How to access the target socket in a Socket.io handler

I'm working with a Socket.io server and I'm trying to access the socket that emitted the event from the client.

There's this example in the docs :

socket.on('private message', function (from, msg) 
{
    console.log('I received a private message by ', from, ' saying ', msg);   
});

Trying to use this, I've noticed that the parameter order has changed in the latest version and the 'from' parameter is actually a function.

I'm having trouble using this to get information about who emitted the event.

Is there another way? or perhaps a way using the parameter to get the info?