struct FileHeader {
    version: u64,
    header: u64,
    channel: u64,
    unhashed: u64,
    total: u64,
    offsets: DbOffsets,
    state: Merkle,

pub struct FileHeader {
    pub version: u64,
    pub header: u64,
    pub channel: u64,
    pub unhashed: u64,
    pub total: u64,
    pub offsets: DbOffsets,
    pub state: Merkle,

struct DbOffsets {
    internal: u64,
    external: u64,
    graph: u64,
    changes: u64,
    revchanges: u64,
    states: u64,
    tags: u64,
    apply_counter: u64,
    size: u64,

pub struct DbOffsets {
    pub internal: u64,
    pub external: u64,
    pub graph: u64,
    pub changes: u64,
    pub revchanges: u64,
    pub states: u64,
    pub tags: u64,
    pub apply_counter: u64,
    pub size: u64,

    header: FileHeader,
    file: std::fs::File,

    pub header: FileHeader,
    pub file: std::fs::File,

const BLOCK_SIZE: usize = 4096;

pub(crate) const BLOCK_SIZE: usize = 4096;