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The `0xCA` wire already carries the two Xbox impulse-trigger motors (v3), and the Rust decode path
already parses them; `datagram_task.rs` dropped them on the floor with a comment naming exactly this
work as what remained. The blocker was the C ABI: every non-Rust client pulls rumble through
`punktfunk_connection_next_rumble_cmd`, whose out-params cannot carry two more channels.
PunktfunkStatus punktfunk_connection_next_rumble_cmd2(
PunktfunkConnection *c, uint16_t *pad, uint16_t *low, uint16_t *high,
uint16_t *left_trigger, uint16_t *right_trigger,
uint32_t *backstop_ms, uint32_t timeout_ms);
⚠️ ADDED, not widened. `_cmd` keeps its signature and its values bit-identical for handle-only
traffic — out-of-tree embedders depend on it and `docs/embedding-the-c-abi.md` documents it, so
silently changing an exported symbol would break every consumer at once. `nm` on the staticlib shows
all four rumble entry points still exported. `ABI_VERSION` 17 → 18; every other site reads it
dynamically, so there are no hardcoded mirrors to drift.
⚠️ ONE HONEST BEHAVIOURAL DELTA, documented in `abi.rs` and pinned by a test: against a
trigger-driving host a `_cmd` caller now receives commands with `low == high == 0` where the demux
previously dropped the update entirely. They are idempotent handle stops, and the redundant-stop
suppression cannot fold them because the command as a whole is not silent. Zero cost today —
nothing sources non-zero triggers.
The dedupe-jitter proof was RE-DERIVED rather than widened, which is the kind of thing that quietly
rots when a tuple grows: the nudge touches only `low` by ±1 LSB and `emit` is only reached with a
non-silent level, so the nudged tuple can collide with the four-field stop sentinel only at
`(1,0,0,0)`. A test pins both directions — refuse at `(1,0,0,0)`, flip freely at `(1,0,lt,0)`.
Apple renders them: `RumbleRenderer` gains `Motor?` slots at `GCHapticsLocality.leftTrigger` /
`.rightTrigger` beside the existing handles. A controller without trigger actuators degrades
silently — a nil engine yields a nil slot and `reconcile` no-ops — and absent localities are never
logged, because on most pads that is the normal case rather than a fault. The macOS DualSense
raw-HID branch stays a deliberate no-op: a DualSense has ADAPTIVE triggers, not trigger rumble
motors, and inventing a mapping there would buzz the wrong thing.
🛑 BUILT AHEAD OF A PRODUCER, DELIBERATELY, AND NOTHING HERE CLAIMS OTHERWISE. Nothing can currently
source trigger rumble on Windows and that is measured, not assumed: `XINPUT_VIBRATION` has two
members, and GameInput — the only four-motor API — does not enumerate an xinputhid-promoted Xbox pad
at all, verified against a REAL Microsoft Elite which is equally invisible to it while classic
XInput reads it live. So this path has never been exercised end to end and the comments say so.
VERIFIED
* `cargo test -p punktfunk-core --features quic --lib` 378 passed on macOS, 203 on Windows;
clippy `-D warnings` clean with and without default features; `cargo fmt --all --check` clean.
* The generated header is regenerated and idempotent on re-run (CI diffs it).
* SWIFT ACTUALLY COMPILES AND RUNS: `swift build` clean and `swift test` 262 passed / 0 failures
in `clients/apple`, against a locally built xcframework. (Editor SourceKit errors about
`PunktfunkCore`/`DualSenseHID` are index noise from that gitignored artifact — a real build
resolves both, and the `DualSenseHID` references are untouched by this change.)
* `cargo build -p punktfunk-host` clean on Windows.
NOT VERIFIED
* End to end — see above; there is no producer.
* Whether a real Xbox pad on Apple actually reports the two trigger localities. The degrade needs
no code, but the positive case is untested.
* `pf-client-core` (the SDL renderer) does not build on macOS at baseline and is unbuilt here. It
only reads `RumbleCommand` fields and never constructs one, so added fields cannot break it, but
it still calls `_cmd`; wiring `SDL_RumbleGamepadTriggers` is separate work.
ANDROID: NOT DONE, and it should stay that way for now. `pack_rumble` packs pad/backstop/low/high
into bits 0..52 of a `jlong` with `-1` reserved as a sentinel — two more `u16` do not fit. The right
fix if ever wanted is the direct-`ByteBuffer` shape `nativeNextHidout` already uses in the same file
(zero-allocation, caller-owned, the established idiom), not a second `jlong` (racy across two calls)
nor `long[]` (an allocation per pull). But no Android device exposes trigger actuators at all, so
there is nothing to render. Separately stale and also not fixed: `NativeBridge.kt`'s KDoc still
documents the v2 `ttl_ms` layout rather than `backstop_ms`.
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