Question

When I want to received UDP datagrams asynchronously, I write call BeginReceiveFrom of a System.Net.Sockets.Socket class. The BeginReceiveFrom method expects an Endpoint as the remoteEP parameter.

public IAsyncResult BeginReceiveFrom (
  byte[] buffer,
  int offset,
  int size,
  SocketFlags socketFlags,
  ref EndPoint remoteEP,
  AsyncCallback callback,
  Object state
)

This Method starts an asynchronous receive and cannot return any result in remoteEP since it returns immediately. Is this parameter for a kind of filtering or will it be modified on receive completion?

In the receive handler I call EndReceiveFrom, where I also have to pass a reference to an Enpoint object as the endPoint parameter.

public int EndReceiveFrom (
  IAsyncResult asyncResult,
  ref EndPoint endPoint
)

The EndReceiveFrom indicates with this Endpoint object the sender of the UDP frame. Why must I pass a remoteEP to the BeginReceiveFrom and can I avoid this?

Answer 1

There’s no overloads that do not require an endpoint, but that doesn’t mean you have to specify specific endpoints. You can specify any ip address as the remoteEP.

EndPoint remoteEP = (EndPoint)(new IPEndPoint(IPAddress.Any, 0));

EndReceiveFrom expects a pass by ref variable that will be populated by the method call itself. You can instantiate the endPoint similarly.

EndPoint receivedFromEP = new IPEndPoint(IPAddress.Any, 0);

After the call is made, simply ignore the value of receivedFromEP if you do not need it.