Avoid interrupting keyboard input while handling a keypress. How?

[Mystic-Mirage]

Hey!

I'm playing around with a keylogger-like example keypress-english and noticed that in root mode it intercepts all keyboard input so all applications don't receive any key events until the program exits.

I want to rewrite my old layout-switcher from Python to Go. So I need to log keyboard events without interrupting keyboard input.

How do you pass events further but keep logging them?

[jezek]

I don't know the answer, but I asked ChatGPT for you. Here's the reply:

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The basic issue is that “grabbing” the keyboard – whether explicitly (via XGrabKeyboard) or indirectly (by using an event‐hook that “steals” events) – causes the X server not to deliver those key events to other clients. To log keys without “eating” them, you have two general options:

1. Avoid an active grab altogether:
    • Instead of using a keyboard grab (or a synchronous grab), use a noninvasive method to monitor events. In X you can do this with the XRecord extension. XRecord lets you “snoop” on all key events without interfering with their normal delivery. This is the preferred approach for a keylogger that doesn’t want to disrupt normal input.

2. Forward events manually after logging them:
    • If you must use a grab (for example, because you’re working within an existing framework that only offers grab‐style callbacks), then after logging the event you need to “allow” the event to continue its normal journey. With the X protocol you do that by calling a function such as XAllowEvents (from the Xlib API) or the corresponding method in your Go binding. For instance, when using xgbutil in a synchronous grab (or when your event hook is “in the way”), you should invoke something like
     xproto.AllowEvents(xu.Conn(), xproto.AsyncKeyboard, currentTime)
    after you log the event. This call tells the X server to resume normal event processing (allowing the keyboard event to be re‐emitted to its original destination).

In short, the “solution” is to either use a passive (noninvasive) approach like XRecord or, if you must grab, then explicitly allow events to continue by calling the appropriate function (e.g. XAllowEvents) after you log each key. This way, your program both logs the event and then “passes it along” to the rest of the system.

For more details on how to use XAllowEvents with xgbutil, see the discussion in the xgbutil documentation and examples (for instance, note how the CallbackMouse’s synchronous grab requires you to call xproto.AllowEvents to avoid locking up the event loop https://pkg.go.dev/github.com/alex11br/xgbutil).

I hope this helps clarify the options available for logging key events without disrupting normal input!

chat link

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Was this helpfull?

[Mystic-Mirage]

Thank you. ChatGPT is the first thing I've tried.
Still, I can't get the answer it gives to work:

Here is the code:

package main

import (
	"log"
	"time"

	"github.com/jezek/xgb/xproto"

	"github.com/jezek/xgbutil"
	"github.com/jezek/xgbutil/keybind"
	"github.com/jezek/xgbutil/xevent"
)

func main() {
	X, err := xgbutil.NewConn()
	if err != nil {
		log.Fatal(err)
	}

	keybind.Initialize(X)

	xevent.KeyPressFun(
		func(X *xgbutil.XUtil, e xevent.KeyPressEvent) {
			modStr := keybind.ModifierString(e.State)
			keyStr := keybind.LookupString(X, e.State, e.Detail)
			if len(modStr) > 0 {
				log.Printf("Key: %s-%s\n", modStr, keyStr)
			} else {
				log.Println("Key:", keyStr)
			}

			if keybind.KeyMatch(X, "Escape", e.State, e.Detail) {
				if e.State&xproto.ModMaskControl > 0 {
					log.Println("Control-Escape detected. Quitting...")
					xevent.Quit(X)
				}
			}
			// xevent.SendRootEvent(X, e, xproto.EventMaskKeyPress)
			xproto.AllowEvents(X.Conn(), xproto.AllowAsyncKeyboard, e.Time)
		}).Connect(X, X.RootWin())

	if err := keybind.GrabKeyboard(X, X.RootWin()); err != nil {
		log.Fatalf("Could not grab keyboard: %s", err)
	}

	xevent.Main(X)
}

Can anyone who has better brain understanding than me try it?