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Cache index files based on contents hash #11044

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Sep 8, 2022
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30 changes: 12 additions & 18 deletions src/cargo/sources/registry/remote.rs
Original file line number Diff line number Diff line change
Expand Up @@ -163,10 +163,9 @@ impl<'cfg> RegistryData for RemoteRegistry<'cfg> {
// Older versions of Cargo used the single value of the hash of the HEAD commit as a `index_version`.
// This is technically correct but a little too conservative. If a new commit is fetched all cached
// files need to be regenerated even if a particular file was not changed.
// Cargo now reads the `index_version` in two parts the cache file is considered valid if `index_version`
// ends with the hash of the HEAD commit OR if it starts with the hash of the file's contents.
// In the future cargo can write cached files with `index_version` = `git_file_hash + ":" + `git_commit_hash`,
// but for now it still uses `git_commit_hash` to be compatible with older Cargoes.
// However if an old cargo has written such a file we still know how to read it, as long as we check for that hash value.
//
// Cargo now uses a hash of the file's contents as provided by git.
fn load(
&mut self,
_root: &Path,
Expand All @@ -178,10 +177,9 @@ impl<'cfg> RegistryData for RemoteRegistry<'cfg> {
}
// Check if the cache is valid.
let git_commit_hash = self.current_version();
if let (Some(c), Some(i)) = (git_commit_hash, index_version) {
if i.ends_with(c.as_str()) {
return Poll::Ready(Ok(LoadResponse::CacheValid));
}
if index_version.is_some() && index_version == git_commit_hash.as_deref() {
// This file was written by an old version of cargo, but it is still up-to-date.
return Poll::Ready(Ok(LoadResponse::CacheValid));
}
// Note that the index calls this method and the filesystem is locked
// in the index, so we don't need to worry about an `update_index`
Expand All @@ -190,18 +188,16 @@ impl<'cfg> RegistryData for RemoteRegistry<'cfg> {
registry: &RemoteRegistry<'_>,
path: &Path,
index_version: Option<&str>,
git_commit_hash: Option<&str>,
) -> CargoResult<LoadResponse> {
let repo = registry.repo()?;
let tree = registry.tree()?;
let entry = tree.get_path(path);
let entry = entry?;
let git_file_hash = entry.id().to_string();
let git_file_hash = Some(entry.id().to_string());

if let Some(i) = index_version {
if i.starts_with(git_file_hash.as_str()) {
return Ok(LoadResponse::CacheValid);
}
// Check if the cache is valid.
if index_version.is_some() && index_version == git_file_hash.as_deref() {
return Ok(LoadResponse::CacheValid);
}

let object = entry.to_object(repo)?;
Expand All @@ -212,13 +208,11 @@ impl<'cfg> RegistryData for RemoteRegistry<'cfg> {

Ok(LoadResponse::Data {
raw_data: blob.content().to_vec(),
index_version: git_commit_hash.map(String::from),
// TODO: When the reading code has been stable for long enough (Say 8/2022)
// change to `git_file_hash + ":" + git_commit_hash`
index_version: git_file_hash,
})
}

match load_helper(&self, path, index_version, git_commit_hash.as_deref()) {
match load_helper(&self, path, index_version) {
Ok(result) => Poll::Ready(Ok(result)),
Err(_) if !self.updated => {
// If git returns an error and we haven't updated the repo, return
Expand Down