Socket Programming

Question

In simulation of a lan-messenger in c# I am using the loopback address just for starters to check the functionality of the code.However after sending a few messages, I am getting a socket exception while using the end-connect method and then a socket exception while sending the data. Is there any reason behind this exception.

    private void button1_Click(object sender, EventArgs e)
    {

        HideCaret(this.textBox1.Handle);
        StringBuilder sb = new StringBuilder(this.textBox1.Text);
        str = this.textBox2.Text;
        Socket newsock = new Socket(AddressFamily.InterNetwork,socketType.Stream,   ProtocolType.Tcp);
        IPEndPoint ip = new IPEndPoint(localaddress, 5555);
        newsock.BeginConnect(ip, new AsyncCallback(connected), newsock);
        if (str != "")
        {
            sb.AppendLine(this.textBox2.Text);
            this.textBox1.Text = sb.ToString();
            this.textBox2.Text = "\0";
            send = Encoding.ASCII.GetBytes(str);
            try
            {
                newsock.BeginSend(send, 0, send.Length, SocketFlags.None, new AsyncCallback(sent), newsock);
            }
            catch (ArgumentException)
            {
                MessageBox.Show("arguments incorrect in begin-send call", "Error", MessageBoxButtons.OK);
            }
            catch (SocketException)
            {
                MessageBox.Show("error in accessing socket while sending", "Error", MessageBoxButtons.OK);
            }
            catch (ObjectDisposedException)
            {
                MessageBox.Show("socket closed while sending", "Error", MessageBoxButtons.OK);
            }
            catch (Exception)
            {
                MessageBox.Show("error while sending", "Error", MessageBoxButtons.OK);
            }

        }                                 

    }

Please help

Answer 1

Do you have a separate thread reading from the socket? If not, your socket buffers are probably filling up.

Answer 2

It's possibly because you're not waiting for the socket to be connected before sending data. You have two options:

1. Send the data asynchronously from your connected callback method.
2. Send the data synchronously by blocking this thread until connected.

You accomplish #1 by combining the data to send and the socket into a new class, then passing that as state in your call to BeginConnect. Then move your send code to the callback method.

You accomplish #2 by setting up a System.Threading.ManualResetEvent and calling WaitOne after BeginConnect. Then call EndConnect in your connected callback method, followed by a Set on your ManualResetEvent. Then proceed to send as you have above.

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You'll also probably learn more if you find out what kind of SocketException you're getting.

From the MSDN Documentation:

If you receive a SocketException, use the SocketException.ErrorCode property to obtain the specific error code. After you have obtained this code, refer to the Windows Sockets version 2 API error code documentation in the MSDN library for a detailed description of the error.