git_pack/data/entry/
decode.rs

1use std::io;
2
3use git_features::decode::{leb64, leb64_from_read};
4
5use super::{BLOB, COMMIT, OFS_DELTA, REF_DELTA, TAG, TREE};
6use crate::data;
7
8/// Decoding
9impl data::Entry {
10    /// Decode an entry from the given entry data `d`, providing the `pack_offset` to allow tracking the start of the entry data section.
11    ///
12    /// # Panics
13    ///
14    /// If we cannot understand the header, garbage data is likely to trigger this.
15    pub fn from_bytes(d: &[u8], pack_offset: data::Offset, hash_len: usize) -> data::Entry {
16        let (type_id, size, mut consumed) = parse_header_info(d);
17
18        use crate::data::entry::Header::*;
19        let object = match type_id {
20            OFS_DELTA => {
21                let (distance, leb_bytes) = leb64(&d[consumed..]);
22                let delta = OfsDelta {
23                    base_distance: distance,
24                };
25                consumed += leb_bytes;
26                delta
27            }
28            REF_DELTA => {
29                let delta = RefDelta {
30                    base_id: git_hash::ObjectId::from(&d[consumed..][..hash_len]),
31                };
32                consumed += hash_len;
33                delta
34            }
35            BLOB => Blob,
36            TREE => Tree,
37            COMMIT => Commit,
38            TAG => Tag,
39            _ => panic!("We currently don't support any V3 features or extensions"),
40        };
41        data::Entry {
42            header: object,
43            decompressed_size: size,
44            data_offset: pack_offset + consumed as u64,
45        }
46    }
47
48    /// Instantiate an `Entry` from the reader `r`, providing the `pack_offset` to allow tracking the start of the entry data section.
49    pub fn from_read(
50        mut r: impl io::Read,
51        pack_offset: data::Offset,
52        hash_len: usize,
53    ) -> Result<data::Entry, io::Error> {
54        let (type_id, size, mut consumed) = streaming_parse_header_info(&mut r)?;
55
56        use crate::data::entry::Header::*;
57        let object = match type_id {
58            OFS_DELTA => {
59                let (distance, leb_bytes) = leb64_from_read(&mut r)?;
60                let delta = OfsDelta {
61                    base_distance: distance,
62                };
63                consumed += leb_bytes;
64                delta
65            }
66            REF_DELTA => {
67                let mut buf = git_hash::Kind::buf();
68                let hash = &mut buf[..hash_len];
69                r.read_exact(hash)?;
70                #[allow(clippy::redundant_slicing)]
71                let delta = RefDelta {
72                    base_id: git_hash::ObjectId::from(&hash[..]),
73                };
74                consumed += hash_len;
75                delta
76            }
77            BLOB => Blob,
78            TREE => Tree,
79            COMMIT => Commit,
80            TAG => Tag,
81            _ => panic!("We currently don't support any V3 features or extensions"),
82        };
83        Ok(data::Entry {
84            header: object,
85            decompressed_size: size,
86            data_offset: pack_offset + consumed as u64,
87        })
88    }
89}
90
91#[inline]
92fn streaming_parse_header_info(mut read: impl io::Read) -> Result<(u8, u64, usize), io::Error> {
93    let mut byte = [0u8; 1];
94    read.read_exact(&mut byte)?;
95    let mut c = byte[0];
96    let mut i = 1;
97    let type_id = (c >> 4) & 0b0000_0111;
98    let mut size = c as u64 & 0b0000_1111;
99    let mut s = 4;
100    while c & 0b1000_0000 != 0 {
101        read.read_exact(&mut byte)?;
102        c = byte[0];
103        i += 1;
104        size += ((c & 0b0111_1111) as u64) << s;
105        s += 7
106    }
107    Ok((type_id, size, i))
108}
109
110/// Parses the header of a pack-entry, yielding object type id, decompressed object size, and consumed bytes
111#[inline]
112fn parse_header_info(data: &[u8]) -> (u8, u64, usize) {
113    let mut c = data[0];
114    let mut i = 1;
115    let type_id = (c >> 4) & 0b0000_0111;
116    let mut size = c as u64 & 0b0000_1111;
117    let mut s = 4;
118    while c & 0b1000_0000 != 0 {
119        c = data[i];
120        i += 1;
121        size += ((c & 0b0111_1111) as u64) << s;
122        s += 7
123    }
124    (type_id, size, i)
125}
git_pack/data/entry/decode.rs

git_pack/data/entry/
decode.rs
