Implement readRSSI on Android and Darwin (#203)

lib/src/models/ble_device.dart

@@ -26,6 +26,19 @@ class BleDevice {
   Future<BleConnectionState> get connectionState =>
       UniversalBle.getConnectionState(deviceId);
 
+  /// Read the RSSI value of this connected device.
+  ///
+  /// Returns the current RSSI value in dBm. This value indicates the signal strength
+  /// between the device and the connected peripheral. Lower (more negative) values
+  /// indicate weaker signal, while higher (less negative) values indicate stronger signal.
+  ///
+  /// **Note**: The device must be connected before reading RSSI.
+  ///
+  /// Throws [BleException] if:
+  /// - The device is not connected
+  /// - Reading RSSI fails
+  Future<int> readRssi() => UniversalBle.readRssi(deviceId);
+
   /// On web, it returns true if the web browser supports receiving advertisements from this device.
   /// The rest of the platforms will always return true.
   bool get receivesAdvertisements =>

lib/src/universal_ble.dart

@@ -340,6 +340,28 @@ class UniversalBle {
     );
   }
 
+  /// Read the RSSI value of a connected device.
+  ///
+  /// Returns the current RSSI value in dBm. This value indicates the signal strength
+  /// between the device and the connected peripheral. Lower (more negative) values
+  /// indicate weaker signal, while higher (less negative) values indicate stronger signal.
+  ///
+  /// **Note**: The device must be connected before reading RSSI.
+  ///
+  /// Throws [BleException] if:
+  /// - The device is not connected
+  /// - Reading RSSI fails
+  static Future<int> readRssi(
+    String deviceId, {
+    Duration? timeout,
+  }) async {
+    return await _bleCommandQueue.queueCommand(
+      () => _platform.readRssi(deviceId),
+      timeout: timeout,
+      deviceId: deviceId,
+    );
+  }
+
   /// Check if a device is paired.
   ///
   /// For `Apple` and `Web`, you have to pass a "pairingCommand" with an encrypted read or write characteristic.

lib/src/universal_ble_linux/universal_ble_linux.dart

@@ -378,6 +378,14 @@ class UniversalBleLinux extends UniversalBlePlatform {
     );
   }
 
+  @override
+  Future<int> readRssi(String deviceId) async {
+    throw UniversalBleException(
+      code: UniversalBleErrorCode.notImplemented,
+      message: "readRssi is not implemented on Linux platform",
+    );
+  }
+
   @override
   Future<bool> pair(String deviceId) async {
     BlueZDevice device = _findDeviceById(deviceId);

lib/src/universal_ble_pigeon/universal_ble.g.dart

@@ -1106,6 +1106,35 @@ class UniversalBlePlatformChannel {
     }
   }
 
+  Future<int> readRssi(String deviceId) async {
+    final pigeonVar_channelName =
+        'dev.flutter.pigeon.universal_ble.UniversalBlePlatformChannel.readRssi$pigeonVar_messageChannelSuffix';
+    final pigeonVar_channel = BasicMessageChannel<Object?>(
+      pigeonVar_channelName,
+      pigeonChannelCodec,
+      binaryMessenger: pigeonVar_binaryMessenger,
+    );
+    final Future<Object?> pigeonVar_sendFuture =
+        pigeonVar_channel.send(<Object?>[deviceId]);
+    final pigeonVar_replyList = await pigeonVar_sendFuture as List<Object?>?;
+    if (pigeonVar_replyList == null) {
+      throw _createConnectionError(pigeonVar_channelName);
+    } else if (pigeonVar_replyList.length > 1) {
+      throw PlatformException(
+        code: pigeonVar_replyList[0]! as String,
+        message: pigeonVar_replyList[1] as String?,
+        details: pigeonVar_replyList[2],
+      );
+    } else if (pigeonVar_replyList[0] == null) {
+      throw PlatformException(
+        code: 'null-error',
+        message: 'Host platform returned null value for non-null return value.',
+      );
+    } else {
+      return (pigeonVar_replyList[0] as int?)!;
+    }
+  }
+
   Future<void> setLogLevel(UniversalBleLogLevel logLevel) async {
     final pigeonVar_channelName =
         'dev.flutter.pigeon.universal_ble.UniversalBlePlatformChannel.setLogLevel$pigeonVar_messageChannelSuffix';

lib/src/universal_ble_pigeon/universal_ble_pigeon_channel.dart

@@ -133,6 +133,10 @@ class UniversalBlePigeonChannel extends UniversalBlePlatform {
       _executeWithErrorHandling(
           () => _channel.requestMtu(deviceId, expectedMtu));
 
+  @override
+  Future<int> readRssi(String deviceId) =>
+      _executeWithErrorHandling(() => _channel.readRssi(deviceId));
+
   @override
   Future<bool> isPaired(String deviceId) =>
       _executeWithErrorHandling(() => _channel.isPaired(deviceId));

lib/src/universal_ble_platform_interface.dart

@@ -79,6 +79,8 @@ abstract class UniversalBlePlatform {
 
   Future<int> requestMtu(String deviceId, int expectedMtu);
 
+  Future<int> readRssi(String deviceId);
+
   Future<bool> isPaired(String deviceId);
 
   Future<bool> pair(String deviceId);

lib/src/universal_ble_web/universal_ble_web.dart

@@ -283,6 +283,15 @@ class UniversalBleWeb extends UniversalBlePlatform {
     );
   }
 
+  /// `Unimplemented`
+  @override
+  Future<int> readRssi(String deviceId) {
+    throw UniversalBleException(
+      code: UniversalBleErrorCode.notImplemented,
+      message: "readRssi is not implemented on Web platform",
+    );
+  }
+
   @override
   Future<bool> isPaired(String deviceId) {
     throw UniversalBleException(