# Moongreet

## Project

Moongreet is a greetd greeter for Wayland, built with Rust + gtk4-rs + gtk4-layer-shell.
Part of the Moonarch ecosystem.

## Tech Stack

- Rust (edition 2024), gtk4-rs 0.11, glib 0.22
- gtk4-layer-shell 0.8 for the Wayland Layer Shell (TOP layer)
- greetd IPC over a Unix domain socket (length-prefixed JSON)
- `cargo test` for unit tests

## Project Structure

- `src/` — Rust source code (main.rs, greeter.rs, ipc.rs, config.rs, users.rs, sessions.rs, i18n.rs, power.rs)
- `resources/` — GResource assets (style.css, default-avatar.svg)
- `config/` — example configuration files for `/etc/moongreet/` and `/etc/greetd/`
- `pkg/` — PKGBUILD for Arch Linux packaging (`makepkg -sf`)

## Commands

```bash
# Run tests
cargo test

# Release build
cargo build --release

# Start the greeter in a window (without greetd/Layer Shell)
MOONGREET_NO_LAYER_SHELL=1 ./target/release/moongreet

# Build and install the package
cd pkg && makepkg -sf && sudo pacman -U moongreet-git-<version>-x86_64.pkg.tar.zst
```

## Architecture

- `ipc.rs` — greetd socket communication (4-byte LE header + JSON)
- `users.rs` — users from /etc/passwd, avatars (AccountsService + ~/.face), symlink rejection
- `sessions.rs` — Wayland/X11 sessions from .desktop files
- `power.rs` — reboot/shutdown via systemctl (`--no-ask-password`)
- `i18n.rs` — locale detection (LANG / /etc/locale.conf) and string tables (DE/EN), all UI and login error messages
- `fingerprint.rs` — fprintd D-Bus probe (gio::DBusProxy) — device detection and enrollment check for UI feedback
- `config.rs` — TOML config ([appearance] background, gtk-theme, cursor-theme, cursor-size, fingerprint-enabled) + wallpaper fallback + blur validation (finite, clamp 0–200) + cursor-size validation (range 1–256)
- `greeter.rs` — GTK4 UI (overlay layout), login flow via greetd IPC (multi-stage auth for fprintd), faillock warning, power confirm (inline confirmation before reboot/shutdown, like moonlock), avatar cache, last-user/last-session persistence (0o700 dirs, 0o600 files)
- `main.rs` — entry point, GTK app, Layer Shell setup, one greeter window on the focused output (no `set_monitor`), `KeyboardMode::Exclusive`, systemd-journal-logger
- `resources/style.css` — Catppuccin-inspired theme

## Design Decisions

- **TOP layer instead of OVERLAY**: the greeter runs under greetd, not above Waybar
- **GResource bundle**: CSS, wallpaper and default avatar are compiled into the binary
- **Async login**: `glib::spawn_future_local` + `gio::spawn_blocking` instead of raw threads
- **Socket cancellation**: `Arc<Mutex<Option<UnixStream>>>` + `AtomicBool` for clean cancellation
- **Avatar cache**: `HashMap<String, gdk::Texture>` in `Rc<RefCell<GreeterState>>`
- **GPU blur via GskBlurNode**: `Snapshot::push_blur()` + `GskRenderer::render_texture()` in the `connect_realize` callback — no CPU blur, no disk cache, no `image` crate. The blurred texture is cached across all monitors via `Rc<RefCell<Option<gdk::Texture>>>` (1 GPU render pass instead of N).
- **Fingerprint via greetd multi-stage PAM**: fprintd D-Bus only as a probe (device/enrollment), the actual verification runs through PAM in the greetd auth loop. `auth_message_type: "secret"` → password, everything else → `None` (PAM decides). 60s socket timeout for fprintd. Device proxy cached in `GreeterState`, generation counter against race conditions on fast user switch.
- **Symmetry with moonlock/moonset**: same patterns (i18n, config, users, power, GResource, GPU blur)
- **Session validation**: relative paths allowed (greetd resolves PATH), only `..`/null bytes are rejected
- **GTK theme validation**: only alphanumeric + `_-+.` allowed, prevents path traversal via config
- **Cursor theme via GtkSettings**: GTK4 under greetd does not read the `XCURSOR_THEME` env reliably — the cursor is set via `gtk::Settings::set_gtk_cursor_theme_name()`, analogous to `gtk-theme`. Same validation (`is_valid_gtk_theme`) against path traversal.
- **Journal logging**: `systemd-journal-logger` instead of file logging — `journalctl -t moongreet`, debug level via the `MOONGREET_DEBUG` env var
- **File permissions**: cache directories 0o700 via `DirBuilder::mode()`, cache files 0o600
- **Testable persistence**: `save_*_to`/`load_*_from` variants with a configurable path for unit tests
- **Shared wallpaper texture**: the `gdk::Texture` is decoded once in `load_background_texture()` and shared by ref-count across all windows — avoids redundant JPEG decoding per monitor
- **Wallpaper validation**: GResource branch via `resources_lookup_data()` + `from_bytes()` (no abort on a missing path), file-size limit 50 MB, non-UTF-8 paths → `None`
- **Error-detail filtering**: GDK/greetd error details only at `debug!` level, `warn!` without internal details — prevents system-info leak into the journal