UDP comm problem when switching from Sync to Async

I have a simple C#/.NET 3.5 client/server apps I am trying to write to get a handle on how to communicate in UDP. I am able to get the sync methods working and sending data back and forth, but now I am trying to switch to the async methods and I keep getting the error, "The requested address is not valid in it's context."

My Client code is as follows:

    IPEndPoint ipep = new IPEndPoint(ipaddr, ipport);
    newsock = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);

    EndPoint remote1 = (EndPoint)ipep;
    AddMessage("Looking for connections");
    byte[] strt = Encoding.ASCII.GetBytes("open");
    newsock.SendTo(strt,remote1);//.BeginSendTo(strt, 0, strt.Length, SocketFlags.None, remote1, new AsyncCallback(OnSend), null);
    IPEndPoint ipeSender = new IPEndPoint(IPAddress.Any, 0);
    EndPoint epSender = (EndPoint)ipeSender;
    newsock.ReceiveFrom(rcv, ref epSender);

My Server is more complicated, as I have already switched to Async communicat开发者_运维技巧ion.

In a worker thread I call:

  try
  {
    IPEndPoint sender = new IPEndPoint(IPAddress.Any, 0);
    EndPoint remote = (EndPoint)sender;
    AddMessage("Beginning Wait for connections");

    newsock.BeginReceiveFrom(rcv, 0, rcv.Length, SocketFlags.None, ref remote, new AsyncCallback(OnReceive), null);

    while (true)
    {
      if (pleasestop.WaitOne(20))
        break;
      ts = DateTime.Now - lastnoop;
      if (senddata)
      {
        //...fill sending byte array...

        IPEndPoint ipep = new IPEndPoint(IPAddress.Any,0);//ipaddr, ipport);
        EndPoint remote1 = (EndPoint)ipep;
        newsock.BeginSendTo(sending, 0, sending.Length, SocketFlags.None, remote1, new AsyncCallback(OnSend), null);
       }
    }

In my OnSend callback function is where I get the error: "The requested address is not valid in it's context."

private void OnSend(IAsyncResult ar)
{
  try
  {
      newsock.EndSendTo(ar);
  }
  catch (Exception ex)
  {
    MessageBox.Show(ex.Message + "\n" + ex.StackTrace, "Server Send Error");
  }
}

I dont think the object state can be null, try this:

newsock.BeginSendTo(sending, 0, sending.Length, SocketFlags.None, 
   remote1, new AsyncCallback(OnSend), newsock);

I found my problem. I wasn't using the correct EndPoint in my server to send a response back to my client.

In my receive callbackup function I now use mySender, which is a SendPoint defined at the class level. I then use this to send a response back to my client.

newsock.EndReceiveFrom(ar, ref mySender);

newsock.BeginSendTo(sending, 0, sending.Length, SocketFlags.None, mySender, new AsyncCallback(OnSend), mySender);

My app is now working correctly.