Receive from UDP Socket and send data back

Question

I'm trying to write a console application that takes a request (size is to be 18 bytes), and then send something (size of 7 bytes) back to the client. I for the life of me can't seem to get this to work. I can receive the data fine, but the data I send back never gets to the client.

Here is my code

 static void Main(string[] args)
 {
        // Data to return
        byte[] ret = { 0xfe, 0xfd, 0x09, 0x00, 0x00, 0x00, 0x00 };

        // tell the user that we are waiting
        Console.WriteLine("Waiting for UDP Connection...");

        // Create a new socket to listen from
        Socket Skt = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
        Skt.EnableBroadcast = true;
        Skt.Bind(new IPEndPoint(IPAddress.Loopback, 27900));

        try
        {
            // Blocks until a message returns on this socket from a remote host.
            Byte[] receiveBytes = new byte[48];
            IPEndPoint sender = new IPEndPoint(IPAddress.Any, 0);
            EndPoint senderRemote = (EndPoint)sender;

            Skt.ReceiveFrom(receiveBytes, ref senderRemote);
            string returnData = Encoding.UTF8.GetString(receiveBytes).Trim();

            Console.WriteLine("This is the message you received " + returnData.ToString());

            // Sent return data
            int sent = Skt.SendTo(ret, senderRemote);
            Console.WriteLine("Sent {0} bytes back", sent);
            Skt.Close();
        }
        catch (Exception e)
        {
            Console.WriteLine(e.ToString());
        }

        Console.ReadLine();
    }

Anyone give me some pointers please?

Answer 1

Here is the sample code i have modified and you can see you can receive and send from this sample. Method Test is acting as client which can be a different process now i have made it in different thread for simulation.

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

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            // Data to return
        byte[] ret = { 0xfe, 0xfd, 0x09, 0x00, 0x00, 0x00, 0x00 };

        // tell the user that we are waiting
        Console.WriteLine("Waiting for UDP Connection...");

        // Create a new socket to listen from
        Socket Skt = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
        Skt.EnableBroadcast = true;
        Skt.Bind(new IPEndPoint(IPAddress.Loopback, 27900));

        try
        {
            // Blocks until a message returns on this socket from a remote host.
            Byte[] receiveBytes = new byte[48];
            IPEndPoint sender = new IPEndPoint(IPAddress.Any, 0);
            EndPoint senderRemote = (EndPoint)sender;

            Thread thr = new Thread(new ThreadStart(Test));
            thr.Start();
            Skt.ReceiveFrom(receiveBytes, ref senderRemote);
            string returnData = Encoding.UTF8.GetString(receiveBytes).Trim();

            Console.WriteLine("This is the message you received " + returnData.ToString());

            // Sent return data
            int sent = Skt.SendTo(ret, senderRemote);
            Console.WriteLine("Sent {0} bytes back", sent);
            Skt.Close();
        }
        catch (Exception e)
        {
            Console.WriteLine(e.ToString());
        }

        Console.ReadLine();

        }



        public static void Test()
        {
            byte[] ret = { 0xfe, 0xfd, 0x09, 0x00, 0x00, 0x00, 0x00 };
            Socket Skt = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
            Skt.EnableBroadcast = true;
            IPEndPoint test=new IPEndPoint(IPAddress.Loopback, 27900);

            int sent = Skt.SendTo(ret, test);
            try
            {
                // Blocks until a message returns on this socket from a remote host.
                Byte[] receiveBytes = new byte[48];
                IPEndPoint sender = new IPEndPoint(IPAddress.Any, 0);
                EndPoint senderRemote = (EndPoint)sender;

                Skt.ReceiveFrom(receiveBytes, ref senderRemote);
                string returnData = Encoding.UTF8.GetString(receiveBytes).Trim();

                Console.WriteLine("This is the message you received " + returnData.ToString());

                // Sent return data
                //int sent = Skt.SendTo(ret, senderRemote);
                Console.WriteLine("Sent {0} bytes back", sent);
                Skt.Close();



            }
            catch (Exception ex)
            {
            }
        }

    }
}