enricobuehlerandClaude Opus 5
a12f1f092c
Phase 4 + WP3.2 of design/audio-quality-and-latency.md. **The defect.** Every client ring primed *up* to a target and clamped at a ceiling, and none walked the depth back *down*. Any transient — a Wi-Fi arrival burst, a host stall, or plain host-DAC-vs-client-DAC skew of a few dozen ppm — therefore added latency permanently, until an underrun happened to re-prime. Android, with no shed at all, converged on its 120 ms hard cap and stayed there for the rest of the session; that is the "audio latency is too high" report. Apple did shed, 40 ms in one go, which its own comment called "one audible blip". All four now share `punktfunk_core::audio::JitterPolicy`: depths in MILLISECONDS rather than device quanta (`3 x quantum` meant 15 ms at a 5 ms quantum and a silent 64 ms at a 20 ms one), a crossfaded 5 ms shed once the depth average has sat above target for 2 s of consumed audio, and de-prime hysteresis. Linux and Windows had never had that hysteresis — they still carried the `if ring.is_empty()` instant re-prime that Android identified as self-inflicted crackle, where one transient drain manufactured a whole target's worth of silence. Android's floor drops 40 -> 25 ms: the policy grows the target on the devices that actually underrun, instead of every device pre-paying for the worst one. The Windows ring moves from raw bytes to interleaved f32 so it can share the policy and the crossfade helper at all. Apple is the one client where the policy is hand-written in a second language, so it gets its own XCTest (`AudioRingDriftTests`). Verified here by compiling `AudioRing.swift` standalone against a simulation harness — +200 ppm for 5 minutes settles at 30 ms with zero silent callbacks, where the old ring would have ridden its 80 ms high-water mark. **WP3.2 — recovery lives in core, not in the clients.** The rebuilt frame is re-inserted into the demux queue in order, so every embedder (including any C-ABI consumer) gets a complete stream without knowing the `0xD2` plane exists, and their `AudioGapTracker` simply stops seeing the gap. `recovery_and_the_gap_tracker_agree` pins exactly that. For the same reason core advertises CLIENT_CAP_AUDIO_RED itself rather than making four embedders remember to. Verified: clippy --all-targets -D warnings and the full test suites for punktfunk-core, pf-client-core, punktfunk-host, pf-host-config under Linux/docker (163 + 61 tests); punktfunk-client-android `cargo ndk check` for aarch64 with the gate proven non-vacuous by a planted type error, and its 6 clippy findings confirmed IDENTICAL to the pristine file (all are the documented arm64-only artifacts); AudioRing.swift type-checked and simulated on macOS; fmt. The Windows client half (audio_wasapi.rs) is still not compile-verified anywhere. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
punktfunk-core
The shared protocol core — the one place where punktfunk's transport, forward error correction, and crypto live. It's linked into the host and every native client, so there's exactly one implementation of the wire format everywhere.
Written in Rust with no async on the per-frame path (native threads only). It exposes both a normal Rust API and a stable, versioned C ABI, so the Swift and Kotlin clients — and any C embedder — link the same code as the Rust ones.
What's in here
- Transport & session (
session.rs,transport/,packet.rs) — thepunktfunk/1data plane over raw UDP: packetization, reassembly (with attacker-bounded limits), pacing, and socket tuning. - FEC (
fec/) — the wall-breaker. Two codes:- GF(2⁸) classic Reed–Solomon with the Cauchy generator matrix — byte-identical to the
nanorslibrary Moonlight uses, so our parity is decodable by a stock Moonlight client. - GF(2¹⁶) Leopard-RS (SIMD, O(n log n)) — up to 65535 shards/block, which removes the ~1 Gbps
FEC ceiling.
punktfunk/1negotiates this one.
- GF(2⁸) classic Reed–Solomon with the Cauchy generator matrix — byte-identical to the
- Crypto (
crypto.rs) — AES-128-GCM session encryption with per-direction nonce salts and sequence-as-AAD; SPAKE2 PIN pairing lives behind thequicfeature. - QUIC control plane (
quic.rs,client.rs, featurequic) — the Hello/Welcome/Start handshake, cert pinning/TOFU, reverse audio, and the embeddableNativeClientconnector. This is the only placetokio/quinnare allowed; the feature is off by default so the core stays runtime-free. - C ABI (
abi.rs) — the versioned surface (punktfunk_abi_version(),PunktfunkConfigcarrying its ownstruct_size) that generatesinclude/punktfunk_core.hvia cbindgen at build time.
Build outputs
The crate builds three ways at once (crate-type = ["lib", "cdylib", "staticlib"]):
| Output | Used by |
|---|---|
lib (rlib) |
the host, probe, and tools link it as a normal Rust crate |
cdylib (.so/.dylib) |
the Swift / Kotlin clients via the C ABI |
staticlib (.a) |
the C test harness and static embedding |
Test
cargo test -p punktfunk-core # unit + proptest + loopback
cargo run -p loss-harness # FEC loss-resilience sweep (no network needed)
bash crates/punktfunk-core/tests/c/run.sh # standalone C-ABI link + round-trip proof
Design invariants (do not regress)
- One core, linked everywhere — protocol/FEC/crypto live only here, behind the stable C ABI.
- No async on the hot path — the per-frame pipeline is native threads only;
quic(tokio/quinn) is control-plane only, feature-gated, off by default. - Security hardening stays intact — the reassembler bounds attacker-controlled fields before
allocating; AES-GCM keeps per-direction nonce salts + seq-as-AAD; the ABI checks
struct_size. Regression tests exist — keep them green.
Related
punktfunk-host— the streaming host built on this core- Clients — the apps that link this core over the C ABI (or directly, in Rust)
- punktfunk-planning:
implementation-plan.md(internal planning repo) — why GF(2¹⁶) FEC, the latency budget, and the architecture thesis