Asynchronous errors can't be caught using try/catch(https://www.dartlang.org/docs/tutorials/futures/) at least unless you are using async/await(https://www.dartlang.org/articles/await-async/)

See also https://github.com/dart-lang/sdk/issues/24278

You can use the done future on the WebSocket object to get that error, e.g.:

import 'dart:async';

import 'dart:io';

main() async {

  // Connect to a web socket.

  WebSocket socket = await WebSocket.connect('ws://echo.websocket.org');

  // Setup listening.

  socket.listen((message) {

    print('message: $message');

  }, onError: (error) {

    print('error: $error');

  }, onDone: () {

    print('socket closed.');

  }, cancelOnError: true);

  // Add message, and then an error.

  socket.add('echo!');

  socket.addError(new Exception('error!'));

  // Wait for the socket to close.

  try {

    await socket.done;

    print('WebSocket donw');

  } catch (error) {

    print('WebScoket done with error $error');

  }

}

　　

I get your point, but I don't understand why this is an asynchronous error. I mean, you get this error before starting to actually asynchronously listen to requests, right? – Alexandr Sep 27 '15 at 16:41
1
HttpServer.bind() is already async (returns a Future<HttpServer>) – Günter Zöchbauer Sep 27 '15 at 16:43
You are right, Gunter. Thank you for this! – Alexandr Sep 28 '15 at 5:35