enricobuehler
810d918d36
`io::read_msg` frames a message with two `quinn::RecvStream::read_exact` calls, and quinn documents `read_exact` as explicitly NOT cancel-safe: the bytes it has already taken out of the stream live only in the future's own buffer and nothing puts them back on drop. Both long-lived control loops drive that read from a `tokio::select!` arm — the client pump alongside `ctrl_rx.recv()` and the resync tick, the host alongside probe/reconfig/clip-offer channels — and neither uses `biased;`, so any sibling that becomes ready ends the iteration and drops a partially-progressed read. `clock_sync` has the same shape via `tokio::time::timeout`, which can fire mid-frame before the session even starts. A control frame only has to straddle two wakeups for this to bite: a ClipOffer carries up to 16 kinds x 128 bytes of MIME, ~2 KB, which exceeds one QUIC packet and is subject to the pacer; any frame whose second half is lost or reordered does it too. Losing the consumed length prefix misaligns the stream permanently — the next read takes two payload bytes as a length, so Reconfigured, ProbeResult, BitrateChanged, ClockEcho and ClipState all decode as garbage and are silently dropped, and a bogus length up to 64 KiB parks the read forever. Mode switches, adaptive bitrate, mid-stream clock resync and clipboard are dead for the rest of the session; only a reconnect recovers, and the log shows at most one `warn!`. Add `io::MsgReader`, which keeps the frame in progress in the reader rather than the future and reads via quinn's cancel-safe `read`, and switch the three cancelling sites to it (client control loop, host control loop, clock_sync). The sequential handshake/pairing callers keep the plain `read_msg`, whose doc comment now states the constraint. No wire bytes and no ABI change — only how the same length-prefixed frames are assembled. Tests: a frame split across two wakeups with the read cancelled in between must resume and leave the following frame correctly framed (confirmed to fail — it hangs on the desynced stream — against the old behavior), plus a zero-length frame round-trip. Co-Authored-By: Claude Opus 4.8 <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