Flutter websockets working in local web but not in Firebase Hosting

Question

I'm doing some tests with web_socket_channel Flutter plugin and I've noticed a very strange behavior. I've implemented flutter-dev's example, just changing the socket kind to HtmlWebSocketChannel in order to make it work in web builds. If I compile my app with flutter build web --release and later I expose it with a local webserver, it works perfectly fine. Same happens if I execute it in debug mode.

However, if I deploy the release version to Firebase hosting (firebase deploy), the widgets where a HtmlWebSocketChannel is present are rendered as a grey box. If I remove those instances, all widgets are rendered as usual. I thought Firebase hosting was nothing more that a very simple web server, I can't see how can it interfere with specific widgets in a Flutter app. Maybe the cause is related to the fact I'm accesing a remote URL?

Any help will be appreciated!

Here's the code of the app I'm deploying:

import 'package:flutter/foundation.dart';
import 'package:web_socket_channel/html.dart';
import 'package:flutter/material.dart';
import 'package:web_socket_channel/web_socket_channel.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final title = 'WebSocket Demo';
    return MaterialApp(
      title: title,
      home: MyHomePage(
        title: title,
        channel: HtmlWebSocketChannel.connect('ws://echo.websocket.org'),
      ),
    );
  }
}

class MyHomePage extends StatefulWidget {
  final String title;
  final WebSocketChannel channel;

  MyHomePage({Key key, @required this.title, @required this.channel})
      : super(key: key);

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  TextEditingController _controller = TextEditingController();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Padding(
        padding: const EdgeInsets.all(20.0),
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.start,
          children: <Widget>[
            Form(
              child: TextFormField(
                controller: _controller,
                decoration: InputDecoration(labelText: 'Send a message'),
              ),
            ),
            StreamBuilder(
              stream: widget.channel.stream,
              builder: (context, snapshot) {
                return Padding(
                  padding: const EdgeInsets.symmetric(vertical: 24.0),
                  child: Text(snapshot.hasData ? '${snapshot.data}' : ''),
                );
              },
            )
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _sendMessage,
        tooltip: 'Send message',
        child: Icon(Icons.send),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }

  void _sendMessage() {
    if (_controller.text.isNotEmpty) {
      widget.channel.sink.add(_controller.text);
    }
  }

  @override
  void dispose() {
    widget.channel.sink.close();
    super.dispose();
  }
}

Answer 1

As mentioned above in my comments this seems to be an issue with trying to access insecure resource from a secure environment as https. Here is a working demo of the same code you used.

https://stackoverlfow-demos.web.app/#/

I just replaced it with wss and deployed it to the firebase hosting.

channel: HtmlWebSocketChannel.connect('wss://echo.websocket.org'),