NAT Traversal with node (0.5.x)

nat-traversal.js

/*
NAT traversal system to let 2 computers behind firewall to communicate.

Example:
Client A (your machine) has public ip 1.1.1.1
Client B (distant machine) has public ip 2.2.2.2

You want to bind port 5556 on your machine
Distant Client want to bind port 5557

Command on A:
node nat-traversal.js 5556 2.2.2.2 5557

Command on B:
node nat-traversal.js 5557 1.1.1.1 5556

When both clients are connected, stdin is sent to other side
*/

var dgram = require("dgram"),
    readline = require('readline');

//0 and 1 are "node" ans "scriptname"
//s is a simple struct
var s = {
  HOSTPORT : parseInt(process.argv[2]),
  DESTIP   : process.argv[3],
  DESTPORT : parseInt(process.argv[4]),
  ACK_GARBAGE : new Buffer("node-transversal-garbage"),
  ACK_MAGICK : new Buffer("node-transversal-magick"),
  server:  dgram.createSocket("udp4"),
  listening : false
}

function sendMSG(msg, indicator) {
  if (indicator==undefined || indicator) process.stdout.write('.');
  s.server.send(
        msg, 0 , 
        msg.length, 
        s.DESTPORT, s.DESTIP);
}

s.server.on("listening", function () {
  var address = s.server.address();
  console.log("server listening " +
      address.address + ":" + address.port);
});

s.server.on("message", function (msg, rinfo) {
  if (s.listening) {
    console.log(msg.toString());
  }
  else if (msg.toString() == s.ACK_MAGICK.toString()) {
    //here we must continue to send datas... ans recieve...
    s.listening = true;

    //now, we can read from stdin and send datas to outside
    (function (){
      //this is encapsulated to not lose locals
      var i = readline.createInterface(
              process.stdin, 
              process.stdout, null);
      var input = "";
      i.input.on('data', function (data){
        if (data!="\r" && data!="\n") {
	        input+=data;
        }else {
          var b = new Buffer(input);
          sendMSG(b, false);
          input = "";
        }
      })
    })();
  }//endif
});

//listen on local port
s.server.bind(s.HOSTPORT);

/*Begin the show ! */
//send some packets to fool outside firewall...
for (var i=0; i<10; i++) {
  setTimeout(function (){sendMSG( s.ACK_GARBAGE); }, 1000*i); 
}
//and last with the magick message...
setTimeout(function (){sendMSG( s.ACK_MAGICK); } , 1000*(i++));
setTimeout(function (){
  console.log("Ready");
},1000*(i++))