gix_pack/data/
delta.rs

1///
2pub mod apply {
3    /// Returned when failing to apply deltas.
4    #[derive(thiserror::Error, Debug)]
5    #[allow(missing_docs)]
6    pub enum Error {
7        #[error("Encountered unsupported command code: 0")]
8        UnsupportedCommandCode,
9        #[error("Delta copy from base: byte slices must match")]
10        DeltaCopyBaseSliceMismatch,
11        #[error("Delta copy data: byte slices must match")]
12        DeltaCopyDataSliceMismatch,
13    }
14}
15
16/// Given the decompressed pack delta `d`, decode a size in bytes (either the base object size or the result object size)
17/// Equivalent to [this canonical git function](https://github.com/git/git/blob/311531c9de557d25ac087c1637818bd2aad6eb3a/delta.h#L89)
18pub(crate) fn decode_header_size(d: &[u8]) -> (u64, usize) {
19    let mut i = 0;
20    let mut size = 0u64;
21    let mut consumed = 0;
22    for cmd in d.iter() {
23        consumed += 1;
24        size |= (u64::from(*cmd) & 0x7f) << i;
25        i += 7;
26        if *cmd & 0x80 == 0 {
27            break;
28        }
29    }
30    (size, consumed)
31}
32
33pub(crate) fn apply(base: &[u8], mut target: &mut [u8], data: &[u8]) -> Result<(), apply::Error> {
34    let mut i = 0;
35    while let Some(cmd) = data.get(i) {
36        i += 1;
37        match cmd {
38            cmd if cmd & 0b1000_0000 != 0 => {
39                let (mut ofs, mut size): (u32, u32) = (0, 0);
40                if cmd & 0b0000_0001 != 0 {
41                    ofs = u32::from(data[i]);
42                    i += 1;
43                }
44                if cmd & 0b0000_0010 != 0 {
45                    ofs |= u32::from(data[i]) << 8;
46                    i += 1;
47                }
48                if cmd & 0b0000_0100 != 0 {
49                    ofs |= u32::from(data[i]) << 16;
50                    i += 1;
51                }
52                if cmd & 0b0000_1000 != 0 {
53                    ofs |= u32::from(data[i]) << 24;
54                    i += 1;
55                }
56                if cmd & 0b0001_0000 != 0 {
57                    size = u32::from(data[i]);
58                    i += 1;
59                }
60                if cmd & 0b0010_0000 != 0 {
61                    size |= u32::from(data[i]) << 8;
62                    i += 1;
63                }
64                if cmd & 0b0100_0000 != 0 {
65                    size |= u32::from(data[i]) << 16;
66                    i += 1;
67                }
68                if size == 0 {
69                    size = 0x10000; // 65536
70                }
71                let ofs = ofs as usize;
72                std::io::Write::write(&mut target, &base[ofs..ofs + size as usize])
73                    .map_err(|_e| apply::Error::DeltaCopyBaseSliceMismatch)?;
74            }
75            0 => return Err(apply::Error::UnsupportedCommandCode),
76            size => {
77                std::io::Write::write(&mut target, &data[i..i + *size as usize])
78                    .map_err(|_e| apply::Error::DeltaCopyDataSliceMismatch)?;
79                i += *size as usize;
80            }
81        }
82    }
83    assert_eq!(i, data.len());
84    assert_eq!(target.len(), 0);
85
86    Ok(())
87}
gix_pack/data/delta.rs

gix_pack/data/
delta.rs
