A bad UDP packet on a flaky link could permanently wedge the voice path,
unrecoverable even across app restarts. Three defects:
1. Anti-replay window was advanced from the UNAUTHENTICATED header seq
before the AEAD tag was checked, and not rolled back on failure. One
corrupted/forged frame shoved recv_highest_ far ahead, after which every
legitimate frame was rejected as "too old" forever. Reorder to
replay-check -> authenticate -> update (RFC 3711 3.3); the window now
moves only after a successful tag check.
2. The wire seq was only the low 16 bits of the nonce counter (zero-extended
on receive). After 65,536 frames the nonce desynced and all frames failed
auth. Widen the voice frame seq u16 -> u64 (header 14 -> 20 bytes). The
core owns all UDP framing, so Swift/C# clients need only a rebuild. This
is a versioned wire change: VOICECAT_PROTOCOL_VERSION 1 -> 2, handshake
rejects on mismatch.
3. Server leaked per-session UDP state on disconnect; unregister_session now
frees udp_endpoints_/udp_tokens_/ssrc_to_session_.
Also add rate-limited dropped-frame logging to MediaRelay so a wedged media
path is observable. New regression tests in test_media_aead.cpp cover the
poison (fails on old code) and the 16-bit wrap. ctest --preset dev
-E external_pcm: 22/22 pass (external_pcm aborts on a pre-existing CoreAudio
shutdown race, unrelated).
Three reported bugs traced to one root cause plus two missing designed features:
1. Stale users + eternal PLC hiss (root cause): ConnSession::close() silently
erased dropped users without broadcasting UserEvent::LEFT, so peers never
learned the user left and their audio engines never called remove_stream —
Opus PLC synthesized comfort noise forever. Fix: broadcast_left() helper
+ close() broadcasts LEFT before erasing.
2. PLC cap (defense-in-depth): on_playback now caps pure PLC at ~2s, then
emits digital silence so a stale stream can never hiss forever even if
remove_stream is skipped. Resets automatically on fresh packets.
3. No timeout / no ping: client never sent Ping, server had no last_seen /
reaper, so half-open connections (NAT timeout, wifi loss, sleep) left
ghost users forever. Fix: client Ping every 15s with RTT measurement,
ConnSession::last_seen bumped on every inbound TCP/UDP frame, steady_timer
reaper sweeps every 15s and drops sessions older than 45s (configurable
via server::Config).
4. UDP KEEPALIVE: client sends plaintext kFrameKeepalive every 5s; server
bumps last_seen + echoes back. Keeps NAT bindings alive and lets media
activity defer the reaper independently of TCP.
5. Graceful client disconnect: vc_disconnect() sends Disconnect{code=0} via
a flag-based io-thread exit (no double-close race); server handles
client-sent Disconnect with immediate close() + LEFT broadcast.
3 new tests: disconnect_left, plc_cap, reaper_timeout. 21/21 ctest green.
Docs: protocol.md §6/§7, voice.md §6, architecture.md §5, PROGRESS.md.
The media AEAD nonce is an implicit per-direction monotonic counter;
open() reconstructs it from the 14-byte header seq field (the AAD), so
the contract is header.seq == the counter seal() used. The SFU relay
decrypted inbound frames with the sender key, re-sealed with the
recipient send_crypto (its own counter), but forwarded the sender
header verbatim -- so seq carried the wrong counter and the recipient
rebuilt the wrong nonce, silently dropping every relayed frame. It only
worked for a single first-ever sender into a fresh recipient, which is
why reverse/3rd-party audio failed.
Rewrite the outgoing header seq to the recipient peek_send_counter()
before re-sealing so each server->client direction is one contiguous
monotonic counter and the nonce always matches. Safe: the jitter buffer
orders by timestamp, not seq. No wire-format/proto/ABI change.
Adds test_relay_interleaved_reseal regression coverage.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Adds the full voice pipeline: 14-byte binary frame header, ChaCha20-Poly1305
AEAD keyed from the TLS exporter, libopus encode/decode with FEC/PLC/DTX,
an adaptive per-ssrc jitter buffer, a miniaudio capture/playback engine, an
APM passthrough stub, and the UdpBinding/StreamAnnounce signaling chain
wired through ConnSession/SessionRegistry into a new server-side SFU
(MediaRelay) that decrypts and re-encrypts frames per channel member.
Exit criterion verified: test_m2_voice — two headless clients relay 50
encrypted Opus frames through the server; ctest --preset m1-dev is 9/9
green. Also corrects protocol.md's UdpBinding diagram, which described the
UDP-side binding packet as AEAD-sealed when it is in fact a plaintext
bootstrap frame (separate from the TCP/TLS UdpBinding ack).
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
