How to handle websocket with dart:io Flutter

Question

I would like to avoid using the package web_socket_channel which despite its vote doesn't seem to not be actively maintained (many github issues not answered) and doesn't handle errors.

I simply need to connect from Flutter to my WebSocket API in AWS.

How can i do that with dart:io package ? Or is it possible with socket_io_client ? I see that the connection is with http and not wss.

score 0 · Accepted Answer · answered Oct 21 '21 at 09:49

I have found a way in addition to the usual try - catch to handle error in the channel.sink.listen StreamSubscription object with the web_socket_channel package.

You can do the following according to this answer :

 _channel = IOWebSocketChannel.connect(
        'ws://yourserver.com:port',
      );

      ///
      /// Start listening to new notifications / messages
      ///
      _channel.stream.listen(
        (dynamic message) {
          debugPrint('message $message');
        },
        onDone: () {
          debugPrint('ws channel closed');
        },
        onError: (error) {
          debugPrint('ws error $error');
        },
      );

This actually works and there is no need to use SocketIO in my use case of course.

score 0 · Answer 2 · answered Jan 30 '23 at 18:23

I recommend you to use this multiplatform websocket package https://pub.dev/packages/websocket_universal . There you can even use low-level webSocket interactions. Complete example:

import 'package:websocket_universal/websocket_universal.dart';

/// Example works with Postman Echo server
void main() async {
  /// Postman echo ws server (you can use your own server URI)
  /// 'wss://ws.postman-echo.com/raw'
  /// For local server it could look like 'ws://127.0.0.1:42627/websocket'
  const websocketConnectionUri = 'wss://ws.postman-echo.com/raw';
  const textMessageToServer = 'Hello server!';
  const connectionOptions = SocketConnectionOptions(
    pingIntervalMs: 3000, // send Ping message every 3000 ms
    timeoutConnectionMs: 4000, // connection fail timeout after 4000 ms
    /// see ping/pong messages in [logEventStream] stream
    skipPingMessages: false,

    /// Set this attribute to `true` if do not need any ping/pong
    /// messages and ping measurement. Default is `false`
    pingRestrictionForce: false,
  );

  /// Example with simple text messages exchanges with server
  /// (not recommended for applications)
  /// [<String, String>] generic types mean that we receive [String] messages
  /// after deserialization and send [String] messages to server.
  final IMessageProcessor<String, String> textSocketProcessor =
      SocketSimpleTextProcessor();
  final textSocketHandler = IWebSocketHandler<String, String>.createClient(
    websocketConnectionUri, // Postman echo ws server
    textSocketProcessor,
    connectionOptions: connectionOptions,
  );

  // Listening to webSocket status changes
  textSocketHandler.socketHandlerStateStream.listen((stateEvent) {
    // ignore: avoid_print
    print('> status changed to ${stateEvent.status}');
  });

  // Listening to server responses:
  textSocketHandler.incomingMessagesStream.listen((inMsg) {
    // ignore: avoid_print
    print('> webSocket  got text message from server: "$inMsg" '
        '[ping: ${textSocketHandler.pingDelayMs}]');
  });

  // Listening to debug events inside webSocket
  textSocketHandler.logEventStream.listen((debugEvent) {
    // ignore: avoid_print
    print('> debug event: ${debugEvent.socketLogEventType}'
        ' [ping=${debugEvent.pingMs} ms]. Debug message=${debugEvent.message}');
  });

  // Listening to outgoing messages:
  textSocketHandler.outgoingMessagesStream.listen((inMsg) {
    // ignore: avoid_print
    print('> webSocket sent text message to   server: "$inMsg" '
        '[ping: ${textSocketHandler.pingDelayMs}]');
  });

  // Connecting to server:
  final isTextSocketConnected = await textSocketHandler.connect();
  if (!isTextSocketConnected) {
    // ignore: avoid_print
    print('Connection to [$websocketConnectionUri] failed for some reason!');
    return;
  }

  textSocketHandler.sendMessage(textMessageToServer);

  await Future<void>.delayed(const Duration(seconds: 30));
  // Disconnecting from server:
  await textSocketHandler.disconnect('manual disconnect');
  // Disposing webSocket:
  textSocketHandler.close();
}

How to handle websocket with dart:io Flutter

2 Answers2