DankyWebServer.cs

using System;
using System.Diagnostics;
using System.Net;
using System.Net.Sockets;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using Newtonsoft.Json;

namespace MyDankyWebServer
{
    public class DankyWebServer
    {
        UTF8Encoding utf8Encoding = new UTF8Encoding(false);
        StringBuilder sb = new StringBuilder();
        void WriteLog(string msg) {
            sb.Append(msg);
        }
        string GetLog()
        {
            return sb.ToString();
        }

        public void Listen(int port, bool send100Continue)
        {


            var listener = new TcpListener(new IPAddress(new byte[] {127, 0, 0, 1}), port);
            listener.Start();

            new Thread(() => ServeOneRequest(listener.AcceptSocket(), send100Continue)).Start();

            //listener.Stop();

        }

        private long ServeOneRequest(Socket socket, bool send100Continue)
        {
            var buffer = new byte[4096];
            var sw = new Stopwatch();

            var receivedBytes = socket.Receive(buffer);
            var receivedString = utf8Encoding.GetString(buffer,0, receivedBytes);

            var receivedHeaderMilliseconds = sw.ElapsedMilliseconds;
            WriteLog($"\n{receivedHeaderMilliseconds} S: Received Header");
            WriteLog(receivedString);

            if (send100Continue) Send100Continue(socket, utf8Encoding);

            do
            {
                receivedBytes = socket.Receive(buffer);
                receivedString = utf8Encoding.GetString(buffer, 0, receivedBytes);
            } while (receivedBytes == 0);

            var timeToBodyReceivedMilliseconds = sw.ElapsedMilliseconds - receivedHeaderMilliseconds;
            WriteLog($"\n{sw.ElapsedMilliseconds} S: Received Request Body " + receivedBytes + $" bytes {timeToBodyReceivedMilliseconds} ms");
            WriteLog(receivedString);

            WriteLog($"\n{sw.ElapsedMilliseconds} S: Sending Response");
            socket.Send(utf8Encoding.GetBytes(@"HTTP/1.1 200 OK
Content-Type: application/json

"));

            var response = JsonConvert.SerializeObject(new {
                Success = true,
                TimeToBodyReceivedMilliseconds = timeToBodyReceivedMilliseconds,
                Logs = GetLog()
            });
            socket.Send(utf8Encoding.GetBytes(response));

            WriteLog($"{sw.ElapsedMilliseconds} S: Sent Response");
            WriteLog(receivedString);
            socket.Close();

            return timeToBodyReceivedMilliseconds;
        }

        private void Send100Continue(Socket socket, UTF8Encoding utf8Encoding)
        {
            var text = @"HTTP/1.1 100 Continue

";
            socket.Send(utf8Encoding.GetBytes(text));
            WriteLog("S: " + text);
        }
    }
}

DankyWebServer.csproj

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net5.0</TargetFramework>
    <PublishTrimmed>true</PublishTrimmed>
    <PublishReadyToRun>true</PublishReadyToRun>
    <PublishSingleFile>true</PublishSingleFile>
    <CrossGenDuringPublish>false</CrossGenDuringPublish>
   </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="NewtonSoft.Json" Version="12.0.3" />
  </ItemGroup>

</Project>

Program.cs

using System;

namespace MyDankyWebServer
{
    class Program
    {
        static void Main(string[] args)
        {
           var ws = new DankyWebServer();
        }
    }


}