C#

public class WebServer
    {
        private readonly TcpListener _listener;
        private readonly Thread _listenerThread;

        public WebServer()
        {
            _listener = new TcpListener(IPAddress.Parse("127.0.0.1"), 80);
            _listenerThread = new Thread(ListenForClients);
        }

        public void StartListening()
        {
            _listenerThread.Start();
        }

        private void ListenForClients()
        {
            _listener.Start();

            while (true)
            {
                TcpClient client = _listener.AcceptTcpClient();

                var clientThread = new Thread(HandleClient);
                clientThread.Start(client);
            }
            _listener.Stop();
        }


        private void HandleClient(object client)
        {
            var tcpClient = client as TcpClient;
            var clientStream = tcpClient.GetStream();
            var encoder = new ASCIIEncoding();
            var message = new byte[4096];

            while (true)
            {
                int bytesRead = 0;
                string fileToGrab;
                try
                {
                    //blocks until a client sends a message
                    bytesRead = clientStream.Read(message, 0, 4096);
                    string msg = encoder.GetString(message);
                    Console.WriteLine("Client {0} connected", tcpClient.Client.LocalEndPoint);
                    Console.WriteLine(msg);

                    string[] parts = msg.Split(' ');

                    fileToGrab = parts[1];

                }
                catch
                {
                    //a socket error has occured
                    break;
                }

                if (bytesRead != 0)
                {
                    if (fileToGrab == "/") fileToGrab = @"/index.html";
                    else if (!File.Exists(Environment.CurrentDirectory + fileToGrab))
                    {
                        fileToGrab = @"/error.html";
                    }

                    byte[] buffer = File.ReadAllBytes(Environment.CurrentDirectory + fileToGrab);


                    clientStream.Write(buffer, 0, buffer.Length);
                    clientStream.Flush();

                    string serverIp = "From server " + _listener.LocalEndpoint;
                    clientStream.Write(encoder.GetBytes(serverIp), 0, serverIp.Length);
                    clientStream.Flush();
     
                    break;

                }
            }

            Console.WriteLine("Client {0} closed",tcpClient.Client.LocalEndPoint);
            tcpClient.Close();
        }
    }

static void Main()
       {
           WebServer server = new WebServer();
           server.StartListening();
       }

public partial class Form1 : Form
    {
        private readonly WebServer _server;

        public Form1(WebServer server)
        {
            _server = server;
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            _server.StartListening();
 
        }
    }