NodeJS Socket.IO simple server

gistfile1.js

var express = require('express');
var app = express();
var server = require('http').createServer(app);
var io = require('socket.io').listen(server);

var users = {};

app.listen(80);

app.get('/', function handler (req, res) {
	res.sendfile(__dirname + '/index.html');
});

io.on('connection', function (socket)
{
	socket.on('user_in', function (username)
	{
		socket.username = username;
	
		usernames[username] = username;

		socket.emit('user_ok');
		socket.broadcast.emit('user_in', username);
	});

	socket.on('send_chat', function (msg)
	{
		io.sockets.emit('upd_chat', socket.username, msg);
	});

	socket.on('disconnect', function()
	{
		delete usernames[socket.username];

		socket.broadcast.emit('user_out', socket.username);
	});
});