Method extract

crates/commitlog/src/commitlog.rs:454–499

(repo: impl Repo)

    }

    fn extract(repo: impl Repo) -> io::Result<Option<Self>> {
        let Some(MostRecentNonEmptySegment {
            empty_segments,
            segment_offset,
            mut segment_reader,
        }) = open_newest_non_empty_segment(&repo)?
        else {
            return Ok(None);
        };
        let offset_index = repo.get_offset_index(segment_offset).ok();
        match segment::Metadata::extract(segment_offset, &mut segment_reader, offset_index.as_ref()) {
            // Segment is intact.
            Ok(metadata) if empty_segments <= 1 => {
                assert!(
                    !metadata.tx_range.is_empty(),
                    "segment was promised to be non-empty but contains zero transactions"
                );
                Ok(Some(CommittedMeta::Complete { metadata }))
            }
            // Segment is good, but there are too many empty segments.
            Ok(metadata) => Ok(Some(CommittedMeta::Prefix {
                metadata,
                error: io::Error::new(
                    io::ErrorKind::InvalidData,
                    format!("repo {}: too many empty segments: {}", repo, empty_segments),
                ),
            })),
            // Segment is non-empty, but first commit is corrupt.
            Err(error::SegmentMetadata::InvalidCommit { sofar, source }) if sofar.tx_range.is_empty() => {
                Err(io::Error::new(
                    io::ErrorKind::InvalidData,
                    format!(
                        "repo {}: first commit in the most recent segment is corrupt: {}",
                        repo, source
                    ),
                ))
            }
            // Some prefix of the segment is good.
            Err(error::SegmentMetadata::InvalidCommit { sofar, source }) => Ok(Some(CommittedMeta::Prefix {
                metadata: sofar,
                error: source,
            })),
            // Something went wrong, including out-of-order errors and such.
            Err(error::SegmentMetadata::Io(e)) => Err(e),
        }
    }
}

impl From<CommittedMeta> for segment::Metadata {