How can I gracefully start my C# TCP client before I start my TCP server

Question

I am writing a fairly simple TCP/IP client application. I am able to successfully connect when I start the server (another seperate application) and then start the client in that order. I would like to make the client robust so that I can start it first and it doesnt break. Also I dont want a special user action to tell the client to try and connect. I'd also like to use non-blocking asynchronous IO on the client.

In order to try and accomplish this I have tried to use the Socket.BeginConnect method. My intention is that this call will spawn a background thread which would be blocked at the EndConnect call until a connection is established. This way my client can call this method at its startup and then continue operation. Here is my code:

public bool Init_Port(string Host)
    {
        IPHostEntry ipHostInfo = Dns.Resolve(Host);
        IPAddress ipAddress = ipHostInfo.AddressList[0];
        IPEndPoint localEndPoint = new IPEndPoint(ipAddress, PORT);

        try
        {
            //Create the connection
            My_Socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);

            My_Socket.BeginConnect(localEndPoint, new AsyncCallback(Connect_To_Port), My_Socket);

        }
        catch (Exception e)
        {
            ErrorHandler(e.Message);
            return false;
        }
        return true;
    }

    private void Connect_To_Port(IAsyncResult ar)
    {
        try
        {
            if (My_Socket != null)
            {
                //will block the thread until a connection is made
                My_Socket.EndConnect(ar);

                Connection_Flag = true;

                //Setup the asynchronous read
                My_Socket.BeginReceive(Rx_Buffer, 0, SOCKET_BUFFER_SIZE, 0,
                                                new AsyncCallback(Read_Port), My_Socket );
            }
        }
        catch (Exception e)
        {
            ErrorHandler(e.Message);
        }
    }

I test this without starting the server application. I am hoping that the thread will be blocked at the EndConnect until my server application is started. What I observe is that EndConnect returns immediately and that I get the error message

No connection could be made because the target machine actively refused it 127.0.0.1:50042

Can anyone tell me what I can do to make this asynchronous connect wait for the server application? Thanks in advance.

Answer 1

Can anyone tell me what I can do to make this asynchronous connect wait for the server application?

Nothing. YOu run it in a loop every X seconds until it starts or you get a logical timeout. TCP will not wait, you have to retry.

Answer 2

Just have the client connect on demand, when the code first needs a connection, according to what the user is doing. If the connection fails, tell the user he can't do that yet, whatever it was.