePathInfo::WifiHotspotCredentials();
+  wifi_hotspot_credentials->set_ssid(ssid);
+  wifi_hotspot_credentials->set_password(password);
+  wifi_hotspot_credentials->set_port(port);
+
+  BandwidthUpgradeNegotiationFrame::UpgradePathInfo *upgrade_path_info =
+      new BandwidthUpgradeNegotiationFrame::UpgradePathInfo();
+  upgrade_path_info->set_medium(
+      BandwidthUpgradeNegotiationFrame::UpgradePathInfo::WIFI_HOTSPOT);
+  upgrade_path_info->set_allocated_wifi_hotspot_credentials(
+      wifi_hotspot_credentials);
+
+  Ptr<BandwidthUpgradeNegotiationFrame> bandwidth_upgrade_negotiation(
+      new BandwidthUpgradeNegotiationFrame());
+  bandwidth_upgrade_negotiation->set_event_type(
+      BandwidthUpgradeNegotiationFrame::UPGRADE_PATH_AVAILABLE);
+  bandwidth_upgrade_negotiation->set_allocated_upgrade_path_info(
+      upgrade_path_info);
+
+  return toBytes(newOfflineFrame(V1Frame::BANDWIDTH_UPGRADE_NEGOTIATION,
+                                 bandwidth_upgrade_negotiation));
+}
+
+ConstPtr<ByteArray>
+OfflineFrames::forLastWriteToPriorChannelBandwidthUpgradeNegotiationEvent() {
+  Ptr<BandwidthUpgradeNegotiationFrame> bandwidth_upgrade_negotiation(
+      new BandwidthUpgradeNegotiationFrame());
+  bandwidth_upgrade_negotiation->set_event_type(
+      BandwidthUpgradeNegotiationFrame::LAST_WRITE_TO_PRIOR_CHANNEL);
+
+  return toBytes(newOfflineFrame(V1Frame::BANDWIDTH_UPGRADE_NEGOTIATION,
+                                 bandwidth_upgrade_negotiation));
+}
+
+ConstPtr<ByteArray>
+OfflineFrames::forSafeToClosePriorChannelBandwidthUpgradeNegotiationEvent() {
+  Ptr<BandwidthUpgradeNegotiationFrame> bandwidth_upgrade_negotiation(
+      new BandwidthUpgradeNegotiationFrame());
+  bandwidth_upgrade_negotiation->set_event_type(
+      BandwidthUpgradeNegotiationFrame::SAFE_TO_CLOSE_PRIOR_CHANNEL);
+
+  return toBytes(newOfflineFrame(V1Frame::BANDWIDTH_UPGRADE_NEGOTIATION,
+                                 bandwidth_upgrade_negotiation));
+}
+
+ConstPtr<ByteArray>
+OfflineFrames::forClientIntroductionBandwidthUpgradeNegotiationEvent(
+    const std::string &endpoint_id) {
+  BandwidthUpgradeNegotiationFrame::ClientIntroduction *client_introduction =
+      new BandwidthUpgradeNegotiationFrame::ClientIntroduction();
+  client_introduction->set_endpoint_id(endpoint_id);
+
+  Ptr<BandwidthUpgradeNegotiationFrame> bandwidth_upgrade_negotiation(
+      new BandwidthUpgradeNegotiationFrame());
+  bandwidth_upgrade_negotiation->set_event_type(
+      BandwidthUpgradeNegotiationFrame::CLIENT_INTRODUCTION);
+  bandwidth_upgrade_negotiation->set_allocated_client_introduction(
+      client_introduction);
+
+  return toBytes(newOfflineFrame(V1Frame::BANDWIDTH_UPGRADE_NEGOTIATION,
+                                 bandwidth_upgrade_negotiation));
+}
+
+ConstPtr<ByteArray> OfflineFrames::forKeepAlive() {
+  Ptr<KeepAliveFrame> keep_alive_frame(new KeepAliveFrame());
+  return toBytes(newOfflineFrame(V1Frame::KEEP_ALIVE, keep_alive_frame));
+}
+
+ConnectionRequestFrame::Medium OfflineFrames::mediumToConnectionRequestMedium(
+    proto::connections::Medium medium) {
+  switch (medium) {
+    case proto::connections::MDNS:
+      return ConnectionRequestFrame::MDNS;
+    case proto::connections::BLUETOOTH:
+      return ConnectionRequestFrame::BLUETOOTH;
+    case proto::connections::WIFI_HOTSPOT:
+      return ConnectionRequestFrame::WIFI_HOTSPOT;
+    case proto::connections::BLE:
+      return ConnectionRequestFrame::BLE;
+    case proto::connections::WIFI_LAN:
+      return ConnectionRequestFrame::WIFI_LAN;
+    default:
+      return ConnectionRequestFrame::UNKNOWN_MEDIUM;
+  }
+}
+
+proto::connections::Medium OfflineFrames::connectionRequestMediumToMedium(
+    ConnectionRequestFrame::Medium medium) {
+  switch (medium) {
+    case ConnectionRequestFrame::MDNS:
+      return proto::connections::Medium::MDNS;
+    case ConnectionRequestFrame::BLUETOOTH:
+      return proto::connections::Medium::BLUETOOTH;
+    case ConnectionRequestFrame::WIFI_HOTSPOT:
+      return proto::connections::Medium::WIFI_HOTSPOT;
+    case ConnectionRequestFrame::BLE:
+      return proto::connections::Medium::BLE;
+    case ConnectionRequestFrame::WIFI_LAN:
+      return proto::connections::Medium::WIFI_LAN;
+    default:
+      return proto::connections::Medium::UNKNOWN_MEDIUM;
+  }
+}
+
+std::vector<proto::connections::Medium>
+OfflineFrames::connectionRequestMediumsToMediums(
+    const ConnectionRequestFrame &connection_request_frame) {
+  std::vector<proto::connections::Medium> result;
+  for (size_t i = 0; i < connection_request_frame.mediums_size(); i++) {
+    result.push_back(
+        connectionRequestMediumToMedium(connection_request_frame.mediums(i)));
+  }
+  return result;
+}
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/offline_frames.h

@@ -0,0 +1,70 @@
+#ifndef CORE_INTERNAL_OFFLINE_FRAMES_H_
+#define CORE_INTERNAL_OFFLINE_FRAMES_H_
+
+#include <cstdint>
+#include <vector>
+
+#include "proto/connections/offline_wire_formats.pb.h"
+#include "platform/byte_array.h"
+#include "platform/exception.h"
+#include "platform/port/string.h"
+#include "platform/ptr.h"
+#include "proto/connections_enums.pb.h"
+
+// Detects the right usage.
+#include "google/protobuf/message_lite.h"
+#define proto_ns google3_proto_compat
+
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+class OfflineFrames {
+ public:
+  static ExceptionOr<ConstPtr<OfflineFrame> > fromBytes(
+      ConstPtr<ByteArray>
+          offline_frame_bytes);  // throws Exception::INVALID_PROTOCOL_BUFFER
+
+  static V1Frame::FrameType getFrameType(ConstPtr<OfflineFrame> offline_frame);
+
+  static ConstPtr<ByteArray> forConnectionRequest(
+      const std::string& endpoint_id, const std::string& endpoint_name,
+      std::int32_t nonce,
+      const std::vector<proto::connections::Medium>& mediums);
+  static ConstPtr<ByteArray> forConnectionResponse(std::int32_t status);
+
+  static ConstPtr<ByteArray> forDataPayloadTransferFrame(
+      const PayloadTransferFrame::PayloadHeader& header,
+      const PayloadTransferFrame::PayloadChunk& chunk);
+  static ConstPtr<ByteArray> forControlPayloadTransferFrame(
+      const PayloadTransferFrame::PayloadHeader& header,
+      const PayloadTransferFrame::ControlMessage& control);
+
+  static ConstPtr<ByteArray>
+  forWifiHotspotUpgradePathAvailableBandwidthUpgradeNegotiationEvent(
+      const std::string& ssid, const std::string& password, std::int32_t port);
+  static ConstPtr<ByteArray>
+  forLastWriteToPriorChannelBandwidthUpgradeNegotiationEvent();
+  static ConstPtr<ByteArray>
+  forSafeToClosePriorChannelBandwidthUpgradeNegotiationEvent();
+  static ConstPtr<ByteArray>
+  forClientIntroductionBandwidthUpgradeNegotiationEvent(
+      const std::string& endpoint_id);
+
+  static ConstPtr<ByteArray> forKeepAlive();
+
+  static ConnectionRequestFrame::Medium mediumToConnectionRequestMedium(
+      proto::connections::Medium medium);
+  static proto::connections::Medium connectionRequestMediumToMedium(
+      ConnectionRequestFrame::Medium medium);
+  static std::vector<proto::connections::Medium>
+  connectionRequestMediumsToMediums(
+      const ConnectionRequestFrame& connection_request_frame);
+};
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#endif  // CORE_INTERNAL_OFFLINE_FRAMES_H_

cpp/core/internal/offline_service_controller.cc

@@ -0,0 +1,110 @@
+#include "core/internal/offline_service_controller.h"
+
+#include <string>
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+template <typename Platform>
+OfflineServiceController<Platform>::OfflineServiceController()
+    : ServiceController<Platform>(),
+      medium_manager_(new MediumManager<Platform>()),
+      endpoint_channel_manager_(
+          new EndpointChannelManager<Platform>(medium_manager_.get())),
+      endpoint_manager_(
+          new EndpointManager<Platform>(endpoint_channel_manager_.get())),
+      payload_manager_(new PayloadManager<Platform>(endpoint_manager_.get())),
+      bandwidth_upgrade_manager_(new BandwidthUpgradeManager<Platform>(
+          medium_manager_.get(), endpoint_channel_manager_.get(),
+          endpoint_manager_.get())),
+      pcp_manager_(new PCPManager<Platform>(
+          medium_manager_.get(), endpoint_channel_manager_.get(),
+          endpoint_manager_.get(), bandwidth_upgrade_manager_.get())) {}
+
+template <typename Platform>
+OfflineServiceController<Platform>::~OfflineServiceController() {}
+
+template <typename Platform>
+Status::Value OfflineServiceController<Platform>::startAdvertising(
+    Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_name,
+    const string& service_id, const AdvertisingOptions& advertising_options,
+    Ptr<ConnectionLifecycleListener> connection_lifecycle_listener) {
+  return pcp_manager_->startAdvertising(client_proxy, endpoint_name, service_id,
+                                        advertising_options,
+                                        connection_lifecycle_listener);
+}
+
+template <typename Platform>
+void OfflineServiceController<Platform>::stopAdvertising(
+    Ptr<ClientProxy<Platform> > client_proxy) {
+  pcp_manager_->stopAdvertising(client_proxy);
+}
+
+template <typename Platform>
+Status::Value OfflineServiceController<Platform>::startDiscovery(
+    Ptr<ClientProxy<Platform> > client_proxy, const string& service_id,
+    const DiscoveryOptions& discovery_options,
+    Ptr<DiscoveryListener> discovery_listener) {
+  return pcp_manager_->startDiscovery(client_proxy, service_id,
+                                      discovery_options, discovery_listener);
+}
+
+template <typename Platform>
+void OfflineServiceController<Platform>::stopDiscovery(
+    Ptr<ClientProxy<Platform> > client_proxy) {
+  pcp_manager_->stopDiscovery(client_proxy);
+}
+
+template <typename Platform>
+Status::Value OfflineServiceController<Platform>::requestConnection(
+    Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_name,
+    const string& endpoint_id,
+    Ptr<ConnectionLifecycleListener> connection_lifecycle_listener) {
+  return pcp_manager_->requestConnection(
+      client_proxy, endpoint_name, endpoint_id, connection_lifecycle_listener);
+}
+
+template <typename Platform>
+Status::Value OfflineServiceController<Platform>::acceptConnection(
+    Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_id,
+    Ptr<PayloadListener> payload_listener) {
+  return pcp_manager_->acceptConnection(client_proxy, endpoint_id,
+                                        payload_listener);
+}
+
+template <typename Platform>
+Status::Value OfflineServiceController<Platform>::rejectConnection(
+    Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_id) {
+  return pcp_manager_->rejectConnection(client_proxy, endpoint_id);
+}
+
+template <typename Platform>
+void OfflineServiceController<Platform>::initiateBandwidthUpgrade(
+    Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_id) {
+  bandwidth_upgrade_manager_->initiateBandwidthUpgradeForEndpoint(
+      client_proxy, endpoint_id, pcp_manager_->getBandwidthUpgradeMedium());
+}
+
+template <typename Platform>
+void OfflineServiceController<Platform>::sendPayload(
+    Ptr<ClientProxy<Platform> > client_proxy,
+    const std::vector<string>& endpoint_ids, ConstPtr<Payload> payload) {
+  payload_manager_->sendPayload(client_proxy, endpoint_ids, payload);
+}
+
+template <typename Platform>
+Status::Value OfflineServiceController<Platform>::cancelPayload(
+    Ptr<ClientProxy<Platform> > client_proxy, std::int64_t payload_id) {
+  return payload_manager_->cancelPayload(client_proxy, payload_id);
+}
+
+template <typename Platform>
+void OfflineServiceController<Platform>::disconnectFromEndpoint(
+    Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_id) {
+  endpoint_manager_->unregisterEndpoint(client_proxy, endpoint_id);
+}
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/offline_service_controller.h

@@ -0,0 +1,85 @@
+#ifndef CORE_INTERNAL_OFFLINE_SERVICE_CONTROLLER_H_
+#define CORE_INTERNAL_OFFLINE_SERVICE_CONTROLLER_H_
+
+#include <cstdint>
+#include <vector>
+
+#include "core/internal/bandwidth_upgrade_manager.h"
+#include "core/internal/client_proxy.h"
+#include "core/internal/endpoint_channel_manager.h"
+#include "core/internal/endpoint_manager.h"
+#include "core/internal/medium_manager.h"
+#include "core/internal/payload_manager.h"
+#include "core/internal/pcp_manager.h"
+#include "core/internal/service_controller.h"
+#include "core/listeners.h"
+#include "core/options.h"
+#include "core/payload.h"
+#include "core/status.h"
+#include "platform/port/string.h"
+#include "platform/ptr.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+template <typename Platform>
+class OfflineServiceController : public ServiceController<Platform> {
+ public:
+  OfflineServiceController();
+  ~OfflineServiceController() override;
+
+  Status::Value startAdvertising(
+      Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_name,
+      const string& service_id, const AdvertisingOptions& advertising_options,
+      Ptr<ConnectionLifecycleListener> connection_lifecycle_listener) override;
+  void stopAdvertising(Ptr<ClientProxy<Platform> > client_proxy) override;
+
+  Status::Value startDiscovery(
+      Ptr<ClientProxy<Platform> > client_proxy, const string& service_id,
+      const DiscoveryOptions& discovery_options,
+      Ptr<DiscoveryListener> discovery_listener) override;
+  void stopDiscovery(Ptr<ClientProxy<Platform> > client_proxy) override;
+
+  Status::Value requestConnection(
+      Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_name,
+      const string& endpoint_id,
+      Ptr<ConnectionLifecycleListener> connection_lifecycle_listener) override;
+  Status::Value acceptConnection(
+      Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_id,
+      Ptr<PayloadListener> payload_listener) override;
+  Status::Value rejectConnection(Ptr<ClientProxy<Platform> > client_proxy,
+                                 const string& endpoint_id) override;
+
+  void initiateBandwidthUpgrade(Ptr<ClientProxy<Platform> > client_proxy,
+                                const string& endpoint_id) override;
+
+  void sendPayload(Ptr<ClientProxy<Platform> > client_proxy,
+                   const std::vector<string>& endpoint_ids,
+                   ConstPtr<Payload> payload) override;
+  Status::Value cancelPayload(Ptr<ClientProxy<Platform> > client_proxy,
+                              std::int64_t payload_id) override;
+
+  void disconnectFromEndpoint(Ptr<ClientProxy<Platform> > client_proxy,
+                              const string& endpoint_id) override;
+
+ private:
+  // Note that the order of declaration of these is crucial, because we depend
+  // on the destructors running (strictly) in the reverse order; a deviation
+  // from that will lead to crashes at runtime.
+  ScopedPtr<Ptr<MediumManager<Platform> > > medium_manager_;
+  ScopedPtr<Ptr<EndpointChannelManager<Platform> > > endpoint_channel_manager_;
+  ScopedPtr<Ptr<EndpointManager<Platform> > > endpoint_manager_;
+  ScopedPtr<Ptr<PayloadManager<Platform> > > payload_manager_;
+  ScopedPtr<Ptr<BandwidthUpgradeManager<Platform> > >
+      bandwidth_upgrade_manager_;
+  ScopedPtr<Ptr<PCPManager<Platform> > > pcp_manager_;
+};
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#include "core/internal/offline_service_controller.cc"
+
+#endif  // CORE_INTERNAL_OFFLINE_SERVICE_CONTROLLER_H_

cpp/core/internal/p2p_cluster_pcp_handler.cc

@@ -0,0 +1,788 @@
+#include "core/internal/p2p_cluster_pcp_handler.h"
+
+#include "platform/api/hash_utils.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+template <typename Platform>
+const BluetoothDeviceName::Version::Value
+    P2PClusterPCPHandler<Platform>::kBluetoothDeviceNameVersion =
+        BluetoothDeviceName::Version::V1;
+
+template <typename Platform>
+const BLEAdvertisement::Version::Value
+    P2PClusterPCPHandler<Platform>::kBleAdvertisementVersion =
+        BLEAdvertisement::Version::V1;
+
+template <typename Platform>
+ConstPtr<ByteArray> P2PClusterPCPHandler<Platform>::generateHash(
+    const string& source, size_t size) {
+  // Initiazing a new HashUtils each time instead of making it a class member
+  // because FoundBluetoothAdvertisementProcessor uses generateHash in its
+  // constructor so this method has to be static. We *could* make a static
+  // ScopedPtr for HashUtils, but that can get into dangerous territory in terms
+  // of time of destruction of that object, so we'll avoid it for now, and stick
+  // with this.
+  ScopedPtr<Ptr<HashUtils>> hash_utils(Platform::createHashUtils());
+
+  ScopedPtr<ConstPtr<ByteArray>> scoped_hash(hash_utils->sha256(source));
+  return MakeConstPtr(new ByteArray(scoped_hash->getData(), size));
+}
+
+template <typename Platform>
+P2PClusterPCPHandler<Platform>::P2PClusterPCPHandler(
+    Ptr<MediumManager<Platform>> medium_manager,
+    Ptr<EndpointManager<Platform>> endpoint_manager,
+    Ptr<EndpointChannelManager<Platform>> endpoint_channel_manager,
+    Ptr<BandwidthUpgradeManager<Platform>> bandwidth_upgrade_manager)
+    : BasePCPHandler<Platform>(endpoint_manager, endpoint_channel_manager,
+                               bandwidth_upgrade_manager),
+      medium_manager_(medium_manager) {}
+
+template <typename Platform>
+P2PClusterPCPHandler<Platform>::~P2PClusterPCPHandler() {}
+
+template <typename Platform>
+Strategy P2PClusterPCPHandler<Platform>::getStrategy() {
+  return Strategy::kP2PCluster;
+}
+
+template <typename Platform>
+PCP::Value P2PClusterPCPHandler<Platform>::getPCP() {
+  return PCP::P2P_CLUSTER;
+}
+
+template <typename Platform>
+std::vector<proto::connections::Medium>
+P2PClusterPCPHandler<Platform>::getConnectionMediumsByPriority() {
+  std::vector<proto::connections::Medium> mediums;
+  if (medium_manager_->isBluetoothAvailable()) {
+    mediums.push_back(proto::connections::BLUETOOTH);
+  }
+  if (medium_manager_->isBleAvailable()) {
+    mediums.push_back(proto::connections::BLE);
+  }
+  return mediums;
+}
+
+template <typename Platform>
+proto::connections::Medium
+P2PClusterPCPHandler<Platform>::getDefaultUpgradeMedium() {
+  return proto::connections::WIFI_LAN;
+}
+
+template <typename Platform>
+Ptr<typename BasePCPHandler<Platform>::StartOperationResult>
+P2PClusterPCPHandler<Platform>::startAdvertisingImpl(
+    Ptr<ClientProxy<Platform>> client_proxy, const string& service_id,
+    const string& local_endpoint_id, const string& local_endpoint_name,
+    const AdvertisingOptions& options) {
+  std::vector<proto::connections::Medium> mediums_started_successfully;
+
+  ScopedPtr<ConstPtr<ByteArray>> scoped_bluetooth_service_id_hash(
+      generateHash(service_id, BluetoothDeviceName::kServiceIdHashLength));
+  proto::connections::Medium bluetooth_medium = startBluetoothAdvertising(
+      client_proxy, service_id, scoped_bluetooth_service_id_hash.get(),
+      local_endpoint_id, local_endpoint_name);
+  if (proto::connections::UNKNOWN_MEDIUM != bluetooth_medium) {
+    mediums_started_successfully.push_back(bluetooth_medium);
+  }
+
+  ScopedPtr<ConstPtr<ByteArray>> scoped_ble_service_id_hash(
+      generateHash(service_id, BLEAdvertisement::kServiceIdHashLength));
+  proto::connections::Medium ble_medium = startBleAdvertising(
+      client_proxy, service_id, scoped_ble_service_id_hash.get(),
+      local_endpoint_id, local_endpoint_name);
+  if (proto::connections::UNKNOWN_MEDIUM != ble_medium) {
+    mediums_started_successfully.push_back(ble_medium);
+  }
+
+  if (mediums_started_successfully.empty()) {
+    // TODO(tracyzhou): Add logging.
+    return BasePCPHandler<Platform>::StartOperationResult::error(
+        Status::BLUETOOTH_ERROR);
+  }
+
+  // The rest of the operations for startAdvertising() will continue
+  // asynchronously via
+  // IncomingBluetoothConnectionProcessor.onIncomingBluetoothConnection(), so
+  // leave it to that to signal any errors that may occur.
+  return BasePCPHandler<Platform>::StartOperationResult::success(
+      mediums_started_successfully);
+}
+
+template <typename Platform>
+Status::Value P2PClusterPCPHandler<Platform>::stopAdvertisingImpl(
+    Ptr<ClientProxy<Platform>> client_proxy) {
+  medium_manager_->stopBleAdvertising(client_proxy->getAdvertisingServiceId());
+  medium_manager_->turnOffBluetoothDiscoverability();
+  medium_manager_->stopListeningForIncomingBleConnections(
+      client_proxy->getAdvertisingServiceId());
+  medium_manager_->stopListeningForIncomingBluetoothConnections(
+      client_proxy->getAdvertisingServiceId());
+  return Status::SUCCESS;
+}
+
+template <typename Platform>
+Ptr<typename BasePCPHandler<Platform>::StartOperationResult>
+P2PClusterPCPHandler<Platform>::startDiscoveryImpl(
+    Ptr<ClientProxy<Platform>> client_proxy, const string& service_id,
+    const DiscoveryOptions& options) {
+  std::vector<proto::connections::Medium> mediums_started_successfully;
+
+  proto::connections::Medium bluetooth_medium =
+      startBluetoothDiscovery(MakePtr(new FoundBluetoothAdvertisementProcessor(
+                                  MakePtr(this), client_proxy, service_id)),
+                              client_proxy, service_id);
+  if (proto::connections::UNKNOWN_MEDIUM != bluetooth_medium) {
+    mediums_started_successfully.push_back(bluetooth_medium);
+  }
+
+  proto::connections::Medium ble_medium = startBleDiscovery(
+      MakePtr(new FoundBleAdvertisementProcessor(MakePtr(this), client_proxy)),
+      client_proxy, service_id);
+  if (proto::connections::UNKNOWN_MEDIUM != ble_medium) {
+    mediums_started_successfully.push_back(ble_medium);
+  }
+
+  if (mediums_started_successfully.empty()) {
+    // TODO(tracyzhou): Add logging.
+    return BasePCPHandler<Platform>::StartOperationResult::error(
+        Status::BLUETOOTH_ERROR);
+  }
+
+  return BasePCPHandler<Platform>::StartOperationResult::success(
+      mediums_started_successfully);
+}
+
+template <typename Platform>
+Status::Value P2PClusterPCPHandler<Platform>::stopDiscoveryImpl(
+    Ptr<ClientProxy<Platform>> client_proxy) {
+  medium_manager_->stopBleScanning(client_proxy->getDiscoveryServiceId());
+  medium_manager_->stopScanningForBluetoothDevices();
+  return Status::SUCCESS;
+}
+
+template <typename Platform>
+typename BasePCPHandler<Platform>::ConnectImplResult
+P2PClusterPCPHandler<Platform>::connectImpl(
+    Ptr<ClientProxy<Platform>> client_proxy,
+    Ptr<typename BasePCPHandler<Platform>::DiscoveredEndpoint> endpoint) {
+  Ptr<BluetoothEndpoint> bluetooth_endpoint =
+      DowncastPtr<BluetoothEndpoint>(endpoint);
+  if (!bluetooth_endpoint.isNull()) {
+    return bluetoothConnectImpl(client_proxy, bluetooth_endpoint);
+  }
+
+  Ptr<BLEEndpoint> ble_endpoint = DowncastPtr<BLEEndpoint>(endpoint);
+  if (!ble_endpoint.isNull()) {
+    return bleConnectImpl(client_proxy, ble_endpoint);
+  }
+
+  return typename BasePCPHandler<Platform>::ConnectImplResult(
+      proto::connections::Medium::UNKNOWN_MEDIUM, Status::ERROR);
+}
+
+/////////////////// START IMPLEMENTATIONS FOR NESTED CLASSES ///////////////////
+
+///////// P2PClusterPCPHandler::IncomingBluetoothConnectionProcessor //////////
+template <typename Platform>
+P2PClusterPCPHandler<Platform>::IncomingBluetoothConnectionProcessor::
+    IncomingBluetoothConnectionProcessor(
+        Ptr<P2PClusterPCPHandler<Platform>> pcp_handler,
+        Ptr<ClientProxy<Platform>> client_proxy,
+        const string& local_endpoint_name)
+    : pcp_handler_(pcp_handler),
+      client_proxy_(client_proxy),
+      local_endpoint_name_(local_endpoint_name) {}
+
+template <typename Platform>
+void P2PClusterPCPHandler<Platform>::IncomingBluetoothConnectionProcessor::
+    onIncomingBluetoothConnection(Ptr<BluetoothSocket> bluetooth_socket) {
+  pcp_handler_->runOnPCPHandlerThread(
+      MakePtr(new OnIncomingBluetoothConnectionRunnable(
+          pcp_handler_, client_proxy_, bluetooth_socket)));
+}
+
+template <typename Platform>
+P2PClusterPCPHandler<Platform>::IncomingBluetoothConnectionProcessor::
+    OnIncomingBluetoothConnectionRunnable::
+        OnIncomingBluetoothConnectionRunnable(
+            Ptr<P2PClusterPCPHandler<Platform>> pcp_handler,
+            Ptr<ClientProxy<Platform>> client_proxy,
+            Ptr<BluetoothSocket> bluetooth_socket)
+    : pcp_handler_(pcp_handler),
+      client_proxy_(client_proxy),
+      bluetooth_socket_(bluetooth_socket) {}
+
+template <typename Platform>
+void P2PClusterPCPHandler<Platform>::IncomingBluetoothConnectionProcessor::
+    OnIncomingBluetoothConnectionRunnable::run() {
+  string remote_device_name = bluetooth_socket_->getRemoteDevice()->getName();
+  ScopedPtr<Ptr<EndpointChannel>> scoped_bluetooth_endpoint_channel(
+      pcp_handler_->endpoint_channel_manager_
+          ->createIncomingBluetoothEndpointChannel(remote_device_name,
+                                                   bluetooth_socket_));
+  if (!scoped_bluetooth_endpoint_channel.isNull()) {
+    // TODO(tracyzhou): Add logging.
+  } else {
+    Exception::Value exception = bluetooth_socket_->close();
+    bluetooth_socket_.destroy();
+    if (Exception::NONE != exception) {
+      if (Exception::IO == exception) {
+        // TODO(tracyzhou): Add logging.
+      }
+    }
+  }
+  pcp_handler_->onIncomingConnection(
+      client_proxy_, remote_device_name,
+      scoped_bluetooth_endpoint_channel.release(),
+      proto::connections::Medium::BLUETOOTH);
+}
+
+//////////// P2PClusterPCPHandler::IncomingBleConnectionProcessor /////////////
+template <typename Platform>
+P2PClusterPCPHandler<Platform>::IncomingBleConnectionProcessor::
+    IncomingBleConnectionProcessor(
+        Ptr<P2PClusterPCPHandler<Platform>> pcp_handler,
+        Ptr<ClientProxy<Platform>> client_proxy,
+        const string& local_endpoint_name)
+    : pcp_handler_(pcp_handler),
+      client_proxy_(client_proxy),
+      local_endpoint_name_(local_endpoint_name) {}
+
+template <typename Platform>
+void P2PClusterPCPHandler<Platform>::IncomingBleConnectionProcessor::
+    onIncomingBleConnection(Ptr<BLESocket> ble_socket,
+                            const string& service_id) {
+  pcp_handler_->runOnPCPHandlerThread(
+      MakePtr(new OnIncomingBleConnectionRunnable(pcp_handler_, client_proxy_,
+                                                  ble_socket)));
+}
+
+template <typename Platform>
+P2PClusterPCPHandler<Platform>::IncomingBleConnectionProcessor::
+    OnIncomingBleConnectionRunnable::OnIncomingBleConnectionRunnable(
+        Ptr<P2PClusterPCPHandler<Platform>> pcp_handler,
+        Ptr<ClientProxy<Platform>> client_proxy, Ptr<BLESocket> ble_socket)
+    : pcp_handler_(pcp_handler),
+      client_proxy_(client_proxy),
+      ble_socket_(ble_socket) {}
+
+template <typename Platform>
+void P2PClusterPCPHandler<Platform>::IncomingBleConnectionProcessor::
+    OnIncomingBleConnectionRunnable::run() {
+  string remote_device_name =
+      ble_socket_->getRemotePeripheral()->getBluetoothDevice()->getName();
+  ScopedPtr<Ptr<EndpointChannel>> scoped_ble_endpoint_channel(
+      pcp_handler_->endpoint_channel_manager_->createIncomingBLEEndpointChannel(
+          remote_device_name, ble_socket_));
+  if (!scoped_ble_endpoint_channel.isNull()) {
+    // TODO(ahlee): Add logging.
+  } else {
+    Exception::Value exception = ble_socket_->close();
+    ble_socket_.destroy();
+    if (Exception::NONE != exception) {
+      if (Exception::IO == exception) {
+        // TODO(ahlee): Add logging.
+      }
+    }
+  }
+  pcp_handler_->onIncomingConnection(client_proxy_, remote_device_name,
+                                     scoped_ble_endpoint_channel.release(),
+                                     proto::connections::Medium::BLE);
+}
+
+///////// P2PClusterPCPHandler::FoundBluetoothAdvertisementProcessor //////////
+template <typename Platform>
+P2PClusterPCPHandler<Platform>::FoundBluetoothAdvertisementProcessor::
+    FoundBluetoothAdvertisementProcessor(
+        Ptr<P2PClusterPCPHandler<Platform>> pcp_handler,
+        Ptr<ClientProxy<Platform>> client_proxy, const string& service_id)
+    : pcp_handler_(pcp_handler),
+      client_proxy_(client_proxy),
+      service_id_(service_id),
+      expected_service_id_hash_(generateHash(
+          service_id, BluetoothDeviceName::kServiceIdHashLength)) {}
+
+template <typename Platform>
+void P2PClusterPCPHandler<Platform>::FoundBluetoothAdvertisementProcessor::
+    onFoundBluetoothDevice(Ptr<BluetoothDevice> bluetooth_device) {
+  pcp_handler_->runOnPCPHandlerThread(
+      MakePtr(new OnFoundBluetoothDeviceRunnable(pcp_handler_, client_proxy_,
+                                                 MakePtr(this), service_id_,
+                                                 bluetooth_device)));
+}
+
+template <typename Platform>
+void P2PClusterPCPHandler<Platform>::FoundBluetoothAdvertisementProcessor::
+    onLostBluetoothDevice(Ptr<BluetoothDevice> bluetooth_device) {
+  pcp_handler_->runOnPCPHandlerThread(MakePtr(new OnLostBluetoothDeviceRunnable(
+      pcp_handler_, client_proxy_, MakePtr(this), service_id_,
+      bluetooth_device)));
+}
+
+template <typename Platform>
+bool P2PClusterPCPHandler<Platform>::FoundBluetoothAdvertisementProcessor::
+    isRecognizedBluetoothEndpoint(
+        const string& found_bluetooth_device_name,
+        Ptr<BluetoothDeviceName> bluetooth_device_name) {
+  if (bluetooth_device_name.isNull()) {
+    // TODO(tracyzhou): Add logging.
+    return false;
+  }
+
+  if (bluetooth_device_name->getPCP() != pcp_handler_->getPCP()) {
+    // TODO(tracyzhou): Add logging.
+    return false;
+  }
+
+  if (*(bluetooth_device_name->getServiceIdHash()) !=
+      *(expected_service_id_hash_.get())) {
+    // TODO(tracyzhou): Add logging.
+    return false;
+  }
+
+  return true;
+}
+
+template <typename Platform>
+P2PClusterPCPHandler<Platform>::FoundBluetoothAdvertisementProcessor::
+    OnFoundBluetoothDeviceRunnable::OnFoundBluetoothDeviceRunnable(
+        Ptr<P2PClusterPCPHandler<Platform>> pcp_handler,
+        Ptr<ClientProxy<Platform>> client_proxy,
+        Ptr<FoundBluetoothAdvertisementProcessor>
+            found_bluetooth_advertisement_processor,
+        const string& service_id, Ptr<BluetoothDevice> bluetooth_device)
+    : pcp_handler_(pcp_handler),
+      client_proxy_(client_proxy),
+      found_bluetooth_advertisement_processor_(
+          found_bluetooth_advertisement_processor),
+      service_id_(service_id),
+      bluetooth_device_(bluetooth_device) {}
+
+template <typename Platform>
+void P2PClusterPCPHandler<Platform>::FoundBluetoothAdvertisementProcessor::
+    OnFoundBluetoothDeviceRunnable::run() {
+  // Make sure we are still discovering before proceeding.
+  if (!client_proxy_->isDiscovering()) {
+    // TODO(tracyzhou): Add logging.
+    return;
+  }
+
+  // Parse the Bluetooth device name.
+  ScopedPtr<Ptr<BluetoothDeviceName>> bluetooth_device_name(
+      BluetoothDeviceName::fromString(bluetooth_device_->getName()));
+
+  // Make sure the Bluetooth device name points to a valid endpoint we're
+  // discovering.
+  if (!found_bluetooth_advertisement_processor_->isRecognizedBluetoothEndpoint(
+          bluetooth_device_->getName(), bluetooth_device_name.get())) {
+    return;
+  }
+
+  // Report the discovered endpoint to the client.
+  // TODO(tracyzhou): Add logging.
+  pcp_handler_->onEndpointFound(
+      client_proxy_,
+      MakePtr(new BluetoothEndpoint(
+          bluetooth_device_.release(), bluetooth_device_name->getEndpointId(),
+          bluetooth_device_name->getEndpointName(), service_id_)));
+}
+
+template <typename Platform>
+P2PClusterPCPHandler<Platform>::FoundBluetoothAdvertisementProcessor::
+    OnLostBluetoothDeviceRunnable::OnLostBluetoothDeviceRunnable(
+        Ptr<P2PClusterPCPHandler<Platform>> pcp_handler,
+        Ptr<ClientProxy<Platform>> client_proxy,
+        Ptr<FoundBluetoothAdvertisementProcessor>
+            found_bluetooth_advertisement_processor,
+        const string& service_id, Ptr<BluetoothDevice> bluetooth_device)
+    : pcp_handler_(pcp_handler),
+      client_proxy_(client_proxy),
+      found_bluetooth_advertisement_processor_(
+          found_bluetooth_advertisement_processor),
+      service_id_(service_id),
+      bluetooth_device_(bluetooth_device) {}
+
+template <typename Platform>
+void P2PClusterPCPHandler<Platform>::FoundBluetoothAdvertisementProcessor::
+    OnLostBluetoothDeviceRunnable::run() {
+  // Make sure we are still discovering before proceeding.
+  if (!client_proxy_->isDiscovering()) {
+    // TODO(tracyzhou): Add logging.
+    return;
+  }
+
+  // Parse the Bluetooth device name.
+  ScopedPtr<Ptr<BluetoothDeviceName>> bluetooth_device_name(
+      BluetoothDeviceName::fromString(bluetooth_device_->getName()));
+
+  // Make sure the Bluetooth device name points to a valid endpoint we're
+  // discovering.
+  if (!found_bluetooth_advertisement_processor_->isRecognizedBluetoothEndpoint(
+          bluetooth_device_->getName(), bluetooth_device_name.get())) {
+    return;
+  }
+
+  // Report the endpoint as lost to the client.
+  // TODO(tracyzhou): Add logging.
+  pcp_handler_->onEndpointLost(
+      client_proxy_,
+      MakePtr(new BluetoothEndpoint(
+          bluetooth_device_.release(), bluetooth_device_name->getEndpointId(),
+          bluetooth_device_name->getEndpointName(), service_id_)));
+}
+
+//////////// P2PClusterPCPHandler::FoundBleAdvertisementProcessor /////////////
+template <typename Platform>
+P2PClusterPCPHandler<Platform>::FoundBleAdvertisementProcessor::
+    FoundBleAdvertisementProcessor(
+        Ptr<P2PClusterPCPHandler<Platform>> pcp_handler,
+        Ptr<ClientProxy<Platform>> client_proxy)
+    : pcp_handler_(pcp_handler), client_proxy_(client_proxy) {}
+
+template <typename Platform>
+void P2PClusterPCPHandler<Platform>::FoundBleAdvertisementProcessor::
+    onFoundBlePeripheral(Ptr<BLE_PERIPHERAL> ble_peripheral,
+                         const string& service_id,
+                         ConstPtr<ByteArray> advertisement_bytes) {
+  pcp_handler_->runOnPCPHandlerThread(MakePtr(new OnFoundBlePeripheralRunnable(
+      pcp_handler_, client_proxy_, MakePtr(this), service_id, ble_peripheral,
+      advertisement_bytes)));
+}
+
+template <typename Platform>
+P2PClusterPCPHandler<Platform>::FoundBleAdvertisementProcessor::
+    OnFoundBlePeripheralRunnable::OnFoundBlePeripheralRunnable(
+        Ptr<P2PClusterPCPHandler<Platform>> pcp_handler,
+        Ptr<ClientProxy<Platform>> client_proxy,
+        Ptr<FoundBleAdvertisementProcessor> found_ble_advertisement_processor,
+        const string& service_id, Ptr<BLE_PERIPHERAL> ble_peripheral,
+        ConstPtr<ByteArray> advertisement_bytes)
+    : pcp_handler_(pcp_handler),
+      client_proxy_(client_proxy),
+      found_ble_advertisement_processor_(found_ble_advertisement_processor),
+      service_id_(service_id),
+      ble_peripheral_(ble_peripheral),
+      advertisement_bytes_(advertisement_bytes),
+      expected_service_id_hash_(
+          generateHash(service_id, BLEAdvertisement::kServiceIdHashLength)) {}
+
+template <typename Platform>
+void P2PClusterPCPHandler<Platform>::FoundBleAdvertisementProcessor::
+    OnFoundBlePeripheralRunnable::run() {
+  // Make sure we are still discovering before proceeding.
+  if (!client_proxy_->isDiscovering()) {
+    // TODO(ahlee): logger.atWarning().log("Skipping discovery of
+    // BLEAdvertisement header %s because we are no longer discovering.",
+    // bytesToString(advertisementBytes));
+    return;
+  }
+
+  ScopedPtr<Ptr<BLEAdvertisement>> scoped_ble_advertisement(
+      BLEAdvertisement::fromBytes(advertisement_bytes_.get()));
+  if (scoped_ble_advertisement.isNull()) {
+    // TODO(ahlee): logger.atVerbose().log("%s doesn't conform to the
+    // BLEAdvertisement format, discarding.",
+    // bytesToSTring(advertisementBytes));
+    return;
+  }
+
+  if (scoped_ble_advertisement->getVersion() != BLEAdvertisement::Version::V1) {
+    // TODO(ahlee): logging
+    return;
+  }
+
+  if (scoped_ble_advertisement->getPCP() != pcp_handler_->getPCP()) {
+    // TODO(ahlee): Add logging
+    return;
+  }
+
+  if (*(scoped_ble_advertisement->getServiceIdHash()) !=
+      *(expected_service_id_hash_.get())) {
+    // TODO(ahlee): Add logging
+    return;
+  }
+
+  // TODO(ahlee): Add logging.
+
+  // Store all the state we need to be able to re-create a BLEEndpoint in
+  // OnLostBlePeripheralRunnable::run(), since that isn't privy to the bytes of
+  // the BLE advertisement itself.
+  found_ble_advertisement_processor_->found_ble_endpoints_.insert(
+      std::make_pair(
+          getBlePeripheralId(ble_peripheral_.get()),
+          BLEEndpointState(scoped_ble_advertisement->getEndpointId(),
+                           scoped_ble_advertisement->getEndpointName())));
+
+  pcp_handler_->onEndpointFound(
+      client_proxy_,
+      MakePtr(new BLEEndpoint(
+          ble_peripheral_.release(), scoped_ble_advertisement->getEndpointId(),
+          scoped_ble_advertisement->getEndpointName(), service_id_)));
+
+  // TODO(b/75047971): Add functionality to connect over Bluetooth.
+}
+
+template <typename Platform>
+void P2PClusterPCPHandler<Platform>::FoundBleAdvertisementProcessor::
+    onLostBlePeripheral(Ptr<BLE_PERIPHERAL> ble_peripheral,
+                        const string& service_id) {
+  pcp_handler_->runOnPCPHandlerThread(MakePtr(new OnLostBlePeripheralRunnable(
+      pcp_handler_, client_proxy_, MakePtr(this), service_id, ble_peripheral)));
+}
+
+template <typename Platform>
+P2PClusterPCPHandler<Platform>::FoundBleAdvertisementProcessor::
+    OnLostBlePeripheralRunnable::OnLostBlePeripheralRunnable(
+        Ptr<P2PClusterPCPHandler<Platform>> pcp_handler,
+        Ptr<ClientProxy<Platform>> client_proxy,
+        Ptr<FoundBleAdvertisementProcessor> found_ble_advertisement_processor,
+        const string& service_id, Ptr<BLE_PERIPHERAL> ble_peripheral)
+    : pcp_handler_(pcp_handler),
+      client_proxy_(client_proxy),
+      found_ble_advertisement_processor_(found_ble_advertisement_processor),
+      service_id_(service_id),
+      ble_peripheral_(ble_peripheral) {}
+
+template <typename Platform>
+void P2PClusterPCPHandler<Platform>::FoundBleAdvertisementProcessor::
+    OnLostBlePeripheralRunnable::run() {
+  // Make sure we are still discovering before proceeding.
+  if (!client_proxy_->isDiscovering()) {
+    // TODO(reznor): logger.atWarning().log("Ignoring lost BlePeripheral %s
+    // because we are no longer discovering.", blePeripheral);
+    return;
+  }
+
+  // Remove this BLEPeripheral from
+  // found_ble_advertisement_processor_->found_ble_endpoints_, and report the
+  // endpoint as lost to the client.
+  typename FoundBLEEndpointsMap::iterator it =
+      found_ble_advertisement_processor_->found_ble_endpoints_.find(
+          getBlePeripheralId(ble_peripheral_.get()));
+  if (it != found_ble_advertisement_processor_->found_ble_endpoints_.end()) {
+    // TODO(reznor): logger.atDebug().log("Lost BlePeripheral %s (with
+    // EndpointId %s and EndpointName %s)", blePeripheral,
+    // bleEndpoint.getEndpointId(), bleEndpoint.getEndpointName());
+
+    // Make a copy since it->second will get destroyed once we call erase()
+    // below.
+    BLEEndpointState ble_endpoint_state(it->second);
+    found_ble_advertisement_processor_->found_ble_endpoints_.erase(it);
+
+    pcp_handler_->onEndpointLost(
+        client_proxy_,
+        MakePtr(new BLEEndpoint(
+            ble_peripheral_.release(), ble_endpoint_state.endpoint_id,
+            ble_endpoint_state.endpoint_name, service_id_)));
+  }
+}
+
+//////////////////// END IMPLEMENTATIONS FOR NESTED CLASSES ////////////////////
+
+template <typename Platform>
+proto::connections::Medium
+P2PClusterPCPHandler<Platform>::startBluetoothAdvertising(
+    Ptr<ClientProxy<Platform>> client_proxy, const string& service_id,
+    ConstPtr<ByteArray> service_id_hash, const string& local_endpoint_id,
+    const string& local_endpoint_name) {
+  // Start listening for connections before advertising in case a connection
+  // request comes in very quickly.
+  if (!medium_manager_->isListeningForIncomingBluetoothConnections(
+          service_id)) {
+    if (!medium_manager_->startListeningForIncomingBluetoothConnections(
+            service_id,
+            MakePtr(new IncomingBluetoothConnectionProcessor(
+                MakePtr(this), client_proxy, local_endpoint_name)))) {
+      // TODO(tracyzhou): Add logging.
+      return proto::connections::UNKNOWN_MEDIUM;
+    }
+
+    // TODO(tracyzhou): Add logging.
+  }
+
+  // Generate a BluetoothDeviceName with which to become Bluetooth discoverable.
+  const string bluetooth_device_name = BluetoothDeviceName::asString(
+      kBluetoothDeviceNameVersion, getPCP(), local_endpoint_id, service_id_hash,
+      local_endpoint_name);
+  if (bluetooth_device_name.empty()) {
+    // TODO(tracyzhou): Add logging.
+    medium_manager_->stopListeningForIncomingBluetoothConnections(service_id);
+    return proto::connections::UNKNOWN_MEDIUM;
+  } else {
+    // TODO(tracyzhou): Add logging.
+  }
+
+  // Become Bluetooth discoverable.
+  if (!medium_manager_->turnOnBluetoothDiscoverability(bluetooth_device_name)) {
+    // TODO(tracyzhou): Add logging.
+    medium_manager_->stopListeningForIncomingBluetoothConnections(service_id);
+    return proto::connections::UNKNOWN_MEDIUM;
+  } else {
+    // TODO(tracyzhou): Add logging.
+  }
+  return proto::connections::BLUETOOTH;
+}
+
+template <typename Platform>
+proto::connections::Medium
+P2PClusterPCPHandler<Platform>::startBluetoothDiscovery(
+    Ptr<FoundBluetoothAdvertisementProcessor> processor,
+    Ptr<ClientProxy<Platform>> client_proxy, const string& service_id) {
+  if (!medium_manager_->startScanningForBluetoothDevices(processor)) {
+    // TODO(tracyzhou): Add logging.
+    return proto::connections::UNKNOWN_MEDIUM;
+  } else {
+    // TODO(tracyzhou): Add logging.
+  }
+
+  return proto::connections::BLUETOOTH;
+}
+
+template <typename Platform>
+proto::connections::Medium P2PClusterPCPHandler<Platform>::startBleAdvertising(
+    Ptr<ClientProxy<Platform>> client_proxy, const string& service_id,
+    ConstPtr<ByteArray> service_id_hash, const string& local_endpoint_id,
+    const string& local_endpoint_name) {
+  // Start listening for connections before advertising in case a connection
+  // request comes in very quickly.
+  if (!medium_manager_->isListeningForIncomingBleConnections(service_id)) {
+    if (!medium_manager_->startListeningForIncomingBleConnections(
+            service_id,
+            MakePtr(new IncomingBleConnectionProcessor(
+                MakePtr(this), client_proxy, local_endpoint_name)))) {
+      // TODO(ahlee): logger.atWarning().log("In startBleAdvertising(%s), client
+      // %d failed to start listening for incoming BLE connections to ServiceId
+      // %s", local_endpoint_name, clientProxy.getClientId(), service_id);
+      return proto::connections::UNKNOWN_MEDIUM;
+    }
+
+    // TODO(ahlee): Add logging.
+  }
+
+  // TODO(b/75047971): Add functionality to connect over Bluetooth.
+
+  // Create a BLEAdvertisement.
+  // TODO(b/75047971): Add a bluetooth_adapter method to get the mac address.
+  string bluetooth_mac_address;
+  ScopedPtr<ConstPtr<ByteArray>> scoped_ble_advertisement_bytes(
+      BLEAdvertisement::toBytes(kBleAdvertisementVersion, getPCP(),
+                                service_id_hash, local_endpoint_id,
+                                local_endpoint_name, bluetooth_mac_address));
+  if (scoped_ble_advertisement_bytes.isNull()) {
+    // TODO(ahlee): Add logging
+    medium_manager_->stopListeningForIncomingBleConnections(service_id);
+    return proto::connections::UNKNOWN_MEDIUM;
+  }
+
+  // TODO(ahlee): Add logging
+
+  if (!medium_manager_->startBleAdvertising(
+          service_id, scoped_ble_advertisement_bytes.release())) {
+    // TODO(ahlee): Add logging
+    medium_manager_->stopListeningForIncomingBleConnections(service_id);
+    return proto::connections::UNKNOWN_MEDIUM;
+  }
+
+  // TODO(ahlee): Add logging
+  return proto::connections::BLE;
+}
+
+template <typename Platform>
+proto::connections::Medium P2PClusterPCPHandler<Platform>::startBleDiscovery(
+    Ptr<FoundBleAdvertisementProcessor> processor,
+    Ptr<ClientProxy<Platform>> client_proxy, const string& service_id) {
+  if (!medium_manager_->startBleScanning(service_id, processor)) {
+    // TODO(ahlee): logger.atDebug().log("In startBleDiscover(), client %d
+    // couldn't start scanning on BLE for service id %s.",
+    // client_proxy.getClientId(), service_id);
+    return proto::connections::UNKNOWN_MEDIUM;
+  }
+
+  // TODO(ahlee): logger.atVerbose().log("In startBleDiscovery(), client %d
+  // started scanning for BLE advertisements for serviceId %s.",
+  // client_proxy.getClietnId(), service_id);
+
+  return proto::connections::BLE;
+}
+
+template <typename Platform>
+typename BasePCPHandler<Platform>::ConnectImplResult
+P2PClusterPCPHandler<Platform>::bluetoothConnectImpl(
+    Ptr<ClientProxy<Platform>> client_proxy,
+    Ptr<BluetoothEndpoint> bluetooth_endpoint) {
+  Ptr<BluetoothDevice> remote_bluetooth_device =
+      bluetooth_endpoint->getBluetoothDevice();
+
+  Ptr<BluetoothSocket> bluetooth_socket =
+      medium_manager_->connectToBluetoothDevice(
+          remote_bluetooth_device, bluetooth_endpoint->getServiceId());
+  if (bluetooth_socket.isNull()) {
+    return typename BasePCPHandler<Platform>::ConnectImplResult(
+        proto::connections::Medium::BLUETOOTH, Status::BLUETOOTH_ERROR);
+  }
+
+  ScopedPtr<Ptr<EndpointChannel>> scoped_bluetooth_endpoint_channel(
+      this->endpoint_channel_manager_->createOutgoingBluetoothEndpointChannel(
+          bluetooth_endpoint->getEndpointId(), bluetooth_socket));
+
+  if (scoped_bluetooth_endpoint_channel.isNull()) {
+    bluetooth_socket->close();
+    bluetooth_socket.destroy();  // Avoid leaks.
+    return typename BasePCPHandler<Platform>::ConnectImplResult(
+        proto::connections::Medium::BLUETOOTH, Status::ERROR);
+  }
+
+  // TODO(tracyzhou): Add logging.
+  return typename BasePCPHandler<Platform>::ConnectImplResult(
+      scoped_bluetooth_endpoint_channel.release());
+}
+
+template <typename Platform>
+typename BasePCPHandler<Platform>::ConnectImplResult
+P2PClusterPCPHandler<Platform>::bleConnectImpl(
+    Ptr<ClientProxy<Platform>> client_proxy, Ptr<BLEEndpoint> ble_endpoint) {
+  Ptr<BLE_PERIPHERAL> remote_ble_peripheral = ble_endpoint->getBlePeripheral();
+
+  Ptr<BLESocket> ble_socket = medium_manager_->connectToBlePeripheral(
+      remote_ble_peripheral, ble_endpoint->getServiceId());
+
+  if (ble_socket.isNull()) {
+    return typename BasePCPHandler<Platform>::ConnectImplResult(
+        proto::connections::Medium::BLE, Status::BLUETOOTH_ERROR);
+  }
+
+  ScopedPtr<Ptr<EndpointChannel>> scoped_ble_endpoint_channel(
+      this->endpoint_channel_manager_->createOutgoingBLEEndpointChannel(
+          ble_endpoint->getEndpointId(), ble_socket));
+
+  if (scoped_ble_endpoint_channel.isNull()) {
+    ble_socket->close();
+    ble_socket.destroy();  // Avoid leaks.
+    return typename BasePCPHandler<Platform>::ConnectImplResult(
+        proto::connections::Medium::BLE, Status::ERROR);
+  }
+
+  // TODO(tracyzhou): Add logging.
+  return typename BasePCPHandler<Platform>::ConnectImplResult(
+      scoped_ble_endpoint_channel.release());
+}
+
+template <typename Platform>
+string P2PClusterPCPHandler<Platform>::getBlePeripheralId(
+    Ptr<BLE_PERIPHERAL> ble_peripheral) {
+#if BLE_V2_IMPLEMENTED
+  return string(ble_peripheral->getId()->getData(),
+                ble_peripheral->getId()->size());
+#else
+  return ble_peripheral->getBluetoothDevice()->getName();
+#endif
+}
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/p2p_cluster_pcp_handler.h

@@ -0,0 +1,378 @@
+#ifndef CORE_INTERNAL_P2P_CLUSTER_PCP_HANDLER_H_
+#define CORE_INTERNAL_P2P_CLUSTER_PCP_HANDLER_H_
+
+#include <vector>
+
+#include "core/internal/bandwidth_upgrade_manager.h"
+#include "core/internal/base_pcp_handler.h"
+#include "core/internal/ble_advertisement.h"
+#include "core/internal/ble_compat.h"
+#include "core/internal/bluetooth_device_name.h"
+#include "core/internal/client_proxy.h"
+#include "core/internal/endpoint_channel_manager.h"
+#include "core/internal/endpoint_manager.h"
+#include "core/internal/medium_manager.h"
+#include "core/internal/pcp.h"
+#include "core/options.h"
+#include "core/strategy.h"
+#include "platform/api/bluetooth_classic.h"
+#include "platform/byte_array.h"
+#include "platform/port/string.h"
+#include "platform/ptr.h"
+#include "proto/connections_enums.pb.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+// Concrete implementation of the PCPHandler for the P2P_CLUSTER PCP. This PCP
+// is reserved for mediums that can connect to multiple devices simultaneously
+// and all devices are considered equal. For asymmetric mediums, where one
+// device is a server and the others are clients, use P2PStarPCPHandler instead.
+//
+// <p>Currently, this implementation advertises/discovers over BLE and Bluetooth
+// and connects over Bluetooth.
+template <typename Platform>
+class P2PClusterPCPHandler : public BasePCPHandler<Platform> {
+ public:
+  P2PClusterPCPHandler(
+      Ptr<MediumManager<Platform> > medium_manager,
+      Ptr<EndpointManager<Platform> > endpoint_manager,
+      Ptr<EndpointChannelManager<Platform> > endpoint_channel_manager,
+      Ptr<BandwidthUpgradeManager<Platform> > bandwidth_upgrade_manager);
+  ~P2PClusterPCPHandler() override;
+
+  Strategy getStrategy() override;
+  PCP::Value getPCP() override;
+
+ protected:
+  std::vector<proto::connections::Medium> getConnectionMediumsByPriority()
+      override;
+  proto::connections::Medium getDefaultUpgradeMedium() override;
+
+  // @PCPHandlerThread
+  Ptr<typename BasePCPHandler<Platform>::StartOperationResult>
+  startAdvertisingImpl(Ptr<ClientProxy<Platform> > client_proxy,
+                       const string& service_id,
+                       const string& local_endpoint_id,
+                       const string& local_endpoint_name,
+                       const AdvertisingOptions& options) override;
+  // @PCPHandlerThread
+  Status::Value stopAdvertisingImpl(
+      Ptr<ClientProxy<Platform> > client_proxy) override;
+
+  // @PCPHandlerThread
+  Ptr<typename BasePCPHandler<Platform>::StartOperationResult>
+  startDiscoveryImpl(Ptr<ClientProxy<Platform> > client_proxy,
+                     const string& service_id,
+                     const DiscoveryOptions& options) override;
+  // @PCPHandlerThread
+  Status::Value stopDiscoveryImpl(
+      Ptr<ClientProxy<Platform> > client_proxy) override;
+
+  // @PCPHandlerThread
+  typename BasePCPHandler<Platform>::ConnectImplResult connectImpl(
+      Ptr<ClientProxy<Platform> > client_proxy,
+      Ptr<typename BasePCPHandler<Platform>::DiscoveredEndpoint> endpoint)
+      override;
+
+ private:
+  template <typename>
+  friend class IncomingBluetoothConnectionProcessor;
+  template <typename>
+  friend class IncomingBleConnectionProcessor;
+  template <typename>
+  friend class FoundBluetoothAdvertisementProcessor;
+  template <typename>
+  friend class FoundBleAdvertisementProcessor;
+
+  class IncomingBluetoothConnectionProcessor
+      : public MediumManager<Platform>::IncomingBluetoothConnectionProcessor {
+   public:
+    IncomingBluetoothConnectionProcessor(
+        Ptr<P2PClusterPCPHandler<Platform> > pcp_handler,
+        Ptr<ClientProxy<Platform> > client_proxy,
+        const string& local_endpoint_name);
+
+    void onIncomingBluetoothConnection(
+        Ptr<BluetoothSocket> bluetooth_socket) override;
+
+   private:
+    class OnIncomingBluetoothConnectionRunnable : public Runnable {
+     public:
+      OnIncomingBluetoothConnectionRunnable(
+          Ptr<P2PClusterPCPHandler<Platform> > pcp_handler,
+          Ptr<ClientProxy<Platform> > client_proxy,
+          Ptr<BluetoothSocket> bluetooth_socket);
+
+      void run() override;
+
+     private:
+      Ptr<P2PClusterPCPHandler<Platform> > pcp_handler_;
+      Ptr<ClientProxy<Platform> > client_proxy_;
+      Ptr<BluetoothSocket> bluetooth_socket_;
+    };
+
+    Ptr<P2PClusterPCPHandler<Platform> > pcp_handler_;
+    Ptr<ClientProxy<Platform> > client_proxy_;
+    const string local_endpoint_name_;
+  };
+
+  class IncomingBleConnectionProcessor
+      : public MediumManager<Platform>::IncomingBleConnectionProcessor {
+   public:
+    IncomingBleConnectionProcessor(
+        Ptr<P2PClusterPCPHandler<Platform> > pcp_handler,
+        Ptr<ClientProxy<Platform> > client_proxy,
+        const string& local_endpoint_name);
+
+    void onIncomingBleConnection(Ptr<BLESocket> ble_socket,
+                                 const string& service_id) override;
+
+   private:
+    class OnIncomingBleConnectionRunnable : public Runnable {
+     public:
+      OnIncomingBleConnectionRunnable(
+          Ptr<P2PClusterPCPHandler<Platform> > pcp_handler,
+          Ptr<ClientProxy<Platform> > client_proxy, Ptr<BLESocket> ble_socket);
+
+      void run() override;
+
+     private:
+      Ptr<P2PClusterPCPHandler<Platform> > pcp_handler_;
+      Ptr<ClientProxy<Platform> > client_proxy_;
+      Ptr<BLESocket> ble_socket_;
+    };
+
+    Ptr<P2PClusterPCPHandler<Platform> > pcp_handler_;
+    Ptr<ClientProxy<Platform> > client_proxy_;
+    const string local_endpoint_name_;
+  };
+
+  class FoundBluetoothAdvertisementProcessor
+      : public MediumManager<Platform>::FoundBluetoothDeviceProcessor {
+   public:
+    FoundBluetoothAdvertisementProcessor(
+        Ptr<P2PClusterPCPHandler<Platform> > pcp_handler,
+        Ptr<ClientProxy<Platform> > client_proxy, const string& service_id);
+
+    void onFoundBluetoothDevice(Ptr<BluetoothDevice> bluetooth_device) override;
+    void onLostBluetoothDevice(Ptr<BluetoothDevice> bluetooth_device) override;
+
+   private:
+    class OnFoundBluetoothDeviceRunnable : public Runnable {
+     public:
+      OnFoundBluetoothDeviceRunnable(
+          Ptr<P2PClusterPCPHandler<Platform> > pcp_handler,
+          Ptr<ClientProxy<Platform> > client_proxy,
+          Ptr<FoundBluetoothAdvertisementProcessor>
+              found_bluetooth_advertisement_processor,
+          const string& service_id, Ptr<BluetoothDevice> bluetooth_device);
+
+      void run() override;
+
+     private:
+      Ptr<P2PClusterPCPHandler<Platform> > pcp_handler_;
+      Ptr<ClientProxy<Platform> > client_proxy_;
+      Ptr<FoundBluetoothAdvertisementProcessor>
+          found_bluetooth_advertisement_processor_;
+      const string service_id_;
+      ScopedPtr<Ptr<BluetoothDevice> > bluetooth_device_;
+    };
+
+    class OnLostBluetoothDeviceRunnable : public Runnable {
+     public:
+      OnLostBluetoothDeviceRunnable(
+          Ptr<P2PClusterPCPHandler<Platform> > pcp_handler,
+          Ptr<ClientProxy<Platform> > client_proxy,
+          Ptr<FoundBluetoothAdvertisementProcessor>
+              found_bluetooth_advertisement_processor,
+          const string& service_id, Ptr<BluetoothDevice> bluetooth_device);
+
+      void run() override;
+
+     private:
+      Ptr<P2PClusterPCPHandler<Platform> > pcp_handler_;
+      Ptr<ClientProxy<Platform> > client_proxy_;
+      Ptr<FoundBluetoothAdvertisementProcessor>
+          found_bluetooth_advertisement_processor_;
+      const string service_id_;
+      ScopedPtr<Ptr<BluetoothDevice> > bluetooth_device_;
+    };
+
+    bool isRecognizedBluetoothEndpoint(
+        const string& found_bluetooth_device_name,
+        Ptr<BluetoothDeviceName> bluetooth_device_name);
+
+    Ptr<P2PClusterPCPHandler<Platform> > pcp_handler_;
+    Ptr<ClientProxy<Platform> > client_proxy_;
+    const string service_id_;
+    ScopedPtr<ConstPtr<ByteArray> > expected_service_id_hash_;
+  };
+
+  class FoundBleAdvertisementProcessor
+      : public MediumManager<Platform>::FoundBlePeripheralProcessor {
+   public:
+    FoundBleAdvertisementProcessor(
+        Ptr<P2PClusterPCPHandler<Platform> > pcp_handler,
+        Ptr<ClientProxy<Platform> > client_proxy);
+
+    void onFoundBlePeripheral(Ptr<BLE_PERIPHERAL> ble_peripheral,
+                              const string& service_id,
+                              ConstPtr<ByteArray> advertisement_bytes) override;
+    void onLostBlePeripheral(Ptr<BLE_PERIPHERAL> ble_peripheral,
+                             const string& service_id) override;
+
+   private:
+    class OnFoundBlePeripheralRunnable : public Runnable {
+     public:
+      OnFoundBlePeripheralRunnable(
+          Ptr<P2PClusterPCPHandler<Platform> > pcp_handler,
+          Ptr<ClientProxy<Platform> > client_proxy,
+          Ptr<FoundBleAdvertisementProcessor> found_ble_advertisement_processor,
+          const string& service_id, Ptr<BLE_PERIPHERAL> ble_peripheral,
+          ConstPtr<ByteArray> advertisement_bytes);
+
+      void run() override;
+
+     private:
+      Ptr<P2PClusterPCPHandler<Platform> > pcp_handler_;
+      Ptr<ClientProxy<Platform> > client_proxy_;
+      Ptr<FoundBleAdvertisementProcessor> found_ble_advertisement_processor_;
+      const string service_id_;
+      ScopedPtr<Ptr<BLE_PERIPHERAL> > ble_peripheral_;
+      ScopedPtr<ConstPtr<ByteArray> > advertisement_bytes_;
+      ScopedPtr<ConstPtr<ByteArray> > expected_service_id_hash_;
+    };
+
+    class OnLostBlePeripheralRunnable : public Runnable {
+     public:
+      OnLostBlePeripheralRunnable(
+          Ptr<P2PClusterPCPHandler<Platform> > pcp_handler,
+          Ptr<ClientProxy<Platform> > client_proxy,
+          Ptr<FoundBleAdvertisementProcessor> found_ble_advertisement_processor,
+          const string& service_id, Ptr<BLE_PERIPHERAL> ble_peripheral);
+
+      void run() override;
+
+     private:
+      Ptr<P2PClusterPCPHandler<Platform> > pcp_handler_;
+      Ptr<ClientProxy<Platform> > client_proxy_;
+      Ptr<FoundBleAdvertisementProcessor> found_ble_advertisement_processor_;
+      const string service_id_;
+      ScopedPtr<Ptr<BLE_PERIPHERAL> > ble_peripheral_;
+    };
+
+    // Holds the state required to re-create a BLEEndpoint we see on a
+    // BLEPeripheral, so OnLostBlePeripheralRunnable::run() can call
+    // BasePCPHandler::onEndpointLost() with the same information as was passed
+    // in to BasePCPHandler::onEndpointFound().
+    struct BLEEndpointState {
+     public:
+      BLEEndpointState(const string& endpoint_id, const string& endpoint_name)
+          : endpoint_id(endpoint_id), endpoint_name(endpoint_name) {}
+
+      const string endpoint_id;
+      const string endpoint_name;
+    };
+
+    Ptr<P2PClusterPCPHandler<Platform> > pcp_handler_;
+    Ptr<ClientProxy<Platform> > client_proxy_;
+    // Maps a BLEPeripheral to its corresponding BLEEndpointState.
+    typedef std::map<string, BLEEndpointState> FoundBLEEndpointsMap;
+    FoundBLEEndpointsMap found_ble_endpoints_;
+  };
+
+  class BluetoothEndpoint
+      : public BasePCPHandler<Platform>::DiscoveredEndpoint {
+   public:
+    Ptr<BluetoothDevice> getBluetoothDevice() {
+      return bluetooth_device_.get();
+    }
+    string getEndpointId() override { return endpoint_id_; }
+    string getEndpointName() override { return endpoint_name_; }
+    string getServiceId() override { return service_id_; }
+    proto::connections::Medium getMedium() override {
+      return proto::connections::Medium::BLUETOOTH;
+    }
+
+   private:
+    BluetoothEndpoint(Ptr<BluetoothDevice> bluetooth_device,
+                      const string& endpoint_id, const string& endpoint_name,
+                      const string& service_id)
+        : bluetooth_device_(bluetooth_device),
+          endpoint_id_(endpoint_id),
+          endpoint_name_(endpoint_name),
+          service_id_(service_id) {}
+
+    friend class FoundBluetoothAdvertisementProcessor;
+
+    ScopedPtr<Ptr<BluetoothDevice> > bluetooth_device_;
+    const string endpoint_id_;
+    const string endpoint_name_;
+    const string service_id_;
+  };
+
+  class BLEEndpoint : public BasePCPHandler<Platform>::DiscoveredEndpoint {
+   public:
+    Ptr<BLE_PERIPHERAL> getBlePeripheral() { return ble_peripheral_.get(); }
+    string getEndpointId() override { return endpoint_id_; }
+    string getEndpointName() override { return endpoint_name_; }
+    string getServiceId() override { return service_id_; }
+    proto::connections::Medium getMedium() override {
+      return proto::connections::Medium::BLE;
+    }
+
+   private:
+    BLEEndpoint(Ptr<BLE_PERIPHERAL> ble_peripheral, const string& endpoint_id,
+                const string& endpoint_name, const string& service_id)
+        : ble_peripheral_(ble_peripheral),
+          endpoint_id_(endpoint_id),
+          endpoint_name_(endpoint_name),
+          service_id_(service_id) {}
+
+    friend class FoundBleAdvertisementProcessor;
+
+    ScopedPtr<Ptr<BLE_PERIPHERAL> > ble_peripheral_;
+    const string endpoint_id_;
+    const string endpoint_name_;
+    const string service_id_;
+  };
+
+  static const BluetoothDeviceName::Version::Value kBluetoothDeviceNameVersion;
+  static const BLEAdvertisement::Version::Value kBleAdvertisementVersion;
+
+  static ConstPtr<ByteArray> generateHash(const string& source, size_t size);
+  static string getBlePeripheralId(Ptr<BLE_PERIPHERAL> ble_peripheral);
+
+  proto::connections::Medium startBluetoothAdvertising(
+      Ptr<ClientProxy<Platform> > client_proxy, const string& service_id,
+      ConstPtr<ByteArray> service_id_hash, const string& local_endpoint_id,
+      const string& local_endpoint_name);
+  proto::connections::Medium startBluetoothDiscovery(
+      Ptr<FoundBluetoothAdvertisementProcessor> processor,
+      Ptr<ClientProxy<Platform> > client_proxy, const string& service_id);
+  typename BasePCPHandler<Platform>::ConnectImplResult bluetoothConnectImpl(
+      Ptr<ClientProxy<Platform> > client_proxy,
+      Ptr<BluetoothEndpoint> bluetooth_endpoint);
+
+  proto::connections::Medium startBleAdvertising(
+      Ptr<ClientProxy<Platform> > client_proxy, const string& service_id,
+      ConstPtr<ByteArray> service_id_hash, const string& local_endpoint_id,
+      const string& local_endpoint_name);
+  proto::connections::Medium startBleDiscovery(
+      Ptr<FoundBleAdvertisementProcessor> processor,
+      Ptr<ClientProxy<Platform> > client_proxy, const string& service_id);
+  typename BasePCPHandler<Platform>::ConnectImplResult bleConnectImpl(
+      Ptr<ClientProxy<Platform> > client_proxy, Ptr<BLEEndpoint> ble_endpoint);
+
+  Ptr<MediumManager<Platform> > medium_manager_;
+};
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#include "core/internal/p2p_cluster_pcp_handler.cc"
+
+#endif  // CORE_INTERNAL_P2P_CLUSTER_PCP_HANDLER_H_

cpp/core/internal/p2p_point_to_point_pcp_handler.cc

@@ -0,0 +1,61 @@
+#include "core/internal/p2p_point_to_point_pcp_handler.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+template <typename Platform>
+P2PPointToPointPCPHandler<Platform>::P2PPointToPointPCPHandler(
+    Ptr<MediumManager<Platform> > medium_manager,
+    Ptr<EndpointManager<Platform> > endpoint_manager,
+    Ptr<EndpointChannelManager<Platform> > endpoint_channel_manager,
+    Ptr<BandwidthUpgradeManager<Platform> > bandwidth_upgrade_manager)
+    : P2PStarPCPHandler<Platform>(medium_manager, endpoint_manager,
+                                  endpoint_channel_manager,
+                                  bandwidth_upgrade_manager),
+      medium_manager_(medium_manager) {}
+
+template <typename Platform>
+Strategy P2PPointToPointPCPHandler<Platform>::getStrategy() {
+  return Strategy::kP2PPointToPoint;
+}
+
+template <typename Platform>
+PCP::Value P2PPointToPointPCPHandler<Platform>::getPCP() {
+  return PCP::P2P_POINT_TO_POINT;
+}
+
+template <typename Platform>
+std::vector<proto::connections::Medium>
+P2PPointToPointPCPHandler<Platform>::getConnectionMediumsByPriority() {
+  std::vector<proto::connections::Medium> mediums;
+  if (medium_manager_->isBluetoothAvailable()) {
+    mediums.push_back(proto::connections::BLUETOOTH);
+  }
+  if (medium_manager_->isBleAvailable()) {
+    mediums.push_back(proto::connections::BLE);
+  }
+  return mediums;
+}
+
+template <typename Platform>
+bool P2PPointToPointPCPHandler<Platform>::canSendOutgoingConnection(
+    Ptr<ClientProxy<Platform> > client_proxy) {
+  // For point to point, we can only send an outgoing connection while we have
+  // no other connections.
+  return !this->hasOutgoingConnections(client_proxy) &&
+      !this->hasIncomingConnections(client_proxy);
+}
+
+template <typename Platform>
+bool P2PPointToPointPCPHandler<Platform>::canReceiveIncomingConnection(
+    Ptr<ClientProxy<Platform> > client_proxy) {
+  // For point to point, we can only receive an incoming connection while we
+  // have no other connections.
+  return !this->hasOutgoingConnections(client_proxy) &&
+      !this->hasIncomingConnections(client_proxy);
+}
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/p2p_point_to_point_pcp_handler.h

@@ -0,0 +1,55 @@
+#ifndef CORE_INTERNAL_P2P_POINT_TO_POINT_PCP_HANDLER_H_
+#define CORE_INTERNAL_P2P_POINT_TO_POINT_PCP_HANDLER_H_
+
+#include "core/internal/bandwidth_upgrade_manager.h"
+#include "core/internal/endpoint_channel_manager.h"
+#include "core/internal/endpoint_manager.h"
+#include "core/internal/medium_manager.h"
+#include "core/internal/p2p_star_pcp_handler.h"
+#include "core/internal/pcp.h"
+#include "core/strategy.h"
+#include "platform/ptr.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+// Concrete implementation of the PCPHandler for the P2P_POINT_TO_POINT. This
+// PCP is for mediums that have limitations on the number of simultaneous
+// connections; all mediums in P2P_STAR are valid for P2P_POINT_TO_POINT, but
+// not all mediums in P2P_POINT_TO_POINT and valid for P2P_STAR.
+//
+// <p>Currently, this implementation advertises/discovers over BLE and Bluetooth
+// and connects over Bluetooth, eventually upgrading to Wifi Hotspot.
+template <typename Platform>
+class P2PPointToPointPCPHandler : public P2PStarPCPHandler<Platform> {
+ public:
+  P2PPointToPointPCPHandler(
+      Ptr<MediumManager<Platform> > medium_manager,
+      Ptr<EndpointManager<Platform> > endpoint_manager,
+      Ptr<EndpointChannelManager<Platform> > endpoint_channel_manager,
+      Ptr<BandwidthUpgradeManager<Platform> > bandwidth_upgrade_manager);
+
+  Strategy getStrategy() override;
+  PCP::Value getPCP() override;
+
+ protected:
+  std::vector<proto::connections::Medium> getConnectionMediumsByPriority()
+      override;
+
+  bool canSendOutgoingConnection(
+      Ptr<ClientProxy<Platform> > client_proxy) override;
+  bool canReceiveIncomingConnection(
+      Ptr<ClientProxy<Platform> > client_proxy) override;
+
+ private:
+  Ptr<MediumManager<Platform> > medium_manager_;
+};
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#include "core/internal/p2p_point_to_point_pcp_handler.cc"
+
+#endif  // CORE_INTERNAL_P2P_POINT_TO_POINT_PCP_HANDLER_H_

cpp/core/internal/p2p_star_pcp_handler.cc

@@ -0,0 +1,71 @@
+#include "core/internal/p2p_star_pcp_handler.h"
+
+#include <vector>
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+template <typename Platform>
+P2PStarPCPHandler<Platform>::P2PStarPCPHandler(
+    Ptr<MediumManager<Platform> > medium_manager,
+    Ptr<EndpointManager<Platform> > endpoint_manager,
+    Ptr<EndpointChannelManager<Platform> > endpoint_channel_manager,
+    Ptr<BandwidthUpgradeManager<Platform> > bandwidth_upgrade_manager)
+    : P2PClusterPCPHandler<Platform>(medium_manager, endpoint_manager,
+                                     endpoint_channel_manager,
+                                     bandwidth_upgrade_manager),
+      medium_manager_(medium_manager) {}
+
+template <typename Platform>
+P2PStarPCPHandler<Platform>::~P2PStarPCPHandler() {}
+
+template <typename Platform>
+Strategy P2PStarPCPHandler<Platform>::getStrategy() {
+  return Strategy::kP2PStar;
+}
+
+template <typename Platform>
+PCP::Value P2PStarPCPHandler<Platform>::getPCP() {
+  return PCP::P2P_STAR;
+}
+
+template <typename Platform>
+std::vector<proto::connections::Medium>
+P2PStarPCPHandler<Platform>::getConnectionMediumsByPriority() {
+  std::vector<proto::connections::Medium> mediums;
+  if (medium_manager_->isBluetoothAvailable()) {
+    mediums.push_back(proto::connections::BLUETOOTH);
+  }
+  if (medium_manager_->isBleAvailable()) {
+    mediums.push_back(proto::connections::BLE);
+  }
+  return mediums;
+}
+
+template <typename Platform>
+proto::connections::Medium
+P2PStarPCPHandler<Platform>::getDefaultUpgradeMedium() {
+  return proto::connections::Medium::WIFI_HOTSPOT;
+}
+
+template <typename Platform>
+bool P2PStarPCPHandler<Platform>::canSendOutgoingConnection(
+    Ptr<ClientProxy<Platform> > client_proxy) {
+  // For star, we can only send an outgoing connection while we have no other
+  // connections.
+  return !this->hasOutgoingConnections(client_proxy) &&
+      !this->hasIncomingConnections(client_proxy);
+}
+
+template <typename Platform>
+bool P2PStarPCPHandler<Platform>::canReceiveIncomingConnection(
+    Ptr<ClientProxy<Platform> > client_proxy) {
+  // For star, we can only receive an incoming connection if we've sent no
+  // outgoing connections.
+  return !this->hasOutgoingConnections(client_proxy);
+}
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/p2p_star_pcp_handler.h

@@ -0,0 +1,60 @@
+#ifndef CORE_INTERNAL_P2P_STAR_PCP_HANDLER_H_
+#define CORE_INTERNAL_P2P_STAR_PCP_HANDLER_H_
+
+#include <vector>
+
+#include "core/internal/bandwidth_upgrade_manager.h"
+#include "core/internal/client_proxy.h"
+#include "core/internal/endpoint_channel_manager.h"
+#include "core/internal/endpoint_manager.h"
+#include "core/internal/medium_manager.h"
+#include "core/internal/p2p_cluster_pcp_handler.h"
+#include "core/internal/pcp.h"
+#include "core/strategy.h"
+#include "platform/ptr.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+// Concrete implementation of the PCPHandler for the P2P_STAR PCP. This PCP is
+// for mediums that have one server with (potentially) many clients; all mediums
+// in P2P_CLUSTER are valid for P2P_STAR, but not all mediums in P2P_STAR and
+// valid for P2P_CLUSTER.
+//
+// <p>Currently, this implementation advertises/discovers over BLE and Bluetooth
+// and connects over Bluetooth, eventually upgrading to a Wifi Hotspot.
+template <typename Platform>
+class P2PStarPCPHandler : public P2PClusterPCPHandler<Platform> {
+ public:
+  P2PStarPCPHandler(
+      Ptr<MediumManager<Platform> > medium_manager,
+      Ptr<EndpointManager<Platform> > endpoint_manager,
+      Ptr<EndpointChannelManager<Platform> > endpoint_channel_manager,
+      Ptr<BandwidthUpgradeManager<Platform> > bandwidth_upgrade_manager);
+  ~P2PStarPCPHandler() override;
+
+  Strategy getStrategy() override;
+  PCP::Value getPCP() override;
+
+ protected:
+  std::vector<proto::connections::Medium> getConnectionMediumsByPriority()
+      override;
+  proto::connections::Medium getDefaultUpgradeMedium() override;
+
+  bool canSendOutgoingConnection(
+      Ptr<ClientProxy<Platform> > client_proxy) override;
+  bool canReceiveIncomingConnection(
+      Ptr<ClientProxy<Platform> > client_proxy) override;
+
+ private:
+  Ptr<MediumManager<Platform> > medium_manager_;
+};
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#include "core/internal/p2p_star_pcp_handler.cc"
+
+#endif  // CORE_INTERNAL_P2P_STAR_PCP_HANDLER_H_

cpp/core/internal/payload_manager.h

@@ -0,0 +1,288 @@
+#ifndef CORE_INTERNAL_PAYLOAD_MANAGER_H_
+#define CORE_INTERNAL_PAYLOAD_MANAGER_H_
+
+#include <cstdint>
+#include <map>
+#include <vector>
+
+#include "core/internal/client_proxy.h"
+#include "core/internal/endpoint_manager.h"
+#include "core/internal/internal_payload.h"
+#include "core/internal/internal_payload_factory.h"
+#include "core/internal/loop_runner.h"
+#include "core/listeners.h"
+#include "core/payload.h"
+#include "core/status.h"
+#include "proto/connections/offline_wire_formats.pb.h"
+#include "platform/api/count_down_latch.h"
+#include "platform/api/lock.h"
+#include "platform/byte_array.h"
+#include "platform/port/string.h"
+#include "platform/ptr.h"
+#include "platform/runnable.h"
+#include "proto/connections_enums.pb.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+namespace payload_manager {
+
+template <typename>
+class SendPayloadRunnable;
+template <typename>
+class ProcessEndpointDisconnectionRunnable;
+template <typename>
+class SendClientCallbacksForFinishedOutgoingPayloadRunnable;
+template <typename>
+class SendClientCallbacksForFinishedIncomingPayloadRunnable;
+template <typename>
+class HandleSuccessfulOutgoingChunkRunnable;
+template <typename>
+class HandleSuccessfulIncomingChunkRunnable;
+
+}  // namespace payload_manager
+
+template <typename Platform>
+class PayloadManager
+    : public EndpointManager<Platform>::IncomingOfflineFrameProcessor {
+ public:
+  explicit PayloadManager(Ptr<EndpointManager<Platform> > endpoint_manager);
+  ~PayloadManager() override;
+
+  void sendPayload(Ptr<ClientProxy<Platform> > client_proxy,
+                   const std::vector<string>& endpoint_ids,
+                   ConstPtr<Payload> payload);
+  Status::Value cancelPayload(Ptr<ClientProxy<Platform> > client_proxy,
+                              std::int64_t payload_id);
+
+  // @EndpointManagerReaderThread
+  void processIncomingOfflineFrame(
+      ConstPtr<OfflineFrame> offline_frame, const string& from_endpoint_id,
+      Ptr<ClientProxy<Platform> > to_client_proxy,
+      proto::connections::Medium current_medium) override;
+
+  // @EndpointManagerThread
+  void processEndpointDisconnection(
+      Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_id,
+      Ptr<CountDownLatch> process_disconnection_barrier) override;
+
+ private:
+  // Information about an endpoint for a particular payload.
+  class EndpointInfo {
+   public:
+    // Status set for the endpoint out-of-band via a ControlMessage.
+    struct Status {
+      enum Value { UNKNOWN, AVAILABLE, CANCELED, ERROR };
+    };
+
+    explicit EndpointInfo(string id);
+
+    string getId() const;
+    typename EndpointInfo::Status::Value getStatus() const;
+    std::int64_t getOffset() const;
+
+    void setStatus(const PayloadTransferFrame::ControlMessage& control_message);
+    void setOffset(std::int64_t offset);
+
+   private:
+    static typename Status::Value controlMessageEventToEndpointInfoStatus(
+        PayloadTransferFrame::ControlMessage::EventType event);
+
+    const string id_;
+    typename Status::Value status_;
+    std::int64_t offset_;
+  };
+
+  // Tracks state for an InternalPayload and the endpoints associated with it.
+  class PendingPayload {
+   public:
+    static Ptr<PendingPayload> createIncoming(
+        Ptr<InternalPayload> internal_payload, const string& endpoint_id);
+    static Ptr<PendingPayload> createOutgoing(
+        Ptr<InternalPayload> internal_payload,
+        const std::vector<string>& endpoint_ids);
+
+    ~PendingPayload();
+
+    std::int64_t getId();
+
+    Ptr<InternalPayload> getInternalPayload();
+
+    bool isLocallyCanceled();
+    void markLocallyCanceled();
+    bool isIncoming();
+
+    // Gets the EndpointInfo objects for the endpoints (still) associated with
+    // this payload.
+    std::vector<Ptr<EndpointInfo> > getEndpoints() const;
+    // Returns the EndpointInfo for a given endpoint ID. Returns null if the
+    // endpoint is not associated with this payload.
+    Ptr<EndpointInfo> getEndpoint(const string& endpoint_id);
+
+    // Removes the given endpoints, e.g. on error.
+    void removeEndpoints(const std::vector<string>& endpoint_ids_to_remove);
+
+    // Sets the status for a particular endpoint.
+    void setEndpointStatusFromControlMessage(
+        const string& endpoint_id,
+        const PayloadTransferFrame::ControlMessage& control_message);
+
+    // Sets the offset for a particular endpoint.
+    void setOffsetForEndpoint(const string& endpoint_id, std::int64_t offset);
+
+    void close();
+
+   private:
+    PendingPayload(Ptr<InternalPayload> internal_payload,
+                   const std::vector<string>& endpoint_ids, bool is_incoming);
+
+    ScopedPtr<Ptr<Lock> > lock_;
+
+    ScopedPtr<Ptr<InternalPayload> > internal_payload_;
+    const bool is_incoming_;
+    ScopedPtr<Ptr<AtomicBoolean> > is_locally_cancelled_;
+    typedef std::map<string, Ptr<EndpointInfo> > EndpointsMap;
+    EndpointsMap endpoints_;
+  };
+
+  // Tracks and manages PendingPayload objects in a synchronized manner.
+  class PendingPayloads {
+   public:
+    PendingPayloads();
+    ~PendingPayloads();
+
+    void startTrackingPayload(std::int64_t payload_id,
+                              Ptr<PendingPayload> pending_payload);
+    Ptr<PendingPayload> stopTrackingPayload(std::int64_t payload_id);
+    Ptr<PendingPayload> getPayload(std::int64_t payload_id);
+    std::vector<Ptr<PendingPayload> > getAllPayloads();
+
+   private:
+    ScopedPtr<Ptr<Lock> > lock_;
+    typedef std::map<std::int64_t, Ptr<PendingPayload> > PendingPayloadsMap;
+    PendingPayloadsMap pending_payloads_;
+  };
+
+  template <typename>
+  friend class payload_manager::SendPayloadRunnable;
+  template <typename>
+  friend class payload_manager::ProcessEndpointDisconnectionRunnable;
+  template <typename>
+  friend class payload_manager::
+      SendClientCallbacksForFinishedOutgoingPayloadRunnable;
+  template <typename>
+  friend class payload_manager::
+      SendClientCallbacksForFinishedIncomingPayloadRunnable;
+  template <typename>
+  friend class payload_manager::HandleSuccessfulOutgoingChunkRunnable;
+  template <typename>
+  friend class payload_manager::HandleSuccessfulIncomingChunkRunnable;
+
+  // Converts the status of an endpoint that's been set out-of-band via a remote
+  // ControlMessage to the PayloadStatus for handling of that endpoint-payload
+  // pair.
+  static proto::connections::PayloadStatus endpointInfoStatusToPayloadStatus(
+      typename EndpointInfo::Status::Value status);
+  // Converts a ControlMessage::EventType for a particular payload to a
+  // PayloadStatus. Called when we've received a ControlMessage with this event
+  // from a remote endpoint; thus the PayloadStatuses are REMOTE_*.
+  static proto::connections::PayloadStatus controlMessageEventToPayloadStatus(
+      PayloadTransferFrame::ControlMessage::EventType event);
+  static PayloadTransferUpdate::Status::Value
+  payloadStatusToTransferUpdateStatus(proto::connections::PayloadStatus status);
+
+  ConstPtr<PayloadTransferFrame::PayloadHeader> createPayloadHeader(
+      ConstPtr<InternalPayload> internal_payload);
+  ConstPtr<PayloadTransferFrame::PayloadChunk> createPayloadChunk(
+      std::int64_t payload_chunk_offset,
+      ConstPtr<ByteArray> payload_chunk_body);
+
+  Ptr<PendingPayload> createIncomingPayload(
+      const PayloadTransferFrame& payload_transfer_frame,
+      const string& endpoint_id);
+
+  void sendClientCallbacksForFinishedOutgoingPayload(
+      Ptr<ClientProxy<Platform> > client_proxy,
+      const std::vector<string>& finished_endpoint_ids,
+      const PayloadTransferFrame::PayloadHeader& payload_header,
+      std::int64_t num_bytes_successfully_transferred,
+      proto::connections::PayloadStatus status);
+  void sendClientCallbacksForFinishedIncomingPayload(
+      Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_id,
+      const PayloadTransferFrame::PayloadHeader& payload_header,
+      std::int64_t offset_bytes, proto::connections::PayloadStatus status);
+
+  void sendControlMessage(
+      const std::vector<string>& endpoint_ids,
+      const PayloadTransferFrame::PayloadHeader& payload_header,
+      std::int64_t num_bytes_successfully_transferred,
+      PayloadTransferFrame::ControlMessage::EventType event_type);
+
+  // Handles a finished outgoing payload for the given endpointIds. All statuses
+  // except for SUCCESS are handled here.
+  void handleFinishedOutgoingPayload(
+      Ptr<ClientProxy<Platform> > client_proxy,
+      const std::vector<string>& finished_endpoint_ids,
+      const PayloadTransferFrame::PayloadHeader& payload_header,
+      std::int64_t num_bytes_successfully_transferred,
+      proto::connections::PayloadStatus status);
+  void handleFinishedIncomingPayload(
+      Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_id,
+      const PayloadTransferFrame::PayloadHeader& payload_header,
+      std::int64_t offset_bytes, proto::connections::PayloadStatus status);
+
+  void handleSuccessfulOutgoingChunk(
+      Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_id,
+      const PayloadTransferFrame::PayloadHeader& payload_header,
+      std::int32_t payload_chunk_flags, std::int64_t payload_chunk_offset,
+      std::int64_t payload_chunk_body_size);
+  void handleSuccessfulIncomingChunk(
+      Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_id,
+      const PayloadTransferFrame::PayloadHeader& payload_header,
+      std::int32_t payload_chunk_flags, std::int64_t payload_chunk_offset,
+      std::int64_t payload_chunk_body_size);
+
+  void processDataPacket(Ptr<ClientProxy<Platform> > to_client_proxy,
+                         const string& from_endpoint_id,
+                         const PayloadTransferFrame& payload_transfer_frame);
+  void processControlPacket(Ptr<ClientProxy<Platform> > to_client_proxy,
+                            const string& from_endpoint_id,
+                            const PayloadTransferFrame& payload_transfer_frame);
+
+  // @PayloadStatusUpdateThread
+  void notifyClientOfIncomingPayloadTransferUpdate(
+      Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_id,
+      const PayloadTransferUpdate& payload_transfer_update,
+      bool done_with_payload);
+
+  Ptr<typename Platform::SingleThreadExecutorType> getOutgoingPayloadExecutor(
+      Payload::Type::Value payload_type);
+
+  void enqueueOutgoingPayload(
+      Ptr<typename Platform::SingleThreadExecutorType> executor,
+      Ptr<Runnable> runnable);
+
+  ScopedPtr<Ptr<InternalPayloadFactory<Platform> > > internal_payload_factory_;
+  ScopedPtr<Ptr<LoopRunner> > send_payload_loop_runner_;
+  ScopedPtr<Ptr<PendingPayloads> > pending_payloads_;
+
+  ScopedPtr<Ptr<typename Platform::SingleThreadExecutorType> >
+      bytes_payload_executor_;
+  ScopedPtr<Ptr<typename Platform::SingleThreadExecutorType> >
+      file_payload_executor_;
+  ScopedPtr<Ptr<typename Platform::SingleThreadExecutorType> >
+      stream_payload_executor_;
+  ScopedPtr<Ptr<typename Platform::SingleThreadExecutorType> >
+      payload_status_update_executor_;
+
+  Ptr<EndpointManager<Platform> > endpoint_manager_;
+};
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#include "core/internal/payload_manager.cc"
+
+#endif  // CORE_INTERNAL_PAYLOAD_MANAGER_H_

cpp/core/internal/pcp.h

@@ -0,0 +1,21 @@
+#ifndef CORE_INTERNAL_PCP_H_
+#define CORE_INTERNAL_PCP_H_
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+struct PCP {
+  enum Value {
+    UNKNOWN = 0,
+    P2P_STAR = 1,
+    P2P_CLUSTER = 2,
+    P2P_POINT_TO_POINT = 3,
+  };
+};
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#endif  // CORE_INTERNAL_PCP_H_

cpp/core/internal/pcp_handler.h

@@ -0,0 +1,63 @@
+#ifndef CORE_INTERNAL_PCP_HANDLER_H_
+#define CORE_INTERNAL_PCP_HANDLER_H_
+
+#include <vector>
+
+#include "core/internal/client_proxy.h"
+#include "core/internal/pcp.h"
+#include "core/listeners.h"
+#include "core/options.h"
+#include "core/status.h"
+#include "core/strategy.h"
+#include "platform/port/string.h"
+#include "proto/connections_enums.pb.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+// Defines the set of methods that need to be implemented to handle the
+// per-PCP-specific operations in the OfflineServiceController.
+//
+// <p>These methods are all meant to be synchronous, and should return only
+// after knowing they've done what they were supposed to do (or unequivocally
+// failed to do so).
+template <typename Platform>
+class PCPHandler {
+ public:
+  virtual ~PCPHandler() {}
+
+  virtual Strategy getStrategy() = 0;
+  virtual PCP::Value getPCP() = 0;
+
+  virtual Status::Value startAdvertising(
+      Ptr<ClientProxy<Platform> > client_proxy, const string& service_id,
+      const string& local_endpoint_name,
+      const AdvertisingOptions& advertising_options,
+      Ptr<ConnectionLifecycleListener> connection_lifecycle_listener) = 0;
+  virtual void stopAdvertising(Ptr<ClientProxy<Platform> > client_proxy) = 0;
+
+  virtual Status::Value startDiscovery(
+      Ptr<ClientProxy<Platform> > client_proxy, const string& service_id,
+      const DiscoveryOptions& discovery_options,
+      Ptr<DiscoveryListener> discovery_listener) = 0;
+  virtual void stopDiscovery(Ptr<ClientProxy<Platform> > client_proxy) = 0;
+
+  virtual Status::Value requestConnection(
+      Ptr<ClientProxy<Platform> > client_proxy,
+      const string& local_endpoint_name, const string& endpoint_id,
+      Ptr<ConnectionLifecycleListener> connection_lifecycle_listener) = 0;
+  virtual Status::Value acceptConnection(
+      Ptr<ClientProxy<Platform> > clientProxy, const string& endpoint_id,
+      Ptr<PayloadListener> payload_listener) = 0;
+  virtual Status::Value rejectConnection(
+      Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_id) = 0;
+
+  virtual proto::connections::Medium getBandwidthUpgradeMedium() = 0;
+};
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#endif  // CORE_INTERNAL_PCP_HANDLER_H_

cpp/core/internal/pcp_manager.cc

@@ -0,0 +1,160 @@
+#include "core/internal/pcp_manager.h"
+
+#include "core/internal/p2p_cluster_pcp_handler.h"
+#include "core/internal/p2p_point_to_point_pcp_handler.h"
+#include "core/internal/p2p_star_pcp_handler.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+template <typename Platform>
+PCPManager<Platform>::PCPManager(
+    Ptr<MediumManager<Platform> > medium_manager,
+    Ptr<EndpointChannelManager<Platform> > endpoint_channel_manager,
+    Ptr<EndpointManager<Platform> > endpoint_manager,
+    Ptr<BandwidthUpgradeManager<Platform> > bandwidth_upgrade_manager)
+    : pcp_handlers_(), current_pcp_handler_() {
+  pcp_handlers_[PCP::P2P_CLUSTER] = MakePtr(new P2PClusterPCPHandler<Platform>(
+      medium_manager, endpoint_manager, endpoint_channel_manager,
+      bandwidth_upgrade_manager));
+  pcp_handlers_[PCP::P2P_STAR] = MakePtr(new P2PStarPCPHandler<Platform>(
+      medium_manager, endpoint_manager, endpoint_channel_manager,
+      bandwidth_upgrade_manager));
+  pcp_handlers_[PCP::P2P_POINT_TO_POINT] =
+      MakePtr(new P2PPointToPointPCPHandler<Platform>(
+          medium_manager, endpoint_manager, endpoint_channel_manager,
+          bandwidth_upgrade_manager));
+}
+
+template <typename Platform>
+PCPManager<Platform>::~PCPManager() {
+  // TODO(tracyzhou): Add logging.
+
+  // clear() instead of destroy() because this is just a reference -- the real
+  // object will be destroyed in the loop below.
+  current_pcp_handler_.clear();
+
+  for (typename PCPHandlersMap::iterator it = pcp_handlers_.begin();
+       it != pcp_handlers_.end(); it++) {
+    it->second.destroy();
+  }
+  pcp_handlers_.clear();
+}
+
+template <typename Platform>
+Status::Value PCPManager<Platform>::startAdvertising(
+    Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_name,
+    const string& service_id, const AdvertisingOptions& advertising_options,
+    Ptr<ConnectionLifecycleListener> connection_lifecycle_listener) {
+  if (!setCurrentPCPHandler(advertising_options.strategy)) {
+    return Status::ERROR;
+  }
+
+  return current_pcp_handler_->startAdvertising(
+      client_proxy, service_id, endpoint_name, advertising_options,
+      connection_lifecycle_listener);
+}
+
+template <typename Platform>
+void PCPManager<Platform>::stopAdvertising(
+    Ptr<ClientProxy<Platform> > client_proxy) {
+  if (!current_pcp_handler_.isNull()) {
+    current_pcp_handler_->stopAdvertising(client_proxy);
+  }
+}
+
+template <typename Platform>
+Status::Value PCPManager<Platform>::startDiscovery(
+    Ptr<ClientProxy<Platform> > client_proxy, const string& service_id,
+    const DiscoveryOptions& discovery_options,
+    Ptr<DiscoveryListener> discovery_listener) {
+  if (!setCurrentPCPHandler(discovery_options.strategy)) {
+    return Status::ERROR;
+  }
+
+  return current_pcp_handler_->startDiscovery(
+      client_proxy, service_id, discovery_options, discovery_listener);
+}
+
+template <typename Platform>
+void PCPManager<Platform>::stopDiscovery(
+    Ptr<ClientProxy<Platform> > client_proxy) {
+  if (!current_pcp_handler_.isNull()) {
+    current_pcp_handler_->stopDiscovery(client_proxy);
+  }
+}
+
+template <typename Platform>
+Status::Value PCPManager<Platform>::requestConnection(
+    Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_name,
+    const string& endpoint_id,
+    Ptr<ConnectionLifecycleListener> connection_lifecycle_listener) {
+  if (current_pcp_handler_.isNull()) {
+    return Status::OUT_OF_ORDER_API_CALL;
+  }
+
+  return current_pcp_handler_->requestConnection(
+      client_proxy, endpoint_name, endpoint_id, connection_lifecycle_listener);
+}
+
+template <typename Platform>
+Status::Value PCPManager<Platform>::acceptConnection(
+    Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_id,
+    Ptr<PayloadListener> payload_listener) {
+  if (current_pcp_handler_.isNull()) {
+    return Status::OUT_OF_ORDER_API_CALL;
+  }
+
+  return current_pcp_handler_->acceptConnection(client_proxy, endpoint_id,
+                                                payload_listener);
+}
+
+template <typename Platform>
+Status::Value PCPManager<Platform>::rejectConnection(
+    Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_id) {
+  if (current_pcp_handler_.isNull()) {
+    return Status::OUT_OF_ORDER_API_CALL;
+  }
+
+  return current_pcp_handler_->rejectConnection(client_proxy, endpoint_id);
+}
+
+template <typename Platform>
+proto::connections::Medium PCPManager<Platform>::getBandwidthUpgradeMedium() {
+  if (current_pcp_handler_.isNull()) {
+    return proto::connections::Medium::UNKNOWN_MEDIUM;
+  }
+
+  return current_pcp_handler_->getBandwidthUpgradeMedium();
+}
+
+template <typename Platform>
+bool PCPManager<Platform>::setCurrentPCPHandler(const Strategy& strategy) {
+  current_pcp_handler_ = getPCPHandler(deducePCP(strategy));
+
+  return !current_pcp_handler_.isNull();
+}
+
+template <typename Platform>
+PCP::Value PCPManager<Platform>::deducePCP(const Strategy& strategy) {
+  if (Strategy::kP2PCluster == strategy) {
+    return PCP::P2P_CLUSTER;
+  } else if (Strategy::kP2PStar == strategy) {
+    return PCP::P2P_STAR;
+  } else if (Strategy::kP2PPointToPoint == strategy) {
+    return PCP::P2P_POINT_TO_POINT;
+  } else {
+    // TODO(tracyzhou): Add logging.
+    return PCP::UNKNOWN;
+  }
+}
+
+template <typename Platform>
+Ptr<PCPHandler<Platform> > PCPManager<Platform>::getPCPHandler(PCP::Value pcp) {
+  return pcp_handlers_[pcp];
+}
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/pcp_manager.h

@@ -0,0 +1,77 @@
+#ifndef CORE_INTERNAL_PCP_MANAGER_H_
+#define CORE_INTERNAL_PCP_MANAGER_H_
+
+#include <map>
+
+#include "core/internal/bandwidth_upgrade_manager.h"
+#include "core/internal/client_proxy.h"
+#include "core/internal/endpoint_channel_manager.h"
+#include "core/internal/endpoint_manager.h"
+#include "core/internal/medium_manager.h"
+#include "core/internal/pcp_handler.h"
+#include "core/listeners.h"
+#include "core/options.h"
+#include "core/status.h"
+#include "core/strategy.h"
+#include "platform/port/string.h"
+#include "platform/ptr.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+// Manages all known PCPHandler implementations, delegating operations to the
+// appropriate one as per the parameters passed in.
+//
+// <p>This will only ever be used by the OfflineServiceController, which has all
+// of its entrypoints invoked serially, so there's no synchronization needed.
+template <typename Platform>
+class PCPManager {
+ public:
+  PCPManager(Ptr<MediumManager<Platform> > medium_manager,
+             Ptr<EndpointChannelManager<Platform> > endpoint_channel_manager,
+             Ptr<EndpointManager<Platform> > endpoint_manager,
+             Ptr<BandwidthUpgradeManager<Platform> > bandwidth_upgrade_manager);
+  ~PCPManager();
+
+  Status::Value startAdvertising(
+      Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_name,
+      const string& service_id, const AdvertisingOptions& advertising_options,
+      Ptr<ConnectionLifecycleListener> connection_lifecycle_listener);
+  void stopAdvertising(Ptr<ClientProxy<Platform> > client_proxy);
+
+  Status::Value startDiscovery(Ptr<ClientProxy<Platform> > client_proxy,
+                               const string& service_id,
+                               const DiscoveryOptions& discovery_options,
+                               Ptr<DiscoveryListener> discovery_listener);
+  void stopDiscovery(Ptr<ClientProxy<Platform> > client_proxy);
+
+  Status::Value requestConnection(
+      Ptr<ClientProxy<Platform> > client_proxy, const string& endpoint_name,
+      const string& endpoint_id,
+      Ptr<ConnectionLifecycleListener> connection_lifecycle_listener);
+  Status::Value acceptConnection(Ptr<ClientProxy<Platform> > client_proxy,
+                                 const string& endpoint_id,
+                                 Ptr<PayloadListener> payload_listener);
+  Status::Value rejectConnection(Ptr<ClientProxy<Platform> > client_proxy,
+                                 const string& endpoint_id);
+
+  proto::connections::Medium getBandwidthUpgradeMedium();
+
+ private:
+  bool setCurrentPCPHandler(const Strategy& strategy);
+  PCP::Value deducePCP(const Strategy& strategy);
+  Ptr<PCPHandler<Platform> > getPCPHandler(PCP::Value pcp);
+
+  typedef std::map<PCP::Value, Ptr<PCPHandler<Platform> > > PCPHandlersMap;
+  PCPHandlersMap pcp_handlers_;
+  Ptr<PCPHandler<Platform> > current_pcp_handler_;
+};
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#include "core/internal/pcp_manager.cc"
+
+#endif  // CORE_INTERNAL_PCP_MANAGER_H_

cpp/core/internal/service_controller.h

@@ -0,0 +1,67 @@
+#ifndef CORE_INTERNAL_SERVICE_CONTROLLER_H_
+#define CORE_INTERNAL_SERVICE_CONTROLLER_H_
+
+#include <cstdint>
+#include <vector>
+
+#include "core/internal/client_proxy.h"
+#include "core/listeners.h"
+#include "core/options.h"
+#include "core/payload.h"
+#include "core/status.h"
+#include "platform/port/string.h"
+#include "platform/ptr.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+template <typename Platform>
+class ServiceController {
+ public:
+  virtual ~ServiceController() {}
+
+  virtual Status::Value startAdvertising(
+      Ptr<ClientProxy<Platform> > client_proxy,
+      const std::string& endpoint_name, const std::string& service_id,
+      const AdvertisingOptions& advertising_options,
+      Ptr<ConnectionLifecycleListener> connection_lifecycle_listener) = 0;
+  virtual void stopAdvertising(Ptr<ClientProxy<Platform> > client_proxy) = 0;
+
+  virtual Status::Value startDiscovery(
+      Ptr<ClientProxy<Platform> > client_proxy, const std::string& service_id,
+      const DiscoveryOptions& discovery_options,
+      Ptr<DiscoveryListener> discovery_listener) = 0;
+  virtual void stopDiscovery(Ptr<ClientProxy<Platform> > client_proxy) = 0;
+
+  virtual Status::Value requestConnection(
+      Ptr<ClientProxy<Platform> > client_proxy,
+      const std::string& endpoint_name, const std::string& endpoint_id,
+      Ptr<ConnectionLifecycleListener> connection_lifecycle_listener) = 0;
+  virtual Status::Value acceptConnection(
+      Ptr<ClientProxy<Platform> > client_proxy, const std::string& endpoint_id,
+      Ptr<PayloadListener> payload_listener) = 0;
+  virtual Status::Value rejectConnection(
+      Ptr<ClientProxy<Platform> > client_proxy,
+      const std::string& endpoint_id) = 0;
+
+  virtual void initiateBandwidthUpgrade(
+      Ptr<ClientProxy<Platform> > client_proxy,
+      const std::string& endpoint_id) = 0;
+
+  virtual void sendPayload(Ptr<ClientProxy<Platform> > client_proxy,
+                           const std::vector<std::string>& endpoint_ids,
+                           ConstPtr<Payload> payload) = 0;
+
+  virtual Status::Value cancelPayload(Ptr<ClientProxy<Platform> > client_proxy,
+                                      std::int64_t payload_id) = 0;
+
+  virtual void disconnectFromEndpoint(Ptr<ClientProxy<Platform> > client_proxy,
+                                      const std::string& endpoint_id) = 0;
+};
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#endif  // CORE_INTERNAL_SERVICE_CONTROLLER_H_

cpp/core/internal/service_controller_router.cc

@@ -0,0 +1,750 @@
+#include "core/internal/service_controller_router.h"
+
+#include "core/internal/offline_service_controller.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+namespace service_controller_router {
+
+// Base class for the following Runnable classes. They all need a
+// ServiceControllerRouter object and a ClientProxy object.
+// ServiceControllerRouter is kept as a reference because the passed in
+// Ptr<ServiceControllerRouter<Platform> > should outlive it.
+template <typename Platform>
+class ServiceControllerRouterRunnable : public Runnable {
+ protected:
+  ServiceControllerRouterRunnable(
+      Ptr<ServiceControllerRouter<Platform> > service_controller_router,
+      Ptr<ClientProxy<Platform> > client_proxy)
+      : service_controller_router_(service_controller_router),
+        client_proxy_(client_proxy) {}
+
+  Ptr<ServiceControllerRouter<Platform> > service_controller_router_;
+  Ptr<ClientProxy<Platform> > client_proxy_;
+};
+
+template <typename Platform>
+class StartAdvertisingRunnable
+    : public ServiceControllerRouterRunnable<Platform> {
+ public:
+  StartAdvertisingRunnable(
+      Ptr<ServiceControllerRouter<Platform> > service_controller_router,
+      Ptr<ClientProxy<Platform> > client_proxy,
+      ConstPtr<StartAdvertisingParams> start_advertising_params)
+      : ServiceControllerRouterRunnable<Platform>(service_controller_router,
+                                                  client_proxy),
+        params_(start_advertising_params) {}
+
+  void run() override {
+    ScopedPtr<Ptr<ResultListener> > result_listener(params_->result_listener);
+
+    Status::Value status =
+        this->service_controller_router_->acquireServiceControllerForClient(
+            this->client_proxy_, params_->advertising_options.strategy);
+    if (Status::SUCCESS != status) {
+      result_listener->onResult(status);
+      return;
+    }
+
+    if (this->client_proxy_->isAdvertising()) {
+      result_listener->onResult(Status::ALREADY_ADVERTISING);
+      return;
+    }
+
+    result_listener->onResult(
+        this->service_controller_router_->current_service_controller_
+            ->startAdvertising(this->client_proxy_, params_->name,
+                               params_->service_id,
+                               params_->advertising_options,
+                               params_->connection_lifecycle_listener));
+  }
+
+ private:
+  ScopedPtr<ConstPtr<StartAdvertisingParams> > params_;
+};
+
+template <typename Platform>
+class StopAdvertisingRunnable
+    : public ServiceControllerRouterRunnable<Platform> {
+ public:
+  StopAdvertisingRunnable(
+      Ptr<ServiceControllerRouter<Platform> > service_controller_router,
+      Ptr<ClientProxy<Platform> > client_proxy,
+      ConstPtr<StopAdvertisingParams> stop_advertising_params)
+      : ServiceControllerRouterRunnable<Platform>(service_controller_router,
+                                                  client_proxy),
+        params_(stop_advertising_params) {}
+
+  void run() override {
+    if (this->service_controller_router_->clientHasAquiredServiceController(
+            this->client_proxy_) &&
+        this->client_proxy_->isAdvertising()) {
+      this->service_controller_router_->current_service_controller_
+          ->stopAdvertising(this->client_proxy_);
+    }
+  }
+
+ private:
+  ScopedPtr<ConstPtr<StopAdvertisingParams> > params_;
+};
+
+template <typename Platform>
+class StartDiscoveryRunnable
+    : public ServiceControllerRouterRunnable<Platform> {
+ public:
+  StartDiscoveryRunnable(
+      Ptr<ServiceControllerRouter<Platform> > service_controller_router,
+      Ptr<ClientProxy<Platform> > client_proxy,
+      ConstPtr<StartDiscoveryParams> start_discovery_params)
+      : ServiceControllerRouterRunnable<Platform>(service_controller_router,
+                                                  client_proxy),
+        params_(start_discovery_params) {}
+
+  void run() override {
+    ScopedPtr<Ptr<ResultListener> > result_listener(params_->result_listener);
+
+    Status::Value status =
+        this->service_controller_router_->acquireServiceControllerForClient(
+            this->client_proxy_, params_->discovery_options.strategy);
+    if (Status::SUCCESS != status) {
+      result_listener->onResult(status);
+      return;
+    }
+
+    if (this->client_proxy_->isDiscovering()) {
+      result_listener->onResult(Status::ALREADY_DISCOVERING);
+      return;
+    }
+
+    result_listener->onResult(
+        this->service_controller_router_->current_service_controller_
+            ->startDiscovery(this->client_proxy_, params_->service_id,
+                             params_->discovery_options,
+                             params_->discovery_listener));
+  }
+
+ private:
+  ScopedPtr<ConstPtr<StartDiscoveryParams> > params_;
+};
+
+template <typename Platform>
+class StopDiscoveryRunnable : public ServiceControllerRouterRunnable<Platform> {
+ public:
+  StopDiscoveryRunnable(
+      Ptr<ServiceControllerRouter<Platform> > service_controller_router,
+      Ptr<ClientProxy<Platform> > client_proxy,
+      ConstPtr<StopDiscoveryParams> stop_discovery_params)
+      : ServiceControllerRouterRunnable<Platform>(service_controller_router,
+                                                  client_proxy),
+        params_(stop_discovery_params) {}
+
+  void run() override {
+    if (this->service_controller_router_->clientHasAquiredServiceController(
+            this->client_proxy_) &&
+        this->client_proxy_->isDiscovering()) {
+      this->service_controller_router_->current_service_controller_
+          ->stopDiscovery(this->client_proxy_);
+    }
+  }
+
+ private:
+  ScopedPtr<ConstPtr<StopDiscoveryParams> > params_;
+};
+
+template <typename Platform>
+class SendConnectionRequestRunnable
+    : public ServiceControllerRouterRunnable<Platform> {
+ public:
+  SendConnectionRequestRunnable(
+      Ptr<ServiceControllerRouter<Platform> > service_controller_router,
+      Ptr<ClientProxy<Platform> > client_proxy,
+      ConstPtr<RequestConnectionParams> request_connection_params)
+      : ServiceControllerRouterRunnable<Platform>(service_controller_router,
+                                                  client_proxy),
+        params_(request_connection_params) {}
+
+  void run() override {
+    ScopedPtr<Ptr<ResultListener> > result_listener(params_->result_listener);
+
+    if (!this->service_controller_router_->clientHasAquiredServiceController(
+            this->client_proxy_)) {
+      result_listener->onResult(Status::OUT_OF_ORDER_API_CALL);
+      return;
+    }
+
+    const string& remote_endpoint_id = params_->remote_endpoint_id;
+
+    if (this->client_proxy_->hasPendingConnectionToEndpoint(
+            remote_endpoint_id) ||
+        this->client_proxy_->isConnectedToEndpoint(remote_endpoint_id)) {
+      result_listener->onResult(Status::ALREADY_CONNECTED_TO_ENDPOINT);
+      return;
+    }
+
+    result_listener->onResult(
+        this->service_controller_router_->current_service_controller_
+            ->requestConnection(this->client_proxy_, params_->name,
+                                remote_endpoint_id,
+                                params_->connection_lifecycle_listener));
+  }
+
+ private:
+  ScopedPtr<ConstPtr<RequestConnectionParams> > params_;
+};
+
+template <typename Platform>
+class AcceptConnectionRequestRunnable
+    : public ServiceControllerRouterRunnable<Platform> {
+ public:
+  AcceptConnectionRequestRunnable(
+      Ptr<ServiceControllerRouter<Platform> > service_controller_router,
+      Ptr<ClientProxy<Platform> > client_proxy,
+      ConstPtr<AcceptConnectionParams> accept_connection_params)
+      : ServiceControllerRouterRunnable<Platform>(service_controller_router,
+                                                  client_proxy),
+        params_(accept_connection_params) {}
+
+  void run() override {
+    ScopedPtr<Ptr<ResultListener> > result_listener(params_->result_listener);
+
+    if (!this->service_controller_router_->clientHasAquiredServiceController(
+            this->client_proxy_)) {
+      result_listener->onResult(Status::OUT_OF_ORDER_API_CALL);
+      return;
+    }
+
+    const string& remote_endpoint_id = params_->remote_endpoint_id;
+
+    if (this->client_proxy_->isConnectedToEndpoint(remote_endpoint_id)) {
+      result_listener->onResult(Status::ALREADY_CONNECTED_TO_ENDPOINT);
+      return;
+    }
+
+    if (this->client_proxy_->hasLocalEndpointResponded(remote_endpoint_id)) {
+      // TODO(tracyzhou): logging
+      result_listener->onResult(Status::OUT_OF_ORDER_API_CALL);
+      return;
+    }
+
+    result_listener->onResult(
+        this->service_controller_router_->current_service_controller_
+            ->acceptConnection(this->client_proxy_, remote_endpoint_id,
+                               params_->payload_listener));
+  }
+
+ private:
+  ScopedPtr<ConstPtr<AcceptConnectionParams> > params_;
+};
+
+template <typename Platform>
+class RejectConnectionRequestRunnable
+    : public ServiceControllerRouterRunnable<Platform> {
+ public:
+  RejectConnectionRequestRunnable(
+      Ptr<ServiceControllerRouter<Platform> > service_controller_router,
+      Ptr<ClientProxy<Platform> > client_proxy,
+      ConstPtr<RejectConnectionParams> reject_connection_params)
+      : ServiceControllerRouterRunnable<Platform>(service_controller_router,
+                                                  client_proxy),
+        params_(reject_connection_params) {}
+
+  void run() override {
+    ScopedPtr<Ptr<ResultListener> > result_listener(params_->result_listener);
+
+    if (!this->service_controller_router_->clientHasAquiredServiceController(
+            this->client_proxy_)) {
+      result_listener->onResult(Status::OUT_OF_ORDER_API_CALL);
+      return;
+    }
+
+    const string& remote_endpoint_id = params_->remote_endpoint_id;
+
+    if (this->client_proxy_->isConnectedToEndpoint(remote_endpoint_id)) {
+      result_listener->onResult(Status::ALREADY_CONNECTED_TO_ENDPOINT);
+      return;
+    }
+
+    if (this->client_proxy_->hasLocalEndpointResponded(remote_endpoint_id)) {
+      // TODO(tracyzhou): logging
+      result_listener->onResult(Status::OUT_OF_ORDER_API_CALL);
+      return;
+    }
+
+    result_listener->onResult(
+        this->service_controller_router_->current_service_controller_
+            ->rejectConnection(this->client_proxy_, remote_endpoint_id));
+  }
+
+ private:
+  ScopedPtr<ConstPtr<RejectConnectionParams> > params_;
+};
+
+template <typename Platform>
+class InitiateBandwidthUpgradeRunnable
+    : public ServiceControllerRouterRunnable<Platform> {
+ public:
+  InitiateBandwidthUpgradeRunnable(
+      Ptr<ServiceControllerRouter<Platform> > service_controller_router,
+      Ptr<ClientProxy<Platform> > client_proxy,
+      ConstPtr<InitiateBandwidthUpgradeParams>
+          initiate_bandwidth_upgrade_params)
+      : ServiceControllerRouterRunnable<Platform>(service_controller_router,
+                                                  client_proxy),
+        params_(initiate_bandwidth_upgrade_params) {}
+
+  void run() override {
+    ScopedPtr<Ptr<ResultListener> > result_listener(params_->result_listener);
+
+    if (!this->service_controller_router_->clientHasAquiredServiceController(
+            this->client_proxy_) ||
+        !this->client_proxy_->isConnectedToEndpoint(
+            params_->remote_endpoint_id)) {
+      result_listener->onResult(Status::OUT_OF_ORDER_API_CALL);
+      return;
+    }
+
+    this->service_controller_router_->current_service_controller_
+        ->initiateBandwidthUpgrade(this->client_proxy_,
+                                   params_->remote_endpoint_id);
+
+    // The caller can listen to
+    // ConnectionLifecycleListener.onBandwidthChanged() to determine success.
+    result_listener->onResult(Status::SUCCESS);
+  }
+
+ private:
+  ScopedPtr<ConstPtr<InitiateBandwidthUpgradeParams> > params_;
+};
+
+template <typename Platform>
+class SendPayloadRunnable : public ServiceControllerRouterRunnable<Platform> {
+ public:
+  SendPayloadRunnable(
+      Ptr<ServiceControllerRouter<Platform> > service_controller_router,
+      Ptr<ClientProxy<Platform> > client_proxy,
+      ConstPtr<SendPayloadParams> send_payload_params)
+      : ServiceControllerRouterRunnable<Platform>(service_controller_router,
+                                                  client_proxy),
+        params_(send_payload_params) {}
+
+  void run() override {
+    ScopedPtr<Ptr<ResultListener> > result_listener(params_->result_listener);
+
+    if (!this->service_controller_router_->clientHasAquiredServiceController(
+            this->client_proxy_)) {
+      result_listener->onResult(Status::OUT_OF_ORDER_API_CALL);
+      return;
+    }
+
+    if (!ServiceControllerRouter<Platform>::
+            clientHasConnectionToAtLeastOneEndpoint(
+                this->client_proxy_, params_->remote_endpoint_ids)) {
+      result_listener->onResult(Status::ENDPOINT_UNKNOWN);
+      return;
+    }
+
+    this->service_controller_router_->current_service_controller_->sendPayload(
+        this->client_proxy_, params_->remote_endpoint_ids, params_->payload);
+
+    // At this point, we've queued up the send Payload request with the
+    // ServiceController; any further failures (e.g. one of the endpoints is
+    // unknown, goes away, or otherwise fails) will be returned to the client
+    // as a PayloadTransferUpdate.
+    result_listener->onResult(Status::SUCCESS);
+  }
+
+ private:
+  ScopedPtr<ConstPtr<SendPayloadParams> > params_;
+};
+
+template <typename Platform>
+class CancelPayloadRunnable : public ServiceControllerRouterRunnable<Platform> {
+ public:
+  CancelPayloadRunnable(
+      Ptr<ServiceControllerRouter<Platform> > service_controller_router,
+      Ptr<ClientProxy<Platform> > client_proxy,
+      ConstPtr<CancelPayloadParams> cancel_payload_params)
+      : ServiceControllerRouterRunnable<Platform>(service_controller_router,
+                                                  client_proxy),
+        params_(cancel_payload_params) {}
+
+  void run() override {
+    ScopedPtr<Ptr<ResultListener> > result_listener(params_->result_listener);
+
+    if (!this->service_controller_router_->clientHasAquiredServiceController(
+            this->client_proxy_)) {
+      result_listener->onResult(Status::OUT_OF_ORDER_API_CALL);
+      return;
+    }
+
+    result_listener->onResult(
+        this->service_controller_router_->current_service_controller_
+            ->cancelPayload(this->client_proxy_, params_->payload_id));
+  }
+
+ private:
+  ScopedPtr<ConstPtr<CancelPayloadParams> > params_;
+};
+
+template <typename Platform>
+class DisconnectFromEndpointRunnable
+    : public ServiceControllerRouterRunnable<Platform> {
+ public:
+  DisconnectFromEndpointRunnable(
+      Ptr<ServiceControllerRouter<Platform> > service_controller_router,
+      Ptr<ClientProxy<Platform> > client_proxy,
+      ConstPtr<DisconnectFromEndpointParams> disconnect_from_endpoint_params)
+      : ServiceControllerRouterRunnable<Platform>(service_controller_router,
+                                                  client_proxy),
+        params_(disconnect_from_endpoint_params) {}
+
+  void run() override {
+    if (this->service_controller_router_->clientHasAquiredServiceController(
+            this->client_proxy_)) {
+      const string& remote_endpoint_id = params_->remote_endpoint_id;
+
+      if (!this->client_proxy_->isConnectedToEndpoint(remote_endpoint_id) &&
+          !this->client_proxy_->hasPendingConnectionToEndpoint(
+              remote_endpoint_id)) {
+        return;
+      }
+      this->service_controller_router_->current_service_controller_
+          ->disconnectFromEndpoint(this->client_proxy_, remote_endpoint_id);
+    }
+  }
+
+ private:
+  ScopedPtr<ConstPtr<DisconnectFromEndpointParams> > params_;
+};
+
+template <typename Platform>
+class StopAllEndpointsRunnable
+    : public ServiceControllerRouterRunnable<Platform> {
+ public:
+  StopAllEndpointsRunnable(
+      Ptr<ServiceControllerRouter<Platform> > service_controller_router,
+      Ptr<ClientProxy<Platform> > client_proxy,
+      ConstPtr<StopAllEndpointsParams> stop_all_endpoints_params)
+      : ServiceControllerRouterRunnable<Platform>(service_controller_router,
+                                                  client_proxy),
+        params_(stop_all_endpoints_params) {}
+
+  void run() override {
+    ScopedPtr<Ptr<ResultListener> > result_listener(params_->result_listener);
+
+    if (this->service_controller_router_->clientHasAquiredServiceController(
+            this->client_proxy_)) {
+      this->service_controller_router_->doneWithStrategySessionForClient(
+          this->client_proxy_);
+    }
+    result_listener->onResult(Status::SUCCESS);
+  }
+
+ private:
+  ScopedPtr<ConstPtr<StopAllEndpointsParams> > params_;
+};
+
+template <typename Platform>
+class ClientDisconnectingRunnable
+    : public ServiceControllerRouterRunnable<Platform> {
+ public:
+  ClientDisconnectingRunnable(
+      Ptr<ServiceControllerRouter<Platform>> service_controller_router,
+      Ptr<ClientProxy<Platform>> client_proxy)
+      : ServiceControllerRouterRunnable<Platform>(service_controller_router,
+                                                  client_proxy) {}
+
+  void run() override {
+    if (!this->service_controller_router_->clientHasAquiredServiceController(
+            this->client_proxy_)) {
+      return;
+    }
+
+    this->service_controller_router_->doneWithStrategySessionForClient(
+        this->client_proxy_);
+
+    // Log the completion of this client's connection.
+    // TODO(tracyzhou): Add logging.
+  }
+};
+
+}  // namespace service_controller_router
+
+template <typename Platform>
+ServiceControllerRouter<Platform>::ServiceControllerRouter()
+    : current_service_controller_clients_(),
+      current_service_controller_(new OfflineServiceController<Platform>()),
+      current_strategy_(),
+      serializer_(Platform::createSingleThreadExecutor()) {}
+
+template <typename Platform>
+ServiceControllerRouter<Platform>::~ServiceControllerRouter() {
+  // TODO(tracyzhou): Add logging.
+
+  // And make sure that cleanup is the last thing we do.
+  serializer_->shutdown();
+
+  current_service_controller_.destroy();
+  current_strategy_.destroy();
+  current_service_controller_clients_.clear();
+}
+
+template <typename Platform>
+void ServiceControllerRouter<Platform>::startAdvertising(
+    Ptr<ClientProxy<Platform> > client_proxy,
+    ConstPtr<StartAdvertisingParams> start_advertising_params) {
+  routeToServiceController(
+      MakePtr(new service_controller_router::StartAdvertisingRunnable<Platform>(
+          MakePtr(this), client_proxy, start_advertising_params)));
+}
+
+template <typename Platform>
+void ServiceControllerRouter<Platform>::stopAdvertising(
+    Ptr<ClientProxy<Platform> > client_proxy,
+    ConstPtr<StopAdvertisingParams> stop_advertising_params) {
+  routeToServiceController(
+      MakePtr(new service_controller_router::StopAdvertisingRunnable<Platform>(
+          MakePtr(this), client_proxy, stop_advertising_params)));
+}
+
+template <typename Platform>
+void ServiceControllerRouter<Platform>::startDiscovery(
+    Ptr<ClientProxy<Platform> > client_proxy,
+    ConstPtr<StartDiscoveryParams> start_discovery_params) {
+  routeToServiceController(
+      MakePtr(new service_controller_router::StartDiscoveryRunnable<Platform>(
+          MakePtr(this), client_proxy, start_discovery_params)));
+}
+
+template <typename Platform>
+void ServiceControllerRouter<Platform>::stopDiscovery(
+    Ptr<ClientProxy<Platform> > client_proxy,
+    ConstPtr<StopDiscoveryParams> stop_discovery_params) {
+  routeToServiceController(
+      MakePtr(new service_controller_router::StopDiscoveryRunnable<Platform>(
+          MakePtr(this), client_proxy, stop_discovery_params)));
+}
+
+template <typename Platform>
+void ServiceControllerRouter<Platform>::requestConnection(
+    Ptr<ClientProxy<Platform> > client_proxy,
+    ConstPtr<RequestConnectionParams> request_connection_params) {
+  routeToServiceController(MakePtr(
+      new service_controller_router::SendConnectionRequestRunnable<Platform>(
+          MakePtr(this), client_proxy, request_connection_params)));
+}
+
+template <typename Platform>
+void ServiceControllerRouter<Platform>::acceptConnection(
+    Ptr<ClientProxy<Platform> > client_proxy,
+    ConstPtr<AcceptConnectionParams> accept_connection_params) {
+  routeToServiceController(MakePtr(
+      new service_controller_router::AcceptConnectionRequestRunnable<Platform>(
+          MakePtr(this), client_proxy, accept_connection_params)));
+}
+
+template <typename Platform>
+void ServiceControllerRouter<Platform>::rejectConnection(
+    Ptr<ClientProxy<Platform> > client_proxy,
+    ConstPtr<RejectConnectionParams> reject_connection_params) {
+  routeToServiceController(MakePtr(
+      new service_controller_router::RejectConnectionRequestRunnable<Platform>(
+          MakePtr(this), client_proxy, reject_connection_params)));
+}
+
+template <typename Platform>
+void ServiceControllerRouter<Platform>::initiateBandwidthUpgrade(
+    Ptr<ClientProxy<Platform> > client_proxy,
+    ConstPtr<InitiateBandwidthUpgradeParams>
+        initiate_bandwidth_upgrade_params) {
+  routeToServiceController(MakePtr(
+      new service_controller_router::InitiateBandwidthUpgradeRunnable<Platform>(
+          MakePtr(this), client_proxy, initiate_bandwidth_upgrade_params)));
+}
+
+template <typename Platform>
+void ServiceControllerRouter<Platform>::sendPayload(
+    Ptr<ClientProxy<Platform> > client_proxy,
+    ConstPtr<SendPayloadParams> send_payload_params) {
+  routeToServiceController(
+      MakePtr(new service_controller_router::SendPayloadRunnable<Platform>(
+          MakePtr(this), client_proxy, send_payload_params)));
+}
+
+template <typename Platform>
+void ServiceControllerRouter<Platform>::cancelPayload(
+    Ptr<ClientProxy<Platform> > client_proxy,
+    ConstPtr<CancelPayloadParams> cancel_payload_params) {
+  routeToServiceController(
+      MakePtr(new service_controller_router::CancelPayloadRunnable<Platform>(
+          MakePtr(this), client_proxy, cancel_payload_params)));
+}
+
+template <typename Platform>
+void ServiceControllerRouter<Platform>::disconnectFromEndpoint(
+    Ptr<ClientProxy<Platform> > client_proxy,
+    ConstPtr<DisconnectFromEndpointParams> disconnect_from_endpoint_params) {
+  routeToServiceController(MakePtr(
+      new service_controller_router::DisconnectFromEndpointRunnable<Platform>(
+          MakePtr(this), client_proxy, disconnect_from_endpoint_params)));
+}
+
+template <typename Platform>
+void ServiceControllerRouter<Platform>::stopAllEndpoints(
+    Ptr<ClientProxy<Platform> > client_proxy,
+    ConstPtr<StopAllEndpointsParams> stop_all_endpoint_params) {
+  routeToServiceController(
+      MakePtr(new service_controller_router::StopAllEndpointsRunnable<Platform>(
+          MakePtr(this), client_proxy, stop_all_endpoint_params)));
+}
+
+template <typename Platform>
+void ServiceControllerRouter<Platform>::clientDisconnecting(
+    Ptr<ClientProxy<Platform>> client_proxy) {
+  routeToServiceController(MakePtr(
+      new service_controller_router::ClientDisconnectingRunnable<Platform>(
+          MakePtr(this), client_proxy)));
+}
+
+template <typename Platform>
+Status::Value
+ServiceControllerRouter<Platform>::acquireServiceControllerForClient(
+    Ptr<ClientProxy<Platform> > client_proxy, const Strategy& strategy) {
+  if (current_strategy_.isNull()) {
+    // Case 1: There is no existing Strategy at all.
+
+    // Set everything up for the first time.
+    Status::Value status = updateCurrentServiceControllerAndStrategy(strategy);
+    if (status != Status::SUCCESS) {
+      return status;
+    }
+    current_service_controller_clients_.insert(client_proxy);
+    return Status::SUCCESS;
+  } else if (strategy == *current_strategy_) {
+    // Case 2: The existing Strategy matches.
+
+    // The new client just needs to be added to the set of clients using the
+    // current ServiceController.
+    current_service_controller_clients_.insert(client_proxy);
+    return Status::SUCCESS;
+  } else {
+    // Case 3: The existing Strategy doesn't match.
+
+    // It's only safe for a client to cause a switch if it's the only client
+    // using the current ServiceController.
+    bool is_the_only_client_of_service_controller =
+        current_service_controller_clients_.size() == 1 &&
+        current_service_controller_clients_.find(client_proxy) !=
+            current_service_controller_clients_.end();
+    if (!is_the_only_client_of_service_controller) {
+      // TODO(tracyzhou): logging
+      return Status::ALREADY_HAVE_ACTIVE_STRATEGY;
+    }
+
+    // If the client still has connected endpoints, they must disconnect before
+    // they can switch.
+    if (!client_proxy->getConnectedEndpoints().empty()) {
+      // TODO(tracyzhou): logging
+      return Status::OUT_OF_ORDER_API_CALL;
+    }
+
+    // By this point, it's safe to switch the Strategy and ServiceController
+    // (and since it's the only client, there's no need to add it to the set of
+    // clients using the current ServiceController).
+    return updateCurrentServiceControllerAndStrategy(strategy);
+  }
+}
+
+template <typename Platform>
+bool ServiceControllerRouter<Platform>::clientHasAquiredServiceController(
+    Ptr<ClientProxy<Platform> > client_proxy) {
+  return (current_service_controller_clients_.find(client_proxy) !=
+          current_service_controller_clients_.end());
+}
+
+template <typename Platform>
+void ServiceControllerRouter<Platform>::releaseServiceControllerForClient(
+    Ptr<ClientProxy<Platform> > client_proxy) {
+  current_service_controller_clients_.erase(client_proxy);
+
+  if (current_service_controller_clients_.empty()) {
+    current_service_controller_.destroy();
+    current_strategy_.destroy();
+  }
+}
+
+/** Clean up all state for this client. The client is now free to switch
+ * strategies. */
+template <typename Platform>
+void ServiceControllerRouter<Platform>::doneWithStrategySessionForClient(
+    Ptr<ClientProxy<Platform> > client_proxy) {
+  // Disconnect from all the connected endpoints tied to this clientProxy.
+  std::vector<string> pending_connected_endpoints =
+      client_proxy->getPendingConnectedEndpoints();
+
+  for (std::vector<string>::iterator it = pending_connected_endpoints.begin();
+       it != pending_connected_endpoints.end(); it++) {
+    current_service_controller_->disconnectFromEndpoint(client_proxy, *it);
+  }
+
+  std::vector<string> connected_endpoints =
+      client_proxy->getConnectedEndpoints();
+
+  for (std::vector<string>::iterator it = connected_endpoints.begin();
+       it != connected_endpoints.end(); it++) {
+    current_service_controller_->disconnectFromEndpoint(client_proxy, *it);
+  }
+
+  // Stop any advertising and discovery that may be underway due to this
+  // clientProxy.
+  current_service_controller_->stopAdvertising(client_proxy);
+  current_service_controller_->stopDiscovery(client_proxy);
+
+  // Finally, clear all state maintained by this clientProxy.
+  client_proxy->reset();
+
+  releaseServiceControllerForClient(client_proxy);
+}
+
+template <typename Platform>
+void ServiceControllerRouter<Platform>::routeToServiceController(
+    Ptr<Runnable> runnable) {
+  serializer_->execute(runnable);
+}
+
+template <typename Platform>
+bool ServiceControllerRouter<Platform>::clientHasConnectionToAtLeastOneEndpoint(
+    Ptr<ClientProxy<Platform> > client_proxy,
+    const std::vector<string>& remote_endpoint_ids) {
+  for (std::vector<string>::const_iterator it = remote_endpoint_ids.begin();
+       it != remote_endpoint_ids.end(); it++) {
+    if (client_proxy->isConnectedToEndpoint(*it)) {
+      return true;
+    }
+  }
+  return false;
+}
+
+template <typename Platform>
+Status::Value
+ServiceControllerRouter<Platform>::updateCurrentServiceControllerAndStrategy(
+    const Strategy& strategy) {
+  if (!strategy.isValid()) {
+    // TODO(tracyzhou): logging
+    return Status::ERROR;
+  }
+
+  current_service_controller_.destroy();
+  current_service_controller_ =
+      MakePtr(new OfflineServiceController<Platform>());
+  current_strategy_.destroy();
+  current_strategy_ = MakePtr(new Strategy(strategy));
+
+  return Status::SUCCESS;
+}
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location

cpp/core/internal/service_controller_router.h

@@ -0,0 +1,151 @@
+#ifndef CORE_INTERNAL_SERVICE_CONTROLLER_ROUTER_H_
+#define CORE_INTERNAL_SERVICE_CONTROLLER_ROUTER_H_
+
+#include <set>
+#include <vector>
+
+#include "core/internal/client_proxy.h"
+#include "core/internal/service_controller.h"
+#include "core/params.h"
+#include "platform/port/string.h"
+#include "platform/ptr.h"
+#include "platform/runnable.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+namespace service_controller_router {
+
+template <typename>
+class StartAdvertisingRunnable;
+template <typename>
+class StopAdvertisingRunnable;
+template <typename>
+class StartDiscoveryRunnable;
+template <typename>
+class StopDiscoveryRunnable;
+template <typename>
+class SendConnectionRequestRunnable;
+template <typename>
+class AcceptConnectionRequestRunnable;
+template <typename>
+class RejectConnectionRequestRunnable;
+template <typename>
+class InitiateBandwidthUpgradeRunnable;
+template <typename>
+class SendPayloadRunnable;
+template <typename>
+class CancelPayloadRunnable;
+template <typename>
+class DisconnectFromEndpointRunnable;
+template <typename>
+class StopAllEndpointsRunnable;
+template <typename>
+class ClientDisconnectingRunnable;
+
+}  // namespace service_controller_router
+
+template <typename Platform>
+class ServiceControllerRouter {
+ public:
+  ServiceControllerRouter();
+  ~ServiceControllerRouter();
+
+  void startAdvertising(
+      Ptr<ClientProxy<Platform> > client_proxy,
+      ConstPtr<StartAdvertisingParams> start_advertising_params);
+  void stopAdvertising(Ptr<ClientProxy<Platform> > client_proxy,
+                       ConstPtr<StopAdvertisingParams> stop_advertising_params);
+
+  void startDiscovery(Ptr<ClientProxy<Platform> > client_proxy,
+                      ConstPtr<StartDiscoveryParams> start_discovery_params);
+  void stopDiscovery(Ptr<ClientProxy<Platform> > client_proxy,
+                     ConstPtr<StopDiscoveryParams> stop_discovery_params);
+
+  void requestConnection(
+      Ptr<ClientProxy<Platform> > client_proxy,
+      ConstPtr<RequestConnectionParams> request_connection_params);
+  void acceptConnection(
+      Ptr<ClientProxy<Platform> > client_proxy,
+      ConstPtr<AcceptConnectionParams> accept_connection_params);
+  void rejectConnection(
+      Ptr<ClientProxy<Platform> > client_proxy,
+      ConstPtr<RejectConnectionParams> reject_connection_params);
+
+  void initiateBandwidthUpgrade(Ptr<ClientProxy<Platform> > client_proxy,
+                                ConstPtr<InitiateBandwidthUpgradeParams>
+                                    initiate_bandwidth_upgrade_params);
+
+  void sendPayload(Ptr<ClientProxy<Platform> > client_proxy,
+                   ConstPtr<SendPayloadParams> send_payload_params);
+  void cancelPayload(Ptr<ClientProxy<Platform> > client_proxy,
+                     ConstPtr<CancelPayloadParams> cancel_payload_params);
+
+  void disconnectFromEndpoint(
+      Ptr<ClientProxy<Platform> > client_proxy,
+      ConstPtr<DisconnectFromEndpointParams> disconnect_from_endpoint_params);
+  void stopAllEndpoints(
+      Ptr<ClientProxy<Platform> > client_proxy,
+      ConstPtr<StopAllEndpointsParams> stop_all_endpoint_params);
+
+  void clientDisconnecting(Ptr<ClientProxy<Platform> > client_proxy);
+
+ private:
+  template <typename>
+  friend class service_controller_router::StartAdvertisingRunnable;
+  template <typename>
+  friend class service_controller_router::StopAdvertisingRunnable;
+  template <typename>
+  friend class service_controller_router::StartDiscoveryRunnable;
+  template <typename>
+  friend class service_controller_router::StopDiscoveryRunnable;
+  template <typename>
+  friend class service_controller_router::SendConnectionRequestRunnable;
+  template <typename>
+  friend class service_controller_router::AcceptConnectionRequestRunnable;
+  template <typename>
+  friend class service_controller_router::RejectConnectionRequestRunnable;
+  template <typename>
+  friend class service_controller_router::InitiateBandwidthUpgradeRunnable;
+  template <typename>
+  friend class service_controller_router::SendPayloadRunnable;
+  template <typename>
+  friend class service_controller_router::CancelPayloadRunnable;
+  template <typename>
+  friend class service_controller_router::DisconnectFromEndpointRunnable;
+  template <typename>
+  friend class service_controller_router::StopAllEndpointsRunnable;
+  template <typename>
+  friend class service_controller_router::ClientDisconnectingRunnable;
+
+  static bool clientHasConnectionToAtLeastOneEndpoint(
+      Ptr<ClientProxy<Platform> > client_proxy,
+      const std::vector<std::string>& remote_endpoint_ids);
+
+  void routeToServiceController(Ptr<Runnable> runnable);
+
+  Status::Value acquireServiceControllerForClient(
+      Ptr<ClientProxy<Platform> > client_proxy, const Strategy& strategy);
+  bool clientHasAquiredServiceController(
+      Ptr<ClientProxy<Platform> > client_proxy);
+  void releaseServiceControllerForClient(
+      Ptr<ClientProxy<Platform> > client_proxy);
+  void doneWithStrategySessionForClient(
+      Ptr<ClientProxy<Platform> > client_proxy);
+  Status::Value updateCurrentServiceControllerAndStrategy(
+      const Strategy& strategy);
+
+  std::set<Ptr<ClientProxy<Platform> > > current_service_controller_clients_;
+  Ptr<ServiceController<Platform> > current_service_controller_;
+  Ptr<Strategy> current_strategy_;
+  ScopedPtr<Ptr<typename Platform::SingleThreadExecutorType> > serializer_;
+};
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location
+
+#include "core/internal/service_controller_router.cc"
+
+#endif  // CORE_INTERNAL_SERVICE_CONTROLLER_ROUTER_H_

cpp/core/internal/wifi_lan_upgrade_handler.cc

@@ -0,0 +1,63 @@
+#include "core/internal/wifi_lan_upgrade_handler.h"
+#include "proto/connections_enums.pb.h"
+
+namespace location {
+namespace nearby {
+namespace connections {
+
+namespace wifi_lan_upgrade_handler {
+
+template <typename Platform>
+class OnIncomingWifiConnectionRunnable : public Runnable {
+ public:
+  void run() {}
+};
+
+}  // namespace wifi_lan_upgrade_handler
+
+template <typename Platform>
+WifiLanUpgradeHandler<Platform>::WifiLanUpgradeHandler(
+    Ptr<MediumManager<Platform> > medium_manager,
+    Ptr<EndpointChannelManager<Platform> > endpoint_channel_manager)
+    : BaseBandwidthUpgradeHandler<Platform>(endpoint_channel_manager),
+      medium_manager_(medium_manager) {}
+
+template <typename Platform>
+WifiLanUpgradeHandler<Platform>::~WifiLanUpgradeHandler() {}
+
+template <typename Platform>
+proto::connections::Medium WifiLanUpgradeHandler<Platform>::getUpgradeMedium() {
+  return proto::connections::Medium::WIFI_LAN;
+}
+
+template <typename Platform>
+void WifiLanUpgradeHandler<Platform>::revertImpl() {}
+
+template <typename Platform>
+void WifiLanUpgradeHandler<Platform>::onIncomingWifiConnection(
+    Ptr<Socket> socket) {}
+
+// TODO(ahlee): This will differ from the Java code (previously threw an
+// UpgradeException). Leaving the return type simple for the skeleton - I'll
+// switch to a pair if the result enum is needed.
+template <typename Platform>
+ConstPtr<ByteArray>
+WifiLanUpgradeHandler<Platform>::initializeUpgradedMediumForEndpoint(
+    const string& endpoint_id) {
+  return ConstPtr<ByteArray>();
+}
+
+// TODO(ahlee): This will differ from the Java code (previously threw an
+// exception).
+template <typename Platform>
+Ptr<EndpointChannel>
+WifiLanUpgradeHandler<Platform>::createUpgradedEndpointChannel(
+    const string& endpoint_id,
+    ConstPtr<BandwidthUpgradeNegotiationFrame::UpgradePathInfo>
+        upgrade_path_info) {
+  return Ptr<EndpointChannel>();
+}
+
+}  // namespace connections
+}  // namespace nearby
+}  // namespace location