greetd-moongreet/DECISIONS.md

Decisions

2026-04-24 – Audit LOW fixes: stdout null, utf-8 path, debug value, hidden sessions (v0.8.6)

• Who: ClaudeCode, Dom
• Why: Four LOW findings cleared in a single pass. (1) power::run_command piped stdout it never read — structurally fragile even though current callers stay well under the pipe buffer. (2) Relative wallpaper paths were resolved via to_string_lossy, silently substituting U+FFFD for non-UTF-8 bytes and producing a path that cannot be opened. (3) MOONGREET_DEBUG escalated log verbosity on mere presence, so an empty variable leaked auth metadata into the journal. (4) Hidden=true and NoDisplay=true .desktop entries appeared in the session dropdown even though they mark disabled or stub sessions.
• Tradeoffs: Gating debug on the literal value "1" is slightly stricter than most tools but matches the security-first posture. Filtering Hidden/NoDisplay means legitimately hidden but functional sessions are now unselectable from the greeter — acceptable, that is the convention these keys signal.
• How: (1) .stdout(Stdio::null()) replaces the unused pipe. (2) to_string_lossy().to_string() replaced by to_str().map(|s| s.to_string()) with a log::warn! fallback for non-UTF-8 paths. (3) match std::env::var("MOONGREET_DEBUG").ok().as_deref() → Some("1") selects Debug, everything else Info. (4) parse_desktop_file reads Hidden= and NoDisplay=, returns None if either is true.

2026-04-24 – Audit MEDIUM fixes: FP double-init, async avatar, symlink, FD leak (v0.8.5)

• Who: ClaudeCode, Dom
• Why: Six MEDIUM findings: (1) i18n test all_string_fields_nonempty missed four string fields — future locales could ship empty strings unnoticed. (2) Fast user-switch could spawn two parallel fprintd init_async calls because both coroutines saw fingerprint_probe = None before either stored its probe. (3) Synchronous avatar decode via Pixbuf::from_file_at_scale on the GTK main thread, stalling clicks. (4) Wallpaper MAX_WALLPAPER_FILE_SIZE = 50 MB bounded decode at up to ~2 s. (5) Fallback wallpaper path used is_file() which follows symlinks, inconsistent with the symlink-rejecting user-config path. (6) After a failed login the cloned greetd_sock descriptor remained in shared state until the next user switch, accumulating stale FDs across retries.
• Tradeoffs: The init-race guard uses a bool flag on GreeterState + a 25 ms polling yield — cheap and race-free, but introduces a very short latency when a second probe waits. Lowering MAX_WALLPAPER_FILE_SIZE to 10 MB and MAX_AVATAR_FILE_SIZE to 5 MB caps worst-case decode but rejects legitimately huge (4K raw) wallpapers; acceptable for a greeter. Async avatar decode shows the default icon for a frame or two on cache miss.
• How: (1) Four new assert! lines in i18n::tests::all_string_fields_nonempty. (2) New fingerprint_probe_initializing: bool on GreeterState, atomic check-and-set under borrow_mut, losing coroutines yield via glib::timeout_future until the winning init completes. (3) set_avatar_from_file uses gio::File::read_future + Pixbuf::from_stream_at_scale_future inside a glib::spawn_future_local, sets the default icon first, swaps on success. (4) Lower both size constants. (5) resolve_background_path_with now applies the same symlink_metadata + !is_symlink check to the Moonarch fallback. (6) After the login worker returns, state.greetd_sock.lock().take() drops the stale clone regardless of login outcome.

2026-04-24 – Audit fix: shrink password-in-memory window (v0.8.4)

• Who: ClaudeCode, Dom
• Why: Security audit flagged the GTK password path as holding more copies of the plaintext password in memory than necessary. attempt_login wrapped the already-Zeroizing<String> caller value into a second Zeroizing<String> (password.to_string()), and the GTK GString backing entry.text() persisted in libc malloc'd memory until the allocator reused the page.
• Tradeoffs: The GTK GString and the libc strdup copy on the PAM FFI boundary remain non-zeroizable — this is an inherent GTK/libc limitation, already documented in CLAUDE.md. This change reduces the Rust-owned copies to one and clears the PasswordEntry text field immediately after extraction to shorten the GTK-side window.
• How: (1) attempt_login now takes password: Zeroizing<String> by value instead of &str, moving ownership into the spawn_blocking closure. (2) The redundant Zeroizing::new(password.to_string()) inside attempt_login is removed. (3) password_entry.set_text("") is called right after the password is extracted from the activate handler, shortening the lifetime of the GTK-internal buffer.

2026-04-21 – Ship polkit rule in moongreet instead of moonarch (v0.8.3)

• Who: ClaudeCode, Dom
• Why: Reboot/shutdown from the greeter silently failed on a fresh install. The polkit rule that grants the greeter user org.freedesktop.login1.{reboot,power-off} lived in the moonarch repo but was never installed by any PKGBUILD. The laptop worked only because the rule had been hand-deployed once.
• Tradeoffs: Rule ownership moves from moonarch (system defaults) to moongreet (greeter-specific auth). Cleaner boundary — moonarch no longer needs to know about the greeter's auth requirements — but it means moongreet is now responsible for a system polkit rule that ties it to a fixed username (greeter).
• How: Source file moved to moongreet/config/polkit/50-moongreet-power.rules, installed to /etc/polkit-1/rules.d/ by moongreet-git/PKGBUILD. Old file removed from the moonarch repo.

2026-04-09 – Monitor hotplug via ListModel items-changed

• Who: ClaudeCode, Dom
• Why: Greeter windows were only created at startup. If a monitor was hotplugged (e.g. HDMI reconnect), it would show no greeter UI. Aligned with moonlock's hotplug fix (same day).
• Tradeoffs: Hotplugged monitors get greeter windows without keyboard input (keyboard stays on the primary monitor). Acceptable — user can still interact on the primary screen.
• How: Connect to display.monitors().connect_items_changed() and create new greeter windows for added monitors. Shared state (config, texture, blur_cache) moved to Rc for the closure.

2026-04-08 – Show greeter UI on all monitors instead of just one

• Who: ClaudeCode, Dom
• Why: moonlock showed its UI on all monitors via ext-session-lock-v1, but moongreet only showed the login UI on one monitor (compositor-picked) with wallpaper-only windows on the rest. Inconsistent UX across the ecosystem.
• Tradeoffs: Each monitor gets its own full greeter widget tree (slightly more memory), but the UI is lightweight. Screen mirroring (e.g., wl-mirror/screencopy) was considered and rejected — it requires an external process, compositor screencopy support, adds latency, and fights Wayland's per-output model. One-window-per-monitor is the established Wayland pattern (swaylock, hyprlock, moonlock all do this).
• How: Create one create_greeter_window() per monitor with set_monitor(), only the first gets KeyboardMode::Exclusive. Removed create_wallpaper_window() (no longer needed). No layer shell fallback keeps single-window mode for development.

2026-04-06 – Restore explicit gtk-theme in moongreet config

• Who: ClaudeCode, Dom
• Why: GTK4 under greetd does not reliably read /etc/xdg/gtk-4.0/settings.ini — likely requires a settings daemon that doesn't run in the greeter session. moongreet fell back to Adwaita/Colloid-default (blue accent) instead of Colloid-Grey-Dark-Catppuccin.
• Tradeoffs: Reverts 094878f ("Remove gtk-theme from app config, use system-wide GTK settings instead"). Duplicates the theme name between settings.ini and moongreet.toml, but the explicit set via set_gtk_theme_name() is the only reliable path in a greetd context.
• How: Added gtk-theme = "Colloid-Grey-Dark-Catppuccin" to example config and deployed /etc/moongreet/moongreet.toml.

2026-04-02 – Replace hardcoded CSS colors with GTK theme variables

• Who: ClaudeCode, Dom
• Why: moongreet used hardcoded colors (#1a1a2e, white, #ff6b6b) while moonset already used @theme_bg_color, @theme_fg_color, @error_color etc. Inconsistent across the ecosystem and broke theme flexibility.
• Tradeoffs: Depends on the active GTK theme defining standard color variables. Catppuccin Colloid provides all needed vars (@theme_bg_color, @theme_fg_color, @error_color, @success_color, @theme_selected_bg_color). Fallback behavior if a theme lacks vars is GTK's default colors — acceptable.
• How: Replaced all hardcoded hex/named colors with GTK theme variables. Coordinated change across moongreet, moonlock, and moonset (all three now use identical pattern).

2026-03-31 – Fourth audit: power timeout, timing mitigation, release profile, GREETD_SOCK caching

• Who: ClaudeCode, Dom
• Why: Fourth triple audit found moongreet power.rs had no timeout on loginctl (greeter could freeze), username enumeration via timing differential, GREETD_SOCK re-read on every login, missing release profile, and missing GResource compression.
• Tradeoffs: 500ms minimum login response time adds slight delay on fast auth but prevents timing-based username enumeration. Power timeout (30s + SIGKILL) matches moonset pattern — aggressive but prevents greeter freeze.
• How: (1) power.rs adapted from moonset with 30s timeout + SIGKILL (nix dependency added). (2) 500ms min response floor in attempt_login via Instant + glib::timeout_future. (3) GREETD_SOCK cached in GreeterState at startup. (4) [profile.release] with LTO, codegen-units=1, strip. (5) compressed="true" on GResource entries. (6) SYNC comments on duplicated blur/background functions.

2026-03-30 – Full audit fix: security, quality, performance (v0.6.2)

• Who: ClaudeCode, Dom
• Why: Three parallel audits (security, code quality, performance) identified 10 actionable findings across the codebase — from world-readable cache dirs to a GPU blur geometry bug to a race condition in fingerprint probing.
• Tradeoffs: too_many_arguments Clippy warnings suppressed with #[allow] rather than introducing a UiWidgets struct — GTK's clone! macro with #[weak] refs requires individual widget parameters, a struct would fight the idiom. Async avatar loading skipped because Pixbuf is !Send; cache already prevents repeat loads. TOCTOU socket pre-check removed entirely — connect() in login_worker already handles errors, the metadata() check gave false security guarantees.
• How: Cache dirs use DirBuilder::mode(0o700) instead of create_dir_all. Blur config clamped to 0.0..=200.0 with is_finite() guard. Blur texture cached in Rc<RefCell<Option<gdk::Texture>>> across monitors. FingerprintProbe device proxy cached in GreeterState with generation counter to prevent stale async writes. GPU blur geometry fixed (-pad origin shift instead of texture stretching). is_valid_gtk_theme extracted as testable function. 9 new tests.

2026-03-29 – Fingerprint authentication via greetd multi-stage PAM

• Who: ClaudeCode, Dom
• Why: moonlock supports fprintd but moongreet rejected multi-stage auth. Users with enrolled fingerprints couldn't use them at the login screen.
• Tradeoffs: Direct fprintd D-Bus verification (like moonlock) can't start a greetd session — greetd controls session creation via PAM. Using greetd multi-stage means PAM decides the auth order (fingerprint first, then password fallback), not truly parallel. Acceptable — matches standard pam_fprintd behavior.
• How: Replace single-pass auth with a loop over auth_message rounds. Secret prompts get the password, non-secret prompts (fprintd) get None and block until PAM resolves. fprintd D-Bus probe (gio::DBusProxy) only for UI — detecting device availability and enrolled fingers. 60s socket timeout when fingerprint available. Config option fingerprint-enabled (default true).

2026-03-28 – Remove embedded wallpaper from binary

• Who: ClaudeCode, Dom
• Why: Wallpaper is installed by moonarch to /usr/share/moonarch/wallpaper.jpg. Embedding a 374K JPEG in the binary is redundant. GTK background color (Catppuccin Mocha base) is a clean fallback.
• Tradeoffs: Without moonarch installed AND without config, greeter shows plain dark background instead of wallpaper. Acceptable — that's the expected minimal state.
• How: Remove wallpaper.jpg from GResources, return None from resolve_background_path when no file found, skip wallpaper window creation and background picture when no path available.

2026-03-28 – GPU blur via GskBlurNode replaces CPU blur

• Who: ClaudeCode, Dom
• Why: CPU-side Gaussian blur (image crate) blocked the GTK main thread for 500ms–2s on 4K wallpapers at cold cache. Disk cache and async orchestration added significant complexity.
• Tradeoffs: GPU blur quality is slightly different (box-blur approximation vs true Gaussian), acceptable for wallpaper backgrounds. Removes image crate dependency entirely (~15 transitive crates eliminated). No disk cache needed.
• How: Snapshot::push_blur() + GskRenderer::render_texture() on connect_realize. Blur happens once on the GPU when the widget gets its renderer, producing a concrete gdk::Texture. Zero startup latency. Symmetric with moonlock and moonset.

2026-03-28 – Optional background blur via image crate (superseded)

• Who: ClaudeCode, Dom
• Why: Blurred wallpaper as greeter background is a common UX pattern for login screens
• Tradeoffs: Adds image crate dependency (~15 transitive crates); CPU-side Gaussian blur at load time adds startup latency proportional to image size and sigma. Acceptable because blur runs once and the texture is shared across monitors.
• How: load_background_texture(bg_path, blur_radius) loads texture, optionally applies imageops::blur(), returns blurred gdk::Texture. Config option background-blur: Option<f32> in [appearance] TOML section.

2026-03-28 – Audit fixes for shared wallpaper texture (v0.4.1)

• Who: ClaudeCode, Dominik
• Why: Quality, performance, and security audits flagged issues in load_background_texture(), debug logging, and greetd error handling
• Tradeoffs: GResource path now requires UTF-8 (returns None for non-UTF-8 instead of aborting); 50 MB wallpaper limit is generous but prevents OOM; debug logging off by default trades observability for security
• How: GResource branch via resources_lookup_data() + from_bytes() (no abort), file size limit, error details only at debug level, MOONGREET_DEBUG env var for log level, greetd retry path truncation matching show_greetd_error()