Trait CacheBackend 

pub trait CacheBackend: Send + Sync {
    // Required methods
    fn get(&self, key: &str) -> Result<Option<PathBuf>>;
    fn put(
        &self,
        key: &str,
        source_dir: &Path,
        description: &str,
    ) -> Result<PathBuf>;
    fn invalidate(&self, key: &str) -> Result<()>;
    fn prune(&self, max_entries: usize, max_bytes: u64) -> Result<usize>;
    fn list(&self) -> Result<Vec<CacheEntry>>;

    // Provided method
    fn stats(&self) -> Result<CacheStats> { ... }
}

Abstraction over directory-based caching.

Used for both OCI layer caching and fully-built rootfs caching. The key is an opaque string (typically a content hash), and the value is a directory tree on disk.

Lifecycle

1. get(key) — check if a cached directory exists for this key
2. On miss: build the content, then put(key, source_dir, desc)
3. prune(max_entries, max_bytes) — evict old entries to stay within limits

Thread Safety

Implementations must be Send + Sync. Concurrent get/put calls with different keys must be safe. Concurrent calls with the same key have implementation-defined behavior (last writer wins is acceptable).

Required Methods

fn get(&self, key: &str) -> Result<Option<PathBuf>>

Retrieve a cached directory by key.

Returns Some(path) if the key exists and the cached content is valid. The returned path points to a directory that the caller can read from. Returns None on cache miss.

Implementations should update the last-accessed timestamp on hit.

fn put( &self, key: &str, source_dir: &Path, description: &str, ) -> Result<PathBuf>

Store a directory tree in the cache under the given key.

Copies (or moves) the contents of source_dir into the cache. If an entry with this key already exists, it is replaced.

Returns the path to the cached directory (which may differ from source_dir).

fn invalidate(&self, key: &str) -> Result<()>

Remove a cached entry by key.

No-op if the key does not exist.

fn prune(&self, max_entries: usize, max_bytes: u64) -> Result<usize>

Evict entries to satisfy the given constraints.

Implementations should evict least-recently-accessed entries first. Returns the number of entries evicted.

fn list(&self) -> Result<Vec<CacheEntry>>

List all cache entries with their metadata.

Provided Methods

fn stats(&self) -> Result<CacheStats>

Get aggregate cache statistics.

Implementors