gix_odb/alternate/
mod.rs

1//! A file with directories of other git object databases to use when reading objects.
2//!
3//! This inherently makes alternates read-only.
4//!
5//! An alternate file in `<git-dir>/info/alternates` can look as follows:
6//!
7//! ```text
8//! # a comment, empty lines are also allowed
9//! # relative paths resolve relative to the parent git repository
10//! ../path/relative/to/repo/.git
11//! /absolute/path/to/repo/.git
12//!
13//! "/a/ansi-c-quoted/path/with/tabs\t/.git"
14//!
15//! # each .git directory should indeed be a directory, and not a file
16//! ```
17//!
18//! Based on the [canonical implementation](https://github.com/git/git/blob/master/sha1-file.c#L598:L609).
19use std::{fs, io, path::PathBuf};
20
21use gix_path::realpath::MAX_SYMLINKS;
22
23///
24pub mod parse;
25
26/// Returned by [`resolve()`]
27#[derive(thiserror::Error, Debug)]
28#[allow(missing_docs)]
29pub enum Error {
30    #[error(transparent)]
31    Io(#[from] io::Error),
32    #[error(transparent)]
33    Realpath(#[from] gix_path::realpath::Error),
34    #[error(transparent)]
35    Parse(#[from] parse::Error),
36    #[error("Alternates form a cycle: {} -> {}", .0.iter().map(|p| format!("'{}'", p.display())).collect::<Vec<_>>().join(" -> "), .0.first().expect("more than one directories").display())]
37    Cycle(Vec<PathBuf>),
38}
39
40/// Given an `objects_directory`, try to resolve alternate object directories possibly located in the
41/// `./info/alternates` file into canonical paths and resolve relative paths with the help of the `current_dir`.
42/// If no alternate object database was resolved, the resulting `Vec` is empty (it is not an error
43/// if there are no alternates).
44/// It is an error once a repository is seen again as it would lead to a cycle.
45pub fn resolve(objects_directory: PathBuf, current_dir: &std::path::Path) -> Result<Vec<PathBuf>, Error> {
46    let mut dirs = vec![(0, objects_directory.clone())];
47    let mut out = Vec::new();
48    let mut seen = vec![gix_path::realpath_opts(&objects_directory, current_dir, MAX_SYMLINKS)?];
49    while let Some((depth, dir)) = dirs.pop() {
50        match fs::read(dir.join("info").join("alternates")) {
51            Ok(input) => {
52                for path in parse::content(&input)?.into_iter() {
53                    let path = objects_directory.join(path);
54                    let path_canonicalized = gix_path::realpath_opts(&path, current_dir, MAX_SYMLINKS)?;
55                    if seen.contains(&path_canonicalized) {
56                        return Err(Error::Cycle(seen));
57                    }
58                    seen.push(path_canonicalized);
59                    dirs.push((depth + 1, path));
60                }
61            }
62            Err(err) if err.kind() == io::ErrorKind::NotFound => {}
63            Err(err) => return Err(err.into()),
64        };
65        if depth != 0 {
66            out.push(dir);
67        }
68    }
69    Ok(out)
70}
gix_odb/alternate/mod.rs

gix_odb/alternate/
mod.rs
