Refactor USB connection handling to use scheduled closure and improve error management in USB services

android/app/src/main/kotlin/com/meshcore/meshcore_open/MainActivity.kt

@@ -105,11 +105,8 @@ class MainActivity : FlutterActivity() {
                     "connect" -> handleUsbConnect(call, result)
                     "write" -> handleUsbWrite(call, result)
                     "disconnect" -> {
-                        usbIoExecutor.execute {
+                        scheduleCloseUsbConnection {
-                            closeUsbConnection()
+                            result.success(null)
-                            mainHandler.post {
-                                result.success(null)
-                            }
                         }
                     }
                     else -> result.notImplemented()
@@ -315,7 +312,7 @@ class MainActivity : FlutterActivity() {
                                         null,
                                     )
                                 }
-                                closeUsbConnection()
+                                scheduleCloseUsbConnection()
                             }
                         },
                     ).also { manager ->
@@ -338,6 +335,16 @@ class MainActivity : FlutterActivity() {
         return driver.ports.firstOrNull()
     }
 
+    private fun scheduleCloseUsbConnection(onComplete: (() -> Unit)? = null) {
+        usbIoExecutor.execute {
+            closeUsbConnection()
+            if (onComplete != null) {
+                mainHandler.post(onComplete)
+            }
+        }
+    }
+
+    @Synchronized
     private fun closeUsbConnection() {
         try {
             ioManager?.stop()
@@ -381,12 +388,13 @@ class MainActivity : FlutterActivity() {
         }
 
         if (connectedDeviceName == detachedName) {
-            closeUsbConnection()
+            scheduleCloseUsbConnection {
-            eventSink?.error(
+                eventSink?.error(
-                "usb_device_detached",
+                    "usb_device_detached",
-                "USB device was disconnected",
+                    "USB device was disconnected",
-                null,
+                    null,
-            )
+                )
+            }
         }
     }
 

lib/connector/meshcore_connector.dart

@@ -1266,14 +1266,23 @@ class MeshCoreConnector extends ChangeNotifier {
     _selfInfoRetryTimer?.cancel();
     if (PlatformInfo.isWeb &&
         _activeTransport == MeshCoreTransportType.bluetooth) {
-      _selfInfoRetryTimer = Timer(const Duration(seconds: 10), () {
+      var attempts = 0;
+      const maxAttempts = 3;
+      _selfInfoRetryTimer = Timer.periodic(const Duration(seconds: 10), (
+        timer,
+      ) {
         if (!isConnected || !_awaitingSelfInfo) {
+          timer.cancel();
           return;
         }
         if (_isLoadingContacts || _isSyncingChannels || _channelSyncInFlight) {
           return;
         }
+        attempts += 1;
         unawaited(sendFrame(buildAppStartFrame()));
+        if (attempts >= maxAttempts) {
+          timer.cancel();
+        }
       });
       return;
     }

lib/services/usb_serial_service_native.dart

@@ -186,8 +186,7 @@ class UsbSerialService {
   }
 
   void dispose() {
-    unawaited(disconnect());
+    unawaited(disconnect().whenComplete(_closeFrameController));
-    unawaited(_frameController.close());
   }
 
   void _handleSerialData(FlSerialEventArgs event) {
@@ -197,7 +196,7 @@ class UsbSerialService {
         _ingestRawBytes(Uint8List.fromList(bytes));
       }
     } catch (error, stack) {
-      _frameController.addError(error, stack);
+      _addFrameError(error, stack);
     }
   }
 
@@ -210,13 +209,13 @@ class UsbSerialService {
       _ingestRawBytes(data.buffer.asUint8List());
       return;
     }
-    _frameController.addError(
+    _addFrameError(
       StateError('Unexpected Android USB event payload: ${data.runtimeType}'),
     );
   }
 
   void _handleSerialError(Object error, [StackTrace? stackTrace]) {
-    _frameController.addError(error, stackTrace);
+    _addFrameError(error, stackTrace);
   }
 
   void _handleSerialDone() {
@@ -231,10 +230,31 @@ class UsbSerialService {
         );
         continue;
       }
-      _frameController.add(packet.payload);
+      _addFrame(packet.payload);
     }
   }
 
+  void _addFrame(Uint8List payload) {
+    if (_frameController.isClosed) {
+      return;
+    }
+    _frameController.add(payload);
+  }
+
+  void _addFrameError(Object error, [StackTrace? stackTrace]) {
+    if (_frameController.isClosed) {
+      return;
+    }
+    _frameController.addError(error, stackTrace);
+  }
+
+  Future<void> _closeFrameController() async {
+    if (_frameController.isClosed) {
+      return;
+    }
+    await _frameController.close();
+  }
+
   void _logFrameSummary(String prefix, Uint8List bytes) {
     if (bytes.isEmpty) {
       debugPrint('$prefix len=0');

lib/services/usb_serial_service_web.dart

@@ -160,8 +160,7 @@ class UsbSerialService {
   }
 
   void dispose() {
-    unawaited(disconnect());
+    unawaited(disconnect().whenComplete(_closeFrameController));
-    unawaited(_frameController.close());
   }
 
   Future<List<JSObject>> _getAuthorizedPorts() async {
@@ -285,12 +284,12 @@ class UsbSerialService {
       }
     } catch (error, stackTrace) {
       if (_status == UsbSerialStatus.connected) {
-        _frameController.addError(error, stackTrace);
+        _addFrameError(error, stackTrace);
       }
     } finally {
       _releaseLock(reader);
       if (_status == UsbSerialStatus.connected && identical(reader, _reader)) {
-        _frameController.addError(StateError('USB serial connection closed'));
+        _addFrameError(StateError('USB serial connection closed'));
       }
     }
   }
@@ -402,10 +401,31 @@ class UsbSerialService {
         );
         continue;
       }
-      _frameController.add(packet.payload);
+      _addFrame(packet.payload);
     }
   }
 
+  void _addFrame(Uint8List payload) {
+    if (_frameController.isClosed) {
+      return;
+    }
+    _frameController.add(payload);
+  }
+
+  void _addFrameError(Object error, [StackTrace? stackTrace]) {
+    if (_frameController.isClosed) {
+      return;
+    }
+    _frameController.addError(error, stackTrace);
+  }
+
+  Future<void> _closeFrameController() async {
+    if (_frameController.isClosed) {
+      return;
+    }
+    await _frameController.close();
+  }
+
   void _logFrameSummary(String prefix, Uint8List bytes) {
     if (bytes.isEmpty) {
       debugPrint('$prefix len=0');