C#

class Proxy
	{
		private string appName = "HSMSProxy";
		/// 
		/// <summary>
		/// The main entry point for the application.
		/// </summary>
		[STAThread]
		static void Main(string[] args)
		{
			new Proxy().Start();
		}

		public void Start()
		{
        		TcpListener listener = new TcpListener(5001);
			listener.Start();
			TcpClient activeEntity = listener.AcceptTcpClient();
			TcpClient passiveEntity = new TcpClient("TargetMachine", 5002); // target IP
		        NetworkStream activeStream = activeEntity.GetStream();
			NetworkStream passiveStream = passiveEntity.GetStream();
			new InterStreamWriter(activeStream, passiveStream).Start();
			new InterStreamWriter(passiveStream, activeStream).Start();
			Console.ReadLine();
		}

		private void Log(string message)
		{
			Console.WriteLine(message);
		}
	}

	class InterStreamWriter
	{
		NetworkStream readStream;
		NetworkStream writeStream;

		public InterStreamWriter(NetworkStream readStream, NetworkStream writeStream)
		{
			this.readStream = readStream;
			this.writeStream = writeStream;
		}

		public void Start()
		{
			new System.Threading.Thread(new System.Threading.ThreadStart(ThreadFunc)).Start();
		}

		private void ThreadFunc()
		{
			while (true)
			{
				ArrayList byteList = new ArrayList();

				byte[] myReadBuffer = new byte[1024];
				int numberOfBytesRead = 0;

				do
				{
					numberOfBytesRead = readStream.Read(myReadBuffer, 0, myReadBuffer.Length);  
					for (int i = 0; i<numberOfBytesRead; ++i)
						byteList.Add(myReadBuffer[i]);
				}
				while(readStream.DataAvailable);

				byte[] totalBuffer = (byte[])byteList.ToArray(typeof(byte));
				
				writeStream.Write(totalBuffer, 0, totalBuffer.Length);
				writeStream.Flush();

				byteList.Clear();
			}
		}
	}