Question

I can only seem emit messages to users when their socket id has been directly stored within the io.sockets.on(‘connect’) function. I don’t know why it doesn’t work when trying to store their socket id after they have logged in.

Working:

  var clients = {};
  /** A new socket connection has been accepted */
  io.sockets.on('connection', function (socket)
  {
    //Used to access session id
    var hs = socket.handshake;            
        clients[socket.id] = socket; // add the client data to the hash   
        users['brownj2'] = socket.id; // connected user with its socket.id

    socket.on('user-login', function(user){
      if(!users[username]){
        //users[username] = socket.id; // connected user with its socket.id
      }
    })

    socket.on('page-load', function(pid)
    {
      if(users['brownj2'])
      {        
        clients[users['brownj2']].emit('hello');
      }
      else
      {
        console.log("NOT FOUND BROWNJ2");
      }
    }
  }

Not working:

  var clients = {};
  /** A new socket connection has been accepted */
  io.sockets.on('connection', function (socket)
  {
    //Used to access session id
    var hs = socket.handshake;            
        clients[socket.id] = socket; // add the client data to the hash            

    socket.on('user-login', function(user){          
      if(!users['brownj2']){
        users['brownj2'] = socket.id; // connected user with its socket.id
      }
    })

    socket.on('page-load', function(pid)
    {
      if(users['brownj2'])
      {        
        clients[users['brownj2']].emit('hello');
      }
      else
      {
        console.log("NOT FOUND BROWNJ2");
      }
    }
  }

JavaScript Client-side code snippet

var socket = io.connect('');
socket.on("hello", function(){
  alert("Hi Jack");
  console.log("WEBSOCKET RECIEVED");
})

Solution: Thanks @alessioalex
I have had to remove the reference to socket.io from the login page, and add the following into io.sockets.on(‘connection’)

var hs = socket.handshake;

sessionStore.get(hs.sessionID, function(err, session){
  console.log("SESSION: " + util.inspect(session));

  clients[socket.id] = socket; // add the client data to the hash
  validUsers[session.username] = socket.id; // connected user with its socket.id
})

Answer 1

There are some problems with your code, the first being you shouldn’t authenticate users through Socket.IO, you should make sure they can connect only after they authenticated. If you are using Express, then the following article can help you a lot: http://www.danielbaulig.de/socket-ioexpress/

Also you should be avoiding sending messages like so, since that is part of Socket.IO internally and may change:

io.sockets.socket(id).emit('hello');

Instead (if you want to send a message to a specific client) it’s better to keep an object for example with the connected clients (and remove the client once disconnected):

// the clients hash stores the sockets
// the users hash stores the username of the connected user and its socket.id
io.sockets.on('connection', function (socket) {
  // get the handshake and the session object
  var hs = socket.handshake;
  users[hs.session.username] = socket.id; // connected user with its socket.id
  clients[socket.id] = socket; // add the client data to the hash
  ...
  socket.on('disconnect', function () {
    delete clients[socket.id]; // remove the client from the array
    delete users[hs.session.username]; // remove connected user & socket.id
  });
}

// we want at some point to send a message to user 'alex'
if (users['alex']) {
  // we get the socket.id for the user alex
  // and with that we can sent him a message using his socket (stored in clients)
  clients[users['alex']].emit("Hello Alex, how've you been");
}

Sure, io.sockets.socket(id) may work (didn’t actually test), but also it can be always changed as it’s part of the Socket.IO internals, so my solution above is more ‘safe’.

Another thing you may want to change in your code on the client side is var socket = io.connect(''); with var socket = io.connect('http://localhost');, as we can see in the official example of Socket.IO here: http://socket.io/#how-to-use