Why IAsyncResult report all port as opened?

Question

i have this method running in a thread , but when i test it report all ports as open. it seems that the method : var result = client.BeginConnect(host, port, null, null); don't working well when passing the results in var success = result.AsyncWaitHandle.WaitOne(tcpTimeout); ...

Any idea how to solve that ?

I have tried client.ConnectAsync(host,port).Wait(TcpTimeout); but this is not working as expected too ....

    public void start()
    {
        Thread thread1 = new Thread(new ThreadStart(RunScanTcp));
        thread1.IsBackground = true;
        thread1.Name = "THREAD ME EMER : " + i;
        thread1.Priority = System.Threading.ThreadPriority.Highest;
        thread1.Start();
   }


public void RunScanTcp()
{
        while (((port = portList.NextPort()) != -1) && (nderprit != true))
        {
            TcpClient client = new TcpClient();
            count = port;
            tcp_count = tcp_count + 1;
            Thread.Sleep(10);
            try
            {
                var mre = new ManualResetEvent(false);
                Console.WriteLine("Current port count : " + port);
                var result = client.BeginConnect(host, port, null, null);
                var success = result.AsyncWaitHandle.WaitOne(tcpTimeout);
                if (success)
                {
                    Console.WriteLine("PORT IS OPEN : " + port);
                    received_tcp = received_tcp + 1;
                    Activity.RunOnUiThread(() =>
                    {

                        mre.Set();
                    });
                    mre.WaitOne();
                    client.Close();
                }
                else
                {
                    client.Close();
                }
            }
            catch (Exception)
            {
                client.Close();
            }
        }
}

Answer 1

Determine if the port is open based upon a non-Exception when executing EndConnect.

Example of a serial port scan:

Note: Use some Linq to break your port list into groups and perform a Parallel.ForEach if you wish to scan multiple ports at the same time (a concurrency of 4 works well and does not overwhelm the Android network stack).

bool portOpen;
for (int portNo = 1; portNo < (fasttScan ? 1025 : 65537); portNo++)
{
    TcpClient client = new TcpClient
    {
        SendTimeout = (fasttScan ? 2 : 10),
        ReceiveTimeout = (fasttScan ? 2 : 10)
    };
    var tcpClientASyncResult = client.BeginConnect(ipAddress, portNo, asyncResult =>
    {
        portOpen = false;
        try
        {
            client.EndConnect(asyncResult);
            portOpen = true;
        }
        catch (SocketException)
        {
        }
        catch (NullReferenceException)
        {
        }
        catch (ObjectDisposedException)
        {
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.Message); // ? unknown socket failure ?
        }
        if (portOpen)
            Console.WriteLine($"{ipAddress}:{portNo}:{portOpen}");
        client.Dispose();
        client = null;
    }, null);
    tcpClientASyncResult.AsyncWaitHandle.WaitOne();
}