C#.NET - Detecting socket is closed

[tichi]

I'm writing a program that in its most simplest form acts as a proxy between a local client and a remote server. But I cannot figure out how to detect when either the connection to the client is close or the connection to the server is closed. I've tried looking at socket.connected - it always returns true, even when the client program has disconnected. I've tried getting an exception from the networkstream.DataAvailable, it always just reads false, and no exceptions. Anyone know how I can detect when these sockets are remotely closed??

TcpListener listener;
            TcpClient client;
            TcpClient server;
            while (true)
            {
                Thread.Sleep(10);
                IPAddress addy = IPAddress.Parse("127.0.0.1");
                listener = new TcpListener(addy, 4001);
                listener.Start();
                client = listener.AcceptTcpClient();
                Console.WriteLine("[[Client connected.]]");
                server = new TcpClient();
                server.Connect("imperian.com", 23);
                Console.WriteLine("[[Server connected.]]");
                NetworkStream cstm = client.GetStream();
                NetworkStream sstm = server.GetStream();
                bool quit = false;
                while (!quit)
                {
                    Thread.Sleep(10);
 
                    if (!client.Client.Connected)
                    {
                        Console.WriteLine("[[Client disconnected]]");
                    }
 
                    try
                    {
                        if (cstm.DataAvailable)
                        {
                            byte[] readBuffer = new byte[1024];
                            StringBuilder builder = new StringBuilder();
                            int numBytes = 0;
                            do
                            {
                                numBytes = cstm.Read(readBuffer, 0, readBuffer.Length);
                                builder.AppendFormat("{0}", Encoding.ASCII.GetString(readBuffer));
                            } while (cstm.DataAvailable);
 
                            byte[] writeBuffer = Encoding.ASCII.GetBytes(builder.ToString());
                            sstm.Write(writeBuffer, 0, writeBuffer.Length);
                        }
 
                        if (sstm.DataAvailable)
                        {
                            byte[] readBuffer = new byte[1024];
                            StringBuilder builder = new StringBuilder();
                            int numBytes = 0;
                            do
                            {
                                numBytes = sstm.Read(readBuffer, 0, readBuffer.Length);
                                builder.AppendFormat("{0}", Encoding.ASCII.GetString(readBuffer));
                            } while (sstm.DataAvailable);
 
                            byte[] writeBuffer = Encoding.ASCII.GetBytes(builder.ToString());
                            cstm.Write(writeBuffer, 0, writeBuffer.Length);
                        }
                    }
                    catch (Exception)
                    {
                        cstm.Close();
                        Console.WriteLine("[[Client disconnected.]]");
                        sstm.Close();
                        Console.WriteLine("[[Server disconnected.]]");
                        break;
                        quit = true;
                    }
                }
            }

[joedeene]

here is a link to a great response similar to your problem.

http://bytes.com/forum/thread234523.html

at the bottom of the linked page, it says something about the .poll() function of the socket class, i think that will help

[Plater]

I wrote this code and use it frequently:

bool SocketConnected(Socket s)
{
   bool part1 = s.Poll(1000, SelectMode.SelectRead);
   bool part2 = (s.Available == 0);
   if (part1 & part2)
   {//connection is closed
      return false;
   }
   return true;
}
 

[tichi]

Thank you so much, that worked!

[ddboarm]

I used that code and it works wonderfully...thanks a bunch!!!

[anhhuycan83]

to: Plater Plater
You are very good. After searching on google in many hours, but I can not find any working solutions. Now, I used that code and it works wonderfully...thanks a bunch!!!
good job!