Refactor USB handling to improve connection management and error cleanup

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

@@ -21,6 +21,8 @@ import io.flutter.plugin.common.EventChannel
 import io.flutter.plugin.common.MethodCall
 import io.flutter.plugin.common.MethodChannel
 import java.util.Locale
+import java.util.concurrent.ExecutorService
+import java.util.concurrent.Executors
 
 class MainActivity : FlutterActivity() {
     private val usbMethodChannelName = "meshcore_open/android_usb_serial"
@@ -29,6 +31,7 @@ class MainActivity : FlutterActivity() {
 
     private lateinit var usbManager: UsbManager
     private val mainHandler = Handler(Looper.getMainLooper())
+    private val usbIoExecutor: ExecutorService = Executors.newSingleThreadExecutor()
 
     private var eventSink: EventChannel.EventSink? = null
     private var usbConnection: UsbDeviceConnection? = null
@@ -112,6 +115,7 @@ class MainActivity : FlutterActivity() {
 
     override fun onDestroy() {
         closeUsbConnection()
+        usbIoExecutor.shutdownNow()
         unregisterReceiver(permissionReceiver)
         super.onDestroy()
     }
@@ -191,13 +195,19 @@ class MainActivity : FlutterActivity() {
             return
         }
 
+        usbIoExecutor.execute {
             try {
                 port.write(data, 1000)
+                mainHandler.post {
                     result.success(null)
+                }
             } catch (error: Exception) {
+                mainHandler.post {
                     result.error("usb_write_failed", error.message, null)
                 }
             }
+        }
+    }
 
     private fun findUsbDevice(portName: String): UsbDevice? {
         return usbManager.deviceList.values.firstOrNull { it.deviceName == portName }

lib/connector/meshcore_connector.dart

@@ -981,7 +981,6 @@ class MeshCoreConnector extends ChangeNotifier {
     _selfInfoRetryTimer = null;
     _hasReceivedDeviceInfo = false;
     _pendingInitialChannelSync = false;
-    _hasReceivedDeviceInfo = false;
   }
 
   bool get _shouldAutoReconnect =>

lib/services/usb_serial_frame_codec.dart

@@ -27,6 +27,7 @@ class UsbSerialDecodedPacket {
 
 class UsbSerialFrameDecoder {
   final List<int> _rxBuffer = <int>[];
+  int _startIndex = 0;
 
   List<UsbSerialDecodedPacket> ingest(Uint8List bytes) {
     if (bytes.isEmpty) {
@@ -37,34 +38,56 @@ class UsbSerialFrameDecoder {
     final packets = <UsbSerialDecodedPacket>[];
 
     while (true) {
-      if (_rxBuffer.isEmpty) {
+      if (_startIndex >= _rxBuffer.length) {
+        _rxBuffer.clear();
+        _startIndex = 0;
         return packets;
       }
 
-      if (_rxBuffer.first != usbSerialRxFrameStart &&
-          _rxBuffer.first != usbSerialTxFrameStart) {
-        _rxBuffer.removeAt(0);
+      if (_rxBuffer[_startIndex] != usbSerialRxFrameStart &&
+          _rxBuffer[_startIndex] != usbSerialTxFrameStart) {
+        _startIndex++;
+        _compactBufferIfNeeded();
         continue;
       }
 
-      if (_rxBuffer.length < usbSerialHeaderLength) {
+      final availableLength = _rxBuffer.length - _startIndex;
+      if (availableLength < usbSerialHeaderLength) {
+        _compactBufferIfNeeded(force: true);
         return packets;
       }
 
-      final payloadLength = _rxBuffer[1] | (_rxBuffer[2] << 8);
+      final payloadLength =
+          _rxBuffer[_startIndex + 1] | (_rxBuffer[_startIndex + 2] << 8);
       final packetLength = usbSerialHeaderLength + payloadLength;
-      if (_rxBuffer.length < packetLength) {
+      if (availableLength < packetLength) {
+        _compactBufferIfNeeded(force: true);
         return packets;
       }
 
-      final frameStart = _rxBuffer.first;
+      final frameStart = _rxBuffer[_startIndex];
       final payload = Uint8List.fromList(
-        _rxBuffer.sublist(usbSerialHeaderLength, packetLength),
+        _rxBuffer.sublist(
+          _startIndex + usbSerialHeaderLength,
+          _startIndex + packetLength,
+        ),
       );
-      _rxBuffer.removeRange(0, packetLength);
+      _startIndex += packetLength;
+      _compactBufferIfNeeded();
       packets.add(
         UsbSerialDecodedPacket(frameStart: frameStart, payload: payload),
       );
     }
   }
+
+  void _compactBufferIfNeeded({bool force = false}) {
+    if (_startIndex == 0) {
+      return;
+    }
+    if (!force && _startIndex < 1024 && _startIndex < (_rxBuffer.length ~/ 2)) {
+      return;
+    }
+    _rxBuffer.removeRange(0, _startIndex);
+    _startIndex = 0;
+  }
 }

lib/services/usb_serial_service_web.dart

@@ -88,8 +88,10 @@ class UsbSerialService {
 
       debugPrint('USB serial opened port=$_connectedPortName via Web Serial');
     } catch (error) {
+      await _cleanupFailedConnect();
       _status = UsbSerialStatus.disconnected;
       _connectedPortName = null;
+      _connectedPortKey = null;
       rethrow;
     }
   }
@@ -205,6 +207,37 @@ class UsbSerialService {
     return port.callMethod<JSPromise<JSAny?>>('open'.toJS, options).toDart;
   }
 
+  Future<void> _cleanupFailedConnect() async {
+    final reader = _reader;
+    final writer = _writer;
+    final port = _port;
+
+    _reader = null;
+    _writer = null;
+    _port = null;
+
+    if (reader != null) {
+      try {
+        await reader.callMethod<JSPromise<JSAny?>>('cancel'.toJS).toDart;
+      } catch (_) {
+        // Ignore cleanup errors after a failed connect.
+      }
+      _releaseLock(reader);
+    }
+
+    if (writer != null) {
+      _releaseLock(writer);
+    }
+
+    if (port != null) {
+      try {
+        await port.callMethod<JSPromise<JSAny?>>('close'.toJS).toDart;
+      } catch (_) {
+        // Ignore cleanup errors after a failed connect.
+      }
+    }
+  }
+
   JSObject? _getReader(JSObject port) {
     final readable = port.getProperty<JSAny?>('readable'.toJS);
     if (readable == null) {