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punktfunk/crates/punktfunk-core
enricobuehler dd558be55b
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fix(core/client): fix the four ways a speed-test probe corrupts ABR and the report tick
There is one `ProbeState` per session and no correlation id, and two independent
requesters share it: the pump's startup link-capacity probe and the embedder's
`NativeClient::request_probe` (the shipped "Test connection" in the Windows GUI
and the Linux GTK app). The startup path had a busy check, a watchdog and a
window rebase; the embedder path had none of them, and the two collide by
default — both shipped speed tests call `request_probe` on the statement right
after `connect()`, and the pump's probe fires 2 s later, inside that burst.

Four defects, one cluster:

- The pump overwrote the shared slot unconditionally. Mid-burst it drops
  `base_packets`/`base_bytes`, the pump re-snapshots them against the host's
  full-burst denominator, and the user's speed test reports roughly an order of
  magnitude low; if the result lands first instead, the reset wipes `done` and
  the embedder's poll loop never sees its own measurement. Now it defers and
  retries rather than stealing the slot.

- An unanswered embedder probe never timed out. `probe_active` gates the entire
  report tick — LossReport, the ABR window feed, the standing-latency ladder and
  a pending ClockResync all live inside it. A host that ignores ProbeRequest is
  an anticipated configuration (the startup path was given a 6 s timeout for
  exactly that) so the embedder path could latch `active` forever and silently
  switch off every adaptation mechanism for the rest of the session. Now a
  watchdog covers a probe of either origin.

- `request_probe` latched `active` before `try_send`, so a full or closed ctrl
  channel returned `Closed` to the caller while leaving the session wedged in
  the state above. It now rolls back, mirroring the startup path.

- Only the startup path rebased the ABR window past the burst. Probe filler is
  counted into `bytes_received` for every accepted datagram but never reaches
  the decoder, and the tick is suppressed for the whole burst, so the first
  post-burst window read the burst rate as `actual_kbps`. That poisons
  `proven_kbps`, a monotone high-water mark that is never decayed, which
  disables the x1.5 evidence-gated climb guard for the session and authorizes a
  climb into a rate the decoder has never carried. The rebase now happens on the
  falling edge of any probe, and covers the loss/packet anchors too so the first
  post-burst LossReport isn't divided by a filler-inflated packet count.

Also: `wants_decode_latency` advertised on two of the three terms the pump
actually requires to arm ABR, omitting `resolved_bitrate_kbps > 0`, so against
an old host that reports no rate an embedder fed decode latency to a controller
that never runs.

No wire or ABI change.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-07-20 07:42:37 +02:00
..

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) — the punktfunk/1 data plane over raw UDP: packetization, reassembly (with attacker-bounded limits), pacing, and socket tuning.
  • FEC (fec/) — the wall-breaker. Two codes:
    • GF(2⁸) classic ReedSolomon with the Cauchy generator matrix — byte-identical to the nanors library 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/1 negotiates this one.
  • Crypto (crypto.rs) — AES-128-GCM session encryption with per-direction nonce salts and sequence-as-AAD; SPAKE2 PIN pairing lives behind the quic feature.
  • QUIC control plane (quic.rs, client.rs, feature quic) — the Hello/Welcome/Start handshake, cert pinning/TOFU, reverse audio, and the embeddable NativeClient connector. This is the only place tokio/quinn are allowed; the feature is off by default so the core stays runtime-free.
  • C ABI (abi.rs) — the versioned surface (punktfunk_abi_version(), PunktfunkConfig carrying its own struct_size) that generates include/punktfunk_core.h via 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.
  • 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