git_ref/store/packed/
buffer.rs

1use crate::store_impl::packed;
2
3impl AsRef<[u8]> for packed::Buffer {
4    fn as_ref(&self) -> &[u8] {
5        &self.data.as_ref()[self.offset..]
6    }
7}
8
9impl AsRef<[u8]> for packed::Backing {
10    fn as_ref(&self) -> &[u8] {
11        match self {
12            packed::Backing::InMemory(data) => data,
13            packed::Backing::Mapped(map) => map,
14        }
15    }
16}
17
18///
19pub mod open {
20    use std::path::PathBuf;
21
22    use memmap2::Mmap;
23
24    use crate::store_impl::packed;
25
26    /// Initialization
27    impl packed::Buffer {
28        /// Open the file at `path` and map it into memory if the file size is larger than `use_memory_map_if_larger_than_bytes`.
29        ///
30        /// In order to allow fast lookups and optimizations, the contents of the packed refs must be sorted.
31        /// If that's not the case, they will be sorted on the fly with the data being written into a memory buffer.
32        pub fn open(path: impl Into<PathBuf>, use_memory_map_if_larger_than_bytes: u64) -> Result<Self, Error> {
33            let path = path.into();
34            let (backing, offset) = {
35                let backing = if std::fs::metadata(&path)?.len() <= use_memory_map_if_larger_than_bytes {
36                    packed::Backing::InMemory(std::fs::read(&path)?)
37                } else {
38                    packed::Backing::Mapped(
39                        // SAFETY: we have to take the risk of somebody changing the file underneath. Git never writes into the same file.
40                        #[allow(unsafe_code)]
41                        unsafe {
42                            Mmap::map(&std::fs::File::open(&path)?)?
43                        },
44                    )
45                };
46
47                let (offset, sorted) = {
48                    let data = backing.as_ref();
49                    if *data.first().unwrap_or(&b' ') == b'#' {
50                        let (records, header) = packed::decode::header::<()>(data).map_err(|_| Error::HeaderParsing)?;
51                        let offset = records.as_ptr() as usize - data.as_ptr() as usize;
52                        (offset, header.sorted)
53                    } else {
54                        (0, false)
55                    }
56                };
57
58                if !sorted {
59                    // this implementation is likely slower than what git does, but it's less code, too.
60                    let mut entries = packed::Iter::new(&backing.as_ref()[offset..])?.collect::<Result<Vec<_>, _>>()?;
61                    entries.sort_by_key(|e| e.name.as_bstr());
62                    let mut serialized = Vec::<u8>::new();
63                    for entry in entries {
64                        serialized.extend_from_slice(entry.target);
65                        serialized.push(b' ');
66                        serialized.extend_from_slice(entry.name.as_bstr());
67                        serialized.push(b'\n');
68                        if let Some(object) = entry.object {
69                            serialized.push(b'^');
70                            serialized.extend_from_slice(object);
71                            serialized.push(b'\n');
72                        }
73                    }
74                    (Backing::InMemory(serialized), 0)
75                } else {
76                    (backing, offset)
77                }
78            };
79            Ok(packed::Buffer {
80                offset,
81                data: backing,
82                path,
83            })
84        }
85    }
86
87    mod error {
88        use crate::packed;
89
90        /// The error returned by [`open()`][super::packed::Buffer::open()].
91        #[derive(Debug, thiserror::Error)]
92        #[allow(missing_docs)]
93        pub enum Error {
94            #[error("The packed-refs file did not have a header or wasn't sorted and could not be iterated")]
95            Iter(#[from] packed::iter::Error),
96            #[error("The header could not be parsed, even though first line started with '#'")]
97            HeaderParsing,
98            #[error("The buffer could not be opened or read")]
99            Io(#[from] std::io::Error),
100        }
101    }
102    pub use error::Error;
103
104    use crate::packed::Backing;
105}
git_ref/store/packed/buffer.rs

git_ref/store/packed/
buffer.rs
