Question

I had recently asked a related question In C# how do I have a socket continue to stay open and accept new data? and somewhat solved it, but now I’m having trouble getting my server to receive data from the same client more than once.

I have written a simple socket server using a windows form in VS that has a button that calls a receive function

public void Receive()
    {
        try
        {
            byte[] bytes = new byte[256];
            received = s1.Accept().Receive(bytes);
            receivedText.Text += System.Text.ASCIIEncoding.ASCII.GetString(bytes);
        }
        catch (SocketException e)
        {
            Console.WriteLine("{0} Error code: {1}.", e.Message, e.ErrorCode);
            return;
        }
    }

It works if the first time I send from my client, but if I try sending anything else and click on receive, my server just loops and never picks up the new data. However, if I send from somewhere else, or restart the connection from my client, I’m able to send data.

I would like to have my server able to receive any amount of data from the same client(s) at a time. Please ask if you need more code/details. Not sure what’s relevant as I’m pretty new to socket programming.

Answer 1

You must call Accept() only once per client, not every time you want to receive new data. Accept() basically waits for a client to connect to your server socket, s1 (and returns a new socket to send/receive data with this client), so here each time your Receive() function is called your socket waits for another client to connect, that’s why it works only once.

Here is an example (the code comes from your previous question) :

s1.Bind(endP);
s1.Listen(10);
Socket s2 = s1.Accept(); // Waits for a client to connect and return a socket, s2, to communicate with him
while (true) {
    Receive(s2);
}
...

Receive() function :

public void Receive(Socket s)
{
    try
    {
        byte[] bytes = new byte[256];
        received = s.Receive(bytes);
        receivedText.Text += System.Text.ASCIIEncoding.ASCII.GetString(bytes);
    }
    catch (SocketException e)
    {
        Console.WriteLine("{0} Error code: {1}.", e.Message, e.ErrorCode);
        return;
    }
}