Testing server whether it is reachable or not in c#

In client server development, we need this feature in many situations including:

• When client starts before server, it should periodically check whether server is UP or not. As soon as it gets server is up, it will connect with it to do its own business.
• Sometimes network between server and client can be broken and to reestablish this you can use reachability testing.

This technique can be used in WCF, .net remoting and socket programming. I have used this technique in several applications. Here testing reach ability is done by asynchronous socket programming with timeout for better performance. You can call isServerUp method at certain inteval according to your requirement. The following method checks whether server is reachable or not. If the server is reachable, It indicates that the network and server is ok and we can start doing business with server  

   1: public static bool isServerUp(string ip, int port, int timout)

   2:        {

   3:            IPAddress validIP;

   4:            if (IPAddress.TryParse(ip, out validIP))

   5:            {

   6:                IPEndPoint remoteEndPoint = new IPEndPoint(validIP, port);

   7:                bool fg = TimeOutSocket.Connect(remoteEndPoint, timout);

   8:                return fg;

   9:            }

  10:            else

  11:            {

  12:                return false;

  13:            }

  14:  

  15:        }

 You will notice that neither of the two classes, System.Net.Sockets.TcpClient nor System.Net.Sockets.Socket has a timeout to connect a socket. I mean a timeout you can set. .NET Sockets do not provide a Connect Timeout when calling the Connect or BeginConnectmethod while establishing a Synchronous or Asynchronous socket connection. Instead, connect is forced to wait a very long time before an Exception is thrown if the server it tried to connect to is not listening or if there is any network error. The default timeout is 20 - 30 seconds. There is an option in socket library named SocketOptionName.SendTimeout, which is used for timeouts on Send data not initial connects. To get this functionality, I have implemented the following class named TimeOutSocket.

   1: class TimeOutSocket

   2:    {

   3:        private static bool IsConnectionSuccessful = false;

   4:        private static Exception socketexception;

   5:        private static ManualResetEvent TimeoutObject = new ManualResetEvent(false);

   6:  

   7:  

   8:        public static  bool  Connect(IPEndPoint remoteEndPoint, int timeoutMSec)

   9:        {

  10:            TimeoutObject.Reset();

  11:            socketexception = null;  

  12:  

  13:            string serverip = Convert.ToString(remoteEndPoint.Address);

  14:            int serverport = remoteEndPoint.Port;           

  15:            TcpClient tcpclient = new TcpClient();

  16:        

  17:            tcpclient.BeginConnect(serverip, serverport, new AsyncCallback(CallBackMethod), tcpclient);

  18:  

  19:            if (TimeoutObject.WaitOne(timeoutMSec, false))

  20:            {

  21:                if (IsConnectionSuccessful)

  22:                {

  23:                    tcpclient.Close();

  24:                    return true;

  25:                }

  26:                else

  27:                {

  28:                    tcpclient.Close();

  29:                    return false;

  30:                }

  31:            }

  32:            else

  33:            {

  34:                tcpclient.Close();

  35:                return false;

  36:            }

  37:        }

  38:        private static void CallBackMethod(IAsyncResult asyncresult)

  39:        {

  40:            try

  41:            {

  42:                IsConnectionSuccessful = false;

  43:                TcpClient tcpclient = asyncresult.AsyncState as TcpClient;

  44:             

  45:                if (tcpclient.Client != null)

  46:                {

  47:                    tcpclient.EndConnect(asyncresult);

  48:                    IsConnectionSuccessful = true;

  49:                }

  50:            }

  51:            catch (Exception ex)

  52:            {

  53:                IsConnectionSuccessful = false;

  54:                socketexception = ex;

  55:            }

  56:            finally

  57:            {

  58:                TimeoutObject.Set();

  59:            }

  60:        }

  61:    }

Here ManualResetEvent plays the main role to implement this. It has a method WaitOne which has an overload WaitOne(TimeSpan,Boolean). According to MSDN, aitOne(TimeSpan, Boolean) blocks the current thread until the current instance receives a signal, using a TimeSpan to measure the time interval  and specifying whether to exit the synchronization domain before the wait.

So in the main thread, we call TimeoutObject.WaitOne(timeoutMSec, false) to block the main thread until timeout or till the signal has been  got using TimeoutObject.Set(). When waitone faces timeout, then it returns timeout exception. Otherwise socket is successfully connected or it faced any network error.

Here BeginConnect of tcpclient is used because this method does not block. After calling BeginConnect, we wait using waitone. If BeginConnect does not complete operation within timeout, then waitone will signal and TimeoutException is returned. IfBeginConnect does complete operation within timeout, then it will signal ManualResetEvent using TimeoutObject.Set() from theCallBackMethod which we passed as delegate in BeginInvoke that references the CallBackMethod to invoke when the operation is complete.

Thanks for reading this write up. I hope that this write up will be helpful for some people. If you guys have any questions, I would love to answer.