kaas-codec

The Kafka wire-protocol codec: frames, primitives, CRC32C, KIP-482 tagged fields, and per-API request/response types with the ApiSpec registry.

The wire boundary of the whole system. Everything here is pinned by fixture tests: every registered API key/version encodes and decodes byte-identically against captures from Apache Kafka 3.7.

Module map: frame.rs (length-prefixed framing, streaming FrameReader), primitives.rs + tagged.rs (Kafka primitive types and KIP-482 compact/tagged encoding), headers.rs (per-API header-version resolution), crc.rs (CRC32C batch verification), errors.rs, one module per API under src/api/, and src/api/registry.rs — the ApiSpec table.

The invariant callers must hold: RecordBatch payloads are byte-opaque. There is no Record struct in this crate, and none may be added — batch bytes travel as Option<bytes::Bytes>, and the only code reading past the fixed v2 header is CRC verification and the batch-header walker (recordbatch_count.rs). Any future violation must bump the counters in tripwires.rs, which tests assert are zero. The full rationale is in Wire protocol & framing.

The registry is load-bearing: src/api/registry.rs::ALL (36 entries, count-asserted by a unit test) drives the ApiVersions response, the header-version lookup, and the book's generated API matrix — adding an API without a registry row is structurally impossible to ship quietly.

Where the boundary sits: kaas-codec knows nothing about storage, Kubernetes, or request handling — its only workspace consumers are kaas-protocol (framing/dispatch) and the handler layer above.

Start reading at src/api/registry.rs, then one small API module (src/api/api_versions.rs) end to end.