Command-line verbs

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Model gemma-mtp, commit ef58254ca7be, 2026-08-16, sources: 6. Edit the code or the hand-written documentation instead.

The handshake mechanism where the client declares its roles (producer, consumer) and name. The client must respond with roles= and name= to allow the harness to determine which checks to run Main.kt:43-46.

The `metadata` verb

Retrieving topic information, including partition IDs, log start offsets, and high watermarks. The client iterates through the topics and partitions returned by the broker to print partition=<id> <start_offset> <high_watermark> Main.kt:98-104.

The `produce` verb and `AckPolicy`

Mechanics of sending records and the behavior of AckPolicy.NONE (silent requests) versus WRITTEN and FORCED. The ack argument is mapped to an AckPolicy as follows:

Argument	`AckPolicy`	Behavior
`none`	`AckPolicy.NONE`	No response is expected; the client returns immediately `Main.kt:117`
`written`	`AckPolicy.WRITTEN`	Client waits for a response `Main.kt:118`
`forced`	`AckPolicy.FORCED`	Client waits for a response `Main.kt:119`

The `produce-keyed` verb and `Partitioner.Fnv1a`

How the client-side partitioner selects a partition based on a key before the broker sees the data. The client first fetches metadata to find available partitions and then uses Partitioner.Fnv1a.partitionFor to select the target partition Main.kt:158.

The `fetch` verb and `maxBytes` truncation

Retrieving records, handling the high watermark, and the edge case where a record exceeds maxBytes resulting in a truncated tail. If a response contains no complete records but the truncated flag is set, the client reports the truncatedRecordBytes Main.kt:182-184.

Exit codes and `ErrorCode` reporting

Distinguishing between client-side failures (non-zero exit) and broker-side refusals (exit zero with error=CODE). A broker refusal is considered a valid result and is reported via error=CODE on stdout Main.kt:84-85, whereas a client-side exception results in a non-zero exit code Main.kt:86.

Key files

File	Lines	What is there
`…/conformance/Main.kt`	`37-88`	The main entry point and verb dispatching logic
`…/conformance/Main.kt`	`108-132`	The `produce` verb implementation
`…/conformance/Main.kt`	`143-166`	The `produceKeyed` verb implementation
`…/conformance/Main.kt`	`168-189`	The `fetch` verb implementation

Behaviour that surprise

BooblikClient.sendProduce returns null when AckPolicy.NONE is used, which is a signal that no response should be read from the socket BooblikClient.kt:48.
A fetch request at the high watermark is not an error; it returns an empty list of records and the current high watermark ServerTest.kt:97-100.
produce-keyed requires the client to perform a metadata request first because the broker does not receive the key to perform partitioning itself Main.kt:136-150.