CODEWITHSUNDEEP
c#sockets
Laurie
Laurie

Reputation: 33

C# Sockets: accept a socket, ignore its message, send one back

We have a C# server that receives TCP messages using sockets. The normal flow is to call socket.Accept(), use socket.BeginReceive() and socket.EndReceive() to receive the message, then use socket.Send() to send a response. This works fine.

When too many requests come in at once, however, we want to reject the overflow immediately, so we don't overwhelm the server. It's easy enough to close the socket directly after Accept(); but that doesn't allow us to send a meaningful "too busy" message back to the client.

What I'd like to do is simply call Accept(), then call Send(), without receiving the incoming message. I have tried this, and the server claims to send my data, but my client receives nothing but an empty response. I have tried using both the synchronous Send() and the asynchronous BeginSend()/EndSend(), but neither gets the message back to the client.

Is it possible to send a message on an accepted socket without first receiving the incoming message? If so, is there a piece I'm missing to make it work?

Here's a code snippet showing what I'm trying to do:

        while (!_Done)
        {
            Socket socket = null;
            try
            {
                socket = _ListeningSocket.Accept();
            }
            catch (Exception) { }

            if (socket != null)
            {
                if (TooBusy())
                {
                    // My new code
                    byte[] send = GetTooBusyResponse();
                    int ret = socket.Send(send);
                    Console.WriteLine("socket.Send() returned " + ret);
                    socket.Close();
                    socket = null;
                }
                else
                {
                    // Existing, working code (using custom objects)
                    ClientConnection connection = new ClientConnection(this, socket, !_RequireAuthentication);
                    lock (_ConnectionsToken)
                        _Connections.Add(connection);
                    connection.BeginReceive();
                }
            }
        }

Upvotes: 3

Views: 1880

Answers (1)

GWLlosa
GWLlosa

Reputation: 24443

According to MSDN,

The Close method closes the remote host connection and releases all managed and unmanaged resources associated with the Socket. Upon closing, the Connected property is set to false.

For connection-oriented protocols, it is recommended that you call Shutdown before calling the Close method. This ensures that all data is sent and received on the connected socket before it is closed.

If you need to call Close without first calling Shutdown, you can ensure that data queued for outgoing transmission will be sent by setting the DontLinger Socket option to false and specifying a non-zero time-out interval. Close will then block until this data is sent or until the specified time-out expires. If you set DontLinger to false and specify a zero time-out interval, Close releases the connection and automatically discards outgoing queued data.

So either call Shutdown first, or set the DontLinger option to false and set a non-zero timeout.

Upvotes: 2

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