Kafka OffsetFetch Request Wire Format v2 — Binary Protocol Layout

What is OffsetFetch?

Consumers call this on startup or after a rebalance to recover their last committed position, and kafka-consumer-groups.sh --describe uses it to show lag. Returns UNKNOWN_TOPIC_OR_PARTITION if the group never committed to a partition, meaning auto.offset.reset applies.

Schema
{
  "GroupId": string,
  "Topics": [{
      "Name": string,
      "PartitionIndexes": [int32]
  }]?
}

Example
{
  "GroupId": "order-processors",
  "Topics": [{
      "Name": "orders",
      "PartitionIndexes": [1, 2, 3]
  }]?
}