Check if port is open to connect to in a thread?

Question

How would I check if a tcp port is available in a thread? I tried using a background worker thread, and it worked, but updated rather slowly. I want to report progress to my UI thread. Is this a correct way?

    BackgroundWorker authStatus = new BackgroundWorker {WorkerReportsProgress = true};
    authStatus.DoWork += AuthStatusWork;
    authStatus.ProgressChanged += AuthStatusProgressChanged;

    public void AuthStatusWork(object sender, EventArgs e)
    {
        var thread = sender as BackgroundWorker;

        using (var socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp))
        {
            socket.SendTimeout = 3;
            while (true)
            {
                try
                {
                    socket.Connect(auth[0], Convert.ToInt32(auth[1]));
                    if (thread != null) thread.ReportProgress(1);
                }
                catch (SocketException ex)
                {
                    if (ex.SocketErrorCode != SocketError.ConnectionRefused &&
                        ex.SocketErrorCode != SocketError.TimedOut) continue;
                    if (thread != null) thread.ReportProgress(0);
                }
            }
        }
    }

    public void AuthStatusProgressChanged(object sender, ProgressChangedEventArgs e)
    {
        switch (e.ProgressPercentage)
        {
            case 0:
                AuthStatus.Foreground = Brushes.Red;
                AuthStatus.Content = "Offline";
                break;
            case 1:
                AuthStatus.Foreground = Brushes.Green;
                AuthStatus.Content = "Online";
                break;
        }
    }

Have you seen this question? http://stackoverflow.com/questions/570098/in-c-how-to-check-if-a-tcp-port-is-available — fassetar, Aug 16 '13 at 03:11
I'm trying to check a remote server's port to see whether or not it is available to connect to. — Tristan McPherson, Aug 16 '13 at 03:22
@TristanMcPherson you should reword your question so it doesn't sound like you're trying to check a local port. "available" usually means to bind to, not to connect to. All you want to do is an async connect. There's tons of resources about how to do that. You don't even need (or want) a thread to do this correctly. — xaxxon, Aug 16 '13 at 03:46
@TristanMcPherson I'm not a c# person, but in general, the best way to do anything to an arbitrarily large number of sockets is asynchronous calls -- in this case you're basically writing a port scanner and you want to use asynchronous connects. — xaxxon, Aug 16 '13 at 03:50

score 2 · Accepted Answer · answered Aug 16 '13 at 03:50

2

Use asynchronous connections, as demonstrated here here

This will allow you to attempt to connect to as many remote tcp ports as you want and let you know when it succeeds or fails. You don't have to worry about how many threads you've started or running out of resources (other than sockets, which is a problem no matter what approach you take).

answered Aug 16 '13 at 03:50

xaxxon

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I have read the article, but cannot figure out when the connection is actually made, and when to signal to my UI thread that it has been. – Tristan McPherson Aug 16 '13 at 04:21

score 0 · Answer 2 · answered Aug 16 '13 at 09:42

0

I'm trying to check a remote server's port to see whether or not it is available to connect to.

So try to connect to it. These games of trying to predict the future in some way are pointless. Try the connection and handle the error. This applies to any resource: the best way to see if any resource is available is to try to use it.

answered Aug 16 '13 at 09:42

user207421

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Exactly, I agree, so how do I do it? – Tristan McPherson Aug 16 '13 at 10:53

Check if port is open to connect to in a thread?

2 Answers2