How to grab keystrokes in Gnome Shell

Question

I'm trying to write my first Shell extension and - as every blog post out there - I am too struggling with the lack of up-to-date documentation...

Namely I am trying to grab all key strokes from the keyboard, and - looking at code online and old mailing list messages - it seems that until recently the correct way of doing was:

const Shell = imports.gi.Shell;
global.set_stage_input_mode(Shell.StageInputMode.FULLSCREEN);
global.stage.connect('key-press-event', myCallbackHere);

However this doesn't seem to work. Both the function set_stage_input_mode and the property StageInputMode seem to have gone, at least on my Fedora 24 running GTK 3.20.6.

What is the correct, current way to have my extension grabbing all keystrokes performed by the user?

Answer 1

I don't think there is a correct way to do this at the moment. You could hack something together that is either X specific or Wayland specific or maybe you could patch Gnome Shell to provide this information.

For Wayland you could start at https://github.com/MaartenBaert/wayland-keylogger and for X you could start by looking at reusing the key detection from autokey (https://github.com/autokey/autokey/blob/master/src/lib/interface.py).

I can guess this is not the answer you were hoping for, because on IRC you wrote that you want to write a replacement for autokey. For getting input from an external program you can use GLib.spawn_async_with_pipes (https://people.gnome.org/~gcampagna/docs/GLib-2.0/GLib.spawn_async_with_pipes.html).

I wrote some time ago some Shell extension code to poll xinput test and log roughly what's happening (think any alphanumeric key vs left ctrl vs return key). You can look at that code here: https://gist.github.com/daniellandau/7679741bf8bbc5c345591593ca05e9f6. It's not robust enough for doing any kind of macro expansion so I'd recommend reusing the detection code from autokey.

In general the docs at https://people.gnome.org/~gcampagna/docs are the place to find API references for libraries usable from Gnome Shell extensions. I hope you get ahead with your project. Starting out writing extensions is frustrating but eventually very fun once you get the hang of it.