Add GattClient#SetCharacteristicNotification for subscribing to a GATT characteristic

PiperOrigin-RevId: 511862183

internal/platform/implementation/apple/ble.h

@@ -184,6 +184,9 @@ class BleMedium : public api::ble_v2::BleMedium {
     bool WriteCharacteristic(const api::ble_v2::GattCharacteristic &characteristic,
                              const ByteArray &value) override;
 
+    bool SetCharacteristicNotification(const api::ble_v2::GattCharacteristic &characteristic,
+                                       bool enable) override;
+
     void Disconnect() override;
 
    private:

internal/platform/implementation/apple/ble.mm

@@ -585,6 +585,12 @@ bool BleMedium::GattClient::WriteCharacteristic(
   return false;
 }
 
+bool BleMedium::GattClient::SetCharacteristicNotification(
+    const api::ble_v2::GattCharacteristic& characteristic, bool enable) {
+  // No op since we can't write characteristics.
+  return false;
+}
+
 void BleMedium::GattClient::Disconnect() {
   [central_ disconnectGattServiceWithPeripheralID:ObjCStringFromCppString(peripheral_id_)];
 }

internal/platform/implementation/ble_v2.h

@@ -25,6 +25,7 @@
 #include <vector>
 
 #include "absl/container/flat_hash_map.h"
+#include "absl/functional/any_invocable.h"
 #include "absl/status/status.h"
 #include "absl/strings/string_view.h"
 #include "internal/platform/byte_array.h"
@@ -180,6 +181,12 @@ class GattClient {
   virtual bool WriteCharacteristic(const GattCharacteristic& characteristic,
                                    const ByteArray& value) = 0;
 
+  // https://developer.android.com/reference/android/bluetooth/BluetoothGatt.html#setCharacteristicNotification(android.bluetooth.BluetoothGattCharacteristic,%20boolean)
+  //
+  // Enable or disable notifications/indications for a given characteristic.
+  virtual bool SetCharacteristicNotification(
+      const GattCharacteristic& characteristic, bool enable) = 0;
+
   // https://developer.android.com/reference/android/bluetooth/BluetoothGatt.html#disconnect()
   virtual void Disconnect() = 0;
 };
@@ -223,6 +230,10 @@ class GattServer {
 // Callback for asynchronous events on the client side of a GATT connection.
 struct ClientGattConnectionCallback {
  public:
+  // Called when the characteristic is changed
+  absl::AnyInvocable<void(const GattCharacteristic& characteristic)>
+      on_characteristic_changed_cb = [](const GattCharacteristic&) {};
+
   // Called when the client is disconnected from the GATT server.
   absl::AnyInvocable<void()> disconnected_cb = []() {};
 };

internal/platform/implementation/g3/ble_v2.cc

@@ -20,6 +20,7 @@
 #include <optional>
 #include <string>
 #include <utility>
+#include <vector>
 
 #include "absl/status/status.h"
 #include "absl/strings/escaping.h"
@@ -452,6 +453,12 @@ bool BleV2Medium::GattClient::WriteCharacteristic(
   return false;
 }
 
+bool BleV2Medium::GattClient::SetCharacteristicNotification(
+    const api::ble_v2::GattCharacteristic& characteristic, bool enable) {
+  // No op since we can't write characteristics.
+  return false;
+}
+
 void BleV2Medium::GattClient::Disconnect() {
   absl::MutexLock lock(&mutex_);
   NEARBY_LOGS(INFO) << "G3 Ble GattClient Disconnect";

internal/platform/implementation/g3/ble_v2.h

@@ -240,6 +240,10 @@ class BleV2Medium : public api::ble_v2::BleMedium {
         const api::ble_v2::GattCharacteristic& characteristic,
         const ByteArray& value) override;
 
+    bool SetCharacteristicNotification(
+        const api::ble_v2::GattCharacteristic& characteristic,
+        bool enable) override;
+
     void Disconnect() override;
 
    private: