Function fetch_segment 

async fn fetch_segment(
    io: &dyn WalObjectIo,
    object_seq: u64,
    entry: &FooterEntry,
) -> Result<Vec<Record>>

Fetches and decodes the segment entry describes in the object object_seq. A segment that does not decode is fetched once more, since the download rather than the object may be damaged; when it still does not decode the error is returned as Error::InvalidWalObject. A failed fetch is returned as is.