fn convert_and_save_cas_info()

in mdb_shard/src/shard_format.rs [411:464]

• 37 lines of code
• 3 McCabe index (conditional complexity)

    fn convert_and_save_cas_info<W: Write>(
        writer: &mut W,
        cas_content: &BTreeMap<MerkleHash, Arc<MDBCASInfo>>,
    ) -> Result<(
        (Vec<u64>, Vec<u32>),        // CAS Lookup Info
        (Vec<u64>, Vec<(u32, u32)>), // Chunk Lookup Info
        usize,                       // Bytes used for CAS Content Info
    )> {
        // CAS info lookup table.
        let mut cas_lookup_keys = Vec::<u64>::with_capacity(cas_content.len());
        let mut cas_lookup_vals = Vec::<u32>::with_capacity(cas_content.len());

        // Chunk lookup table.
        let mut chunk_lookup_keys = Vec::<u64>::with_capacity(cas_content.len()); // may grow
        let mut chunk_lookup_vals = Vec::<(u32, u32)>::with_capacity(cas_content.len()); // may grow

        let mut index: u32 = 0;
        let mut bytes_written = 0;

        for (cas_hash, content) in cas_content {
            cas_lookup_keys.push(truncate_hash(cas_hash));
            cas_lookup_vals.push(index);

            bytes_written += content.metadata.serialize(writer)?;

            for (i, chunk) in content.chunks.iter().enumerate() {
                bytes_written += chunk.serialize(writer)?;

                chunk_lookup_keys.push(truncate_hash(&chunk.chunk_hash));
                chunk_lookup_vals.push((index, i as u32));
            }

            index += 1 + content.chunks.len() as u32;
        }

        // Serialize a single bookend entry as a guard for sequential reading.
        bytes_written += CASChunkSequenceHeader::bookend().serialize(writer)?;

        // No need to sort cas_lookup_ because BTreeMap is ordered and we truncate by the first 8 bytes.

        // Sort chunk lookup table by key.
        let mut chunk_lookup_combined = chunk_lookup_keys.iter().zip(chunk_lookup_vals.iter()).collect::<Vec<_>>();

        chunk_lookup_combined.sort_unstable_by_key(|&(k, _)| k);

        Ok((
            (cas_lookup_keys, cas_lookup_vals),
            (
                chunk_lookup_combined.iter().map(|&(k, _)| *k).collect(),
                chunk_lookup_combined.iter().map(|&(_, v)| *v).collect(),
            ),
            bytes_written,
        ))
    }