Roadmap

Phase 2 has landed. The library was admin-first with a browse-shaped read path; it now has a real producer and both consumer-group protocols, which is what "general-purpose Kafka client" was shorthand for.

The milestone breakdown with acceptance criteria lives in PLAN.md (M0–M19). This page is what shipped, what is deliberately still missing, and what nothing in this repository can move.

What phase 2 delivered (M12–M19)

The producer — kafka-produce.

Both traps this page flagged before M12 was written got resolved rather than discovered:

• acks=0 is not offered. A request with no response would leave a pending oneshot in the connection actor forever, so every successful write would report a timeout. It is refused at the config boundary rather than given a fire-and-forget path.
• The max_in_flight warning turned out to be the wrong worry. At most one batch per partition is on the wire regardless, so ordering does not depend on the setting at all. The clamp — one without idempotence, five with — is defence for the connection layer, not the mechanism keeping the log in order.

The consumer — kafka-consume.

M18 was conditional on the classic protocol being needed, and it was: the acceptance suite runs a mixed group with one Rust member and one kafka-console-consumer.sh, which is the case that makes byte-compatible assignor payloads non-optional.

Two gaps found after the fact and since closed: a caller had no way to flush per-partition state before revocation, so on_rebalance now runs on_revoke while the member still owns the partitions and before the auto-commit; and the classic path advertised only eager assignors, so cooperative-sticky joined them.

Publishing. The crates are on crates.io, releasing in lockstep at a single version — see RELEASING.md. kafka-consume joins the published set at 0.3.0.

Next

Nothing here is structural. These are ordinary gaps with no blocker beyond someone doing them.

• Java's StickyAssignor. The classic path ships three of the four assignors PLAN.md lists — range, round-robin and cooperative-sticky. Plain sticky is the eager one that keeps assignments stable across a rebalance without the two-round handover, and it is the remaining name a mixed group might vote for.
• KIP-699 batched FindCoordinator. The v4+ coordinator_keys shape is already used, but with one key per request. Batching is one round trip instead of one per group, which matters for a UI rendering hundreds.
• DescribeQuorum — the one KRaft-adjacent API a cluster UI plausibly wants. Present in the ApiKey enum and reachable through generic dispatch; there is no typed method.
• Delegation token management. Only the ACL resource type exists today; Create/Renew/Expire/DescribeDelegationToken do not.
• OffsetForLeaderEpoch, UpdateFeatures, ListConfigResources — routing entries only, no user-facing surface.

Blocked upstream

Not roadmap items, because nothing in this repository can move them. See The upstream schema gap:

• Streams groups (KIP-1071) — no schema in kafka-protocol 0.17, so a 4.1+ cluster running Kafka Streams reports groupType=streams in ListGroups and we surface it as Unrecognized rather than describing it.
• ListOffsets -6 (EARLIEST_PENDING_UPLOAD_TIMESTAMP) — needs v11; the codec caps at v10. The other five sentinels are surfaced.
• Error codes past Kafka 4.1 — surfaced as Unknown(i16) until upstream names them.