punktfunk/CLAUDE.md

CLAUDE.md — punktfunk

Low-latency desktop/game streaming stack, Linux-first, with a shared Rust protocol core (punktfunk-core) exposed over a C ABI and native clients per platform. Full design: docs/implementation-plan.md. Status table: README.md.

Where the work stands

• M1 (punktfunk-core + C ABI): complete and hardened. FEC recovery, loopback-under-loss, proptests, C ABI harness all green; 13 adversarial-review findings fixed + regression-tested (a913042).
• M2 (GameStream host): working end-to-end with a stock Moonlight client. Validated live on this box: pairing (persists across restarts), serverinfo/applist (app catalog from ~/.config/punktfunk/apps.json → each entry picks a compositor + nested command), RTSP, ENet control, audio, and video at the client's native resolution and refresh — the host creates a per-session virtual output via per-compositor VirtualDisplay backends: KWin (zkde_screencast stream_virtual_output, needs KWin ≥ 6.5.6 headless; >60 Hz via custom modes), gamescope (spawned headless at WxH@Hz, its PipeWire node captured, needs gamescope ≥ 3.16.22 — older deadlocks on PipeWire ≥ 1.6), Mutter (D-Bus RecordVirtual virtual monitor; validated live on headless GNOME Shell 50, zero-copy), Sway/wlroots (swaymsg create_output + custom mode, xdpw portal capture with a managed chooser config; validated live on sway 1.11, zero-copy). Performance work landed and measured: GPU zero-copy on all paths (tiled dmabuf → EGL/GL → CUDA; LINEAR dmabuf → Vulkan bridge → CUDA → NVENC), auto 2-way NVENC split-encode above ~1 Gpix/s (5K@240), infinite GOP + RFI keyframes (killed the periodic freeze), encode|send thread split with sendmmsg batching. Stable 240 fps at 5120×1440. Input: mouse/keyboard (libei via RemoteDesktop portal on KWin/GNOME, gamescope's own EIS socket, wlr protocols on Sway) and gamepads (uinput X-Box-360 pads + rumble back-channel; validated live — pad created/destroyed with the session). Management REST API + checked-in OpenAPI doc (mgmt.rs).
• M3 (punktfunk/1, the native protocol): full session planes, validated live. QUIC control plane (punktfunk-core quic feature: Hello{mode}/Welcome{full Config}/Start), data plane = the hardened M1 Session over raw UDP with GF(2¹⁶) Leopard FEC + AES-GCM (inexpressible in GameStream), host creates the native virtual output at the client's requested mode. m3-host is a persistent listener (sessions back to back; --max-sessions). QUIC datagrams carry the side planes, demuxed by first byte: input 0xC8 (incl. gamepads — incremental events accumulated into the uinput xpad), Opus audio 0xC9 (48 kHz stereo, 5 ms, host→client), rumble 0xCA (host→client). Trust: host serves its persistent identity (~/.config/punktfunk/cert.pem, shared with GameStream pairing) and logs the SHA-256 fingerprint; clients pin it (TOFU on first connect — endpoint::client_pinned), and a PIN pairing ceremony (host displays a 4-digit PIN, proof = HMAC over both cert fingerprints, single attempt) establishes mutual trust: clients present persistent identities via QUIC client auth, the host stores paired fingerprints (punktfunk1-paired.json) and can gate sessions with --require-pairing. Mid-stream mode renegotiation: Reconfigure on the still-open control stream — the host rebuilds output+encoder at the new mode in ~90 ms while the data plane runs on (validated live: one .h265 with 720p and 1080p segments). Measured on-box at 720p120: 1680/1680 frames, p50 0.83 ms capture→…→reassembled; audio measured live (~200 pkts/s). punktfunk-client-rs is the working reference client (--pin, datagram counters, --input-test incl. gamepad). The embeddable connector (NativeClient) exposes it all over the C ABI: punktfunk_connect (pin/TOFU) + next_au/next_audio/next_rumble/send_input.

What's left

1. M4 — client decode + present: macOS stage 1 done, first light achieved (2026-06-10). PunktfunkKit compiles and is tested on macOS (AnnexB → VideoToolbox → AVSampleBufferDisplayLayer, GCMouse/GCKeyboard capture, PunktfunkClient app shell); validated live Mac ↔ this box at 720p60 — vkcube on glass, input injected via gamescope EIS. Tests: swift test in clients/apple (unit + real-codec round trip), test-loopback.sh (Swift client vs synthetic m3-host on loopback — runs on macOS), RemoteFirstLightTests (full pipeline over the LAN). See clients/apple/README.md. Next: stage 2 presenter (VTDecompressionSession + CAMetalLayer frame pacing), glass-to-glass numbers via tools/latency-probe (scaffold), iOS variant. The Linux reference client (punktfunk-client-rs) gets VAAPI + wgpu on the same connector later.
2. Sub-frame pipelining: overlap encode and transmit within a frame. Requires a direct NVENC SDK wrapper (libavcodec only emits whole AUs) — the next big latency lever (~2–4 ms at high res).
3. punktfunk/1 protocol growth: concurrent sessions (today: one at a time, extras wait in the accept queue); mgmt REST endpoints for the punktfunk/1 paired-client list.
4. M2 polish: HDR negotiation, reconnect-at-new-mode robustness.
5. Native clients (clients/{apple,android} scaffolds) consuming punktfunk_core.h.

Box one-time setup is complete: udev rule + input group (gamepads validated live), gamescope 3.16.22 installed system-wide (no PATH override), gnome-shell installed (Mutter backend validated live). All three compositor backends are live-validated.

Build / test / run

cargo build --workspace          # green on Linux and macOS
cargo test  --workspace          # unit + loopback + proptest + C ABI harness (~100 tests)
cargo clippy --workspace --all-targets -- -D warnings
cargo fmt --all --check

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

Generated artifacts are checked in and CI fails on drift: include/punktfunk_core.h (cbindgen from punktfunk-core/src/abi.rs) and docs/api/openapi.json (regenerate with cargo run -p punktfunk-host -- openapi > docs/api/openapi.json; spec lives in mgmt.rs).

Layout

crates/punktfunk-core/        protocol · FEC · crypto · quic (punktfunk/1 control plane, feature-gated)
crates/punktfunk-host/
  gamestream/             Moonlight compat: nvhttp · pairing · rtsp · control · stream · gamepad · apps
  vdisplay/{kwin,gamescope,mutter,wlroots}.rs   per-compositor client-sized virtual outputs
  zerocopy/{egl,cuda,vulkan}.rs         dmabuf → CUDA → NVENC (tiled via EGL/GL, LINEAR via Vulkan)
  inject/{libei,wlr,gamepad}.rs         input backends (+ uinput virtual gamepads)
  capture.rs · encode.rs · audio.rs · m0.rs · m3.rs · mgmt.rs
crates/punktfunk-client-rs/   punktfunk/1 reference client (M3 headless; M4 adds decode+present)
tools/{loss-harness,latency-probe}/     measurement (plan §10)
scripts/                  60-punktfunk.rules · punktfunk-host.service · host.env.example · headless/
include/punktfunk_core.h      generated C header

Design invariants — do not regress

• One core, linked everywhere. Protocol/FEC/crypto live only in punktfunk-core, behind a stable, versioned C ABI. tokio/quinn exist only behind the quic feature (control plane); no async on the per-frame path — native threads only.
• Native client resolution, no scaling. A session gets a virtual output at exactly the client's WxH@Hz via the VirtualDisplay trait (create(mode) → VirtualOutput { node_id, remote_fd, preferred_mode, keepalive }, RAII teardown). There is no cross-compositor protocol for this — each compositor keeps its own backend.
• FEC is the wall-breaker. GF(2⁸) (≤255 shards/block, Moonlight-compatible) and GF(2¹⁶) Leopard (≤65535 shards/block) — punktfunk/1 negotiates the latter, removing the ~1 Gbps ceiling.
• M1 security hardening stays intact: reassembler bounds attacker-controlled fields before allocating (ReassemblerLimits); AES-GCM per-direction nonce salts + seq-as-AAD; ABI struct_size checks. Regression tests exist — keep them green.
• PipeWire consumer discipline: our capture streams set node.dont-reconnect and tear down promptly on negotiation timeout — one wedged link head-blocks the daemon's shared work queue system-wide.

Running on this box

Headless QEMU VM (Ubuntu 26.04, kernel 7.0), passthrough RTX 5070 Ti (driver 595 open module — a kernel update silently drops it; reinstall nvidia-driver-595-open), no KMS scanout → KWin --drm impossible; everything renders offscreen via renderD128.

# compositor session (shell 1, or the systemd unit in scripts/): full headless Plasma.
# The script sets XDG_MENU_PREFIX=plasma- & co. — without it plasmashell runs but the
# launcher menu is EMPTY (no apps, no System Settings).
bash scripts/headless/run-headless-kde.sh 1920x1080

# host (shell 2):
WAYLAND_DISPLAY=wayland-kde XDG_CURRENT_DESKTOP=KDE PUNKTFUNK_VIDEO_SOURCE=virtual \
PUNKTFUNK_ZEROCOPY=1 cargo run -rp punktfunk-host -- serve

# punktfunk/1 native loopback test (no Moonlight needed; same env as serve, listener persists
# across sessions — bound it with --max-sessions):
cargo run -rp punktfunk-host -- m3-host --source virtual --seconds 10 --max-sessions 1
cargo run -rp punktfunk-client-rs -- --mode 1280x720x120 --out /tmp/a.h265 --input-test  # + --pin HEX

Pinned crate facts: ashpd 0.13 + pipewire 0.9 (must match ashpd's) + ffmpeg-next 8.x (system FFmpeg 8 / libavcodec 62). Env knobs: PUNKTFUNK_VIDEO_SOURCE=virtual|portal, PUNKTFUNK_COMPOSITOR=kwin|gamescope|mutter, PUNKTFUNK_ZEROCOPY=1, PUNKTFUNK_GAMESCOPE_APP=..., PUNKTFUNK_INPUT_BACKEND=..., PUNKTFUNK_PERF=1 (per-stage timing), PUNKTFUNK_VIDEO_DROP=N (FEC test), PUNKTFUNK_FEC_PCT=N.

Conventions

• Rust 2021, rustfmt + clippy -D warnings clean before commit.
• Match the surrounding code's comment density and naming.
• Commit messages end with the Co-Authored-By trailer (see git log).
• pkill caution on this box: match exact comm names (pkill -x gamescope-wl, pkill -x punktfunk-host) — pkill -f self-matches the invoking shell.