Program.cs

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

namespace RxDemoServer
{
    class Program
    {
        static void Main(string[] args)
        {
            TcpListener listener = new TcpListener(IPAddress.Loopback, 4000);
            listener.Start();

            while (true)
            {
                var client = listener.AcceptTcpClient();
                var stream = client.GetStream();

                var message1Bytes = Encoding.UTF8.GetBytes("Hello World");
                var size1Bytes = BitConverter.GetBytes(message1Bytes.Length);

                Console.WriteLine("Sending message 1 length");
                stream.Write(size1Bytes, 0, size1Bytes.Length);

                Console.WriteLine("Sending message 1 bytes");
                stream.Write(message1Bytes, 0, message1Bytes.Length);

                var message2Bytes = Encoding.UTF8.GetBytes("Does this work?");
                var size2Bytes = BitConverter.GetBytes(message2Bytes.Length);


                byte[] combined = new byte[6];
                Buffer.BlockCopy(size2Bytes, 2, combined, 0, 2);
                Buffer.BlockCopy(message2Bytes, 0, combined, 2, 4);

                Console.WriteLine("Sending 2 bytes of message 2 length");
                stream.Write(size2Bytes, 0, 2);

                Console.WriteLine("Sending 2 bytes of message 2 length + 4 bytes of message");
                stream.Write(combined, 0, 6);

                Console.WriteLine("Sending remaining messag 2 bytes");
                stream.Write(message2Bytes, 4, message2Bytes.Length - 4);

                Console.WriteLine("Closing socket");
                stream.Close();
                client.Close();
            }
        }
    }
}