Fix closing of connection

+ Tested multiple cases (including edufolly#60)
+ Fix try-catch for connecting inside `ChatPage` of example app
+ Minor updated debug log at disconnecting in platform code
+ `cancel` on `BluetoothConnection` is deprecated now, use `close` instead. 
  It was stupid to name `cancel` something that `close`s (it was even documented that way, lol).
- `cancel` on subscription of `input.listen` does not close connection (from now?)
- I think it might prevent easily detectable disconnection side ("was it by remote or locally")

android/src/main/java/io/github/edufolly/flutterbluetoothserial/FlutterBluetoothSerialPlugin.java

@@ -1143,14 +1143,14 @@ protected void onDisconnected(boolean byRemote) {
                 @Override
                 public void run() {
                     if (byRemote) {
-                        Log.d(TAG, "Connection onDisconnected by remote");
+                        Log.d(TAG, "onDisconnected by remote (id: " + id + ")");
                         if (readSink != null) {
                             readSink.endOfStream();
                             readSink = null;
                         }
                     }
                     else {
-                        Log.d(TAG, "Connection onDisconnected by local");
+                        Log.d(TAG, "onDisconnected by local (id: " + id + ")");
                     }
                 }
             });

example/lib/ChatPage.dart

@@ -37,21 +37,23 @@ class _ChatPage extends State<ChatPage> {
   @override
   void initState() {
     super.initState();
-    try {
-      BluetoothConnection.toAddress(widget.server.address).then((_connection) {
-        print('Connected to the device');
-        connection = _connection;
-        setState(() {
-          isConnecting = false;
-        });
-
-        connection.input.listen(_onDataReceived).onDone(() {
-          print('Disconnected by remote request');
-        });
+
+    BluetoothConnection.toAddress(widget.server.address).then((_connection) {
+      print('Connected to the device');
+      connection = _connection;
+      setState(() {
+        isConnecting = false;
       });
-    } catch (exception) {
+
+      connection.input.listen(_onDataReceived).onDone(() {
+        if (this.mounted) {
+          setState(() {});
+        }
+      });
+    }).catchError((error) {
       print('Cannot connect, exception occured');
-    }
+      print(error);
+    });
   }
 
   @override

lib/BluetoothConnection.dart

@@ -1,10 +1,24 @@
 part of flutter_bluetooth_serial;
 
-/// Represents Bluetooth connection to remote device.
+/// Represents ongoing Bluetooth connection to remote device.
 class BluetoothConnection {
+  // Note by PsychoX at 2019-08-19 while working on issue #60:
+  // Fixed and then tested whole thing multiple times:
+  // - [X] basic `connect`, use `output`/`input` and `disconnect` by local scenario,
+  // - [X] fail on connecting to device that isn't listening,
+  // - [X] working `output` if no `listen`ing to `input`,
+  // - [X] closing by local if no `input` written,
+  // - [X] closing by local if no `listen`ing to `input` (this was the #60),
+  // - [X] closing by remote if no `input` written,
+  // - [X] closing by remote if no `listen`ing to `input`,
+  //    It works, but library user is notifed either by error on `output.add` or
+  //    by observing `connection.isConnected`. In "normal" conditions user can
+  //    listen to `input` even just for the `onDone` to proper detect closing.
+  // 
+
   /// This ID identifies real full `BluetoothConenction` object on platform side code.
   final int _id;
-  
+
   final EventChannel _readChannel;
   StreamSubscription<Uint8List> _readStreamSubscription;
   StreamController<Uint8List> _readStreamController;
@@ -31,14 +45,12 @@ class BluetoothConnection {
     this._id = id,
     this._readChannel = EventChannel('${FlutterBluetoothSerial.namespace}/read/$id')
   {
-    _readStreamController = StreamController<Uint8List>(onCancel: () {
-      cancel();
-    });
+    _readStreamController = StreamController<Uint8List>();
 
     _readStreamSubscription = _readChannel.receiveBroadcastStream().cast<Uint8List>().listen(
       _readStreamController.add,
       onError: _readStreamController.addError,
-      onDone: _readStreamController.close,
+      onDone: this.close,
     );
 
     input = _readStreamController.stream;
@@ -61,16 +73,24 @@ class BluetoothConnection {
 
 
   /// Closes connection (rather immediately), in result should also disconnect.
-  Future<void> cancel() async {
-    await output.close();
-    await _readStreamController.close();
-    await _readStreamSubscription.cancel();
+  Future<void> close() {
+    return Future.wait([
+      output.close(),
+      _readStreamSubscription.cancel(),
+      (!_readStreamController.isClosed) 
+        ? _readStreamController.close()
+        : Future.value(/* Empty future */)
+    ], eagerError: true);
   }
 
+  /// Closes connection (rather immediately), in result should also disconnect.
+  @Deprecated('Use `close` instead')
+  Future<void> cancel() => this.close();
+
   /// Closes connection (rather gracefully), in result should also disconnect.
   Future<void> finish() async {
     await output.allSent;
-    await cancel();
+    close();
   }
 
 }