Sending data on UDP connection

Question

Hi!
Now that I've established a UDP P2P (peer-to-peer) connection with the remote device, I have to send data.

On a TCP connection (stream) I read the bytes of the file to send and send them on the stream.  The fact that when looking at the sniffer, I see that the data is broken into packets doesn't interest me - it gets successfully to the device.

TCP:
NetworkStream stream = tcpClient.GetStream();
if (stream.CanWrite)
{
    stream.Write(sendMsg, 0, sendLen);
    PutMessageOnForm("TCP: sent param len = " + sendLen);
}
stream.Close();

Using UDP, I tried something similar, and I got an error when I looked at the sniffer file that the data length is too big for a packet.  I guess I assumed that C# implementation of UDP would "know" how to break the data into packets.

UDP:
udpClient = new UdpClient(udpLocalPort);
udpClient.Send(sendMsg, sendLen, UDPremote);
PutMessageOnForm("UDP: sent param len = " + sendLen + " to " +
                            UDPremote.Address.ToString() +" on port " + UDPremote.Port.ToString());
udpClient.Close();

I'd appreciate any ideas about what the correct packet lengths should be and if C# can do it for me or do I have to break the data up manually.
Thanks!
Mechi

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Mechi

Answer 1

Mr. Blum gives us a great example of UDP communications:

/*
C# Network Programming 
by Richard Blum

Publisher: Sybex 
ISBN: 0782141765
*/
using System;
using System.Net;
using System.Net.Sockets;
using System.Text;

public class BestUdpClient
{
   private static byte[] data = new byte[1024];
   private static IPEndPoint sender = new IPEndPoint(IPAddress.Any, 0);
   private static EndPoint Remote = (EndPoint)sender;
   private static int size = 30;

   private static int AdvSndRcvData(Socket s, byte[] message, EndPoint rmtdevice)
   {
      int recv = 0;
      int retry = 0;

      while (true)
      {
         Console.WriteLine("Attempt #{0}", retry);
         try
         {
            s.SendTo(message, message.Length, SocketFlags.None, rmtdevice);
            data = new byte[size];
            recv = s.ReceiveFrom(data, ref Remote);
         } catch (SocketException e)
         {
            if (e.ErrorCode == 10054)
               recv = 0;
            else if (e.ErrorCode == 10040)
            {
               Console.WriteLine("Error receiving packet");
               size += 10;
               recv = 0;
            }
         }

         if (recv > 0)
         {
            return recv;
         } else
         {
            retry++;
            if (retry > 4)
            {
               return 0;
            }
         }
      }
   }

   public static void Main()
   {
      string input, stringData;
      int recv;
      IPEndPoint ipep = new IPEndPoint(
                      IPAddress.Parse("127.0.0.1"), 9050);

      Socket server = new Socket(AddressFamily.InterNetwork,
                     SocketType.Dgram, ProtocolType.Udp);

      int sockopt = (int)server.GetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReceiveTimeout);
      Console.WriteLine("Default timeout: {0}", sockopt);
      server.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReceiveTimeout, 3000);
      sockopt = (int)server.GetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ReceiveTimeout);
      Console.WriteLine("New timeout: {0}", sockopt);
 
      string welcome = "Hello, are you there?";
      data = Encoding.ASCII.GetBytes(welcome);

      recv = AdvSndRcvData(server, data, ipep);
      if (recv > 0)
      {
         stringData = Encoding.ASCII.GetString(data, 0, recv);
         Console.WriteLine(stringData);
      } else
      {
         Console.WriteLine("Unable to communicate with remote host");
         return;
      }

      while(true)
      {
         input = Console.ReadLine();
         if (input == "exit")
            break;
         recv = AdvSndRcvData(server, Encoding.ASCII.GetBytes(input), ipep);
         if (recv > 0)
         {
            stringData = Encoding.ASCII.GetString(data, 0, recv);
            Console.WriteLine(stringData);
         } else
            Console.WriteLine("Did not receive an answer");
      }
      Console.WriteLine("Stopping client");
      server.Close();
   }
}

    

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Javaman

Answer 2

Thanks!
I've seen this - I didn't really want to go down tot he socket level - but I guess i have no choice!
Mechi

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Mechi