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Kafka OffsetFetch Response Wire Format v4 — 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.

Related Errors

COORDINATOR_NOT_AVAILABLE · GROUP_AUTHORIZATION_FAILED · INVALID_GROUP_ID · NOT_COORDINATOR · TOPIC_AUTHORIZATION_FAILED · UNKNOWN_TOPIC_ID · UNSTABLE_OFFSET_COMMIT

Wire Diagram

Response Header
message_size int32 · 4B
correlation_id int32 · 4B
OffsetFetchResponse v4
ThrottleTimeMs int32 · 4B
Topics array
ErrorCode int16 · 2B
Name string
Partitions array
PartitionIndex int32 · 4B
CommittedOffset int64 · 8B
Metadata? string
ErrorCode int16 · 2B

Schema & Example

Schema
{
  "ThrottleTimeMs": int32,
  "Topics": [{
      "Name": string,
      "Partitions": [{
          "PartitionIndex": int32,
          "CommittedOffset": int64,
          "Metadata": string?,
          "ErrorCode": int16
      }]
  }],
  "ErrorCode": int16
}
Example
{
  "ThrottleTimeMs": 0,
  "Topics": [{
      "Name": "orders",
      "Partitions": [{
          "PartitionIndex": 3,
          "CommittedOffset": 150382,
          "Metadata": "",
          "ErrorCode": 0
      }]
  }],
  "ErrorCode": 0
}