gix_pack/index/
init.rs

1use std::{mem::size_of, path::Path};
2
3use crate::index::{self, Version, FAN_LEN, V2_SIGNATURE};
4
5/// Returned by [`index::File::at()`].
6#[derive(thiserror::Error, Debug)]
7#[allow(missing_docs)]
8pub enum Error {
9    #[error("Could not open pack index file at '{path}'")]
10    Io {
11        source: std::io::Error,
12        path: std::path::PathBuf,
13    },
14    #[error("{message}")]
15    Corrupt { message: String },
16    #[error("Unsupported index version: {version})")]
17    UnsupportedVersion { version: u32 },
18}
19
20const N32_SIZE: usize = size_of::<u32>();
21
22/// Instantiation
23impl index::File {
24    /// Open the pack index file at the given `path`.
25    ///
26    /// The `object_hash` is a way to read (and write) the same file format with different hashes, as the hash kind
27    /// isn't stored within the file format itself.
28    pub fn at(path: impl AsRef<Path>, object_hash: gix_hash::Kind) -> Result<index::File, Error> {
29        Self::at_inner(path.as_ref(), object_hash)
30    }
31
32    fn at_inner(path: &Path, object_hash: gix_hash::Kind) -> Result<index::File, Error> {
33        let data = crate::mmap::read_only(path).map_err(|source| Error::Io {
34            source,
35            path: path.to_owned(),
36        })?;
37        let idx_len = data.len();
38        let hash_len = object_hash.len_in_bytes();
39
40        let footer_size = hash_len * 2;
41        if idx_len < FAN_LEN * N32_SIZE + footer_size {
42            return Err(Error::Corrupt {
43                message: format!("Pack index of size {idx_len} is too small for even an empty index"),
44            });
45        }
46        let (kind, fan, num_objects) = {
47            let (kind, d) = {
48                let (sig, d) = data.split_at(V2_SIGNATURE.len());
49                if sig == V2_SIGNATURE {
50                    (Version::V2, d)
51                } else {
52                    (Version::V1, &data[..])
53                }
54            };
55            let d = {
56                if let Version::V2 = kind {
57                    let (vd, dr) = d.split_at(N32_SIZE);
58                    let version = crate::read_u32(vd);
59                    if version != Version::V2 as u32 {
60                        return Err(Error::UnsupportedVersion { version });
61                    }
62                    dr
63                } else {
64                    d
65                }
66            };
67            let (fan, bytes_read) = read_fan(d);
68            let (_, _d) = d.split_at(bytes_read);
69            let num_objects = fan[FAN_LEN - 1];
70
71            (kind, fan, num_objects)
72        };
73        Ok(index::File {
74            data,
75            path: path.to_owned(),
76            version: kind,
77            num_objects,
78            fan,
79            hash_len,
80            object_hash,
81        })
82    }
83}
84
85fn read_fan(d: &[u8]) -> ([u32; FAN_LEN], usize) {
86    assert!(d.len() >= FAN_LEN * N32_SIZE);
87
88    let mut fan = [0; FAN_LEN];
89    for (c, f) in d.chunks_exact(N32_SIZE).zip(fan.iter_mut()) {
90        *f = crate::read_u32(c);
91    }
92    (fan, FAN_LEN * N32_SIZE)
93}
gix_pack/index/init.rs

gix_pack/index/
init.rs
