Question

I am getting into trouble with this part of code.
In fact I want to set a Client/Server Application.
In the client part I launch a Thread which function is only to check everytime if it is connected to the server (if the connection to the server is still established)
TraceLog is a class that uses its Info() method to write in a file.
this is is the client code :

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Net.Sockets;
using System.Net;
using System.Threading;
using System.IO;

namespace ClientApp
{
    class ClientOpenConnection
    {
        private static Thread threadConnect;
        static TcpClient myClient = new TcpClient();
        static String host = "";
        static Int32 port = 0;

        //Function that makes the client runs
        public static void RunClient(String hostname, Int32 hostport)
        {
            host = hostname;
            port = hostport;
            int _tryAgain = 0;

            while (!myClient.Connected) {
                try
                {   //I start the connection
                    myClient.Connect(host, port);
                }
                catch {

                }
                _tryAgain += 10;
                if (_tryAgain == 1000)
                    break;
                 //_tryAgain allows me to define how long will the client try to connect to the server.
            }
            TraceLog.Info("Out of the while ", ""); // This is to know where am I

            if (_tryAgain != 1000)
            {    //If I get out because _tryAgain is less than 1000. It means that I am already connected to the server
                //Here I start a Thread to be sure that I am always connected to the server
                threadConnect = new Thread(isConnected);
                threadConnect.Start();
                TraceLog.Info("Launch the thread","");
            }
            //While threadConnect is executing parallely I continue my program
        }

        private static void isConnected() { 
            //I keep my eyes on the network connection
            while (myClient.Connected) { 
                //Nothing is done
            }
            TraceLog.Info("The connection has been lost","");
            RunClient(host,port);
        }
    }
}

The problem that I am having, when I start the client before the server I enter the first WHILE loop. it is OK at this level.
and when I start the server after, I launch the threadConnect but the problem is that if now I stop the server, normally i should have inside the log file “The connection has been lost” but I have nothing.
What is wrong with this part of code?
Have you already done something like this in the past?

I come with a modification but still having problem to obtain what I want, ie the client still get trying to contact the server eveytime even if the server is stopped .

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Net.Sockets;
using System.Net;
using System.Threading;
using System.IO;

namespace ClientApp
{
    class ClientOpenConnection
    {
        private static Thread threadConnect;
        static TcpClient myClient = new TcpClient();
        static String host = "";
        static Int32 port = 0;

        //Function that makes the client runs
        public static void RunClient(String hostname, Int32 hostport)
        {
            host = hostname;
            port = hostport;

            TraceLog.Info(" -> "+myClient.Connected,"");

            while (!myClient.Connected) {
                try
                {
                    myClient.Connect(host, port);
                    TraceLog.Info(" <-> " + myClient.Connected, "");
                }
                catch {
                    TraceLog.Info("Trying to contact the server","");
                }
            }
            TraceLog.Info("I am connected ", "");

            //Here I start a Thread to be sure that I am always connected to the server
            threadConnect = new Thread(isConnected);
            threadConnect.Start();
            TraceLog.Info("Launch the thread to be sure I am constantly online","");
        }

        private static void isConnected() { 
            //I keep my eyes on the network connection
            TraceLog.Info("->>"+myClient.Connected,"");
            while (myClient.Connected) {

                Thread.Sleep(500);

                try
                {
                    NetworkStream stream = myClient.GetStream();

                    ASCIIEncoding ascii = new ASCIIEncoding();

                    byte[] _incomingMsg = new byte[1024];

                    stream.Read(_incomingMsg, 0, _incomingMsg.Length);

                    String strToGet = System.Text.Encoding.ASCII.GetString(_incomingMsg);

                    strToGet = strToGet.Trim();

                    if (!strToGet.Equals("ONLINE"))
                        if (strToGet.Equals(""))
                        {
                            TraceLog.Info("The message receive is empty","");
                            break;
                        }
                }
                catch {
                    break;
                }
            }          
            TraceLog.Info("The connection has been lost", "");
            RunClient(host, port);
        }
    }
}

But when I call the RunClient() in the isConnected() function it executes in the WHILE and output TraceLog.Info(“Trying to contact the server”,””); even if I start the server again, the client remains in the while loop and never connects at all.

Answer 1

From MSDN:

The Connected property gets the connection state of the Client socket
as of the last I/O operation. When it returns false, the Client socket
was either never connected, or is no longer connected.

Because the Connected property only reflects the state of the
connection as of the most recent operation, you should attempt to send
or receive a message to determine the current state. After the message
send fails, this property no longer returns true. Note that this
behavior is by design. You cannot reliably test the state of the
connection because, in the time between the test and a send/receive,
the connection could have been lost. Your code should assume the
socket is connected, and gracefully handle failed transmissions.

In other words, in order to check if you are still connected, you need to send or receive some data and then check the connection state.

Since your code doesn’t send any packets after the connection is made, the connected property always returns true, and the loop never exits.