Module persistent_cache 

Cross-session persistent cache for decoded thumbnails and media fingerprints.

The in-memory crate::dedup_cache LRU cache is discarded at process exit. This module adds a lightweight JSON-backed persistent store so that expensive thumbnail decoding and perceptual hash computation are reused across deduplication sessions.

Design

PersistentFingerprintCache maintains a flat JSON file on disk. Each entry records:

• The source file path.
• Its BLAKE3 hex digest (64 chars) — used to detect when the file changes and the cached fingerprint is stale.
• The 64-bit perceptual hash.
• An optional thumbnail (8×8 grayscale pixel bytes, base64-encoded).
• The modification timestamp at cache time.

On load, all entries are read from disk. On save, the current entries are written back atomically (write to a temp file then rename).

Staleness is detected by comparing the stored BLAKE3 digest with a freshly computed digest of the source file. get_valid returns None for stale or missing entries.

Example

use oximedia_dedup::persistent_cache::{PersistentFingerprintCache, CachedEntry};

let dir = std::env::temp_dir().join("oximedia_pc_doctest");
std::fs::create_dir_all(&dir).ok();
let cache_path = dir.join("fps.json");

let mut cache = PersistentFingerprintCache::new(cache_path.clone());
cache.insert(CachedEntry {
    path: "/media/clip.mp4".to_string(),
    blake3_hex: "0".repeat(64),
    phash: 0xDEAD_BEEF_1234_5678,
    thumbnail: None,
    modified_secs: 1_700_000_000,
});

cache.save().expect("save ok");

let cache2 = PersistentFingerprintCache::load(cache_path).expect("load ok");
assert_eq!(cache2.len(), 1);

Structs

CachedEntry

A single entry in the persistent fingerprint cache.

PersistentFingerprintCache

Cross-session persistent cache mapping file paths to their fingerprints.