The map

Every expedition starts with a map. kacrab’s territory is small on purpose: three client surfaces sharing one transport, one config system, and one generated protocol — each layer a crate or module with a sharp boundary.

flowchart TB
  subgraph app[Your application]
    P["Producer<br/>send / flush / transactions"]
    K["Consumer<br/>subscribe / poll / commit"]
    AD["AdminClient<br/>62 operations"]
  end
  subgraph kacrab[kacrab crate]
    CFG["config<br/>Java-style ClientConfig,<br/>typed configs, validation"]
    COM["common<br/>TopicPartition, Node,<br/>OffsetAndMetadata, …"]
    WIRE["wire<br/>broker sessions, request pipeline,<br/>SASL/TLS, metadata, reconnect"]
  end
  subgraph proto[kacrab-protocol crate]
    GEN["generated request/response types,<br/>record batch v2, compression, CRC32C"]
  end
  P --> WIRE
  K --> WIRE
  AD --> WIRE
  WIRE --> GEN
  P -.uses.-> CFG
  K -.uses.-> CFG
  AD -.uses.-> CFG
  P -.shares.-> COM
  K -.shares.-> COM
  AD -.shares.-> COM

The regions

• config — the Kafka property surface (bootstrap.servers, acks, group.id, compression.type, sasl.*, ssl.*, …) with typed parsing and validation, generated from official Kafka config metadata and drift-checked against it. The field guide is the practical tour of this surface.
• wire — the async transport every client rides: per-broker Tokio sessions, a bounded in-flight request pipeline, the SASL/TLS handshakes, metadata fetch + leader-change invalidation, and reconnect/backoff. See First contact and Security.
• common — shared org.apache.kafka.common domain types (TopicPartition, OffsetAndMetadata, Node, …), always compiled and re-exported by every surface, so a TopicPartition is the same type whether a producer, consumer, or admin call hands it to you.
• producer — batching accumulator, the dispatch path that groups batches per broker leader, and the idempotent/transactional state machine. See Following one record and Exactly once.
• consumer — manual assignment and group subscription over both group protocols, the fetch/position/offset state machines, and incremental fetch sessions. See The consumer client.
• admin — the full Apache Kafka 4.3.0 Admin operation surface with controller/coordinator/per-leader/broadcast routing. See The admin client.
• kacrab-protocol — the generated wire types, record-batch v2 encode/decode, compression codecs, and CRC32C. Zero hand-written byte patching. See Learning the language.

The parts left blank

Kafka Streams and share groups (queues) are deliberately outside this map — they are separate products built on clients, not client surfaces. Everything a Kafka 4.3 client does — produce, consume, administer, authenticate — is implemented.

Choosing your provisions

Every surface is a Cargo feature and default = [], so you enable exactly what you use:

[dependencies]
kacrab = { version = "0.1", features = ["producer", "consumer", "admin"] }

consumer pulls in the compression meta-feature (fetched batches must be decodable regardless of what the producer chose). zstd and lz4-hc compile C code; a pure-Rust build is possible — the trade-offs are in Traveling light and the field guide.