C# Connecting two tcp sockets together

Question

I'm not sure if the title is all that informative.

I am trying to find/write a socket server that will accept a connection from the client (telnet) and then on behalf of the connected client, connect to one of four telnet servers inside the network.

Once connected I keep a counter of how many connections there are, and then if there are 4 total connections, disallow any new connections until one of the four is available.

I have written this:

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

namespace ConsoleApplication1
{
class Program
{
    static int nodeCount = 4;
    static int currentNode = 1;

    static void Main(string[] args)
    {
        ServerProgram server = new ServerProgram();
    }

    class ServerProgram
    {
        private TcpListener tcpPrimaryListener;
        private Thread listenThread;

        public ServerProgram()
        {
            this.tcpPrimaryListener = new TcpListener(IPAddress.Any, 23);
            Console.WriteLine("Telnet BBS Port Concentrator Server Started.");
            Console.WriteLine("--------------------------------------------");

            this.listenThread = new Thread(new ThreadStart(ListenForClients));
            this.listenThread.Start();
        }

        private void ListenForClients()
        {
            this.tcpPrimaryListener.Start();

            while (true)
            {
                TcpClient client = this.tcpPrimaryListener.AcceptTcpClient();
                Thread clientThread = new Thread(new ParameterizedThreadStart(HandleClientComm));
                clientThread.Start(client);
            }
        }

        private void HandleClientComm(object client)
        {
            if (currentNode <= nodeCount)
            {
                Console.WriteLine("Connection thread created.");

                StreamWriter swStream;
                StreamWriter swStream2;
                StreamReader srStream;
                StreamReader srStream2;

                TcpClient tcpClient = (TcpClient)client;
                NetworkStream tcpClientStream = tcpClient.GetStream();

                TcpClient telnet = new TcpClient("192.168.100.5" + currentNode, 23);
                NetworkStream telnetStream = telnet.GetStream();

                currentNode++;

                while (true)
                {
                    srStream = new StreamReader(tcpClient.GetStream());
                    swStream2 = new StreamWriter(tcpClient.GetStream());

                    srStream2 = new StreamReader(telnet.GetStream());
                    swStream = new StreamWriter(telnet.GetStream());

                    swStream.Write(srStream.ReadToEnd());
                    swStream2.Write(srStream2.ReadToEnd());

                }
            }
        }
    }
}
}

I've changed this example multiple times, so I don't really know anymore what I have and have not tried. I'm willing to try anything.

The purpose is actually running this to allow one telnet port open through the firewall, and allowing connections into a small network of DOS machines running telnet fossil driver BBS software. I would just like to redirect telnet traffic to an available system using only one port.

The problem is that I cannot figure out how to actually connect the two sockets together and pass data between them as it happens. The incoming socket and the socket I created on behalf of the server to the server.

Thanks.

UPDATE:

This is what is working for me, I'm still looking over for bugs but it's working so far.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Net.Sockets;
using System.Threading;
using System.Net;
using System.IO;
using System.Threading.Tasks;

namespace ConsoleApplication1
{
class Program
{
    static int nodeCount = 2;
    static int currentNode = 1;

    static void Main(string[] args)
    {
        ServerProgram server = new ServerProgram();
    }

    class ServerProgram
    {
        private TcpListener tcpPrimaryListener;
        private Thread listenThread;

        public ServerProgram()
        {
            this.tcpPrimaryListener = new TcpListener(IPAddress.Any, 23);
            Console.WriteLine("Telnet BBS Port Concentrator Server Started.");
            Console.WriteLine("--------------------------------------------");

            this.listenThread = new Thread(new ThreadStart(ListenForClients));
            this.listenThread.Start();
        }

        private void ListenForClients()
        {
            this.tcpPrimaryListener.Start();

            while (true)
            {
                TcpClient client = this.tcpPrimaryListener.AcceptTcpClient();
                Thread clientThread = new Thread(new ParameterizedThreadStart(HandleClientComm));
                clientThread.Start(client);
            }
        }

        private void HandleClientComm(object client)
        {
            string noNodes = "Sorry all nodes are occupied.";

            if (currentNode <= nodeCount)
            {
                Console.WriteLine("Client connected.");

                TcpClient tcpClient = (TcpClient)client;
                NetworkStream tcpClientStream = tcpClient.GetStream();

                TcpClient telnet = new TcpClient("10.24.9.11", 23);
                //TcpClient telnet = new TcpClient("192.168.100.5" + currentNode, 23);
                NetworkStream telnetStream = telnet.GetStream();

                currentNode++;

                ByPass linkedSockets = new ByPass(tcpClientStream, telnetStream);
            }
            else
            {
                TcpClient tcpClient = (TcpClient)client;
                NetworkStream tcpClientStream = tcpClient.GetStream();

                ASCIIEncoding encoder = new ASCIIEncoding();
                tcpClientStream.Write(Encoding.ASCII.GetBytes(noNodes), 0, noNodes.Length);
            }
        }
    }

    public class ByPass
    {
        public ByPass(Stream s1, Stream s2)
        {
            var cTokenSource = new CancellationTokenSource();
            var cToken = cTokenSource.Token;
            Task.Factory.StartNew(() => Process(s1, s2, cToken, cTokenSource), cToken);
            Task.Factory.StartNew(() => Process(s2, s1, cToken, cTokenSource), cToken);
            cToken.Register(() => cancelNotification());
        }

        public void Process(Stream s1, Stream s2, CancellationToken ct, CancellationTokenSource cTokenSource)
        {
            byte[] buf = new byte[0x10000];

            while (true)
            {
                if (ct.IsCancellationRequested)
                {
                    break;
                }

                try
                {
                    int len = s1.Read(buf, 0, buf.Length);
                    s2.Write(buf, 0, len);
                }
                catch
                {
                    s1.Close(); s2.Close();
                    cTokenSource.Cancel();
                    break;
                }
            }
        }
    }

    static void cancelNotification()
    {
        Console.WriteLine("Client disconnected.");
        currentNode--;
    }
}
}

Answer 1

I have made little changes and it works perfect on my side

    public class StreamTransmitter
    {
        static TaskCompletionSource<bool> ts;

        public static async Task Start(Stream s1, Stream s2, CancellationToken token)
        {
            ts = new TaskCompletionSource<bool>();

            Process(s1, s2, token);
            Process(s2, s1, token);

            await ts.Task;
        }

        private static async Task Process(Stream sIn, Stream sOut, CancellationToken token)
        {
            byte[] buf = new byte[0x10000];
            int len = 0;
            do
            {
                len = await sIn.ReadAsync(buf, 0, buf.Length, token);
                await sOut.WriteAsync(buf, 0, len, token);
            }
            while (len > 0 && !token.IsCancellationRequested);

            ts.SetResult(true);
        }
    }

Answer 2

I think, you can create a class similar to below to pass data between two streams

public class ByPass
{
    public ByPass(Stream s1, Stream s2)
    {

        Task.Factory.StartNew(() => Process(s1, s2));
        Task.Factory.StartNew(() => Process(s2, s1));
    }

    public void Process(Stream sIn, Stream sOut)
    {
        byte[] buf = new byte[0x10000];
        while (true)
        {
            int len = sIn.Read(buf, 0, buf.Length);
            sOut.Write(buf, 0, len);
        }
    }
}