CODEWITHSUNDEEP
dart
arkhon
arkhon

Reputation: 765

dart: howto output stream data to websocket

im fiddling around with dart on the server side. I'm trying to send data periodically to clients connected to my server via websockets.

import 'dart:io';
import 'dart:async';

class WebSocketHandler {
static void handleWebSocket(WebSocket socket) {
    print("Client connected!");
    var stream = new Stream.periodic(const Duration(seconds: 5), (count) {
        return count;
    });

    stream.listen((num) {
        print(num);
        socket.add(num);
    });

    socket.listen((message) {
        print("Client send: $message");
        socket.add(message);
    });
}
}

This is my WebSocketHandler, which works fine for messages but the stream.listen in combination with the socket.add producess the following error:

Uncaught Error: Illegal argument(s): 0
Stack Trace: 
#0      _WebSocketOutgoingTransformer.add (dart:io/websocket_impl.dart:502)
#1      _handleData (dart:async/stream_transformers.dart:116)
#2      _rootRunUnary (dart:async/zone.dart:730)
#3      _RootZone.runUnary (dart:async/zone.dart:864)
#4      _BaseZone.runUnaryGuarded (dart:async/zone.dart:582)
#5      _BufferingStreamSubscription._sendData (dart:async/stream_impl.dart:333)
#6      _BufferingStreamSubscription._add (dart:async/stream_impl.dart:263)
#7      _StreamController&&_SyncStreamControllerDispatch._sendData (dart:async/stream_controller.dart:535)
#8      _StreamController._add (dart:async/stream_controller.dart:442)
#9      _StreamController.add (dart:async/stream_controller.dart:399)
#10     _WebSocketConsumer.addStream.<anonymous closure> (dart:io/websocket_impl.dart:709)
#11     _rootRunUnary (dart:async/zone.dart:730)
#12     _RootZone.runUnary (dart:async/zone.dart:864)
#13     _BaseZone.runUnaryGuarded (dart:async/zone.dart:582)
#14     _BufferingStreamSubscription._sendData (dart:async/stream_impl.dart:333)
#15     _BufferingStreamSubscription._add (dart:async/stream_impl.dart:263)
#16     _StreamController&&_SyncStreamControllerDispatch._sendData (dart:async/stream_controller.dart:535)
#17     _StreamController._add (dart:async/stream_controller.dart:442)
#18     _StreamController.add (dart:async/stream_controller.dart:399)
#19     _StreamSinkImpl.add (dart:io/io_sink.dart:143)
#20     _WebSocketImpl.add (dart:io/websocket_impl.dart:928)
#21     WebSocketHandler.handleWebSocket.<anonymous closure> (file:///D:/Webdev/Websites/webradio-dart/server/WebSocketHandler.dart:13:14)
#22     _rootRunUnary (dart:async/zone.dart:730)
#23     _RootZone.runUnary (dart:async/zone.dart:864)
#24     _BaseZone.runUnaryGuarded (dart:async/zone.dart:582)
#25     _BufferingStreamSubscription._sendData (dart:async/stream_impl.dart:333)
#26     _BufferingStreamSubscription._add (dart:async/stream_impl.dart:263)
#27     _StreamController&&_SyncStreamControllerDispatch._sendData (dart:async/stream_controller.dart:535)
#28     _StreamController._add (dart:async/stream_controller.dart:442)
#29     _StreamController.add (dart:async/stream_controller.dart:399)
#30     Stream.Stream.periodic.sendEvent (dart:async/stream.dart:118)
#31     Stream.Stream.periodic.startPeriodicTimer.<anonymous closure> (dart:async/stream.dart:124)
#32     _handleTimeout (dart:io/timer_impl.dart:292)
#33     _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:124)


Unhandled exception:
Illegal argument(s): 0
#0      _rootHandleUncaughtError.<anonymous closure>.<anonymous closure> (dart:async/zone.dart:713)
#1      _asyncRunCallbackLoop (dart:async/schedule_microtask.dart:23)
#2      _asyncRunCallback (dart:async/schedule_microtask.dart:32)
#3      _asyncRunCallback (dart:async/schedule_microtask.dart:36)
#4      _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:128)

Here is the Stacktrace.

Upvotes: 2

Views: 586

Answers (1)

JAre
JAre

Reputation: 4756

Just replace this: 

stream.listen((num) {
    print(num);
    socket.add(num);
});

with this:

stream.listen((num) {
    print(num);
    socket.add(num.toString());
});

Full source:

html:

<!DOCTYPE html>

<html>
  <head>
    <meta charset="utf-8">
    <title>ClientTest</title>
    <link rel="stylesheet" href="clientstreamperiodictest.css">
  </head>
  <body>
    <p>Response:</p>

    <div id="response">
    </div>

    <script type="application/dart" src="clientstreamperiodictest.dart"></script>
    <script src="packages/browser/dart.js"></script>
  </body>
</html>

Client: 

import 'dart:html';
void main() {
  WebSocket ws = new WebSocket('ws://127.0.0.1:4040');
  ws.onMessage.listen((MessageEvent e) {
    querySelector('#response').appendHtml('<p>${e.data}</p>');
  });
}

Server: 

import 'dart:io';
import 'dart:async';
main() {
  HttpServer.bind('127.0.0.1', 4040).then((server) {
    server.listen((HttpRequest request) {
      WebSocketTransformer.upgrade(request).then((socket) {
        var streamPeriodic =
            new Stream.periodic(const Duration(seconds: 5), (count) {
          return count;
        });
        streamPeriodic.listen((num) {
          print(num);
          socket.add(num.toString());
        });
      });
    });
  });
}

Upvotes: 2

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