implement read_directory and is_directory for android asset reader

crates/bevy_asset/src/io/android.rs

@@ -1,18 +1,20 @@
 use crate::io::{
-    get_meta_path, AssetReader, AssetReaderError, AssetWatcher, EmptyPathStream, PathStream,
-    Reader, VecReader,
+    get_meta_path, AssetReader, AssetReaderError, AssetWatcher, PathStream, Reader, VecReader,
 };
 use anyhow::Result;
-use bevy_log::error;
 use bevy_utils::BoxedFuture;
-use std::{ffi::CString, path::Path};
+use futures_lite::stream;
+use std::{
+    ffi::{CString, OsString},
+    os::unix::ffi::OsStringExt as _,
+    path::{Path, PathBuf},
+};
 
 /// [`AssetReader`] implementation for Android devices, built on top of Android's [`AssetManager`].
 ///
 /// Implementation details:
 ///
-/// - [`load_path`](AssetIo::load_path) uses the [`AssetManager`] to load files.
-/// - [`read_directory`](AssetIo::read_directory) always returns an empty iterator.
+/// - [`AssetManager`] to load files and directories, and check if a path is a directory.
 /// - Watching for changes is not supported. The watcher method will do nothing.
 ///
 /// [AssetManager]: https://developer.android.com/reference/android/content/res/AssetManager
@@ -58,19 +60,57 @@ impl AssetReader for AndroidAssetReader {
 
     fn read_directory<'a>(
         &'a self,
-        _path: &'a Path,
+        path: &'a Path,
     ) -> BoxedFuture<'a, Result<Box<PathStream>, AssetReaderError>> {
-        let stream: Box<PathStream> = Box::new(EmptyPathStream);
-        error!("Reading directories is not supported with the AndroidAssetReader");
-        Box::pin(async move { Ok(stream) })
+        Box::pin(async move {
+            let asset_manager = bevy_winit::ANDROID_APP
+                .get()
+                .expect("Bevy must be setup with the #[bevy_main] macro on Android")
+                .asset_manager();
+
+            let opened_dir = asset_manager
+                .open_dir(&CString::new(path.to_str().unwrap()).unwrap())
+                .ok_or(AssetReaderError::NotFound(path.to_path_buf()))?;
+
+            // collecting it since AssetDir can't be sent between threads
+            let paths = opened_dir
+                .filter_map(|path| {
+                    // convert from CString to PathBuf, only works on unix which android is.
+                    let bytes = path.to_bytes().to_vec();
+                    let path: PathBuf = OsString::from_vec(bytes).into();
+
+                    // filter out meta files as they are not considered assets
+                    if let Some(ext) = path.extension().and_then(|e| e.to_str()) {
+                        if ext.eq_ignore_ascii_case("meta") {
+                            return None;
+                        }
+                    }
+
+                    Some(path)
+                })
+                .collect::<Vec<_>>();
+            let stream: Box<PathStream> = Box::new(stream::iter(paths));
+            Ok(stream)
+        })
     }
 
     fn is_directory<'a>(
         &'a self,
-        _path: &'a Path,
+        path: &'a Path,
     ) -> BoxedFuture<'a, std::result::Result<bool, AssetReaderError>> {
-        error!("Reading directories is not supported with the AndroidAssetReader");
-        Box::pin(async move { Ok(false) })
+        Box::pin(async move {
+            let asset_manager = bevy_winit::ANDROID_APP
+                .get()
+                .expect("Bevy must be setup with the #[bevy_main] macro on Android")
+                .asset_manager();
+
+            // HACK: AssetManager API sucks so this hack is all we can do...
+            // This will only return either not found or true
+            asset_manager
+                .open_dir(&CString::new(path.to_str().unwrap()).unwrap())
+                .ok_or(AssetReaderError::NotFound(path.to_path_buf()))
+                .map(|_| true)
+        })
     }
 
     fn watch_for_changes(