use std::path::{Path, PathBuf}; use crate::data; /// Instantiationimpl data::File<crate::MMap> {    /// Try opening a data file at the given `path`.    ///    /// The `object_hash` is a way to read (and write) the same file format with different hashes, as the hash kind    /// isn't stored within the file format itself.    ///    /// This constructor leaves allocation limiting disabled, allowing allocations of any size dictated by pack data.    /// Use [`Self::from_data()`] together with [`File::with_alloc_limit_bytes()`][crate::data::File::with_alloc_limit_bytes()]    /// when working with untrusted input.    pub fn at(path: impl AsRef<Path>, object_hash: gix_hash::Kind) -> Result<Self, data::header::decode::Error> {        Self::at_inner(path.as_ref(), object_hash)    }     fn at_inner(path: &Path, object_hash: gix_hash::Kind) -> Result<Self, data::header::decode::Error> {        let data = crate::mmap::read_only(path).map_err(|e| data::header::decode::Error::Io {            source: e,            path: path.to_owned(),        })?;        Self::from_data(data, path.to_owned(), object_hash)    }} impl<T> data::File<T>where    T: crate::FileData,{    /// Instantiate a data file from `data` as assumed to be read or memory-mapped from `path`.    ///    /// This constructor leaves allocation limiting disabled, allowing allocations of any size dictated by pack data.    /// Call [`File::with_alloc_limit_bytes()`][crate::data::File::with_alloc_limit_bytes()] before decoding entries from untrusted input.    pub fn from_data(data: T, path: PathBuf, object_hash: gix_hash::Kind) -> Result<Self, data::header::decode::Error> {        use crate::data::header::N32_SIZE;        let hash_len = object_hash.len_in_bytes();        let pack_len = data.len();        let id = gix_features::hash::crc32(path.as_os_str().to_string_lossy().as_bytes());        if pack_len < N32_SIZE * 3 + hash_len {            return Err(data::header::decode::Error::Corrupt(format!(                "Pack data of size {pack_len} is too small for even an empty pack with shortest hash"            )));        }        let (kind, num_objects) =            data::header::decode(&data[..12].try_into().expect("enough data after previous check"))?;        Ok(Self {            data,            path,            id,            version: kind,            num_objects,            object_hash,            alloc_limit_bytes: None,        })    }     /// Configure the maximum size of a single allocation caused by user-controlled on-disk pack data.    ///    /// Use `None` to disable the limit, which is also the default.    ///    /// This is currently enforced when decoding pack entries and resolving delta chains.    /// Callers that allocate from pack metadata directly should consult [`File::alloc_limit_bytes()`][crate::data::File::alloc_limit_bytes]    /// and apply the same limit themselves.    pub fn with_alloc_limit_bytes(mut self, alloc_limit_bytes: Option<usize>) -> Self {        self.alloc_limit_bytes = alloc_limit_bytes;        self    }}