How to uniquely identify a socket with Node.js

Question

TLDR; How to identify sockets in event based programming model.

I am just starting up with node.js , in the past i have done most of my coding part in C++ and PHP s

Answer 1

How to identify a client based on its socket id. Useful for private messaging and other stuff.

Using socket.io v1.4.5

client side:

var socketclientid = "john"; //should be the unique login id
var iosocket = io.connect("http://localhost:5000", {query: "name=john"});

var socketmsg = JSON.stringify({
  type: "private messaging",
  to: "doe",
  message: "whats up!"
});                        
iosocket.send(socketmsg);

server side:

io.on('connection', function(socket){
  var sessionid = socket.id;
  var name = socket.handshake.query['name'];
  //store both data in json object and put in array or something

socket.on('message', function(msg){
  var thesessionid = socket.id;      
  var name = ???? //do lookup in the user array using the sessionid
  console.log("Message receive from: " + name);

  var msgobject = JSON.parse(msg);
  var msgtype = msgobject.type;
  var msgto = msgobject.to;
  var themessage = msgobject.message;

  //do something with the msg
  //john want to send private msg to doe
  var doesocketid = ???? //use socket id lookup for msgto in the array
                         //doe must be online
  //send to doe only
  if (msgtype == "private messaging") 
     socket.to(doesocketid).emit('message', 'themessage');

});