C#端口映射程序

class Program
{
    static void Main(string[] args)
    {
        TcpListener listener = new TcpListener(new IPEndPoint(IPAddress.Loopback, 8000));
        listener.Start();
        while (true)
        {
            var client = listener.AcceptTcpClient();

            Console.WriteLine("connected");
            var proxy = new TcpClient();
            Console.WriteLine("remote connected");
            proxy.Connect(new IPEndPoint(IPAddress.Loopback, 21));

            new SyncProxy("client->remote",proxy.GetStream(), client.GetStream());
            new SyncProxy("remote->client",client.GetStream(), proxy.GetStream());
        }
    }
}

class SyncProxy
{
    NetworkStream read;
    NetworkStream write;
    string name;

    public SyncProxy(string name, NetworkStream read,NetworkStream write)
    {
        this.name = name;
        this.read = read;
        this.write = write;

        System.Threading.ThreadPool.QueueUserWorkItem(PipeStream);
    }

    void PipeStream(object state)
    {
        byte[] buffer = new byte[1500];
        int count = 0;
        while (true)
        {
            try
            {
                count = read.Read(buffer, 0, buffer.Length);
            }
            catch (Exception)
            {
                count = 0;
            }

            if (count == 0)
            {
                Console.WriteLine(name+" closed");
                write.Close();
                break;
            }

            Console.Write(name + ": "+ Encoding.Default.GetString(buffer, 0, count));
            write.Write(buffer, 0, count);
        }
    }
}