Kafka Conformance

Surgewave aims to be a drop-in replacement for Apache Kafka. This section is the authoritative, externally-verifiable statement of what's in scope, what's implemented, and what is intentionally out of scope. Pages are kept in sync with the wire-protocol code and tracked in CI.

If you're integrating a Kafka client against Surgewave, these pages tell you whether your client's path is on the wired, advertised-only, or unsupported side of the matrix — without having to read source.

Headline numbers

  • Kafka 4.0 wire-protocol RPCs implemented: 56 / ~55
  • Kafka 4.2 wire-protocol RPCs advertised: 60 of 93 enum entries
  • Wired with full handler logic: 72 RPCs (admin surface complete)
  • Advertised but not wired: 0 — every advertised admin RPC has a handler
  • Major KIPs implemented: 15 (KIP-98, KIP-516, KIP-595, KIP-714, KIP-848, KIP-853 (wire-only), KIP-892, KIP-894 (partial), KIP-903, KIP-932, KIP-936, KIP-985, KIP-994, KIP-1071, KIP-895)
  • Confluent Schema Registry: wire format + REST API audited compatible (details)
  • Cross-client tested: Confluent.Kafka 2.x (.NET), librdkafka 2.14 (CGv2 e2e), Confluent.SchemaRegistry contract-pinned

Sections

Page Scope
Kafka API matrix Per-RPC table across all 93 ApiKey enum entries — status, handler, version range, notes
KIP coverage Per-KIP status with evidence pointers, conformance test inventory, cross-client matrix, known gaps
Schema Registry Confluent Schema Registry wire-format + REST API compatibility

Status legend

Status Meaning
Wired A real handler processes the request and returns a meaningful response. Round-trip-tested against at least one Kafka client.
Wired (rejects) Handler is registered and returns a precise structured error (e.g., LogDirNotFound for JBOD operations on a single-dir broker, UnsupportedVersion for unimplemented online voter changes). Better than the dispatcher's generic UNSUPPORTED_VERSION because admin tools see the precise reason.
Stub Handler exists; accepts the request and returns a well-formed but degenerate response (e.g. empty subscription set). Clients see success and continue. Documented per row.
gRPC-only Functionality lives in Kuestenlogik.Surgewave.Api.Grpc; no Kafka wire handler is registered. A Kafka-wire client will see UNSUPPORTED_VERSION (35).
Advertised, not wired ApiVersions lists the key, but no handler is registered. Currently empty — every advertised RPC has a handler.
Not implemented No handler, not advertised. Hard UnsupportedApiKey response if a client somehow calls it.

Source of truth

The canonical document is CONFORMANCE.md at the repository root. The pages here mirror it for navigability inside the docs site.

The matrix is generated from the same code that runs at runtime:

When a new RPC is wired or a version is bumped, the source plus this docs section update in the same PR.

Non-goals (intentional)

  • Kafka MirrorMaker 2 control plane. Surgewave.Replication ships its own cluster-link control plane; MirrorMaker is not emulated.
  • ZooKeeper protocol. Surgewave is KRaft-native; the legacy ZK control plane is intentionally absent.
  • Wire-level emulation of internal Kafka controller RPCs (AlterPartition, Envelope, ControllerRegistration, AssignReplicasToDirs). Surgewave has its own controller; clients never see these.
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