Question

I am trying to implement a class that can listen for incoming TCP data. I am trying to do so using tasks.

I have two central methods

    private async void ReceiveAsync()
    {
        while (true)
        {
            int bytesRead = await Receive();

            if (bytesRead > 0)
            {

                byte[] result = new byte[bytesRead];
                Buffer.BlockCopy(_buffer, 0, result, 0, bytesRead);

                Console.WriteLine(Encoding.UTF8.GetString(result));
            }
        }
    }

and

    private Task<int> Receive()
    {
            return Task.Run(() =>
            {
                if (sock.Poll(-1, SelectMode.SelectRead))
                    if (sock.Available > 0)
                        return sock.Receive(_buffer, _buffer.Length, SocketFlags.None);
                return -1;
            }
            );
    }

In my main program, I call ReceiveAsync() and then send some data down the TCP pipeline, to which the receiver responds. I do get this reply, but now I am caught in an endless loop inside the while(true), and further data sent from the “receiver” is not being received.

There is something completely wrong. What is it?

Answer 1

Try:

int bytesRead;
do {
    bytesRead = await Receive();

    if(bytesRead > 0) {...}
} while (bytesRead > 0);

i.e. use bytesRead as an exit condition.

Also: you can probably use async here very nicely:

// for illustration ONLY
TaskCompletionSource<int> source = new TaskCompletionSource<int>();
sock.BeginReceive(_buffer, 0, _buffer.Length, SocketFlags.None, ar =>
{
    try
    {
        int val = ((Socket)ar.AsyncState).EndReceive(ar);
        source.SetResult(val);
    }
    catch (Exception ex)
    {
        source.SetException(ex);
    }
}, sock);
return source.Task;