Issue with WH_KEYBOARD_LL Hook and getUserMedia Interaction

[leeroy]

We have implemented a low-level keyboard hook in our CEF application to monitor specific keyboard input events, especially to intercept and process Windows key events.

Hook Setup:

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SetWindowsHookExA(WH_KEYBOARD_LL, KeyManager::LowLevelKeyboardProc, m_hinstance, 0);

LRESULT CALLBACK KeyManager::LowLevelKeyboardProc(int nCode, WPARAM wParam, LPARAM lParam) {
  LOG(INFO) << "LowLevelKeyboardProc: nCode: " << nCode << ", wParam: " << wParam << ", lParam: " << lParam;
  // Logic to block windows key and other processing...
}


This approach has been working seamlessly until we encountered web pages that make a call to getUserMedia:

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navigator.mediaDevices.getUserMedia({ audio: true });


Upon invoking getUserMedia, we observe that the LowLevelKeyboardProc callback is not triggered as long as CEF retains focus. However, when the focus is shifted away from the CEF window, the callback works as expected.

I've been considering alternatives like OnPreKeyEvent in CEF, but I'm not fully versed with its implementation, especially for trapping specific keys like the Windows key.

Environment:

Windows Versions: 10/11
Observed in CEF Versions: 5672, 5845 (There might be more affected versions)

Any insights or workarounds to address this interaction would be greatly appreciated.

[amaitland]

Sounds similar to https://github.com/chromiumembedded/cef/issues/2609

[leeroy]

Thank you amaitland, that certainly looks like the issue! Is there no other way to achieve this functionality without having to remove this from the chromium source?

[HarmlessDave]

When we looked at the chromium source a couple of years ago it seemed to be grabbing raw input, so you would need to patch the source to prevent that and deal with any side effects. We chose not to do that, but I would not be surprised if it breaks something like the player controls for a video widget.

[amaitland]

CefKeyboardHandler is the supported option for key press interception in CEF.

[leeroy]

Thanks amaitland and HarmlessDave. For whatever reason I can seem to get OnPreKeyEvent working and identify the windows key, but I cannot seem to consume it by returning true. Is there more to this formula I'm missing?

[leeroy]

In the OnPreKeyEvent handler, I've implemented code to intercept the Windows key. While it successfully logs the keystroke, it fails to block the key's default action. I gather I'm missing a critical step somewhere?

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if (event.type == KEYEVENT_RAWKEYDOWN || event.type == KEYEVENT_KEYDOWN) {
    if (event.windows_key_code == VK_LWIN  || // 0x5B
        event.windows_key_code == VK_RWIN) { // 0x5C
      LOG(INFO) << "!!!!! WINDOW KEY PRESSED";
      return true;
    }
  }


[KatrinaS]

I think it may count as a 'is_keyboard_shortcut', so set bool* is_keyboard_shortcut to true, return false, and handle it (return true) in OnKeyEvent instead,, it's worth a go anyway

[leeroy]

Thank you for your suggestion, KatrinaS. Unfortunately, it didn't resolve the issue either.

[KatrinaS]

It's hard to know if this problem is a bug or a feature, the *.h says bing but the outcome is actually bong, very strange