C＃通过UDP接收

Question

I am writing a program that has to send data over UDP to a specific server (which works) and also receive data from that server (which doesn't work). The problem is, that the port i am sending data to is not the same that dat from the server come from.

Server: Listens on one port, creates new sockets (on different ports) for each client to send data.

I have the following code (client side):

socker = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);
IPEndPoint epLocal = new IPEndPoint(myIp, localPort);
socket.Bind(epLocal);
IPAddress ipAddressremote = IPAddress.Parse(remoteIp);
remoteEP = new IPEndPoint(ipAddressremote, port);
socket.Connect(remoteEP);

byte[] buffer = new byte[1024];
socket.BeginReceive(buffer, 0, buffer.Length, SocketFlags.None, new AsyncCallback(MessageCallBack), buffer);
socket.Send(someByteArray);

This successfully connects to my server application and sends the data it's supposed to. However, MessageCallBack never gets called:

private void MessageCallBack(IAsyncResult iAsyncResult)
{
byte[] receivedData = (byte[])iAsyncResult.AsyncState;
ASCIIEncoding eEncoding = new ASCIIEncoding();
string receievedMessage = eEncoding.GetString(receivedData);
handleMessage(receievedMessage);

byte[] buffer = new byte[1024];
socket.BeginReceive(buffer, 0, buffer.Length, SocketFlags.None, new AsyncCallback(MessageCallBack), buffer);
}

I think the problem is that the client socket is still connected to the port on the server, and only accepts data from that port, but to my knowledge this isn't a problem when using BeginReceive instead of BeginReceiveFrom.

Answer 1

When using UDP you can't use the Send and BeginReceive methods, because those are connection-oriented (TCP). Instead use the Socket.SendTo and Socket.BeginReceiveFrom. It should work using those methods.