fegger
7be8d59d07
Add mDNS/DNS-SD discovery and JSON session negotiation so two peers on a LAN connect without hard-coded addresses. - Discovery (Avahi threaded-poll client): the receiver announces _screencast._tcp with its signaling port; senders browse and resolve peers. Strict lock ordering (poll lock before state mutex) keeps the callbacks deadlock-free; name collisions rename via avahi_alternative_service_name. - Signaling: one JSON object per newline-terminated TCP line. The receiver hosts a server (port 5005) and answers session offers with its RTP port; senders connect, offer, and stream to the negotiated endpoint. WebSocket was deferred: no WS library is installed, the skill permits plain TCP, and the wire format is transport-agnostic. - Dual-stack transports: this machine resolves its own services over IPv6, so getaddrinfo now runs AF_UNSPEC and listeners bind IPv6 with IPV6_V6ONLY=0 (IPv4 fallback), covering UDP and TCP alike. The signaling client shutdown now uses shutdown() so a reader blocked in recv() cannot hang the join (a plain close() does not wake it). - CLI: --discover lists receivers (deduped to one entry per host); --send auto-disovers when exactly one receiver is found; --peer targets a receiver directly; --signaling-port overrides the default. Validation: meson test 5/5 (new signaling round-trip test), valgrind clean. End-to-end over loopback: --discover finds the announced receiver, a probe negotiated a session and streamed 60 frames over both IPv4 and IPv6, and the receiver reported stream started. mDNS resolution was verified against avahi-browse as an independent reference.
3.4 KiB
Development Phases
This file breaks the project into incremental milestones. Each phase produces a working, testable slice of functionality. Do not start a phase until the previous one is validated.
Phase 1 — Project Skeleton
Goal: configure, compile, and run tests with no real dependencies.
- Meson build files (
meson.build,meson_options.txt). - Public module headers with
namespace sc. - Unit test that exercises a trivial utility function.
README.mdwith build instructions.
Validation: meson setup build && meson compile -C build && meson test -C build.
Phase 2 — Software H.264 Encode / Decode
Goal: encode raw pixel buffers to H.264 and decode them back, purely with FFmpeg software paths.
- Add
libavcodec,libavutil,libswscaledependencies. - Implement
EncoderFactory::create()andEncoder::encode(). - Implement
DecoderFactory::create()andDecoder::decode(). - Round-trip test: synthetic RGB frames → H.264 → decoded RGB.
Validation: unit test produces visually/structurally correct round-trip frames.
Phase 3 — PipeWire Screen Capture
Goal: capture the desktop and feed frames into the encoder.
- Add
libpipewire-0.3dependency. - Implement
CaptureFactory::create()using the xdg-desktop-portal. - Wire
CaptureSession::next_frame()→Encoder::encode()in a local smoke test that just writes a few encoded frames to disk.
Validation: manual run on a real Linux desktop session produces a valid H.264 bitstream.
Phase 4 — RTP Framing
Goal: packetize NAL units into RTP and depacketize them.
- Implement
RtpHeaderandRtpPacketserialize/parse. - Add H.264 NAL splitting and FU-A fragmentation.
- Unit test for serialization, fragmentation, and reassembly.
Validation: unit tests cover single-NAL and fragmented packet paths.
Phase 5 — Local UDP Sender → Receiver Loopback
Goal: send RTP packets over UDP and render the result locally.
- Implement
RtpTransportwith ASIO or raw UDP sockets. - Wire sender pipeline: capture → encode → RTP → localhost UDP.
- Wire receiver pipeline: localhost UDP → RTP → decode → renderer.
- Add SDL2/SDL3 dependency and a minimal
Renderer.
Validation: screencast --send and screencast --receive on the same
machine show the captured desktop in a window.
Phase 6 — LAN Signaling and Discovery
Goal: two peers on the same LAN can find each other and negotiate a session.
- Implement mDNS/DNS-SD discovery with Avahi.
- Implement JSON signaling (newline-delimited JSON over TCP for now; the WebSocket transport is deferred to Phase 7 with its dependency).
- Extend CLI with
--peerand--discover.
Validation: two peers connect without hard-coded IP addresses. Validated end-to-end over loopback: discovery finds the announced receiver, the sender negotiates a session over the signaling channel, and streams to the negotiated endpoint over both IPv4 and IPv6.
Phase 7 — Resilience and Polish
Goal: loss recovery, hardware acceleration, and packaging.
- NACK / PLI feedback loop.
- Jitter buffer on the receiver.
- VAAPI/NVENC hardware encode probes and fallback.
- Optional GUI target behind
meson -Dgui=true. .desktopfile, icon, packaging notes.
Validation: sustained streaming under packet loss; hardware accel smoke where available.
Current phase
Phase 7 — Resilience and Polish.