[bercedev]

Description

KafkaAckableMessage.nack() seeked only the partition of raw_message[0]. A batch can span partitions, as in the issue's [(0, 1), (0, 2), (1, 0), (1, 1), (2, 0), (2, 1)]. With AckPolicy.NACK_ON_ERROR, only partition 0 was rewound, and the next successful batch's commit() committed past the records of partitions 1 and 2 that were never processed.

nack() now collects the lowest offset the batch holds in each partition and seeks every one of them. A single message works as before: one seek to its own offset. The confluent KafkaMessage.nack() had the same raw_message[0] pattern, so it gets the same change: one seek(topic, partition, offset) per partition in the batch. Records without a topic, partition or offset are still skipped.

Fixes #3280

Type of change

• Bug fix (a non-breaking change that resolves an issue)

Checklist

• My code adheres to the style guidelines of this project: ruff check, ruff format --check (0.14.14) and mypy (1.19.1) are clean on the changed files. I didn't run the full just lint.
• I have conducted a self-review of my own code
• I have added tests to validate the effectiveness of my fix or the functionality of my new feature
• Both new and existing unit tests pass successfully on my local environment by running just test-coverage: not run in full, see below.

New tests in tests/brokers/kafka/test_message_nack.py and tests/brokers/confluent/test_message_nack.py build the message with a stub consumer that records its seek() calls:

• a batch over three partitions, with the records out of order within a partition, seeks partition 0 to 1, partition 1 to 0 and partition 2 to 4;
• a single message seeks its own partition and offset.

Without the change, the two batch tests fail (one seek, for partition 0 only), and the single-message tests pass. I had no Kafka broker, so I didn't rerun the issue's real-broker scenario. In my container, the test_test_client.py suites for both backends gave 167 passed and 10 failed. The first failure is KafkaConnectionError: Unable to bootstrap from localhost:9092 (a test that wants a real broker). I didn't compare the other nine against main.

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[IvanKirpichnikov]

Hi. I have to close your Pull Request because someone else submitted #3281 before you, and I merged it.