frame for instantiation of multi-pack-index (#279)

git-pack/src/lib.rs

@@ -36,3 +36,5 @@ pub use find_traits::{Find, FindExt};
 
 ///
 pub mod index;
+///
+pub mod multi_index;

git-pack/src/multi_index.rs

@@ -0,0 +1,39 @@
+#![allow(missing_docs, unused)]
+use filebuffer::FileBuffer;
+
+/// A representation of an index file for multiple packs at the same time, typically stored in a file
+/// named 'multi-pack-index'.
+pub struct File {
+    data: FileBuffer,
+    path: std::path::PathBuf,
+}
+
+///
+pub mod init {
+    use crate::multi_index::File;
+    use std::convert::TryFrom;
+    use std::path::Path;
+
+    mod error {
+        #[derive(Debug, thiserror::Error)]
+        pub enum Error {
+            #[error(transparent)]
+            Io(#[from] std::io::Error),
+        }
+    }
+    pub use error::Error;
+
+    impl File {
+        pub fn at(path: impl AsRef<Path>) -> Result<Self, Error> {
+            Self::try_from(path.as_ref())
+        }
+    }
+
+    impl TryFrom<&Path> for File {
+        type Error = Error;
+
+        fn try_from(path: &Path) -> Result<Self, Self::Error> {
+            todo!()
+        }
+    }
+}

git-pack/tests/fixtures/make_pack_gen_repo_multi_index.sh

@@ -0,0 +1,39 @@
+#!/bin/bash
+set -eu -o pipefail
+
+git init -q
+git config commit.gpgsign false
+
+function write_files() {
+  local base_dir=${1:?directory to write them into}
+  local num_files=${2:?amount of files to write}
+  local nonce=${3:?something to make files more unique}
+
+  mkdir -p "$base_dir"
+  for file_id in $(seq -w "$num_files"); do
+    seq "$file_id" > "$base_dir/$file_id"
+    echo "$nonce" >> "$base_dir/$file_id"
+  done
+}
+
+dirs=(. a b c a/a a/b a/c a/a/a)
+rounds=15
+
+git checkout -q -b main
+for round in $(seq $rounds); do
+  dir_index=$(( round % ${#dirs[@]} ))
+  num_files=$(( (round + 1) * 6 ))
+  write_files "${dirs[$dir_index]}" $num_files "$round"
+  git add .
+  git commit -qm "$round $num_files"
+done
+
+echo hello world > referee
+git add referee
+git commit -qm "to be forgotten"
+git tag -m "a tag object" referrer
+git reset --hard HEAD~1
+
+# speed up all access by creating a pack
+git gc --aggressive
+git multi-pack-index write

git-pack/tests/pack/mod.rs

@@ -34,3 +34,4 @@ mod bundle;
 mod data;
 mod index;
 mod iter;
+mod multi_index;

git-pack/tests/pack/multi_index.rs

@@ -0,0 +1,8 @@
+#[test]
+#[ignore]
+fn access() {
+    let path = git_testtools::scripted_fixture_repo_read_only("make_pack_gen_repo_multi_index.sh")
+        .unwrap()
+        .join(".git/objects/pack/multi-pack-index");
+    let _file = git_pack::multi_index::File::at(path).unwrap();
+}