decode = async rawData => {
  const decoder = new Decoder(rawData)
  return {
    responses: decoder.readArray(decodeResponses),
    errorCode: decoder.readInt16(),
  }
}
OffsetFetch Response (Version: 2) => [responses] error_code
  responses => topic [partition_responses]
    topic => STRING
    partition_responses => partition offset metadata error_code
      partition => INT32
      offset => INT64
      metadata => NULLABLE_STRING
      error_code => INT16
  error_code => INT16