ndk/input_queue: Replace InputQueueError with std::io::Error and …

…add missing docs

These `AInputQueue` functions all return [standard `errno.h` error
codes] which can and should be communicated back to the user instead of
appearing as some opaque magic struct.

In addition import the NDK documentation for all these functions and
make the scope of `unsafe` blocks smaller.

[standard `errno.h` error codes]: https://cs.android.com/android/platform/superproject/+/master:frameworks/base/core/jni/android_view_InputQueue.cpp;l=112;drc=7b3193e1e86ab5c0fcb784cb8616864045dd2515

ndk-examples/examples/looper.rs

@@ -118,7 +118,8 @@ fn main() {
                         let input_queue = input_queue.as_ref().expect("Input queue not attached");
                         assert!(input_queue.has_events().unwrap());
                         // Consume as many events as possible
-                        while let Some(event) = input_queue.get_event() {
+
+                        while let Ok(event) = input_queue.get_event() { // Returns std::io::ErrorKind::WouldBlock if no event is available
                             // Pass the event by a possible IME (Input Method Editor, ie. an open keyboard) first
                             if let Some(event) = input_queue.pre_dispatch(event) {
                                 info!("Input event {:?}", event);

ndk/src/input_queue.rs

@@ -1,30 +1,35 @@
-// TODO: mod docs
+//! Bindings for [`AInputQueue`]
+//!
+//! [`AInputQueue`]: https://developer.android.com/ndk/reference/group/input#ainputqueue
 
+use std::io::{Error, Result};
 use std::os::raw::c_int;
-use std::ptr;
-use std::ptr::NonNull;
+use std::ptr::{self, NonNull};
 
 use crate::event::InputEvent;
+#[cfg(doc)]
+use crate::event::KeyEvent;
 use crate::looper::ForeignLooper;
 
-// TODO docs
+/// A native [`AInputQueue *`]
+///
+/// An input queue is the facility through which you retrieve input events.
+///
+/// [`AInputQueue *`]: https://developer.android.com/ndk/reference/group/input#ainputqueue
 #[derive(Debug)]
 pub struct InputQueue {
     ptr: NonNull<ffi::AInputQueue>,
 }
 
-// It gets shared between threads in android_native_app_glue
+// It gets shared between threads in `ndk-glue`
 unsafe impl Send for InputQueue {}
 unsafe impl Sync for InputQueue {}
 
-#[derive(Debug)]
-pub struct InputQueueError;
-
 impl InputQueue {
-    /// Construct an `InputQueue` from the native pointer.
+    /// Construct an [`InputQueue`] from the native pointer.
     ///
     /// # Safety
-    /// By calling this function, you assert that the pointer is a valid pointer to an NDK `AInputQueue`.
+    /// By calling this function, you assert that the pointer is a valid pointer to an NDK [`ffi::AInputQueue`].
     pub unsafe fn from_ptr(ptr: NonNull<ffi::AInputQueue>) -> Self {
         Self { ptr }
     }
@@ -33,45 +38,61 @@ impl InputQueue {
         self.ptr
     }
 
-    pub fn get_event(&self) -> Option<InputEvent> {
-        unsafe {
-            let mut out_event = ptr::null_mut();
-            if ffi::AInputQueue_getEvent(self.ptr.as_ptr(), &mut out_event) < 0 {
-                None
-            } else {
+    /// Returns the next available [`InputEvent`] from the queue.
+    ///
+    /// Returns [`std::io::ErrorKind::WouldBlock`] if no event is available.
+    pub fn get_event(&self) -> Result<InputEvent> {
+        let mut out_event = ptr::null_mut();
+        match unsafe { ffi::AInputQueue_getEvent(self.ptr.as_ptr(), &mut out_event) } {
+            0 => {
                 debug_assert!(!out_event.is_null());
-                Some(InputEvent::from_ptr(NonNull::new_unchecked(out_event)))
+                Ok(unsafe { InputEvent::from_ptr(NonNull::new_unchecked(out_event)) })
             }
+            r if r < 0 => Err(Error::from_raw_os_error(-r)),
+            r => unreachable!("AInputQueue_getEvent returned positive integer {}", r),
         }
     }
 
-    pub fn has_events(&self) -> Result<bool, InputQueueError> {
-        unsafe {
-            match ffi::AInputQueue_hasEvents(self.ptr.as_ptr()) {
-                0 => Ok(false),
-                1 => Ok(true),
-                x if x < 0 => Err(InputQueueError),
-                x => unreachable!("AInputQueue_hasEvents returned {}", x),
-            }
+    /// Returns [`true`] if there are one or more events available in the input queue.
+    pub fn has_events(&self) -> Result<bool> {
+        match unsafe { ffi::AInputQueue_hasEvents(self.ptr.as_ptr()) } {
+            0 => Ok(false),
+            1 => Ok(true),
+            r if r < 0 => Err(Error::from_raw_os_error(-r)),
+            r => unreachable!("AInputQueue_hasEvents returned non-boolean {}", r),
         }
     }
 
+    /// Sends the key for standard pre-dispatching that is, possibly deliver it to the current IME
+    /// to be consumed before the app.
+    ///
+    /// Returns [`Some`] if it was not pre-dispatched, meaning you can process it right now. If
+    /// [`None`] is returned, you must abandon the current event processing and allow the event to
+    /// appear again in the event queue (if it does not get consumed during pre-dispatching).
+    ///
+    /// Also returns [`None`] if `event` is not a [`KeyEvent`].
     pub fn pre_dispatch(&self, event: InputEvent) -> Option<InputEvent> {
-        unsafe {
-            if ffi::AInputQueue_preDispatchEvent(self.ptr.as_ptr(), event.ptr().as_ptr()) == 0 {
-                Some(event)
-            } else {
-                None
-            }
+        if unsafe {
+            ffi::AInputQueue_preDispatchEvent(self.ptr.as_ptr(), event.ptr().as_ptr()) == 0
+        } {
+            Some(event)
+        } else {
+            None
         }
     }
 
+    /// Report that dispatching has finished with the given [`InputEvent`].
+    ///
+    /// This must be called after receiving an event with [`InputQueue::get_event()`].
     pub fn finish_event(&self, event: InputEvent, handled: bool) {
         unsafe {
-            ffi::AInputQueue_finishEvent(self.ptr.as_ptr(), event.ptr().as_ptr(), handled as c_int);
+            ffi::AInputQueue_finishEvent(self.ptr.as_ptr(), event.ptr().as_ptr(), handled as c_int)
         }
     }
 
+    /// Add this input queue to a [`ForeignLooper`] for processing.
+    ///
+    /// See [`ForeignLooper::add_fd()`] for information on the `ident`, `callback`, and `data` params.
     pub fn attach_looper(&self, looper: &ForeignLooper, id: i32) {
         unsafe {
             ffi::AInputQueue_attachLooper(
@@ -80,13 +101,12 @@ impl InputQueue {
                 id,
                 None,
                 std::ptr::null_mut(),
-            );
+            )
         }
     }
 
+    /// Remove this input queue from the [`ForeignLooper`] it is currently attached to.
     pub fn detach_looper(&self) {
-        unsafe {
-            ffi::AInputQueue_detachLooper(self.ptr.as_ptr());
-        }
+        unsafe { ffi::AInputQueue_detachLooper(self.ptr.as_ptr()) }
     }
 }