Thanks a lot for reporting the issue. v0.4.0 is released where the issue should be fixed. Can you please update your dependencies?

from start.

It's OK.
I've tested with dart websocket client.

Thank a lot.
And I would like to contribute 'start' project some more.

// Copyright (c) 2019, the Dart project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

import 'package:web_socket_channel/io.dart';
import 'package:web_socket_channel/status.dart' as status;

main() async {
final channel = await IOWebSocketChannel.connect("ws://localhost:3000/socket");

channel.sink.add("connected");
channel.stream.listen((msg) {
print (msg);
channel.sink.add("pong");
}, onDone: () => print("Stream is closed"));
}

===================================================

Result : It's successed with v0.4.0.

% dart client.dart
ping:"data-from-ping"
Stream is closed

from start.