app.js

var express = require('express');
var app = express();
var server = require('http').Server(app);
var io = require('socket.io')(server);
var sockets = {};
var g_id = 0;

if (process.argv.length != 3) {
  console.log("Usage: nodejs app.js <port-number>");
  process.exit(-1);
}

server.listen(Number(process.argv[2]));
app.set('views', __dirname + '/views');
app.set('view engine', 'pug');
app.use(express.static(__dirname + '/public'));

app.get('/sender', function(req, res) {
  res.render('sender', {'localId':0});
});

app.get('/receiver', function(req, res) {
  g_id++;
  res.render('receiver', {'localId':g_id, 'remoteId':0});
});

function client(socket) {
  this.socket = socket;
}

pending_msgs = {};

io.on('connection', function(socket) {
  socket.on('id', function(id) {
    sockets[id] = socket;

    if (id in pending_msgs) {
      for (var i = 0; i < pending_msgs[id].length; i++) {
        socket.emit('msg', pending_msgs[id][i]);
      }

      delete pending_msgs[id];
    }
  });

  socket.on('msg', function(data) {
    if (data.to in sockets) {
      sockets[data.to].emit('msg', data);
    } else {
      if (!(data.to in pending_msgs)) {
        pending_msgs[data.to] = [];
      }

      pending_msgs[data.to].push(data);
    }
  });
});