Expo with socket.io websocket failing to connect

Question

I am attempting to connect to a socket.io server from within an Expo app. I am having issues being able to connect to my server. I have a web app that connect to the server fine, so the server is working OK. I have also looked at some examples, including one from the Expo repo, to no avail.

My client:

componentDidMount() {

    const socket = socketIOClient('http://192.168.1.210:80', {
      transports: ['websocket']
    });

    socket.on('connect', () => {
      console.log('Connected.');
    });

    socket.on('connect_error', (err) => {
      console.log(err);
    });
}

Server:

this.httpServer = HttpServer.createServer((req, res) => {
  res.writeHead(200, {'Content-Type': 'text/html'});
  res.end('');
});

this.httpServer.listen(80);

this.io = new IOServer({
  pingInterval: 10000,
  pingTimeout: 5000,
});

this.io.listen(this.httpServer);
this.io.set('transports', ['websocket']);

this.onConnection();

this.io.on('connection', (socket) => {/* events */}

The on connect event will never fire, only the connect_error event which simply says 'timeout'. Native websockets work fine when testing against https://www.websocket.org/echo.html .

Answer 1

This was a bug with socket.io to do with loading in the incorrect WebSocket implementation.

It was looking for self.WebSocket , but self does not exist in React Native, so it was falling back to require('ws') , the Node.js implementation. In reality, it should have been using the native WebSocket implementation in React Native.

I've made a PR to solve this: https://github.com/socketio/engine.io-client/pull/607

The reason that turning on remote debugging makes it work is since the code runs in a browser (Chrome) in this mode, it's able to use the browser's WebSocket implementation.

Answer 2

is it related to the https issue?, tried on localhost works on https, but http, seems the https://github.com/expo/examples/tree/master/with-socket-io mentioned something about

React Native provides a socket-io compatible WebSocket implementation, some people get tripped up on the https requirement so this example helps to clarify how you can get it running.