enricobuehler
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Rework the client READMEs to be accurate and inviting to first-time
visitors, and fill in the gaps where crates and tools had none.
- Rewrite clients/{apple,android,decky} READMEs (features-first, trim
dense internal narrative; drop the stale "one session at a time" /
"renegotiation not implemented" section from the Apple README).
- Add READMEs for clients/{linux,windows,probe}, which had none.
- Add crate READMEs for punktfunk-host, punktfunk-core, pf-driver-proto.
- Add brief READMEs for tools/{loss-harness,latency-probe}.
- Fix packaging/README duplicate "Option B" heading (bootc -> Option C).
- Fix docs-site/README stale docs/ -> design/ reference.
- De-stale packaging/windows/drivers/pf-dualsense README (drop "M0 spike"
/ external-checkout framing; reflect in-tree workspace + shipped +
installer-bundled + multi-pad), keeping the driver-authoring lore.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
62 lines
3.3 KiB
Markdown
62 lines
3.3 KiB
Markdown
# punktfunk-core
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The **shared protocol core** — the one place where punktfunk's transport, forward error correction,
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and crypto live. It's linked into the [host](../punktfunk-host/README.md) and every native client, so
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there's exactly one implementation of the wire format everywhere.
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Written in Rust with **no async on the per-frame path** (native threads only). It exposes both a
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normal Rust API and a **stable, versioned C ABI**, so the Swift and Kotlin clients — and any C
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embedder — link the same code as the Rust ones.
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## What's in here
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- **Transport & session** (`session.rs`, `transport/`, `packet.rs`) — the `punktfunk/1` data plane
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over raw UDP: packetization, reassembly (with attacker-bounded limits), pacing, and socket tuning.
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- **FEC** (`fec/`) — the wall-breaker. Two codes:
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- **GF(2⁸)** classic Reed–Solomon with the *Cauchy* generator matrix — byte-identical to the
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`nanors` library Moonlight uses, so our parity is decodable by a stock Moonlight client.
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- **GF(2¹⁶) Leopard-RS** (SIMD, O(n log n)) — up to 65535 shards/block, which removes the ~1 Gbps
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FEC ceiling. `punktfunk/1` negotiates this one.
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- **Crypto** (`crypto.rs`) — AES-128-GCM session encryption with per-direction nonce salts and
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sequence-as-AAD; SPAKE2 PIN pairing lives behind the `quic` feature.
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- **QUIC control plane** (`quic.rs`, `client.rs`, feature `quic`) — the Hello/Welcome/Start handshake,
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cert pinning/TOFU, reverse audio, and the embeddable `NativeClient` connector. This is the **only**
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place `tokio`/`quinn` are allowed; the feature is **off by default** so the core stays runtime-free.
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- **C ABI** (`abi.rs`) — the versioned surface (`punktfunk_abi_version()`, `PunktfunkConfig` carrying
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its own `struct_size`) that generates [`include/punktfunk_core.h`](../../include/punktfunk_core.h)
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via cbindgen at build time.
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## Build outputs
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The crate builds three ways at once (`crate-type = ["lib", "cdylib", "staticlib"]`):
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| Output | Used by |
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|--------|---------|
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| `lib` (rlib) | the host, probe, and tools link it as a normal Rust crate |
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| `cdylib` (`.so`/`.dylib`) | the Swift / Kotlin clients via the C ABI |
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| `staticlib` (`.a`) | the C test harness and static embedding |
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## Test
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```sh
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cargo test -p punktfunk-core # unit + proptest + loopback
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cargo run -p loss-harness # FEC loss-resilience sweep (no network needed)
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bash crates/punktfunk-core/tests/c/run.sh # standalone C-ABI link + round-trip proof
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```
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## Design invariants (do not regress)
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- **One core, linked everywhere** — protocol/FEC/crypto live only here, behind the stable C ABI.
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- **No async on the hot path** — the per-frame pipeline is native threads only; `quic` (tokio/quinn)
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is control-plane only, feature-gated, off by default.
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- **Security hardening stays intact** — the reassembler bounds attacker-controlled fields before
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allocating; AES-GCM keeps per-direction nonce salts + seq-as-AAD; the ABI checks `struct_size`.
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Regression tests exist — keep them green.
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## Related
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- **[`punktfunk-host`](../punktfunk-host/README.md)** — the streaming host built on this core
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- **[Clients](../../clients/)** — the apps that link this core over the C ABI (or directly, in Rust)
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- **[`design/implementation-plan.md`](../../design/implementation-plan.md)** — why GF(2¹⁶) FEC, the
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latency budget, and the architecture thesis
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