enricobuehler
dda9ed1aa2
146 sites, 141 of them in `abi.rs`, the `extern "C"` surface `cbindgen` turns into `punktfunk_core.h`. Writing 141 independent arguments would have been the wrong answer and would have read like it: they are instances of ONE contract in six shapes — opaque handles reached only through `as_mut()`/`as_ref()` (so null becomes a status, never a dereference), caller-owned out-params (null-checked exactly where the header calls them optional), NUL-terminated-or-null C strings through `opt_cstr`, unchanged forwarding to a versioned entry point, fixed-length output buffers, and `addr_of!` reads. So the contract is stated once at the top of the file, the way `pf-win-display`'s CCD contract is, and each site says which instance it is. Two properties that hold everywhere are stated there and not repeated 141 times: no pointer is retained past the call that received it, and every entry point runs inside `guard`'s `catch_unwind`, so a panic becomes a status code instead of unwinding into C. The `addr_of!` sites got a real proof rather than a shape, because that one is load-bearing and non-obvious: it forms a raw pointer WITHOUT creating a reference precisely because the caller's struct may be an older, smaller version, so the field must be read by offset and not through a `&`. `transport/udp/linux.rs`'s five are genuinely individual — two `zeroed()` POD initialisations, and the `sendmmsg`/`recvmmsg`/`CMSG` trio, where the argument worth writing down is that `msg_controllen` is set to `CMSG_SPACE(size_of::<u16>())` and the `CmsgBuf` is 64 bytes, so the kernel cannot write past the control buffer. punktfunk-core now denies `undocumented_unsafe_blocks`. Verified: Linux .21 fmt + both CI clippy steps rc=0, and — since this is the C surface and comments alone should not change it — the C ABI harness still passes, 4 frames round-tripped byte-exact through lossy loopback.
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