WebSocket connection to 'wss://' Error during WebSocket handshake: Unexpected response code: 400

Question

I use socket.io in my node.js app that's running on express.

Everything words fine on the local version (localhost) however when I switch to my production server (which is served via https using a custom certificate), I get the following error in my browser console:

websocket.js:112 WebSocket connection to 'wss://infranodus.com/socket.io/?EIO=3&transport=websocket&sid=j_WBxkPY_RlpF9_ZAANP' failed: Error during WebSocket handshake: Unexpected response code: 400

I made a research (issue referenced here) and it turns out this happens because my app / hosting provider blocks connections like wss and my socket.io falls back on AJAX to make requests (which functions OK, but sometimes there are bugs).

So I wanted to ask you if I could do modifications to my app to get rid of this error?

Just FYI currently all requests to http://infranodus.com are forwarded (via static .htaccess) to https://infranodus.com and my app.js file (the part of the server activation looks like that):

var http = require('http');

var app = express();

var server = http.Server(app);
var io = require('socket.io')(server);

app.set('port', process.env.PORT || 3000);
app.set('views', __dirname + '/views');
app.set('view engine', 'ejs');

and the way I require sockets in my front-end file:

<script src="/socket.io/socket.io.js"></script>

and then

var socket = io();

Maybe the problem is that I activate server in my node.js app using http and not https? But I would not like to switch to that because I don't know where my certificates are stored and I would not like to change the backend code too much.

UPDATE (21/10/2018): We figured out the problem is with nginx server and due to the limitations of some hosting providers who do not allow users to edit nginx servers, websockets over secure protocol get blocked or get 400 error. It would be nice to resolve this in sockets.io as it's a problem that many users have. Any ideas?

TO REPRODUCE THE ISSUE: Please, go open your Javascript Console and go to https://infranodus.com/news/english

SOURCE CODE: https://github.com/noduslabs/infranodus

Answer 1

I solved it with this:

var socket = io.connect("http://localhost:3000", {
   forceNew: true,
   transports: ["polling"],
});

Answer 2

Check if you using express-status-monitor as a middleware on express, this makes http call on the first (request) handshake of WebSocket goes failed, if not maybe another factor like proxy (nginx) or similar like that

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