Function git_pack::data::header::decode

pub fn decode(data: &[u8; 12]) -> Result<(Version, u32), Error>

Parses the first 12 bytes of a pack file, returning the pack version as well as the number of objects contained in the pack.

Examples found in repository

src/data/file/init.rs (line 31)

    fn at_inner(path: &Path, object_hash: git_hash::Kind) -> Result<data::File, data::header::decode::Error> {
        use crate::data::header::N32_SIZE;
        let hash_len = object_hash.len_in_bytes();

        let data = crate::mmap::read_only(path).map_err(|e| data::header::decode::Error::Io {
            source: e,
            path: path.to_owned(),
        })?;
        let pack_len = data.len();
        if pack_len < N32_SIZE * 3 + hash_len {
            return Err(data::header::decode::Error::Corrupt(format!(
                "Pack data of size {} is too small for even an empty pack with shortest hash",
                pack_len
            )));
        }
        let (kind, num_objects) =
            data::header::decode(&data[..12].try_into().expect("enough data after previous check"))?;
        Ok(data::File {
            data,
            path: path.to_owned(),
            id: git_features::hash::crc32(path.as_os_str().to_string_lossy().as_bytes()),
            version: kind,
            num_objects,
            hash_len,
            object_hash,
        })
    }

src/data/input/bytes_to_entries.rs (line 61)

    pub fn new_from_header(
        mut read: BR,
        mode: input::Mode,
        compressed: input::EntryDataMode,
        object_hash: git_hash::Kind,
    ) -> Result<BytesToEntriesIter<BR>, input::Error> {
        let mut header_data = [0u8; 12];
        read.read_exact(&mut header_data)?;

        let (version, num_objects) = crate::data::header::decode(&header_data)?;
        assert_eq!(
            version,
            crate::data::Version::V2,
            "let's stop here if we see undocumented pack formats"
        );
        Ok(BytesToEntriesIter {
            read,
            decompressor: None,
            compressed,
            offset: 12,
            had_error: false,
            version,
            objects_left: num_objects,
            hash: (mode != input::Mode::AsIs).then(|| {
                let mut hash = git_features::hash::hasher(object_hash);
                hash.update(&header_data);
                hash
            }),
            mode,
            compressed_buf: None,
            hash_len: object_hash.len_in_bytes(),
            object_hash,
        })
    }

src/cache/delta/from_offsets.rs (line 76)

    pub fn from_offsets_in_pack(
        pack_path: impl AsRef<std::path::Path>,
        data_sorted_by_offsets: impl Iterator<Item = T>,
        get_pack_offset: impl Fn(&T) -> data::Offset,
        resolve_in_pack_id: impl Fn(&git_hash::oid) -> Option<data::Offset>,
        mut progress: impl Progress,
        should_interrupt: &AtomicBool,
        object_hash: git_hash::Kind,
    ) -> Result<Self, Error> {
        let mut r = io::BufReader::with_capacity(
            8192 * 8, // this value directly corresponds to performance, 8k (default) is about 4x slower than 64k
            fs::File::open(pack_path).map_err(|err| Error::Io {
                source: err,
                message: "open pack path",
            })?,
        );

        let anticpiated_num_objects = if let Some(num_objects) = data_sorted_by_offsets.size_hint().1 {
            progress.init(Some(num_objects), progress::count("objects"));
            num_objects
        } else {
            0
        };
        let mut tree = Tree::with_capacity(anticpiated_num_objects)?;

        {
            // safety check - assure ourselves it's a pack we can handle
            let mut buf = [0u8; PACK_HEADER_LEN];
            r.read_exact(&mut buf).map_err(|err| Error::Io {
                source: err,
                message: "reading header buffer with at least 12 bytes failed - pack file truncated?",
            })?;
            crate::data::header::decode(&buf)?;
        }

        let then = Instant::now();

        let mut previous_cursor_position = None::<u64>;

        let hash_len = object_hash.len_in_bytes();
        for (idx, data) in data_sorted_by_offsets.enumerate() {
            let pack_offset = get_pack_offset(&data);
            if let Some(previous_offset) = previous_cursor_position {
                Self::advance_cursor_to_pack_offset(&mut r, pack_offset, previous_offset)?;
            };
            let entry = crate::data::Entry::from_read(&mut r, pack_offset, hash_len).map_err(|err| Error::Io {
                source: err,
                message: "EOF while parsing header",
            })?;
            previous_cursor_position = Some(pack_offset + entry.header_size() as u64);

            use crate::data::entry::Header::*;
            match entry.header {
                Tree | Blob | Commit | Tag => {
                    tree.add_root(pack_offset, data)?;
                }
                RefDelta { base_id } => {
                    resolve_in_pack_id(base_id.as_ref())
                        .ok_or(Error::UnresolvedRefDelta { id: base_id })
                        .and_then(|base_pack_offset| {
                            tree.add_child(base_pack_offset, pack_offset, data).map_err(Into::into)
                        })?;
                }
                OfsDelta { base_distance } => {
                    let base_pack_offset = pack_offset
                        .checked_sub(base_distance)
                        .expect("in bound distance for deltas");
                    tree.add_child(base_pack_offset, pack_offset, data)?;
                }
            };
            progress.inc();
            if idx % 10_000 == 0 && should_interrupt.load(Ordering::SeqCst) {
                return Err(Error::Interrupted);
            }
        }

        progress.show_throughput(then);
        Ok(tree)
    }