getServers.js

var dgram = require('dgram');

function getIP(data) {
  var a = data.slice(0, 1).readUInt8();
  var b = data.slice(1, 2).readUInt8();
  var c = data.slice(2, 3).readUInt8();
  var d = data.slice(3, 4).readUInt8();
  return (a + "." + b + "." + c + "." + d);
}

function getPort(data) {
  return data.slice(4, 6).readUInt16BE();
}

function parse(data) {
  var res = [];
  data = data.slice(6);
  while (data.length) {
    ip = getIP(data);
    port = getPort(data);
    res.push([ip, port]);
    data = data.slice(6);
  }
  return res;
}


var start = new Buffer([0x31]);
var location = new Buffer([0xFF]);
var ipPort = new Buffer("0.0.0.0:0");
var filters = new Buffer([0]);
var message = Buffer.concat([start, location, ipPort, filters]);

var socket = dgram.createSocket("udp4");
socket.bind(1234, function() {
  socket.send(message, 0, message.length, 27011, "hl2master.steampowered.com");
  socket.on('message', function(msg, rinfo) {
    console.log(parse(msg));
    socket.close();
  });
});