add a workaround for dart-lang/sdk#27414

lib/src/engine/transport/websocket_transport.dart

@@ -1,3 +1,4 @@
+import 'dart:async';
 /**
  * websocket_transport.dart
  *
@@ -18,10 +19,11 @@ class WebSocketTransport extends Transport {
   static Logger _logger = new Logger('socket_io:transport.WebSocketTransport');
   bool get handlesUpgrades => true;
   bool get supportsFraming => true;
+  StreamSubscription subscription;
   WebSocketTransport(connect): super(connect) {
     this.name = 'websocket';
     this.connect = connect;
-    connect.websocket.listen(this.onData, onError: this.onError, onDone: this.onClose);
+    subscription = connect.websocket.listen(this.onData, onError: this.onError, onDone: this.onClose);
     writable = true;
   }
 
@@ -56,6 +58,15 @@ class WebSocketTransport extends Transport {
       PacketParser.encodePacket(packet, supportsBinary: this.supportsBinary, callback: (_) => send(_, packet));
     }
   }
+  void onClose() {
+    super.onClose();
+
+    // workaround for https://github.com/dart-lang/sdk/issues/27414
+    if (subscription != null) {
+      subscription.cancel();
+      subscription = null;
+    }
+  }
   void doClose([fn]) {
     this.connect.websocket.close();
     if (fn != null)

pubspec.yaml

@@ -1,6 +1,6 @@
 name: socket_io
 description: Dartlang port of socket.io
-version: 0.8.1
+version: 0.8.2
 author: jumperchen <[email protected]>
 homepage: https://www.zkoss.org