BAT_ProtocolTests/TcpTestApp/Program.cs

using System.Net;
using System.Net.Sockets;
using System.Text;

namespace TcpTestApp;

internal class Program
{
    private static Thread? serverThread;
    private static CancellationTokenSource? cts;
    private static TcpListener? listener;

    public static bool applicationQuitRequested { get; private set; }

    static void Main(string[] args)
    {
        while (applicationQuitRequested == false)
        {
            Console.WriteLine($"----- TCP Server for Protocol Testing -----");
            Console.WriteLine($"Command list:");
            Console.WriteLine($"s = start server");
            Console.WriteLine($"e = stop server");
            Console.WriteLine($"q = quit");

            var key = Console.ReadKey(true);

            switch (key.Key)
            {
                // start server
                case ConsoleKey.S:
                    Console.Write($"Write port number to listen on: ");
                    string? portString = Console.ReadLine();
                    int port;

                    if (portString == null ||
                        portString == "" ||
                        Int32.TryParse(portString, out port) == false)
                    {
                        Console.WriteLine($"Invalid port entered.");
                        break;
                    }

                    var ipEndPoint = new IPEndPoint(IPAddress.Any, port);
                    listener = new(ipEndPoint);

                    try
                    {
                        listener.Start();
                    }
                    catch (Exception ex)
                    {
                        Console.WriteLine($"Could not start TCP server. \n {ex}");
                        break;
                    }

                    cts = new CancellationTokenSource();  // reset token
                    serverThread = new Thread(() => HandleTcp(cts));
                    serverThread.Start();

                    Console.WriteLine("Started TCP server.");
                    break;

                // stop server
                case ConsoleKey.E:
                    cts?.Cancel();
                    serverThread?.Join();
                    serverThread = null;
                    listener?.Stop();
                    Console.WriteLine("Stopped TCP server.");
                    break;

                // quit
                case ConsoleKey.Q:
                    applicationQuitRequested = true;
                    break;

                default:
                    Console.WriteLine($"{Environment.NewLine}Did not recognize key.. {Environment.NewLine}");
                    break;
            }


        }
    }

    static async void HandleTcp(CancellationTokenSource cts)
    {
        while (!cts.IsCancellationRequested)
        {
            try
            {
                using TcpClient handler = await listener!.AcceptTcpClientAsync(cts.Token);
                if(handler != null)
                {
                    Console.WriteLine($"Accepted connection from client {handler.Client.RemoteEndPoint}");
                    await using NetworkStream stream = handler.GetStream();

                    var message = $"Welcome to the test TCP server.\n Current Time: {DateTime.Now}\n";
                    var dateTimeBytes = Encoding.UTF8.GetBytes(message);
                    await stream.WriteAsync(dateTimeBytes);

                    Console.WriteLine($"Sent message to client: \"{message}\"");
                }
            }
            catch(Exception ex) 
            {
                listener?.Stop();
                Console.WriteLine($"Listener was stopped because of exception: {ex}");
            }
        }
    }
}