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use std::{mem::size_of, path::Path};
use crate::index::{self, Version, FAN_LEN, V2_SIGNATURE};
/// Returned by [`index::File::at()`].
#[derive(thiserror::Error, Debug)]
#[allow(missing_docs)]
pub enum Error {
#[error("Could not open pack index file at '{path}'")]
Io {
source: std::io::Error,
path: std::path::PathBuf,
},
#[error("{message}")]
Corrupt { message: String },
#[error("Unsupported index version: {version})")]
UnsupportedVersion { version: u32 },
}
const N32_SIZE: usize = size_of::<u32>();
/// Instantiation
impl index::File {
/// Open the pack index 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.
pub fn at(path: impl AsRef<Path>, object_hash: gix_hash::Kind) -> Result<index::File, Error> {
Self::at_inner(path.as_ref(), object_hash)
}
fn at_inner(path: &Path, object_hash: gix_hash::Kind) -> Result<index::File, Error> {
let data = crate::mmap::read_only(path).map_err(|source| Error::Io {
source,
path: path.to_owned(),
})?;
let idx_len = data.len();
let hash_len = object_hash.len_in_bytes();
let footer_size = hash_len * 2;
if idx_len < FAN_LEN * N32_SIZE + footer_size {
return Err(Error::Corrupt {
message: format!("Pack index of size {idx_len} is too small for even an empty index"),
});
}
let (kind, fan, num_objects) = {
let (kind, d) = {
let (sig, d) = data.split_at(V2_SIGNATURE.len());
if sig == V2_SIGNATURE {
(Version::V2, d)
} else {
(Version::V1, &data[..])
}
};
let d = {
if let Version::V2 = kind {
let (vd, dr) = d.split_at(N32_SIZE);
let version = crate::read_u32(vd);
if version != Version::V2 as u32 {
return Err(Error::UnsupportedVersion { version });
}
dr
} else {
d
}
};
let (fan, bytes_read) = read_fan(d);
let (_, _d) = d.split_at(bytes_read);
let num_objects = fan[FAN_LEN - 1];
(kind, fan, num_objects)
};
Ok(index::File {
data,
path: path.to_owned(),
version: kind,
num_objects,
fan,
hash_len,
object_hash,
})
}
}
fn read_fan(d: &[u8]) -> ([u32; FAN_LEN], usize) {
let mut fan = [0; FAN_LEN];
for (c, f) in d.chunks(N32_SIZE).zip(fan.iter_mut()) {
*f = crate::read_u32(c);
}
(fan, FAN_LEN * N32_SIZE)
}
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