fix(cache): refresh response entries on cache hits

The response cache is byte-bounded and evicts from an order queue when inserting a new entry would exceed the configured capacity. Before this change, that queue only reflected insertion order: a frequently reused cached response could still be evicted ahead of colder entries if it happened to be inserted earlier.

Refresh the cache order on successful, unexpired get calls. The cached bytes are cloned before mutating the order queue, the hit counter behavior is preserved, and expired entries still remove their stored bytes and order entry before recording a miss.

Update the eviction regression test so it exercises true least-recently-used behavior: after warming entry a, inserting entry f evicts b rather than the recently read a. Cache size accounting, TTL parsing, cacheability rules, entry-size rejection, and the public ResponseCache API remain unchanged.

Author: maybeknott

src/cache.rs

@@ -53,8 +53,11 @@ impl ResponseCache {
         let mut inner = self.inner.lock().unwrap();
         if let Some(entry) = inner.entries.get(key) {
             if entry.expires > now {
+                let bytes = entry.bytes.clone();
+                inner.order.retain(|k| k != key);
+                inner.order.push_back(key.to_string());
                 self.hits.fetch_add(1, Ordering::Relaxed);
-                return Some(entry.bytes.clone());
+                return Some(bytes);
             }
             let size = entry.bytes.len();
             inner.entries.remove(key);
@@ -215,15 +218,17 @@ mod tests {
     }
 
     #[test]
-    fn fifo_eviction_when_full() {
+    fn least_recently_used_entry_is_evicted_when_full() {
         let c = ResponseCache::new(1000);
         c.put("a".into(), vec![0u8; 200], Duration::from_secs(60));
         c.put("b".into(), vec![0u8; 200], Duration::from_secs(60));
         c.put("c".into(), vec![0u8; 200], Duration::from_secs(60));
         c.put("d".into(), vec![0u8; 200], Duration::from_secs(60));
         c.put("e".into(), vec![0u8; 200], Duration::from_secs(60));
+        assert!(c.get("a").is_some());
         c.put("f".into(), vec![0u8; 200], Duration::from_secs(60));
-        assert!(c.get("a").is_none());
+        assert!(c.get("a").is_some());
+        assert!(c.get("b").is_none());
         assert!(c.get("f").is_some());
     }