v5.1.1

A major release since 5.0.2: new Admin/Consumer/Producer endpoints, streaming of poll
responses, large reliability and performance improvements, Windows service support,
an OpenAPI specification, and a substantially expanded test suite (90+ new tests).

Added

Admin endpoints

• describe-features, update-feature, delete-records, abort-transaction
• describe-group-configs, alter-group-config, delete-group-config
• create-topics — batch creation with a per-topic status (limit of 200 entries)
• set-topic-config renamed to alter-topic-config (old name kept as a deprecated alias)
• Topic deletion by id and a per-topic deletion status in delete-topics
• Optional validateOnly and retryOnQuotaViolation in create-topic(s)
• Optional timeoutMs on every admin request

Consumer endpoints

• unsubscribe, get-group-metadata, get-committed, get-partitions
  (replaces the deprecated list-partitions)
• seek-to-beginning / seek-to-end now accept multiple partitions

Producer endpoints

• Transactions: begin-transaction, commit-transaction, abort-transaction

System

• GET /health — liveness probe, no authentication required
• GET /version — now accessible without authentication

Streaming, performance, deployment

• Consumer poll responses are streamed with Transfer-Encoding: chunked in bounded
  chunks (-Dnetty.responseChunkBytes) instead of a single buffer
• One active request per connection (HttpRequestFlowControlHandler) for correct keep-alive
• Producer send via the Kafka callback (no virtual-thread blocking); blocking admin
  operations offloaded to virtual threads
• Asynchronous Kafka client close with bounded parallelism (-Dclient.close.parallelism)
• TCP_NODELAY, epoll transport, configurable Netty settings (worker threads, backlog,
  request size limits, timeouts), graceful shutdown within a single configurable deadline
• Windows service support via Apache Procrun (install-windows-service.ps1)
• Daily log file rolling (gzip, 30-day retention); console-only logging when -Dlog.dir is unset
• systemd unit hardening (LimitNOFILE, TimeoutStopSec, WorkingDirectory)
• OpenAPI 3.1 specification for all modules with a Swagger UI setup guide

Changed

• The /consumer/poll field timeout is deprecated in favor of timeoutMs; the poll
  timeout is capped by -Dnetty.readTimeoutSeconds (300 s by default)
• describe-topic accepts topicId as a string; the topic id in list-topics is a
  base64url string
• The distribution is laid out at the archive root (no version-nested directory) and
  includes README.md and the docs/ directory
• Kafka timeouts now return 504; woken-up consumers (WakeupException) return 503;
  a client config rejected by Kafka on create returns 400 (instead of 500)
• Content-Type / Accept are parsed as media types rather than exact strings
  (parameters and any casing are accepted)
• Response header names are always written in canonical case
• Instance expiration is measured with a monotonic clock (immune to system clock changes)
• Binary producer send preserves duplicate Kafka message header keys

Fixed

• Binary consumer poll truncation — clients received partial responses. Multiple root
  causes eliminated: timed-out connections no longer write a response over an in-flight
  chunked body; the read timeout counts only client idle time (not request processing or
  streaming); Transfer-Encoding is sent in canonical case for case-sensitive clients;
  leftover request content is discarded without closing the channel; pipeline exceptions
  are propagated to the inbound handler correctly
• create-topic endpoints occasionally not sending a response
• A race condition in describe-cluster responses
• consumer.wakeup() is now invoked before close() to avoid a close/poll race
• Data races (volatile expiration timestamp and Basic-auth user map)
• Heap exhaustion via unbounded length fields in the binary deserializer
• A ByteBuf leak on binary serialization errors
• Locale-dependent case folding pinned to Locale.ROOT
• Empty SCRAM username/password are rejected with 400 at instance creation

Dependencies

• Netty 4.2.17.Final, kafka-clients 4.1.2, hibernate-validator 9.1.3, log4j 2.26.1,
  jackson 2.22.1, JUnit 6.1.3