Reuse the same wifi lan listening port number if endpoint ID stays the same.

PiperOrigin-RevId: 810534040

connections/implementation/mediums/wifi_lan.cc

@@ -106,17 +106,25 @@ ErrorOr<bool> WifiLan::StartAdvertising(const std::string& service_id,
   }
   nsd_service_info.SetServiceType(GenerateServiceType(service_id));
   const auto& it = server_sockets_.find(service_id);
+  std::string mdns_service_name = nsd_service_info.GetServiceName();
+  int port = 0;
   if (it != server_sockets_.end()) {
-    nsd_service_info.SetPort(it->second.GetPort());
+    port = it->second.GetPort();
   } else {
-    int port = 0;
+    if (!mdns_service_name.empty() &&
+        mdns_service_name == last_mdns_service_name_) {
+      VLOG(1) << __func__
+              << " reusing server port number: " << last_server_port_;
+      port = last_server_port_;
+    }
     ErrorOr<int> port_result = StartAcceptingConnectionsLocked(
         service_id, port, std::move(callback));
     if (port_result.has_error()) {
       return {port_result.error()};
     }
-    nsd_service_info.SetPort(port_result.value());
+    port = port_result.value();
   }
+  nsd_service_info.SetPort(port);
   if (!medium_.StartAdvertising(nsd_service_info)) {
     LOG(INFO) << "Failed to turn on WifiLan advertising with nsd_service_info="
               << &nsd_service_info
@@ -126,6 +134,8 @@ ErrorOr<bool> WifiLan::StartAdvertising(const std::string& service_id,
     return {Error(
         OperationResultCode::CONNECTIVITY_WIFI_LAN_START_ADVERTISING_FAILURE)};
   }
+  last_mdns_service_name_ = std::move(mdns_service_name);
+  last_server_port_ = port;
 
   LOG(INFO) << "Turned on WifiLan advertising with nsd_service_info="
             << &nsd_service_info

connections/implementation/mediums/wifi_lan.h

@@ -226,6 +226,9 @@ class WifiLan {
   // A map of IpAddress -> MultiplexSocket.
   absl::flat_hash_map<std::string, mediums::multiplex::MultiplexSocket*>
       multiplex_sockets_ ABSL_GUARDED_BY(mutex_);
+
+  std::string last_mdns_service_name_ ABSL_GUARDED_BY(mutex_);
+  int last_server_port_ ABSL_GUARDED_BY(mutex_) = 0;
 };
 
 }  // namespace connections

connections/implementation/mediums/wifi_lan_test.cc

@@ -61,6 +61,51 @@ class WifiLanTest : public ::testing::TestWithParam<FeatureFlags> {
   MediumEnvironment& env_{MediumEnvironment::Instance()};
 };
 
+TEST_P(WifiLanTest, AdvertiseSameServiceNameReusesPort) {
+  FeatureFlags feature_flags = GetParam();
+  env_.SetFeatureFlags(feature_flags);
+  env_.Start();
+  WifiLan wifi_lan_server;
+  std::string service_id(kServiceID);
+  std::string endpoint_info_name(kEndpointName);
+
+  WifiLanSocket socket_for_server;
+  NsdServiceInfo nsd_service_info;
+  nsd_service_info.SetServiceName(std::string(kServiceInfoName));
+  wifi_lan_server.StartAdvertising(service_id, nsd_service_info, {});
+  auto [address, port] = wifi_lan_server.GetCredentials(service_id);
+  wifi_lan_server.StopAdvertising(service_id);
+  wifi_lan_server.StopAcceptingConnections(service_id);
+
+  wifi_lan_server.StartAdvertising(service_id, nsd_service_info, {});
+  auto [address2, port2] = wifi_lan_server.GetCredentials(service_id);
+  EXPECT_EQ(port, port2);
+  env_.Stop();
+}
+
+TEST_P(WifiLanTest, AdvertiseDifferentServiceNameUsesDifferentPort) {
+  FeatureFlags feature_flags = GetParam();
+  env_.SetFeatureFlags(feature_flags);
+  env_.Start();
+  WifiLan wifi_lan_server;
+  std::string service_id(kServiceID);
+  std::string endpoint_info_name(kEndpointName);
+
+  WifiLanSocket socket_for_server;
+  NsdServiceInfo nsd_service_info;
+  nsd_service_info.SetServiceName(std::string(kServiceInfoName));
+  wifi_lan_server.StartAdvertising(service_id, nsd_service_info, {});
+  auto [address, port] = wifi_lan_server.GetCredentials(service_id);
+  wifi_lan_server.StopAdvertising(service_id);
+  wifi_lan_server.StopAcceptingConnections(service_id);
+
+  nsd_service_info.SetServiceName("ServiceInfoName2");
+  wifi_lan_server.StartAdvertising(service_id, nsd_service_info, {});
+  auto [address2, port2] = wifi_lan_server.GetCredentials(service_id);
+  EXPECT_NE(port, port2);
+  env_.Stop();
+}
+
 TEST_P(WifiLanTest, CanConnect) {
   FeatureFlags feature_flags = GetParam();
   env_.SetFeatureFlags(feature_flags);

internal/platform/implementation/g3/wifi_lan.h

@@ -203,7 +203,7 @@ class WifiLanMedium : public api::WifiLanMedium {
   // Returns the port range as a pair of min and max port.
   absl::optional<std::pair<std::int32_t, std::int32_t>> GetDynamicPortRange()
       override {
-    return std::make_pair(49152, 65535);
+    return std::nullopt;
   }
 
  private:

internal/platform/implementation/windows/nearby_server_socket.cc

@@ -71,6 +71,15 @@ bool NearbyServerSocket::Listen(const std::string& ip_address, int port) {
   } else {
     serv_addr.sin_addr.s_addr = inet_addr(ip_address.c_str());
   }
+  // Set REUSEADDR if a specific port is needed.
+  if (port != 0) {
+    BOOL flag = TRUE;
+    if (setsockopt(socket_, SOL_SOCKET, SO_REUSEADDR, (const char*)&flag,
+                   sizeof(flag)) == SOCKET_ERROR) {
+      LOG(WARNING) << "Failed to set SO_REUSEADDR with error "
+                   << WSAGetLastError();
+    }
+  }
 
   if (bind(/*s=*/socket_, /*addr=*/(struct sockaddr*)&serv_addr,
            /*namelen=*/sizeof(serv_addr)) == SOCKET_ERROR) {