//! a pack data fileuse std::{convert::TryInto, path::Path}; /// The offset to an entry into the pack data file, relative to its beginning.pub type Offset = u64; /// An identifier to uniquely identify all packs loaded within a known context or namespace.pub type Id = u32; use memmap2::Mmap; /// An representing an full- or delta-object within a pack#[derive(PartialEq, Eq, Debug, Hash, Ord, PartialOrd, Clone)]#[cfg_attr(feature = "serde1", derive(serde::Serialize, serde::Deserialize))]pub struct Entry {    /// The entry's header    pub header: entry::Header,    /// The decompressed size of the object in bytes    pub decompressed_size: u64,    /// absolute offset to compressed object data in the pack, just behind the entry's header    pub data_offset: Offset,} mod file;pub use file::{decode_entry, verify, Header, ResolvedBase};///pub mod header; ///pub mod init {    pub use super::header::decode::Error;} ///pub mod entry; ///pub mod input; /// Utilities to encode pack data entries and write them to a `Write` implementation to resemble a pack data file.pub mod output; /// A slice into a pack file denoting a pack entry.////// An entry can be decoded into an object.pub type EntryRange = std::ops::Range<Offset>; /// Supported versions of a pack data file#[derive(PartialEq, Eq, Debug, Hash, Ord, PartialOrd, Clone, Copy)]#[cfg_attr(feature = "serde1", derive(serde::Serialize, serde::Deserialize))]#[allow(missing_docs)]pub enum Version {    V2,    V3,} impl Default for Version {    fn default() -> Self {        Version::V2    }} /// A pack data filepub struct File {    data: Mmap,    path: std::path::PathBuf,    /// A value to represent this pack uniquely when used with cache lookup, or a way to identify this pack by its location on disk.    /// The same location on disk should yield the same id.    ///    /// These must be unique per pack and must be stable, that is they don't change if the pack doesn't change.    /// If the same id is assigned (or reassigned) to different packs, pack creation or cache access will fail in hard-to-debug ways.    ///    /// This value is controlled by the owning object store, which can use it in whichever way it wants as long as the above constraints are met.    pub id: Id,    version: Version,    num_objects: u32,    /// The size of the hash contained within. This is entirely determined by the caller, and repositories have to know which hash to use    /// based on their configuration.    hash_len: usize,    object_hash: git_hash::Kind,} /// Information about the pack data file itselfimpl File {    /// The pack data version of this file    pub fn version(&self) -> Version {        self.version    }    /// The number of objects stored in this pack data file    pub fn num_objects(&self) -> u32 {        self.num_objects    }    /// The length of all mapped data, including the pack header and the pack trailer    pub fn data_len(&self) -> usize {        self.data.len()    }    /// The kind of hash we use internally.    pub fn object_hash(&self) -> git_hash::Kind {        self.object_hash    }    /// The position of the byte one past the last pack entry, or in other terms, the first byte of the trailing hash.    pub fn pack_end(&self) -> usize {        self.data.len() - self.hash_len    }     /// The path to the pack data file on disk    pub fn path(&self) -> &Path {        &self.path    }     /// Returns the pack data at the given slice if its range is contained in the mapped pack data    pub fn entry_slice(&self, slice: EntryRange) -> Option<&[u8]> {        let entry_end: usize = slice.end.try_into().expect("end of pack fits into usize");        let entry_start = slice.start as usize;        self.data.get(entry_start..entry_end)    }     /// Returns the CRC32 of the pack data indicated by `pack_offset` and the `size` of the mapped data.    ///    /// _Note:_ finding the right size is only possible by decompressing    /// the pack entry beforehand, or by using the (to be sorted) offsets stored in an index file.    ///    /// # Panics    ///    /// If `pack_offset` or `size` are pointing to a range outside of the mapped pack data.    pub fn entry_crc32(&self, pack_offset: Offset, size: usize) -> u32 {        let pack_offset: usize = pack_offset.try_into().expect("pack_size fits into usize");        git_features::hash::crc32(&self.data[pack_offset..pack_offset + size])    }} pub(crate) mod delta;