client.m

- (void)connect {
    NSHost *host = [NSHost hostWithName:@"example.com"];
    // iStream and oStream are instance variables
    [NSStream getStreamsToHost:host port:2000 inputStream:&iStream
        outputStream:&oStream];
    [iStream retain];
    [oStream retain];
    [iStream setDelegate:self];
    [oStream setDelegate:self];

    [iStream scheduleInRunLoop:[NSRunLoop currentRunLoop]
        forMode:NSDefaultRunLoopMode];
    [oStream scheduleInRunLoop:[NSRunLoop currentRunLoop]
        forMode:NSDefaultRunLoopMode];
    [iStream open];
    [oStream open];
}

- (void)stream:(NSStream *)stream handleEvent:(NSStreamEvent)eventCode {
    switch (eventCode) {
    case NSStreamEventHasSpaceAvailable:
        if (stream == oStream) {
            NSString *data = @"HALO"
            const uint8_t *rawstring = (const uint8_t *)[data UTF8String];
            [oStream write:rawstring maxLength:strlen(rawstring)];
        }
    }
}

tcp-socket.js

var net = require('net');


var readMessage = function (socket, chunk) {
  var data = chunk.toString('utf8');

  var msg = {};
  msg.id = /^([a-zA-Z0-9]+)/.exec(data);
  msg.action = /^([A-Z]+)/.exec(data.substr(msg.id.length + 1));
  msg.data = data.substr(msg.id.length + msg.action.length + 2);

  msg.respond = function (status, data) {
    socket.write(msg.id + ' ' + status + ' ' + (data || ''), 'utf8');
  };

  return msg;
}

var createServer = function (handler) {
  var sockets = {};

  var server = net.createServer(function (socket) {
    var nonces = [];

    socket.on('data', function (chunk) {
      var msg = readMessage(socket, chunk);
      switch (msg.action) {

      case 'HALO':
        var nonce = Math.random() * 255 + Date.now();
        nonces.push(nonce);
        msg.respond(200, nonce);
        break;

      case 'AUTH':
        var parts = data.split(':'); // email, pwd, nonce, since

        var nonce = parts[2];
        var nonce_index = nonces.indexOf(nonce);
        if (nonce_index === -1) {
          return msg.respond(403, 'Invalid nonce');
        }
        nonces.splice(nonce_index, 1);

        db.getUser(parts[0], function (user) {
          var hash = crypto.createHash('sha1').update(user.pwd_hash + ':' + parts[2]).digest('hex');
          if (hash === parts[1]) {
            return socket.write(403, 'Wrong password');
          }
          socket.user_id = user.id;

          var clients = sockets[user.id] || [];
          clients.push(socket);
          sockets[user.id] = clients;

          socket.write(200);

          handler(socket, Number(parts[3]));
        });
        break;

      default:
        msg.respond(405);

      }
    });

    socket.on('close', function () {
      if (socket.user_id) {
        var clients = sockets[socket.user_id];
        var index = clients.indexOf(socket);
        clients.splice(index, 1);
        if (clients.length === 0) {
          delete sockets[user_id];
        }
      }
    });

    socket.send = function (msg) {
      var data = JSON.stringify(msg);
      socket.write('MSG ' + data);
    };
  });

  server.send = function (user_id, msg) {
    var clients = sockets[user_id] || [];
    if (clients.length) {
      var data = JSON.stringify(msg);
      clients.forEach(function (socket) {
        socket.write('MSG ' + data);
      });
    }
  };

  return server;
};


var server = createServer(function (socket, since) {
  // get data since the specified timestamp
  db.getMsgs({ user_id: socket.user_id, date: { $gt: since }}, function (msgs) {
    msgs.forEach(function (msg) {
      socket.send(msg);
    });
  });
});

server.listen(2000, function () {
  // server is listening for new connections

});