Discover Focusrite Control Server on the network

index.js

const PORT = 61392;
const dgram = require('dgram');
const client = dgram.createSocket('udp4');

// Make the discovery message
const msg = '<client-discovery app="SAFFIRE-CONTROL" version="4" device="iOS"/>';
const hex = ('000000' + msg.length.toString(16)).substr(-6);
const announce = 'Length=' + hex + ' ' + msg;

// Start the udp socket
client.bind(PORT);

// Start a polling timer to broadcast the message every 1 second
client.on('listening', function () {
  let address = client.address();
  console.log('UDP Client listening on ' + address.address + ":" + address.port);
  client.setBroadcast(true)
  client.setMulticastTTL(128);
  setInterval(broadcast, 1000)
});

// Send udp broadcast message on ports 30096, 30097 and 30098
// The iOS client does this, so I'm just copying its behaviour.
const broadcast = () =>
{
  let message = Buffer.from(announce);
  client.send(message, 0, message.length, 30096, "255.255.255.255");
  client.send(message, 0, message.length, 30097, "255.255.255.255");
  client.send(message, 0, message.length, 30098, "255.255.255.255");
}

// Focusrite Control Server sends back a xml-tag stylew message
client.on('message', function (message, remote)
{
  let str = message.toString();
  let ip = remote.address;
  let port = str.match(/port\=\'([0-9]*)\'/)[1];
  console.log(str, ip, port)
  // got it!
});