Question

I’m trying to set up some Network stuff. For this reason I need to send and receive data over network. In particular HTTP-Messages. I want to implement this with asynchronous Methods in C#. When im receiving the HTTP-Response from a Webserver, I want to receive data until the webserver closed the connection or (connection: keep alive) until i received all bytes of the HTTP-Response. I already tried to set this up method but failed. Can you tell me how to implement this. I’ve seen this example on msdn:

    private static void Receive(Socket client) {
    try {
        // Create the state object.
        StateObject state = new StateObject();
        state.workSocket = client;

        // Begin receiving the data from the remote device.
        client.BeginReceive( state.buffer, 0, StateObject.BufferSize, 0,
            new AsyncCallback(ReceiveCallback), state);
    } catch (Exception e) {
        Console.WriteLine(e.ToString());
    }
}

private static void ReceiveCallback( IAsyncResult ar ) {
    try {
        // Retrieve the state object and the client socket 
        // from the asynchronous state object.
        StateObject state = (StateObject) ar.AsyncState;
        Socket client = state.workSocket;

        // Read data from the remote device.
        int bytesRead = client.EndReceive(ar);

        if (bytesRead > 0) {
            // There might be more data, so store the data received so far.
        state.sb.Append(Encoding.ASCII.GetString(state.buffer,0,bytesRead));

            // Get the rest of the data.
            client.BeginReceive(state.buffer,0,StateObject.BufferSize,0,
                new AsyncCallback(ReceiveCallback), state);
        } else {
            // All the data has arrived; put it in response.
            if (state.sb.Length > 1) {
                response = state.sb.ToString();
            }
            // Signal that all bytes have been received.
            receiveDone.Set();
        }
    } catch (Exception e) {
        Console.WriteLine(e.ToString());
    }
}

With the State Object:

public class StateObject {
// Client socket.
public Socket workSocket = null;
// Size of receive buffer.
public const int BufferSize = 256;
// Receive buffer.
public byte[] buffer = new byte[BufferSize];
// Received data string.
public StringBuilder sb = new StringBuilder();
}

If I would use similar code to this, I’m afraid to run into horrible sideeffects because all Threads use the same state-object. Furthermore, I have to resend the data received data immediately.

Answer 1

I tried to implement the asynchronous Receive method. Well, its not finished yet, but the basic structure should be clear.

private void BeginReceiveFromWebserver(ClientSocket clientSocket)
    {
        try
        {
            clientSocket.CommunicationSocket.BeginReceive(clientSocket.Buffer, 0, clientSocket.Buffer.Length,
                                                         SocketFlags.None, new AsyncCallback(ReceiveFromWebserverCallback), clientSocket);

        }
        catch (Exception e)
        {
            Console.WriteLine(e.Message + "\nfrom Source: " + e.Source + "\nand Stack Trace: " + e.StackTrace);
            //XXX TODO
        }
    }

    private void ReceiveFromWebserverCallback(IAsyncResult ar)
    {            
        ClientSocket clientSocket = ar.AsyncState as ClientSocket;

        try
        {
            int bytesRead = clientSocket.CommunicationSocket.EndReceive(ar);

            if (bytesRead > 0)
            {
                if(!clientSocket.AllBytesReceived)
                {
                    // No locks needed here, because it works like a loop
                    clientSocket.TotalBytesReceived+=bytesRead;
                    clientSocket.BufferUsed++;
                    clientSocket.AddBuffer();
                    clientSocket.SendingToBrowserCompleted.WaitOne();
                    BeginSend(clientSocket, bytesRead);
                    clientSocket.CommunicationSocket.BeginReceive(clientSocket.Buffer, 0, clientSocket.Buffer.Length,
                                                        SocketFlags.None, new AsyncCallback(ReceiveFromWebserverCallback), clientSocket);
                }
                else
                {
                    // all bytes Received
                }
            }
            else
            {
                Console.WriteLine("Webserver Closed Connection");
                //XXX TODO, Webserver closed the Connection
            }
        }
        catch (Exception e)
        {
            Console.WriteLine(e.Message + "\nfrom Source: " + e.Source + "\nand Stack Trace: " + e.StackTrace);
            //XXX TODO
        }
    }

Every peace of the message received, is resendet to Browser. To ensure that the Browser gets those peaces in the right order, I’ve got the SendingToBrowserCompleted-AutoResetEvent here. If your interested in more code, just ask.