Extra params with socket.io

Question

How can I send extra parameters with the connection in socket.io? So when a client connects, they send additional information, and server-side it is received as

io.on('connection', function(client, param1, param2, param3) {
    // app code
}

Answer 1

Here's a little trick which should work. First, you create your own Socket client that sends a message on first connection (containing all your additional info).

// Client side

io.MySocket = function(your_info, host, options){
  io.Socket.apply(this, [host, options]);
  this.on('connect', function(){
    this.send({__special:your_info});
  });
};
io.util.inherit(io.MySocket, io.Socket);

var my_info = {a:"ping"}
var socket  = io.MySocket(my_info);

Then on the server side, you modify your socket to listen for the special message and fire off an event when it does.

// Server side

var io = require('socket.io').listen(app);
io.on('connection', function(client){
  client.on('message', function(message){
    if (message.__special) {
      io.emit('myconnection', client, message.__special);
    }
  });
});

io.on('myconnection', function(client, my_info) {
  // Do your thing here
  client.on('message', ...); // etc etc
}

This is the technique I used to link my session handling into Socket.IO for a package I wrote.