server.js

var express = require('express'),
    io = require('socket.io'),
    // Map clients to sessions by IP
    clients = {};

var app = express.createServer();

app.use(express.cookieParser());
app.use(express.session({ secret: "keyboard cat" }));

app.get('/', function(req, res){ 
   res.send('Hello World'); 
});

app.listen(3000); 
  
var socket = io.listen(app); 

socket.on('connection', function(){
  // New client.
  clients[client.request.socket.remoteAddress] = client.sessionID;

  client.on('message', function(){
    var session = getSession(client);
  });
  client.on('disconnect', function(){ … });
});

function getSession(client) {
  var sid = clients[client.request.socket.remoteAddress];
  return socket.clients
}