X11/Xlib: Grab key events and then pass them to sub-windows

Question

I'm tinkering with X11 using Go and Xlib (using cgo) and I'm trying to program basic window management functionalities, but I'm having problems with input management (keyboard in this case).

So far I've created a basic reparenting window manager where client windows (i.e. windows managed by this program) are wrapped within container windows created by this program. Container windows are direct children of root window and client windows are direct children of their container windows.

I'm trying to grab the entire keyboard and check if a key event is directed towards the window manager in order to process certain things. In case this key event is not something related to the window manager I would like to pass it along to client windows. I know that there is the option to select only specific keys or modifiers (using XGrabKey) for this matter (I was able to do it), but I would like to be able to grab the entire keyboard in this case.

So far I have the following code which doesn't work and keys are not passed to client windows.

...

C.XGrabKeyboard(
    display,
    rootWindow,
    0,
    C.GrabModeAsync,
    C.GrabModeAsync,
    C.CurrentTime,
)

...

for {
    var event C.XEvent
    C.XNextEvent(display, &event)

    eventType := (*C.int)(unsafe.Pointer(&event[0]))
    switch *eventType {
    ...

    case C.KeyPress:
        eventPayload := (*C.XKeyEvent)(unsafe.Pointer(&event[0]))

        // Value of eventPayload.root here equals rootWindow.
        // Value of eventPayload.window here equals rootWindow.
        // Value of eventPayload.subwindow here equals a ContainerWindow.

        if SOME_CONDITIONS_ARE_MET {
            // Key event is directed towards the window manager. Process this key event.
            ...
            continue
        }

        // Window manager has nothing to do with this key event. Pass it along.
        C.XAllowEvents(display, C.ReplayKeyboard, C.CurrentTime)

    ...
    }
}

It is worth mentioning that in this case I've used C.XSynchronize(display, 1) so calling XSync is no longer required. Also calling XFlush after XAllowEvents did not solve the problem either.

By the way I originally saw the XAllowEvents solution in this Stack Overflow question and this website.