Question

I have an asynchronous read method…

private void read(IAsyncResult ar) {
        //Get the Server State Object
        ServerState state = (ServerState)ar.AsyncState;

        //read from the socket
        int readCount = state.socket.EndReceive(ar);

        //check if reading is done, move on if so, trigger another read if not
        if (readCount > 0) {
            //purge the buffer and start another read
            state.purgeBuffer();
            state.socket.BeginReceive(state.buffer, 0, ServerState.bufferSize, 0, new AsyncCallback(read), state);
        }
        else {
            //all bytes have been read, dispatch the message
            dispatch(state);
        }
    }

The problem that I am having is that read is only 0 if the connection is closed. How do I say, this is the end of that message and pass the data on to the dispatcher, while leaving the socket open to accept new messages.

Thank you!

Answer 1

You should not rely on what is in the TCP buffer. You must process the incoming bytes as a stream somewhere. You can’t really know whether its complete. Only one layer above can know when the message completed.

Example:
If you read HTTP responses the HTTP header will contain the byte count which is in the HTTP body. So you know how much to read.

You only know how much to read if the data follows a certain protocol and you interprete it. Imagine you receive a file over the socket. The first thing you would receive is the file size. Without that you would never know how much to read.