Reset offsets increments sent offset by 1

[presjednik]

I couldn't find any documentation about this feature, so I hope someone can explain to me why the KafkaConsumerState class that handles the offset committing increments the sent offsets from TopicPartitionOffsetMetadata by one?

Here is the code:

      for (TopicPartitionOffsetMetadata t : offsetCommitRequest.getOffsets()) {
        if (t.getMetadata() == null) {
          offsetMap.put(
              new TopicPartition(t.getTopic(), t.getPartition()),
              new OffsetAndMetadata(t.getOffset() + 1));
        } else {
          offsetMap.put(
              new TopicPartition(t.getTopic(), t.getPartition()),
              new OffsetAndMetadata(t.getOffset() + 1, t.getMetadata()));
        }
      }

With this behaviour, if you want to commit the offset for a partition you need to send the wanted offset - 1. For example, if I want to set the offset to 0 i need to send this body:

{
	"offsets": [
		{
			"topic": "test-topic",
			"partition": 0,
			"offset": -1
		}
	]
}