const CRC_KEY: &str = "mira.crc32";Expand description
CRC32 of the record-batch body, stored in the footer’s custom metadata along with the exact byte length it covers. arrow-ipc has no checksum of its own: a valid footer over a corrupt body decodes silently into wrong answers.
The length is stored rather than derived from the footer offset because
finish() appends an end-of-stream marker after the last batch and before
the footer, so “everything before the footer” and “everything the writer had
emitted when we snapshotted” differ by those bytes.