Subsystem.SetTeardownHook installs a callback the subsystem invokes
just before closing per-stream Sources in onProcessStop. Used by the
WHEP Handler in M3 to drain its per-stream peer index before the
underlying Sources go away — closes the 'subscribers fan out into a
closed channel' race the design's §6 error matrix calls out as
'Publisher disconnects / FFmpeg exits'.
Single consumer by design (one subsystem, one handler). Calling
SetTeardownHook again replaces the previous callback; nil detaches.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Introduces the subsystem layer that sits alongside api.API and wires
the M1 core/webrtc primitives into the per-process restream lifecycle.
app/webrtc/subsystem.go:
- Subsystem struct holding the global WebRTC config, core PeerFactory,
per-process stream map, and logger
- New(config.DataWebRTC, logger) constructor
- Enabled(), Hooks(), Close(), lookup() methods
app/webrtc/lifecycle.go:
- onProcessStart: allocates an adjacent UDP port pair, binds two
Pion Sources (video on V, audio on V+1), registers them under the
process id, and returns the two RTP output legs to append to the
FFmpeg command.
- onProcessStop: tears down the pair.
- allocAdjacentPair: retries up to 10 times to find a free (V, V+1)
pair since the kernel's ephemeral picker can hand us an odd port.
- splitRTPLegs: converts BuildArgs' flat []string into two ConfigIO
entries by splitting on the second -map token.
core/webrtc/peer.go + forward.go:
- Adds PeerFactory.CreatePeerFromSources for the M2 two-source
forwarding mode (video and audio on separate UDP ports, no
payload-type sniffing). Leaves CreatePeer intact for the M1 PoC.
- Adds forwardRTPSplit companion goroutine.
config/data.go:
- Promote anonymous WebRTC struct to named type DataWebRTC so
app/webrtc can accept it by value.
