Function read_bytes 

pub(super) fn read_bytes(
    conn: &Connection,
    zone_id: &str,
    name: &str,
    offset: i64,
    len: i64,
) -> Result<Vec<u8>, StoreError>

Bytes [offset, offset + len) of a file, straight from its parts (never the cache). A missing part reads as zeros, as append_data_at pads it.