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

General tip: in your exception handlers, incorporate the Exception.Message string into what you display, as it contains more specific information. — Daniel Earwicker
– Daniel Earwicker, Commented Mar 30, 2009 at 6:43

lc. · Accepted Answer · 2009-03-30 05:44:22Z

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

Send the data asynchronously from your connected callback method.
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.

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.

Dan Breslau · Accepted Answer · 2009-03-30 05:37:47Z

0

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

answered Mar 30, 2009 at 5:37

Dan Breslau

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1 Comment

Avik Over a year ago

I have made an asynchronous call for receiving messages.

xxbbcc · Accepted Answer · 2012-10-28 02:46:04Z

0

You can also use .Net Socket.Connect method it will block your code until connection. So, you don't need to use ManualResetEvent and calling WaitOne. And you can further use other socket asynchronous methods too.

edited Oct 28, 2012 at 2:46

xxbbcc

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answered Mar 11, 2012 at 17:21

varun

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