gix_pack/data/file/decode/
header.rs

1use gix_features::zlib;
2
3use crate::{
4    data,
5    data::{delta, file::decode::Error, File},
6};
7
8/// A return value of a resolve function, which given an [`ObjectId`][gix_hash::ObjectId] determines where an object can be found.
9#[derive(Debug, PartialEq, Eq, Hash, Ord, PartialOrd, Clone)]
10#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
11pub enum ResolvedBase {
12    /// Indicate an object is within this pack, at the given entry, and thus can be looked up locally.
13    InPack(data::Entry),
14    /// Indicates the object of `kind` was found outside of the pack.
15    OutOfPack {
16        /// The kind of object we found when reading the header of the out-of-pack base.
17        kind: gix_object::Kind,
18        /// The amount of deltas encountered if the object was packed as well.
19        num_deltas: Option<u32>,
20    },
21}
22
23/// Additional information and statistics about a successfully decoded object produced by [`File::decode_header()`].
24///
25/// Useful to understand the effectiveness of the pack compression or the cost of decompression.
26#[derive(Debug, PartialEq, Eq, Hash, Ord, PartialOrd, Clone, Copy)]
27#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
28pub struct Outcome {
29    /// The kind of resolved object.
30    pub kind: gix_object::Kind,
31    /// The decompressed size of the object.
32    pub object_size: u64,
33    /// The amount of deltas in the chain of objects that had to be resolved beforehand.
34    pub num_deltas: u32,
35}
36
37/// Obtain object information quickly.
38impl File {
39    /// Resolve the object header information starting at `entry`, following the chain of entries as needed.
40    ///
41    /// The `entry` determines which object to decode, and is commonly obtained with the help of a pack index file or through pack iteration.
42    /// `inflate` will be used for (partially) decompressing entries, and will be reset before first use, but not after the last use.
43    ///
44    /// `resolve` is a function to lookup objects with the given [`ObjectId`][gix_hash::ObjectId], in case the full object id
45    /// is used to refer to a base object, instead of an in-pack offset.
46    pub fn decode_header(
47        &self,
48        mut entry: data::Entry,
49        inflate: &mut zlib::Inflate,
50        resolve: &dyn Fn(&gix_hash::oid) -> Option<ResolvedBase>,
51    ) -> Result<Outcome, Error> {
52        use crate::data::entry::Header::*;
53        let mut num_deltas = 0;
54        let mut first_delta_decompressed_size = None::<u64>;
55        loop {
56            match entry.header {
57                Tree | Blob | Commit | Tag => {
58                    return Ok(Outcome {
59                        kind: entry.header.as_kind().expect("always valid for non-refs"),
60                        object_size: first_delta_decompressed_size.unwrap_or(entry.decompressed_size),
61                        num_deltas,
62                    });
63                }
64                OfsDelta { base_distance } => {
65                    num_deltas += 1;
66                    if first_delta_decompressed_size.is_none() {
67                        first_delta_decompressed_size = Some(self.decode_delta_object_size(inflate, &entry)?);
68                    }
69                    entry = self.entry(entry.base_pack_offset(base_distance))?;
70                }
71                RefDelta { base_id } => {
72                    num_deltas += 1;
73                    if first_delta_decompressed_size.is_none() {
74                        first_delta_decompressed_size = Some(self.decode_delta_object_size(inflate, &entry)?);
75                    }
76                    match resolve(base_id.as_ref()) {
77                        Some(ResolvedBase::InPack(base_entry)) => entry = base_entry,
78                        Some(ResolvedBase::OutOfPack {
79                            kind,
80                            num_deltas: origin_num_deltas,
81                        }) => {
82                            return Ok(Outcome {
83                                kind,
84                                object_size: first_delta_decompressed_size.unwrap_or(entry.decompressed_size),
85                                num_deltas: origin_num_deltas.unwrap_or_default() + num_deltas,
86                            })
87                        }
88                        None => return Err(Error::DeltaBaseUnresolved(base_id)),
89                    }
90                }
91            };
92        }
93    }
94
95    #[inline]
96    fn decode_delta_object_size(&self, inflate: &mut zlib::Inflate, entry: &data::Entry) -> Result<u64, Error> {
97        let mut buf = [0_u8; 32];
98        let used = self
99            .decompress_entry_from_data_offset_2(entry.data_offset, inflate, &mut buf)?
100            .1;
101        let buf = &buf[..used];
102        let (_base_size, offset) = delta::decode_header_size(buf);
103        let (result_size, _offset) = delta::decode_header_size(&buf[offset..]);
104        Ok(result_size)
105    }
106}
107
108#[cfg(test)]
109mod tests {
110    use super::*;
111
112    #[test]
113    fn size_of_decode_entry_outcome() {
114        assert_eq!(
115            std::mem::size_of::<Outcome>(),
116            16,
117            "this shouldn't change without use noticing as it's returned a lot"
118        );
119    }
120}
gix_pack/data/file/decode/header.rs

gix_pack/data/file/decode/
header.rs
