wl-webrtc/AGENTS.md

AGENTS.md

Sources of truth

• Trust current Rust source, Cargo.toml, shell.nix, and tests over docs/superpowers/* or analysis.md; those docs contain historical/aspirational modules that are not in the tree.
• Crate edition is 2021, not the default Rust 2024. The package exposes a library, three binaries (wl-webrtc, vaapi_import_bench, sw_encode_bench), and two examples (list_globals, test_portal).

Setup and build

• Native prerequisites are FFmpeg 6+ dev libs with VAAPI, Wayland protocols/libs, libdrm, PipeWire, and libclang. shell.nix provides FFmpeg/Wayland/libdrm/Mesa/libva/clang and LIBCLANG_PATH, but does not currently list PipeWire.
• Normal build: cargo build. Release binary required by README and integration tests: cargo build --release.
• Cargo.toml sets clippy::undocumented_unsafe_blocks = "deny"; every unsafe block and unsafe impl must carry a // SAFETY: comment or the build fails. For unsafe impl Send on FFmpeg wrappers, see the convention in src/avhw/mod.rs — justification must be at the C-API level (atomic refcounts, libva VADisplay thread safety), not Rust borrow level.

Testing and verification

• Unit/focused tests can run with filters, e.g. cargo test transform, cargo test fps_limit, cargo test backend_detect.
• Full cargo test includes tests/integration_test.rs, which shells out to target/release/wl-webrtc; run cargo build --release first or those tests fail before reaching code behavior.
• Hardware/live tests are marked ignored; run them only on a Wayland session with VAAPI-capable GPU and writable output: cargo test -- --ignored.
• CLI smoke test surface: target/release/wl-webrtc --help and invalid-argument rejection. Real capture needs Wayland plus either wlr-screencopy or XDG Portal/PipeWire.
• The README CLI table is stale for --backend and --no-persist; src/args.rs is authoritative for flags.

Runtime architecture

• src/main.rs is the real entrypoint: parse Args, initialize tracing from RUST_LOG or -v, reject non-H.264, require --output or --port, detect backend, then run one of two loops.
• Backend detection in src/backend_detect.rs: explicit --backend portal|screencopy wins; otherwise wlr-screencopy is preferred when the Wayland global zwlr_screencopy_manager_v1 exists, else Portal/PipeWire is used if D-Bus ScreenCast is available.
• Do not use ashpd for backend availability checks; backend_detect.rs intentionally uses raw zbus because ashpd caches a zbus::Connection in a global and can hang after its owning Tokio runtime is dropped.
• src/state.rs drives the wlroots path using a mio Wayland fd loop and State<CapWlrScreencopy>; src/state_portal.rs drives the Portal/PipeWire path through CapPortal frame channels.
• src/webrtc.rs is a small embedded HTTP/WebRTC signaling server using str0m; --port 0 means file-output mode, --port > 0 enables WebRTC mode.

Unsafe and FFI work

• FFmpeg/VAAPI/PipeWire code relies on raw FFI and many unsafe blocks. Preserve nearby // SAFETY: explanations and add one for any new unsafe block.
• src/avhw/ (split from the former src/avhw.rs in commit d53e881) owns FFmpeg AVBufferRef / frame / codec contexts. Five types (AvHwDevCtx, AvHwFrameCtx, EncState, SwEncState, SwEncEncode) carry unsafe impl Send; soundness was Oracle-audited on 2026-07-09 against FFmpeg/libva threading semantics. Moving them across threads is sound because the C APIs use atomic refcounts, not because of any Rust-side exclusivity — see src/avhw/mod.rs for the full convention.
• CapPortal stores the portal restore token under the user cache directory (wl-webrtc/portal-restore-token); use --no-persist when manually testing fresh authorization behavior.

Useful manual commands

• List Wayland globals: cargo run --example list_globals.
• Portal permission smoke test: cargo run --example test_portal.
• Portal/VAAPI benchmarks require a screen-share dialog and hardware: cargo run --bin vaapi_import_bench -- --output /tmp/vaapi_bench.mp4 and cargo run --bin sw_encode_bench -- --output /tmp/bench_test.mp4.