fix: recover disabled macOS event taps

src/macos/listen.rs

@@ -2,16 +2,25 @@
 use crate::macos::common::*;
 use crate::rdev::{Event, ListenError};
 use core::ptr::NonNull;
-use objc2_core_foundation::{CFMachPort, CFRunLoop, kCFRunLoopCommonModes};
+use objc2_core_foundation::{CFMachPort, CFRetained, CFRunLoop, kCFRunLoopCommonModes};
 use objc2_core_graphics::{
     CGEvent, CGEventTapCallBack, CGEventTapLocation, CGEventTapOptions, CGEventTapPlacement,
     CGEventTapProxy, CGEventType, kCGEventMaskForAllEvents,
 };
 use objc2_foundation::NSAutoreleasePool;
 use std::ffi::c_void;
-use std::ptr::null_mut;
 
-static mut GLOBAL_CALLBACK: Option<Box<dyn FnMut(Event)>> = None;
+struct EventTapContext {
+    callback: Box<dyn FnMut(Event)>,
+    tap: Option<CFRetained<CFMachPort>>,
+}
+
+fn is_tap_disabled_event(event_type: CGEventType) -> bool {
+    matches!(
+        event_type,
+        CGEventType::TapDisabledByTimeout | CGEventType::TapDisabledByUserInput
+    )
+}
 
 #[link(name = "Cocoa", kind = "framework")]
 unsafe extern "C" {}
@@ -20,18 +29,22 @@ unsafe extern "C-unwind" fn raw_callback(
     _proxy: CGEventTapProxy,
     event_type: CGEventType,
     cg_event: NonNull<CGEvent>,
-    _user_info: *mut c_void,
+    user_info: *mut c_void,
 ) -> *mut CGEvent {
+    let context = unsafe { &mut *user_info.cast::<EventTapContext>() };
+    if is_tap_disabled_event(event_type) {
+        if let Some(tap) = context.tap.as_deref() {
+            CGEvent::tap_enable(tap, true);
+            eprintln!("rdev: macOS event tap was disabled ({event_type:?}); re-enabled");
+        }
+        return cg_event.as_ptr();
+    }
+
     let opt = KEYBOARD_STATE.lock();
     if let Ok(mut keyboard) = opt {
         unsafe {
             if let Some(event) = convert(event_type, cg_event, &mut keyboard) {
-                // Reborrowing the global callback pointer.
-                // Totally UB. but not sure there's a great alternative.
-                let ptr = &raw mut GLOBAL_CALLBACK;
-                if let Some(callback) = &mut *ptr {
-                    callback(event);
-                }
+                (context.callback)(event);
             }
         }
     }
@@ -43,18 +56,22 @@ where
     T: FnMut(Event) + 'static,
 {
     unsafe {
-        GLOBAL_CALLBACK = Some(Box::new(callback));
         let _pool = NSAutoreleasePool::new();
-        let callback: CGEventTapCallBack = Some(raw_callback);
+        let raw_callback: CGEventTapCallBack = Some(raw_callback);
+        let mut context = Box::new(EventTapContext {
+            callback: Box::new(callback),
+            tap: None,
+        });
         let tap = CGEvent::tap_create(
             CGEventTapLocation::HIDEventTap, // HID, Session, AnnotatedSession,
             CGEventTapPlacement::HeadInsertEventTap,
             CGEventTapOptions::ListenOnly,
             kCGEventMaskForAllEvents.into(),
-            callback,
-            null_mut(),
+            raw_callback,
+            (&mut *context as *mut EventTapContext).cast(),
         )
         .ok_or(ListenError::EventTapError)?;
+        context.tap = Some(tap.clone());
         let loop_ = CFMachPort::new_run_loop_source(None, Some(&tap), 0)
             .ok_or(ListenError::LoopSourceError)?;
 
@@ -66,3 +83,16 @@ where
     }
     Ok(())
 }
+
+#[cfg(test)]
+mod tests {
+    use super::is_tap_disabled_event;
+    use objc2_core_graphics::CGEventType;
+
+    #[test]
+    fn identifies_both_event_tap_disable_reasons() {
+        assert!(is_tap_disabled_event(CGEventType::TapDisabledByTimeout));
+        assert!(is_tap_disabled_event(CGEventType::TapDisabledByUserInput));
+        assert!(!is_tap_disabled_event(CGEventType::FlagsChanged));
+    }
+}