Question

I have an application that communicate through sockets using the *Async methods (like SendAsync). I’m getting this strange behavior where SendAsync is executed but the data is not sent over the wire.

I’ve enabled network tracing and got the following log:

System.Net.Sockets Verbose: 0 : [4300] Socket#5024928::SendAsync()
System.Net.Sockets Verbose: 0 : [4300] Socket#5024928::SendAsync(Boolean#1)
System.Net.Sockets Verbose: 0 : [7320] Data from Socket#5024928::FinishOperation(SendAsync)
System.Net.Sockets Verbose: 0 : [7320] 00000E8C : 01 99 27 00 00 00 01 00-00 00 00 00 00 00 00 00 : ..'.............
System.Net.Sockets Verbose: 0 : [7320] 00000E9C : 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 : ................
System.Net.Sockets Verbose: 0 : [7320] 00000EAC : 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 : ................
System.Net.Sockets Verbose: 0 : [7320] 00000EBC : 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 : ................
System.Net.Sockets Verbose: 0 : [7320] 00000ECC : 00 00 B3 F4                                     : ....
System.Net.Sockets Verbose: 0 : [7320] Socket#5024928::ReceiveAsync()
System.Net.Sockets Verbose: 0 : [7320] Exiting Socket#5024928::ReceiveAsync()   -> Boolean#1
System.Net.Sockets Error: 0 : [7320] Socket#5024928::UpdateStatusAfterSocketError() - TimedOut

Although the trace shows that the data was sent (and a receive timeout occurred), the data was not really sent. I’ve checked with Microsoft’s Network Monitor and there’s no log of this data being sent.

The send method is pretty straightfoward:

 public void Send(AsyncClientState state, byte[] data) {
            var socket = state.Socket;
            var dataTransferredEventArgs = new DataTransferredEventArgs(data, _maxBytes) { State = state };
            state.Events.RaiseBeforeSend(dataTransferredEventArgs);
            byte[] bytesToSend = dataTransferredEventArgs.Bytes.ToArray();
            SocketAsyncEventArgs args = GetSocketAsyncEventArgsArgs(socket, bytesToSend.Length);
            if (args == null) {
                state.Events.RaiseTimeout(Operation.Send);
                return;
            }
            args.Completed += SendCompleted;
            args.UserToken = state;
            Buffer.BlockCopy(bytesToSend, 0, args.Buffer, args.Offset, bytesToSend.Length);
            bool sendAsync = socket.SendAsync(args);
            if (!sendAsync) {
                SendCompleted(this, args);
            }
        }

        private void SendCompleted(object sender, SocketAsyncEventArgs e) {
            var state = (AsyncClientState) e.UserToken;
            var events = state.Events;
            try {
                if (e.SocketError != SocketError.Success) {
                    events.RaiseError(new ErrorEventArgs("(SendSocketError)" + e.SocketError));
                    return;
                }
                if (e.LastOperation == SocketAsyncOperation.Send) {
                    e.Completed -= SendCompleted;
                    _asyncEventArgsPool.PutBack(e);
                    events.RaiseAfterSend(new StateEventArgs(state));
                }
            }
            catch (ObjectDisposedException) { }
            catch (SocketException ex) {
                events.RaiseError(new ErrorEventArgs(string.Format("{0}: {1}", ex.SocketErrorCode, ex.Message)));
            }
        }

Am I missing something here? Is the network tracing really reliable?

UPDATE

I tried to use Begin/End*, but still the same problem. Here is the trace:

System.Net.Sockets Verbose: 0 : [6632] Socket#29357909::BeginSend()
System.Net.Sockets Verbose: 0 : [6632] Exiting Socket#29357909::BeginSend()     -> OverlappedAsyncResult#30136159
System.Net.Sockets Verbose: 0 : [6500] Data from Socket#29357909::PostCompletion
System.Net.Sockets Verbose: 0 : [6500] 00000000 : 01 99 27 00 00 00 01 00-00 00 00 00 00 00 00 00 : ..'.............
System.Net.Sockets Verbose: 0 : [6500] 00000010 : 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 : ................
System.Net.Sockets Verbose: 0 : [6500] 00000020 : 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 : ................
System.Net.Sockets Verbose: 0 : [6500] 00000030 : 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 : ................
System.Net.Sockets Verbose: 0 : [6500] 00000040 : 00 00 B3 F4                                     : ....
System.Net.Sockets Verbose: 0 : [6500] Socket#29357909::EndSend(OverlappedAsyncResult#30136159)
System.Net.Sockets Verbose: 0 : [6500] Exiting Socket#29357909::EndSend()   -> Int32#68
System.Net.Sockets Verbose: 0 : [6500] Socket#29357909::BeginReceive()
System.Net.Sockets Verbose: 0 : [6500] Exiting Socket#29357909::BeginReceive()  -> OverlappedAsyncResult#63504289
System.Net.Sockets Verbose: 0 : [6500] Socket#29357909::EndReceive(OverlappedAsyncResult#63504289)
System.Net.Sockets Error: 0 : [6500] Socket#29357909::UpdateStatusAfterSocketError() - TimedOut
System.Net.Sockets Error: 0 : [6500] Exception in Socket#29357909::EndReceive - A connection attempt failed because the connected party did not properly respond after a period of time or established connection failed because connected host has failed to respond.
System.Net.Sockets Verbose: 0 : [6500] Exiting Socket#29357909::EndReceive()    -> Int32#0

Answer 1

After talking to our network administrator, we found that the problem was a network misconfiguration. I’m not “into” networking but the problem was related to the fact that the equipment I was communicating were into our DMZ.