Reverse engineering the Unity Network Discovery protocol to broadcast from a 3rd party source

UnityNetworkDiscoveryReimplementation.cs

// see blog post here: https://shoreparty.org/reverse-engineering-the-unity-network-discovery-protocol-9cd01280ed08

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.NetworkInformation;
using System.Net.Sockets;
using System.Text;
using System.Threading;

namespace UnityNetworkDicoveryReimplementation
{
    class Program
    {
        private static byte[] GetBytesForInt(int i) => BitConverter.GetBytes(i).Reverse().ToArray();

        private static byte[] CreateMessage()
        {
            var l = new List<byte>();

            l.AddRange(new byte[] {0x00, 0x00, 0x09}); // prefix

            var rand = new byte[2];
            new Random().NextBytes(rand);
            l.AddRange(rand); // random value per started session

            l.AddRange(GetBytesForInt(36001)); // KEY

            l.AddRange(Enumerable.Repeat(0, 4*8).Select(x => (byte)x)); // padding

            l.AddRange(GetBytesForInt(1)); // VER

            l.AddRange(GetBytesForInt(1)); // SUBVER

            l.AddRange(Encoding.ASCII.GetBytes("test data please ignore").Select(x => new byte[]{x, 0x00}).SelectMany(y => y)); // DATA

            return l.ToArray();
        }

        static void Main(string[] args)
        {
            var interfaces = NetworkInterface.GetAllNetworkInterfaces().Where(x => x.GetIPProperties().GatewayAddresses.Any()).ToList();
            var dict = interfaces.ToDictionary(x => x, y => y.GetIPProperties().GatewayAddresses[0].Address);

            var msg = CreateMessage();
            var uc = new UdpClient();

            while (true)
            {
                Thread.Sleep(2000);
                foreach (var id in dict)
                {
                    Console.WriteLine($"Sending broadcast for interface {id.Key.Name} {id.Value}");

                    var broadcastIp = new IPAddress(id.Value.GetAddressBytes().Take(3).Concat(new[] {(byte) 0xff}).ToArray());
                    uc.Send(msg, msg.Length, broadcastIp.ToString(), 64764);
                }
            }
        }
    }
}