publicserver.js

#!/usr/bin/env node

// based on http://www.bford.info/pub/net/p2pnat/index.html

var socketA = null;
var socketB = null;

var detailsA = {
	name: 'A',
	localAddress: null,
	localPort: null,
	remoteAddress: null,
	remotePort: null
};

var detailsB = {
	name: 'B',
	localAddress: null,
	localPort: null,
	remoteAddress: null,
	remotePort: null
};


// assuming A will connect first:
var server = require('net').createServer(function (socket) {
	if(!socketA) {
		aConnects(socket);
	}else{
		bConnects(socket);
	}
});

server.listen(9999, function (err) {
	if(err) return console.log(err);

	console.log('server listening on', server.address().address + ':' + server.address().port);
});



function aConnects (socket) {
	socketA = socket;
	console.log('> (A) assuming A is connecting');
	console.log('> (A) remote address and port are:', socket.remoteAddress, socket.remotePort);
	console.log('> (A) storing this for when B connects');

	detailsA.remoteAddress = socket.remoteAddress;
	detailsA.remotePort = socket.remotePort;

	socket.on('data', function (data) {
		console.log('> (A) incomming data from A:', data.toString());

		var localDataA = JSON.parse(data.toString());
		if(!localDataA.name || localDataA.name != 'A') return console.log('> (A) this is not the local data of A');

		console.log('> (A) storing this for when B connects');
		console.log('');
		detailsA.localAddress = localDataA.localAddress;
		detailsA.localPort = localDataA.localPort;
		console.log('> (A) sending remote details back to A');
		socket.write(JSON.stringify(detailsA));

		console.log('> (A)', detailsA.localAddress + ':' + detailsA.localPort, '===> (NAT of A)', detailsA.remoteAddress + ':' + detailsA.remotePort, '===> (S)', socket.localAddress + ':' + socket.localPort);
	});

	socket.on('end', function () {
	    console.log('> (A) connection closed.');
	    socketA = null;
	});

	socket.on('error', function (err) {
	    console.log('> (A) connection closed with err (',err,').');
	    socketA = null;
	});
}

function bConnects(socket) {
	socketB = socket;

	console.log('> (B) assuming B is connecting');
	console.log('> (B) remote address and port are:', socket.remoteAddress, socket.remotePort);
	console.log('> (B) storing this');
	detailsB.remoteAddress = socket.remoteAddress;
	detailsB.remotePort = socket.remotePort;

	socket.on('data', function (data) {
		console.log('> (B) incomming data from B:', data.toString());

		var localDataB = JSON.parse(data.toString());
		if(!localDataB.name || localDataB.name != 'B') return console.log('> (B) this is not the local data of B');
		console.log('> (B) storing this');
		console.log('');
		detailsB.localAddress = localDataB.localAddress;
		detailsB.localPort = localDataB.localPort;
		console.log('> (B) sending remote details back to B');
		socket.write(JSON.stringify(detailsB));

		console.log('> (B)', detailsB.localAddress + ':' + detailsB.localPort, '===> (NAT of B)', detailsB.remoteAddress + ':' + detailsB.remotePort, '===> (S)', socket.localAddress + ':' + socket.localPort);



		console.log('> (S->A) sending B\'s details:', detailsB);
		socketA.write(JSON.stringify(detailsB));

		console.log('> (S->B) sending A\'s details:', detailsA);
		socketB.write(JSON.stringify(detailsA));


		console.log('');
	});

	socket.on('end', function () {
	    console.log('> (B) connection closed.');
	    socketB = null;
	});

	socket.on('error', function (err) {
	    console.log('> (B) connection closed with err (',err,').');
	    socketB = null;
	});
}