Method from_segment_tail

nodedb-columnar/src/format.rs:304–347

Parse a footer from the tail of a segment byte slice. Reads footer_len and CRC from the last 8 bytes, then deserializes the footer and validates the CRC.

(data: &[u8])

    /// Reads footer_len and CRC from the last 8 bytes, then deserializes
    /// the footer and validates the CRC.
    pub fn from_segment_tail(data: &[u8]) -> Result<Self, crate::error::ColumnarError> {
        if data.len() < 8 {
            return Err(crate::error::ColumnarError::TruncatedSegment {
                expected: 8,
                got: data.len(),
            });
        }

        let tail = &data[data.len() - 8..];
        let footer_len = u32::from_le_bytes(tail[0..4].try_into().map_err(|_| {
            crate::error::ColumnarError::Corruption {
                segment_id: None,
                reason: "footer length field: expected 4 bytes at segment tail - 8".into(),
                offset: Some((data.len() - 8) as u64),
            }
        })?) as usize;
        let stored_crc = u32::from_le_bytes(tail[4..8].try_into().map_err(|_| {
            crate::error::ColumnarError::Corruption {
                segment_id: None,
                reason: "footer CRC field: expected 4 bytes at segment tail - 4".into(),
                offset: Some((data.len() - 4) as u64),
            }
        })?);

        let footer_start = data.len().checked_sub(8 + footer_len).ok_or(
            crate::error::ColumnarError::TruncatedSegment {
                expected: 8 + footer_len,
                got: data.len(),
            },
        )?;

        let footer_bytes = &data[footer_start..footer_start + footer_len];
        let computed_crc = crc32c::crc32c(footer_bytes);

        if computed_crc != stored_crc {
            return Err(crate::error::ColumnarError::FooterCrcMismatch {
                stored: stored_crc,
                computed: computed_crc,
            });
        }

        zerompk::from_msgpack(footer_bytes)
            .map_err(|e| crate::error::ColumnarError::Serialization(e.to_string()))
    }
}

#[cfg(test)]