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, nul

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();
}