Android: enforce 2s delay between connect and disconnect

Marianannn · Jul 23, 2024 · 4015129 · 4015129
1 parent 9c77b29
commit 4015129
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Showing 2 changed files with 43 additions and 1 deletion.
diff --git a/lib/src/bluetooth_device.dart b/lib/src/bluetooth_device.dart
@@ -131,6 +131,11 @@ class BluetoothDevice {
       // Start listening now, before invokeMethod, to ensure we don't miss the response
       Future<BmConnectionStateResponse> futureState = responseStream.first;
 
+      // record connection time
+      if (Platform.isAndroid) {
+        FlutterBluePlus._connectTimestamp[remoteId] = DateTime.now();
+      }
+
       // invoke
       bool changed = await FlutterBluePlus._invokeMethod('connect', request.toMap());
 
@@ -178,7 +183,17 @@ class BluetoothDevice {
   ///   - [queue] If true, this disconnect request will be executed after all other operations complete.
   ///     If false, this disconnect request will be executed right now, i.e. skipping to the front
   ///     of the fbp operation queue, which is useful to cancel an in-progress connection attempt.
-  Future<void> disconnect({int timeout = 35, bool queue = true}) async {
+  ///   - [androidDelay] Android only. Minimum gap in milliseconds between connect and disconnect to
+  ///     workaround a race condition that leaves connection stranded. A stranded connection in this case
+  ///     refers to a connection that FBP and Android Bluetooth stack are not aware of and thus cannot be
+  ///     disconnected because there is no gatt handle.
+  ///     https://issuetracker.google.com/issues/37121040
+  ///     From testing, 2 second delay appears to be enough.
+  Future<void> disconnect({
+    int timeout = 35,
+    bool queue = true,
+    int androidDelay = 2000,
+  }) async {
     // Only allow a single disconnect operation at a time
     _Mutex dtx = _MutexFactory.getMutexForKey("disconnect");
     await dtx.take();
@@ -203,13 +218,21 @@ class BluetoothDevice {
       // Start listening now, before invokeMethod, to ensure we don't miss the response
       Future<BmConnectionStateResponse> futureState = responseStream.first;
 
+      // Workaround Android race condition: ensure minimum connect disconnect gap is met
+      await _ensureAndroidDisconnectionDelay(androidDelay);
+
       // invoke
       bool changed = await FlutterBluePlus._invokeMethod('disconnect', remoteId.str);
 
       // only wait for disconnection if weren't already disconnected
       if (changed) {
         await futureState.fbpEnsureAdapterIsOn("disconnect").fbpTimeout(timeout, "disconnect");
       }
+
+      if (Platform.isAndroid) {
+        // Disconnected, remove connect timestamp
+        FlutterBluePlus._connectTimestamp.remove(remoteId);
+      }
     } finally {
       dtx.give();
       if (queue) {
@@ -664,6 +687,24 @@ class BluetoothDevice {
     return gatt?.characteristics._firstWhereOrNull((chr) => chr.uuid == servicesChangedUuid);
   }
 
+  /// Workaround race condition between connect and disconnect leaving connection stranded by enforcing a small delay
+  /// between connect and disconnect call.
+  /// https://issuetracker.google.com/issues/37121040
+  Future<void> _ensureAndroidDisconnectionDelay(int androidDelay) async {
+    if (Platform.isAndroid) {
+      if (FlutterBluePlus._connectTimestamp.containsKey(remoteId)) {
+        Duration minGap = Duration(milliseconds: androidDelay);
+        Duration elapsed = DateTime.now().difference(FlutterBluePlus._connectTimestamp[remoteId]!);
+        if (elapsed.compareTo(minGap) < 0) {
+          Duration timeLeft = minGap - elapsed;
+          print("[FBP] disconnect: enforcing ${minGap.inMilliseconds}ms disconnect gap, delaying "
+              "${timeLeft.inMilliseconds}ms");
+          await Future<void>.delayed(timeLeft);
+        }
+      }
+    }
+  }
+
   @override
   bool operator ==(Object other) =>
       identical(this, other) ||

diff --git a/lib/src/flutter_blue_plus.dart b/lib/src/flutter_blue_plus.dart
@@ -29,6 +29,7 @@ class FlutterBluePlus {
   static final Map<DeviceIdentifier, Map<String, List<int>>> _lastDescs = {};
   static final Map<DeviceIdentifier, List<StreamSubscription>> _deviceSubscriptions = {};
   static final Map<DeviceIdentifier, List<StreamSubscription>> _delayedSubscriptions = {};
+  static final Map<DeviceIdentifier, DateTime> _connectTimestamp = {};
   static final List<StreamSubscription> _scanSubscriptions = [];
   static final Set<DeviceIdentifier> _autoConnect = {};