DarkRoom/apps/darkroom-android/src/lib.rs

//! DarkRoom Android entry point.
//!
//! The counterpart to `darkroom-desktop`'s `main`, with two differences that
//! come from the platform rather than from choice:
//!
//! * There are no command-line paths. Android's SAF hands out document URIs,
//!   not filesystem paths (ARCH §6.9), so the viewer opens with an empty
//!   browsing list and the library grid is the only way in.
//! * Logging goes to logcat. `env_logger` writes to stderr, which Android
//!   discards.
//!
//! The first of those has one exception, and it is the launch `Intent`: a
//! gallery, a file manager or the share sheet can name images to open, and
//! those arrive as URIs on an `Intent` rather than as words on a command line.
//! [`intents`] turns them into paths, and from there they are the same list
//! the desktop builds from `argv` (FR-PLAT-AND-6).

// The whole module is JNI against classes that exist only in the APK, so it
// is gated with everything else that cannot compile off-device.
#[cfg(target_os = "android")]
mod intents;

// `slint::android` exists only when compiling for Android, so the whole entry
// point is gated on the target rather than on a feature. Without this the
// crate is still a workspace member on the host, and `cargo test --workspace`
// fails to compile it — a build break that only ever appears off-device.
#[cfg(target_os = "android")]
/// TRACES: M-13 | M-14
/// Android application entry point, called by android-activity's glue.
#[no_mangle]
fn android_main(app: slint::android::AndroidApp) {
    android_logger::init_once(
        android_logger::Config::default()
            .with_max_level(log::LevelFilter::Info)
            .with_tag("DarkRoom"),
    );

    // Panics go to stderr, and Android discards stderr. Without this hook a
    // worker thread that panics is invisible: the process survives, the
    // channel it was writing to closes, and the UI reports only that
    // something "failed unexpectedly" with no way to find out what.
    std::panic::set_hook(Box::new(|info| {
        log::error!("panic: {info}");
    }));

    log::info!("DarkRoom v{}", env!("CARGO_PKG_VERSION"));

    // Before anything opens a store: Android has no $HOME and no XDG
    // directories, so the default guess resolves to a path the app cannot
    // write. Nothing failed loudly — the session list went to a doomed path, so
    // the account survived only as long as the process and backgrounding the app
    // lost the sign-in. `internal_data_path` is the app's private directory
    // (ARCH §6.9).
    match app.internal_data_path() {
        Some(dir) => {
            log::info!("data dir: {}", dir.display());
            dr_sync::account::set_data_dir(dir);
        }
        None => log::error!("no internal data path; settings will not persist"),
    }

    // After the data dir and before anything asks whether a model is present.
    install_bundled_face_models(&app);

    // Before `init_with_event_listener`, which takes `app` by value and is the
    // last moment anything can ask the activity a question. Not an ordering
    // preference — after that line there is no `app` left to read the Intent
    // through.
    let opened_with = intents::launch_images(&app);

    // TRACES: FR-PLAT-AND-5
    // The listener is the whole reason this is not the one-line
    // `slint::android::init(app)`. Slint owns the event loop on Android, so
    // the platform's lifecycle and memory events reach the application only if
    // it asks for them here — and it must ask *before* the loop starts, which
    // is why this sits between the data directory and `dr_ui::run`.
    //
    // The listener runs inside `poll_events`, on the same thread the event
    // loop and every interface cache live on, which is what lets
    // `dr_ui::memory` be a thread-local registry of plain `Fn()` rather than a
    // cross-thread channel (see its module documentation).
    //
    // # Why two events and not eight
    //
    // FR-PLAT-AND-5 names `onTrimMemory`, whose `TRIM_MEMORY_*` levels grade
    // how badly the system wants the memory back. Those levels do not exist
    // here: `ComponentCallbacks2` is a Java interface implemented by an
    // `Activity` or `Application`, and this app has neither — it is a bare
    // `NativeActivity`, whose native callback table offers only the ungraded
    // `onLowMemory`. android-activity surfaces exactly that as `LowMemory`.
    // Reading the grades would mean shipping a Java subclass to forward them,
    // which is a distribution-manifest change and not this one.
    //
    // `Stop` recovers the one grade that matters most anyway, and for free.
    // It is the moment the activity stops being visible — `TRIM_MEMORY_UI_HIDDEN`
    // in all but name — and it is the cheapest possible time to give memory
    // back, because nothing that is freed has to be drawn again before anyone
    // sees it. `Pause` deliberately does not qualify: a permission dialog or
    // the share sheet pauses an activity that is still on screen behind it,
    // and throwing away its render pipeline would make every such interruption
    // cost a full re-render.
    use slint::android::android_activity::{MainEvent, PollEvent};
    if let Err(e) = slint::android::init_with_event_listener(app, |event| match event {
        PollEvent::Main(MainEvent::LowMemory) => {
            dr_ui::memory::relieve(dr_ui::memory::Level::Critical);
        }
        PollEvent::Main(MainEvent::Stop) => {
            dr_ui::memory::relieve(dr_ui::memory::Level::UiHidden);
        }
        _ => {}
    }) {
        log::error!("Slint Android backend failed to initialise: {e}");
        return;
    }

    // The launch Intent's images, where there were any, standing in for the
    // desktop's argv — `launch::startup_action` treats a non-empty list as
    // "the user asked for these specifically", which is exactly what a share
    // or a tap in a gallery is. Empty for an ordinary launch, and the library
    // opens as before.
    //
    // Returning from `android_main` ends the process, so a failure here is
    // logged rather than propagated — there is no shell to show `Err` to.
    if let Err(e) = dr_ui::run(opened_with) {
        log::error!("DarkRoom exited with error: {e:#}");
    }
}

/// Unpack the face models the APK carries, if it carries any.
///
/// # Why Android needs this and no other platform does
///
/// The weights are not a build input and are not in the repository — the
/// InsightFace grant is research-only and incompatible with this project's
/// licence (docs/faces.md §2), so a desktop user fetches them, runs
/// `tools/fix-face-model-shapes.sh` over them, and drops the result into
/// `~/.local/share/darkroom/models/`. **That gesture does not exist on
/// Android.** `internal_data_path` is app-private, `run-as` needs a debuggable
/// build, and there is no picker and no fetch in the app, so a phone had no way
/// to acquire a model at all and face indexing reported itself permanently off.
///
/// So a locally-built APK may carry the pair in `assets/models/`, which
/// `assemble-apk.sh` includes when the tree has them and omits when it does
/// not. Nothing changes about what the repository holds or what a published
/// build could redistribute; this only gives a self-built APK the same route a
/// desktop build has always had.
///
/// Absent assets are the ordinary case, not an error — the same quiet "no model
/// installed" state a fresh desktop install is in.
#[cfg(target_os = "android")]
fn install_bundled_face_models(app: &slint::android::AndroidApp) {
    use std::io::Read;

    // The **shape-fixed** names, matching what `library::face_models` looks
    // for: tract cannot parse either InsightFace graph with its dynamic input
    // dimension, so what ships here has already been through
    // `tools/fix-face-model-shapes.sh`.
    const BUNDLED: [(&std::ffi::CStr, &str); 2] = [
        (c"models/scrfd_500m_640.onnx", "scrfd_500m_640.onnx"),
        (c"models/arcface_mbf_b1.onnx", "arcface_mbf_b1.onnx"),
    ];

    let dir = dr_ui::shared_face_models_dir();
    let assets = app.asset_manager();

    for (asset_path, name) in BUNDLED {
        let dest = dir.join(name);
        // Already unpacked. Not re-read on every launch: this is 15 MB through
        // a decompressor on the startup path, and the file does not change
        // without the APK changing, at which point the install wiped it anyway.
        if dest.is_file() {
            continue;
        }
        let Some(mut asset) = assets.open(asset_path) else {
            log::info!("no bundled {name} in this APK; face indexing stays off");
            continue;
        };
        let mut bytes = Vec::new();
        if let Err(e) = asset.read_to_end(&mut bytes) {
            log::error!("bundled {name} could not be read: {e}");
            continue;
        }
        if let Err(e) = std::fs::create_dir_all(&dir) {
            log::error!("cannot create {}: {e}", dir.display());
            return;
        }
        // Written under a temporary name and renamed, because
        // `library::face_models` decides face indexing is available on
        // `is_file()` alone. A truncated write — the process backgrounded and
        // killed mid-copy — would otherwise leave a file that passes that test
        // and fails inside tract, reported to the user as a broken model rather
        // than a missing one.
        let part = dir.join(format!("{name}.part"));
        match std::fs::write(&part, &bytes).and_then(|()| std::fs::rename(&part, &dest)) {
            Ok(()) => log::info!("installed bundled {name} ({} bytes)", bytes.len()),
            Err(e) => {
                log::error!("cannot install {name}: {e}");
                let _ = std::fs::remove_file(&part);
            }
        }
    }
}

/// TRACES: FR-PLAT-AND-6
/// The declarations that make this app a receiver, held to on the host.
///
/// Everything FR-PLAT-AND-6 does on a device is unreachable from `cargo test`:
/// there is no `Intent` off-device and no `ContentProvider` to instantiate. But
/// the requirement is not only behaviour — half of it is *declaration*, and a
/// declaration can be wrong in ways that compile perfectly and fail silently.
/// An intent filter that is deleted takes the app out of every gallery's "open
/// with" menu with nothing to notice; an authority that stops matching the
/// class it names raises a `SecurityException` in whichever other app opened
/// the share sheet, which is the last place anybody would look for it.
///
/// The manifest is read by aapt2 and the Java by javac, so a Rust build sees
/// neither. `include_str!` is what puts them where a test can reach them, and
/// this is the only place in the workspace that does.
#[cfg(test)]
mod tests {
    /// The manifest with its comments removed and its whitespace flattened, so
    /// a match is about the declaration and not about how it is indented.
    fn manifest() -> String {
        let xml = include_str!("../android/AndroidManifest.xml");
        let mut out = String::with_capacity(xml.len());
        let mut rest = xml;
        // Comments first, and not by regex over the whole file: several of them
        // quote the very attribute names the assertions below look for, so a
        // test that read them would pass on the strength of the prose
        // explaining an entry that had been deleted.
        while let Some(start) = rest.find("<!--") {
            out.push_str(&rest[..start]);
            match rest[start..].find("-->") {
                Some(end) => rest = &rest[start + end + 3..],
                None => {
                    rest = "";
                    break;
                }
            }
        }
        out.push_str(rest);
        out.split_whitespace().collect::<Vec<_>>().join(" ")
    }

    /// The body of each `<intent-filter>`, so an action and a MIME type are
    /// checked to be in the *same* filter. Two filters, one naming the action
    /// and one naming the type, register for neither.
    fn intent_filters(manifest: &str) -> Vec<&str> {
        manifest
            .split("<intent-filter>")
            .skip(1)
            .filter_map(|filter| filter.split("</intent-filter>").next())
            .collect()
    }

    /// The single `<provider>` element, attributes and all.
    fn provider(manifest: &str) -> String {
        let start = manifest
            .find("<provider")
            .expect("no <provider> in the manifest");
        let rest = &manifest[start..];
        let end = rest.find("/>").expect("unterminated <provider> element");
        rest[..end + 2].to_string()
    }

    fn attribute(element: &str, name: &str) -> Option<String> {
        let key = format!("{name}=\"");
        let start = element.find(&key)? + key.len();
        let value = element[start..].split('"').next()?;
        Some(value.to_string())
    }

    #[test]
    fn a_gallery_can_open_a_photograph_in_this_app() {
        let manifest = manifest();
        let registered = intent_filters(&manifest).iter().any(|filter| {
            filter.contains("android.intent.action.VIEW")
                && filter.contains("android.intent.category.DEFAULT")
                && filter.contains(r#"android:mimeType="image/*""#)
        });
        assert!(
            registered,
            "no VIEW filter for image/*: nothing will offer DarkRoom for a photograph"
        );
    }

    #[test]
    fn the_share_sheet_can_send_one_image_or_several() {
        let manifest = manifest();
        let registered = intent_filters(&manifest).iter().any(|filter| {
            // The closing quote matters: SEND is a prefix of SEND_MULTIPLE, so
            // a bare substring test passes on a filter that declares only the
            // second and would not be offered for a single photograph.
            filter.contains(r#"android.intent.action.SEND""#)
                && filter.contains(r#"android.intent.action.SEND_MULTIPLE""#)
                && filter.contains("android.intent.category.DEFAULT")
                && filter.contains(r#"android:mimeType="image/*""#)
        });
        assert!(
            registered,
            "no SEND/SEND_MULTIPLE filter for image/*, so the share sheet will not list DarkRoom"
        );
    }

    #[test]
    fn one_activity_ever_so_a_second_launch_cannot_start_a_second_one() {
        // Not style. Another app can now launch this activity while it is
        // already running, and the default launch mode answers that by
        // creating a second NativeActivity in this process — a second
        // android_main, a second Slint backend, a second wgpu device.
        assert!(
            manifest().contains(r#"android:launchMode="singleTask""#),
            "the activity must be singleTask; see the manifest comment"
        );
    }

    #[test]
    fn the_provider_authority_is_the_one_the_class_answers_to() {
        let manifest = manifest();
        let element = provider(&manifest);

        let declared =
            attribute(&element, "android:authorities").expect("the provider declares no authority");
        let java = include_str!("../android/java/paris/tourolle/darkroom/ExportProvider.java");
        let constant = java
            .split("AUTHORITY = \"")
            .nth(1)
            .and_then(|rest| rest.split('"').next())
            .expect("ExportProvider declares no AUTHORITY constant");

        assert_eq!(
            declared, constant,
            "the manifest and ExportProvider disagree about the authority; \
             a share would fail as a SecurityException inside the receiving app"
        );

        let class = attribute(&element, "android:name").expect("the provider declares no class");
        let (package, _) = class
            .rsplit_once('.')
            .expect("the provider class is unqualified");
        assert!(
            java.contains(&format!("package {package};")),
            "the manifest names {class}, which is not the class in ExportProvider.java"
        );
    }

    #[test]
    fn the_provider_hands_out_one_file_at_a_time_and_nothing_by_itself() {
        let manifest = manifest();
        let element = provider(&manifest);
        // The two halves are not redundant. Without the grant, every share
        // target fails; exported, every app on the device could read this
        // app's private directory.
        assert_eq!(
            attribute(&element, "android:exported").as_deref(),
            Some("false"),
            "an exported provider would serve the app's private directory to anything installed"
        );
        assert_eq!(
            attribute(&element, "android:grantUriPermissions").as_deref(),
            Some("true"),
            "without URI grants the share sheet opens and every target fails to read the file"
        );
    }
}