c# sockets read data and then reply

I am using the following code (built from answers to my previous questions on SO):

public void Start()
{
    listener = new TcpListener(IPAddress.Any, 9030);
    listener.Start();
    Console.WriteLine("Listening...");
    StartAccept();
}

private void StartAccept()
{        
    listener.BeginAcceptTcpClient(HandleAsyncConnection, listener);            
}

private void HandleAsyncConnection(IAsyncResult res)
{
    StartAccept();
    TcpClient client = listener.EndAcceptTcpClient(res);

    StringBuilder sb = new StringBuilder();
    var data = new byte[client.ReceiveBufferSize];

    using (NetworkStream ns = client.GetStre开发者_如何学编程am())
    {
        int readCount;
        while ((readCount = ns.Read(data, 0, client.ReceiveBufferSize)) != 0)
        {
            sb.Append(Encoding.UTF8.GetString(data, 0, readCount));
        }

        // Do work

        // Test reply
        Byte[] replyData = System.Text.Encoding.ASCII.GetBytes(DateTime.Now.ToString());
        ns.Write(replyData, 0, replyData.Length);
        ns.Flush();
        ns.Close();
    }

    client.Close();
}

The line "Do work" represents where I will do the required processing for my client.

However I can't see how to use this code to read the client's data and then reply to it. When using this code I can read perfectly what is sent by my client, however once that occurs the client locks up and eventually complains that the connection was terminated. It does not receive my reply.

Any ideas on how to fix this?

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Okay, first of all, you are mixing asynchronous calls (BeginAcceptTcpClient) and synchronous (Read and Write) calls. That completely kills the purpose of asynchronous code. Second, maybe this is why your socket gets closed ? Performing a sync op on an async socket. I'm not sure, but without the client code it's impossible to tell.

Anyway, this is NOT how you build an asynchronous, multi-client server.

Here is a fully asynchronous server implementation : http://msdn.microsoft.com/en-us/library/fx6588te.aspx

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i think you should use a length byte to alloc your buffer. ReceiveBufferSize could be called multiple times, i think there is no gurantee you receive everything in one block.

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You have misunderstood how Read works. It blocks until something is received from the other end point. The only time it returns 0 is when the other side have disconnected, hence you will continue reading until the other side disconnects.

When using TCP you need to know when a message ends. You can do that either by sending the message length first as a header or by using a suffix (as a line feed) after each message. Then you should keep reading until the complete message has arrived.