---
phase: 03-communication-protocol
plan: 01
subsystem: protocol
tags: [udp, wled, protocol, animation, led, struct, asyncio, tdd]

# Dependency graph
requires:
  - phase: 02-audio-engine
    provides: "FastAPI app with lifespan pattern and app.state for shared resources"
provides:
  - "WLED-compatible DRGB/DRGBW/DNRGB UDP frame encoders"
  - "Custom 0xAC animation command packet encoder/decoder (16 bytes)"
  - "UDPSender async transport wrapper (single shared socket)"
  - "SK6812Device.encode_animation_cmd — real 16-byte packets, not empty stub"
  - "WS2801Device.encode_animation_cmd — real 16-byte packets, not empty stub"
affects:
  - lightsync/protocol/ (new package)
  - lightsync/devices/sk6812.py
  - lightsync/devices/ws2801.py

# Tech tracking
tech-stack:
  added: []
  patterns:
    - "TDD RED-GREEN: failing tests committed first, implementation committed to pass them"
    - "Single shared asyncio DatagramTransport — one socket sends to N device addresses (no socket pool)"
    - "WLED DRGB/DRGBW: 2-byte header [type, timeout] + RGB/RGBW body per pixel"
    - "WLED DNRGB: 4-byte header [type, timeout, start_hi, start_lo] + RGB chunks per packet"
    - "struct.pack('>BBH') for big-endian DNRGB start index (critical per WLED spec)"
    - "struct.pack('>BBBBf') for 0xAC animation command header + float32 speed"
    - "_NullProtocol swallows OS UDP errors — fire-and-forget is correct for LED delivery"

key-files:
  created:
    - lightsync/protocol/__init__.py
    - lightsync/protocol/drgb.py
    - lightsync/protocol/animation_cmd.py
    - lightsync/protocol/udp_sender.py
    - tests/__init__.py
    - tests/test_protocol.py
  modified:
    - lightsync/devices/sk6812.py
    - lightsync/devices/ws2801.py

key-decisions:
  - "TDD approach: tests committed as RED before implementation — forces verification of test coverage"
  - "0xAC animation command marker chosen well above WLED 0x01-0x04 range — no firmware collision"
  - "UDPSender uses asyncio DatagramTransport over asyncudp library — no dependency needed, stdlib suffices"
  - "Device stubs delegate to encode_animation_cmd via import alias _encode_cmd — clean, no code duplication"
  - "pytest added as dev dependency via uv add --dev pytest — was missing from pyproject.toml"

# Metrics
duration: ~4min
completed: 2026-04-06
---

# Phase 3 Plan 01: Protocol Encoders Summary

**WLED-compatible UDP protocol layer implemented — DRGB/DRGBW/DNRGB frame encoders, custom 0xAC animation command packet with full roundtrip, async UDPSender transport, and SK6812/WS2801 device stubs replaced with real 16-byte packets — all tested with 27 passing tests**

## Performance

- **Duration:** ~4 min
- **Started:** 2026-04-06T21:38:29Z
- **Completed:** 2026-04-06T21:42:37Z
- **Tasks:** 2 (Task 1 TDD, Task 2 auto)
- **Tests:** 27 passing

## Accomplishments

### Task 1: Protocol encoders — DRGB/DRGBW/DNRGB + animation command (TDD)

RED phase: 27 failing tests committed covering all encoder behaviors including byte layout, MTU truncation, DNRGB multi-packet splitting, big-endian start index, animation roundtrip, flags byte, and defaults.

GREEN phase: Implemented `lightsync/protocol/drgb.py` with:
- `encode_drgb`: 2-byte header + 3-byte-per-pixel body, truncates at 490 px (MTU)
- `encode_drgbw`: 2-byte header + 4-byte-per-pixel body, truncates at 367 px (MTU)
- `encode_dnrgb_packets`: splits at 489 px/packet with big-endian start index via `struct.pack(">BBH")`

Implemented `lightsync/protocol/animation_cmd.py` with:
- `ANIMATION_IDS` and `ANIMATION_NAMES` dicts mapping 7 animation names to IDs 0-6
- `encode_animation_cmd`: 16-byte packet (0xAC marker, version, type ID, flags, speed float32, primary/secondary color, white, density)
- `decode_animation_cmd`: full inverse — roundtrips correctly for all 7 types

All 27 tests pass.

### Task 2: UDP sender + device stub completion

Created `lightsync/protocol/udp_sender.py`:
- `_NullProtocol` swallows OS-level send errors (UDP delivery is best-effort)
- `UDPSender` opens single shared DatagramTransport at `local_addr=("0.0.0.0", 0)`
- `send(payload, ip, port)` is synchronous fire-and-forget
- `start()`/`stop()` async lifecycle methods for FastAPI lifespan integration
- `is_running` property reflects transport state

Updated `lightsync/devices/sk6812.py` and `ws2801.py`:
- Added `from lightsync.protocol.animation_cmd import encode_animation_cmd as _encode_cmd`
- Replaced `return b""` stub with `return _encode_cmd(animation, params)`
- SK6812: `encode_animation_cmd("solid_color", {"color":[255,0,0], "white":128})` → `ac0100003f000000ff00000000008000` (16 bytes, starts 0xAC)
- WS2801: `encode_animation_cmd("chase", {"color":[0,255,0], "speed":0.7})` → `ac0101003f33333300ff000000000000` (16 bytes, starts 0xAC)

## Task Commits

1. **Task 1 RED: Failing protocol tests** — `ffc4ef6` (test)
2. **Task 1 GREEN: WLED encoders + animation cmd** — `5e13da3` (feat)
3. **Task 2: UDP sender + device stubs** — `f17e77f` (feat)

## Files Created/Modified

- `lightsync/protocol/__init__.py` — empty package init
- `lightsync/protocol/drgb.py` — DRGB/DRGBW/DNRGB encoders with WLED constants
- `lightsync/protocol/animation_cmd.py` — 0xAC animation command encoder/decoder
- `lightsync/protocol/udp_sender.py` — async UDP transport wrapper
- `tests/__init__.py` — test package init
- `tests/test_protocol.py` — 27 tests for protocol correctness
- `lightsync/devices/sk6812.py` — stub replaced with real encoding
- `lightsync/devices/ws2801.py` — stub replaced with real encoding

## Decisions Made

- **TDD approach applied**: Tests written and committed as RED before implementation, ensuring coverage is meaningful not retrofitted
- **0xAC marker**: Well above WLED 0x01-0x04 range — firmware can dispatch on first byte without ambiguity
- **No asyncudp library**: Python stdlib asyncio DatagramTransport is sufficient and avoids an extra dependency
- **pytest added as dev dep**: Was missing from pyproject.toml, added via `uv add --dev pytest`

## Deviations from Plan

### Auto-fixed Issues

**1. [Rule 3 - Blocking] pytest not installed**
- **Found during:** TDD RED phase (running tests)
- **Issue:** `uv run python -m pytest` failed with "No module named pytest"
- **Fix:** `uv add --dev pytest` — added to pyproject.toml [project.optional-dependencies] dev section
- **Files modified:** pyproject.toml (by uv)
- **Commit:** (included in uv lockfile update before ffc4ef6)

## Verification Results

- `python -m pytest tests/test_protocol.py -v` — 27 passed in 0.04s
- `from lightsync.protocol.drgb import encode_drgb, encode_drgbw, encode_dnrgb_packets` — imports OK
- `from lightsync.protocol.udp_sender import UDPSender` — imports OK
- SK6812Device.encode_animation_cmd returns 16-byte 0xAC packet — PASS
- WS2801Device.encode_animation_cmd returns 16-byte 0xAC packet — PASS

## Known Stubs

None — all planned stubs replaced with real implementations. The `encode_animation_cmd` stubs in SK6812Device and WS2801Device that returned `b""` are now wired to the real protocol encoder.

## Self-Check

Files created/modified:
- lightsync/protocol/__init__.py — FOUND
- lightsync/protocol/drgb.py — FOUND
- lightsync/protocol/animation_cmd.py — FOUND
- lightsync/protocol/udp_sender.py — FOUND
- tests/__init__.py — FOUND
- tests/test_protocol.py — FOUND
- lightsync/devices/sk6812.py — FOUND
- lightsync/devices/ws2801.py — FOUND

Commits:
- ffc4ef6 — test(03-01) RED phase
- 5e13da3 — feat(03-01) GREEN phase
- f17e77f — feat(03-01) Task 2

## Self-Check: PASSED

---
*Phase: 03-communication-protocol*
*Completed: 2026-04-06*