code: function discover(host, cb) {
  
    const TIMEOUT = 5000;
  
    var socket = dgram.createSocket('udp4');
    var buffer = new Buffer(text.__('Long live Jenkins!'));
    var parser = new xml2js.Parser();
  
    socket.on('error', function (err) {
      socket.close();
      cb(err);
    });
  
    socket.on('message', function (result) {
      socket.close();
      parser.addListener('end', function (result) {
        cb(null, result);
      });
      parser.parseString(result);
    });
  
    socket.send(buffer, 0, buffer.length, 33848, host, function (err, result) {
      if (err) {
        socket.close();
        cb(err);
      }
    });
  
    setTimeout(function () {
      cb(new Error(text.__('Unable to find any Jenkins instance on %s', host)));
    }, TIMEOUT);
  }
docs: Discover whether there's a Jenkins instance running on the specified host.
  
  @param {String} host: hostname
  @param {Function} cb: standard cb(err, result) callback