// Educational Purposes Only
// UDP reverse connection:

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

namespace UDP_Reverse_Connection
{
    class Program
    {
        static void Main(string[] args)
        {
            // Data buffer for incoming data.
            byte[] bytes = new byte[1024];

            // Establish the local endpoint for the socket.
            // Dns.GetHostName returns the name of the 
            // host running the application.
            IPHostEntry ipHostInfo = Dns.GetHostEntry(Dns.GetHostName());
            IPAddress ipAddress = ipHostInfo.AddressList[0];
            IPEndPoint localEndPoint = new IPEndPoint(ipAddress, 11000);

            // Create a TCP/IP socket.
            Socket listener = new Socket(AddressFamily.InterNetwork,
                SocketType.Stream, ProtocolType.Tcp);

            // Bind the socket to the local endpoint and 
            // listen for incoming connections.
            try
            {
                listener.Bind(localEndPoint);
                listener.Listen(10);

                // Start listening for connections.
                while (true)
                {
                    Console.WriteLine("Waiting for a connection...");
                    // Program is suspended while waiting for an incoming connection.
                    Socket handler = listener.Accept();
                    data = null;

                    // An incoming connection needs to be processed.
                    while (true)
                    {
                        bytes = new byte[1024];
                        int bytesRec = handler.Receive(bytes);
                        data += Encoding.ASCII.GetString(bytes, 0, bytesRec);
                        if (data.IndexOf("<EOF>") > -1)
                        {
                            break;
                        }
                    }

                    // Show the data on the console.
                    Console.WriteLine("Text received : {0}", data);

                    // Echo the data back to the client.
                    byte[] msg = Encoding.ASCII.GetBytes(data);

                    handler.Send(msg);
                    handler.Shutdown(SocketShutdown.Both);
                    handler.Close();
                }

            }
            catch (Exception e)
            {
                Console.WriteLine(e.ToString());
            }

            Console.WriteLine("\nPress ENTER to continue...");
            Console.Read();

        }
    }
}

//This is the client side of the UDP reverse connection.

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


namespace UDP_Reverse_Connection
{
    class Program
    {
        static void Main(string[] args)
        {
            // Data buffer for incoming data.
            byte[] bytes = new byte[1024];

            // Connect to a remote device.
            try
            {
                // Establish the remote endpoint for the socket.
                // This example uses port 11000 on the local computer.
                IPHostEntry ipHostInfo = Dns.GetHostEntry(Dns.GetHostName());
                IPAddress ipAddress = ipHostInfo.AddressList[0];
                IPEndPoint remoteEP = new IPEndPoint(ipAddress, 11000);

                // Create a TCP/IP  socket.
                Socket sender = new Socket(AddressFamily.InterNetwork,
                    SocketType.Stream, ProtocolType.Tcp);

                // Connect the socket to the remote endpoint. Catch any errors.
                try
                {
                    sender.Connect(remoteEP);

                    Console.WriteLine("Socket connected to {0}",
                        sender.RemoteEndPoint.ToString());

                    // Encode the data string into a byte array.
                    byte[] msg = Encoding.ASCII.GetBytes("This is a test<EOF>");

                    // Send the data through the socket.
                    int bytesSent = sender.Send(msg);

                    // Receive the response from the remote device.
                    int bytesRec = sender.Receive(bytes);
                    Console.WriteLine("Echoed test = {0}",
                        Encoding.ASCII.GetString(bytes, 0, bytesRec));

                    // Release the socket.
                    sender.Shutdown(SocketShutdown.Both);
                    sender.Close();

                }
                catch (ArgumentNullException ane)
                {
                    Console.WriteLine("ArgumentNullException : {0}", ane.ToString());
                }
                catch (SocketException se)
                {
                    Console.WriteLine("SocketException : {0}", se.ToString());
                }
                catch (Exception e)
                {
                    Console.WriteLine("Unexpected exception : {0}", e.ToString());
                }

            }
            catch (Exception e)
            {
                Console.WriteLine(e.ToString());
            }

            Console.WriteLine("\nPress ENTER to continue...");
            Console.Read();

        }
    }
}