How to protect against distributed denial-of-service attacks in Node.js with Socket.io?

Question

I have been learning node.js and socket.io lately. My question is how can I protect server against client side attacks?

This is my server code

io.sockets.on('connection', function (socket) { 
//users.push(socket);       
socket.on('message', function (data) {      

    socket.on('disconnect', function () { });           

    socket.on('bcast', function (data) {        
        socket.emit('news', { 'data': data });
        socket.broadcast.emit('news', { 'data': data });     
    });

    socket.on('login', function(data){
      socket.emit('login', {'data': [ socket.id, data ] });
    });
   });
 });

For example if a client uses chrome developer tools to do the flowing code

 for(var i = 0; i<99999999999; i++)
 {
        socket.emit('bcast', {data: 'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX'});
 }

its going to kill the server.

Answer 1

Look into JS event throttling and debouncing!

Those techniques will help you prevent and detect attacks to a certain point (which is, in my opinion, enough for a small multiplayer socket game)...

EDIT:

In this jsfiddle: http://jsfiddle.net/y4tq9/9/

var sIO = {};

sIO.on = (function(){
    var messages = {};
    var speedLimit = 5; //5ms
    return function(message, handler) {
        messages[message] = messages[message] || {};
        if(messages[message].timestamp && new Date().getTime() - messages[message].timestamp < speedLimit) return false;
        else messages[message].timestamp = new Date().getTime();

        handler();
        return true;
        //execute code, Ex:
    }
}());

you can see that every request sent faster than 5ms will return false, otherwise the handler get run.

You simple disconnect the sockets who send request faster than 5ms (or 2ms, or 3ms depending on your network and your application's weight...).

You might as well using js event throttling on client site to make sure all of your requests doesn't send faster than the speed limit!

This technique will not provide absolute protection from exploiting, but it will prevent your server from crashing when attackers try to Dos...