---
name: Processor Service
description: processor service: Phase 1 complete (all 11 tasks), key patterns, conventions, and quirks
type: project
---

Phase 1 complete. All 11 tasks landed. The throughput pipeline is done: consumer + writer + metrics + integration test + Docker + CI.

**Architecture divergence from tcp-ingestion:**
- ESLint `import/no-restricted-paths` zone: `src/core/` cannot import `src/domain/` (preemptive for Phase 2).
- `INSTANCE_ID` defaults to `'processor-1'` (fixed string, not random UUID). Deterministic for container environments.
- `REDIS_CONSUMER_NAME` defaults to `INSTANCE_ID` at runtime (after schema parse), not as a zod schema default.
- `connectRedis` lives in `src/core/consumer.ts` (not `src/db/`). Rationale: only the consumer needs a Redis connection in Phase 1.

**Buffer.toJSON() gotcha in JSON.stringify replacers:**
- `Buffer.isBuffer(value)` is false inside a `JSON.stringify` replacer for nested Buffer properties because `Buffer.prototype.toJSON()` fires before the replacer.
- Must handle both `instanceof Uint8Array` (direct reference) AND the `{ type: 'Buffer', data: number[] }` shape. See `serializeAttributes` in `src/core/writer.ts`.

**writer.ts — RETURNING duplicate detection:**
- `ON CONFLICT DO NOTHING` does not return conflicting rows. Duplicates detected via set-diff on (device_id, ts) between input and RETURNING rows.

**LRU Map trick (state.ts):**
- Plain `Map` with `delete` + `set` on every update. `keys().next().value` is always the oldest. O(1), no external library.

**Metrics (task 1.9):**
- `src/observability/metrics.ts` exports: `createMetrics()`, `startMetricsServer()`, `createPostgresHealthCheck()`, `createConsumerLagSampler()`.
- `createPostgresHealthCheck`: cached `SELECT 1`, 5 s TTL, background interval, sync `isReady()` accessor for `/readyz`.
- `createConsumerLagSampler`: uses `XINFO GROUPS` → `lag` field (Redis 7.2+); falls back to `XLEN` if absent.
- `processor_device_state_size` is a gauge updated via `metrics.observe()` in the sink (not in state.ts — avoids coupling state to metrics).
- prom-client counters with label dims do NOT emit `{label} 0` at init. Test accordingly (check label-less counters for zero baseline).

**Integration test (task 1.10):**
- `test/pipeline.integration.test.ts`: 4 scenarios. Skip-on-no-Docker pattern: try container start in `beforeAll`, set `dockerAvailable = false` on error, each `it` early-returns.
- TimescaleDB image: `timescale/timescaledb:latest-pg16` (not stock postgres).
- Consumer uses a separate `connectRedis` connection; test XADD uses a separate `redisClient`. Mirrors production topology.
- Test 4 (retry): stops pgContainer then restarts it. `pgContainer.restart()` returns a new `StartedTestContainer`. Must reassign `pgContainer` for the `afterAll` cleanup to reference the right instance.

**Test patterns:**
- `connectWithRetry` tests: use `maxAttempts=1` for process.exit test to avoid fake-timer noise.
- Consumer tests: sink calls `void consumerRef?.stop()` to exit the loop.
- Inline `import()` type annotations forbidden by ESLint (`@typescript-eslint/consistent-type-imports`). Always use top-level `import type`.

**Dockerfile:**
- `EXPOSE 9090` only (no TCP listener — Processor has none).
- `HEALTHCHECK` uses `${METRICS_PORT:-9090}` default.
- Label `org.opencontainers.image.source` not included (not in tcp-ingestion original either).

**Why:**
Phase 1 is the throughput pipeline + operational baseline. Phase 2 (domain logic) and Phase 3 (hardening) build on top.

**How to apply:**
Phase 2 adds domain logic to `src/domain/` — no changes to `src/core/`. Phase 3 adds graceful shutdown polish, XAUTOCLAIM, and state rehydration.