Socket.io gives CORS error even if I allowed cors it on server

Question

My node server and client are running on different ports(3001,5347 respectively). On client I had used,

var socket = io(\'http://127.0.0.1:3001\');


        

Answer 1

If you are using Express then define a middleware like this before your serve start code...

app.use(function(request, response, next) {
  response.header("Access-Control-Allow-Origin", "*");
  response.header("Access-Control-Allow-Headers", "Origin, X-Requested-With, Content-Type, Accept");
  next();
});

Answer 2

If running Express as follows:

var app = express();
var server = app.listen(3000);

So to start socket.io, we can do the following:

var io = require('socket.io').listen(server);

The problem was because of following code:

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

The server object passed to socket.io was not the same as the server object I'm listening on.

Answer 3

Following code helped:

const PORT = process.env.PORT || 4000;
const app = express();
const server = app.listen(PORT, () => {
    console.log(`Server running on port ${PORT}`);
});
const io = socket(server);

Answer 4

The accepted answer is outdated

According to the official docs, you can add it to an existing http Server https://socket.io/docs/server-initialization/#Attached-to-an-existing-HTTP-server

const server = require('http').createServer();
const options = { /* ... */ };
const io = require('socket.io')(server, options);
io.on('connection', socket => { /* ... */ });
server.listen(3000);

to enable cors using this options object seemed to do the trick

options={
 cors:true,
 origins:["http://127.0.0.1:5347"],
}

Answer 5

Note that you can use cors() with app before you pass app into require('http'), which is then passed into socket.io. In this order. This should work too.

const app = express();

app.use(cors());
const http = require('http').Server(app);
const io = require('socket.io')(http);

Hope it helps.