style: cargo fmt

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/ctx.rs

@@ -760,9 +760,9 @@ mod tests {
         for i in 0..5u16 {
             let ctx = ctx.clone();
             let buf = build_wire_query(100 + i, "coalesce-test.example.com", QueryType::A);
-            handles.push(tokio::spawn(async move {
-                handle_query(buf, src, &ctx).await
-            }));
+            handles.push(tokio::spawn(
+                async move { handle_query(buf, src, &ctx).await },
+            ));
         }
 
         for h in handles {
@@ -800,7 +800,11 @@ mod tests {
         h2.await.unwrap().unwrap();
 
         let actual = query_count.load(std::sync::atomic::Ordering::Relaxed);
-        assert!(actual >= 2, "A and AAAA should resolve independently, got {}", actual);
+        assert!(
+            actual >= 2,
+            "A and AAAA should resolve independently, got {}",
+            actual
+        );
         assert!(ctx.inflight.lock().unwrap().is_empty());
 
         crate::recursive::reset_udp_state();

src/recursive.rs

@@ -21,7 +21,8 @@ const UDP_FAIL_THRESHOLD: u8 = 3;
 
 static QUERY_ID: AtomicU16 = AtomicU16::new(1);
 static UDP_FAILURES: std::sync::atomic::AtomicU8 = std::sync::atomic::AtomicU8::new(0);
-pub(crate) static UDP_DISABLED: std::sync::atomic::AtomicBool = std::sync::atomic::AtomicBool::new(false);
+pub(crate) static UDP_DISABLED: std::sync::atomic::AtomicBool =
+    std::sync::atomic::AtomicBool::new(false);
 
 fn next_id() -> u16 {
     QUERY_ID.fetch_add(1, Ordering::Relaxed)

src/srtt.rs

@@ -108,6 +108,13 @@ impl SrttCache {
         self.entries.is_empty()
     }
 
+    #[cfg(test)]
+    fn set_updated_at(&mut self, ip: IpAddr, at: Instant) {
+        if let Some(entry) = self.entries.get_mut(&ip) {
+            entry.updated_at = at;
+        }
+    }
+
     fn maybe_evict(&mut self) {
         if self.entries.len() < MAX_ENTRIES {
             return;
@@ -203,6 +210,99 @@ mod tests {
         assert_eq!(addrs, original);
     }
 
+    fn age(secs: u64) -> Instant {
+        Instant::now() - std::time::Duration::from_secs(secs)
+    }
+
+    /// Cache with ip(1) saturated at FAILURE_PENALTY_MS
+    fn saturated_penalty_cache() -> SrttCache {
+        let mut cache = SrttCache::new(true);
+        for _ in 0..30 {
+            cache.record_rtt(ip(1), FAILURE_PENALTY_MS, false);
+        }
+        cache
+    }
+
+    #[test]
+    fn no_decay_within_threshold() {
+        let mut cache = SrttCache::new(true);
+        cache.record_rtt(ip(1), 5000, false);
+        cache.set_updated_at(ip(1), age(DECAY_AFTER_SECS));
+        assert_eq!(cache.get(ip(1)), cache.entries[&ip(1)].srtt_ms);
+    }
+
+    #[test]
+    fn one_decay_period() {
+        let mut cache = saturated_penalty_cache();
+        let raw = cache.entries[&ip(1)].srtt_ms;
+        cache.set_updated_at(ip(1), age(DECAY_AFTER_SECS + 1));
+        let expected = (raw + INITIAL_SRTT_MS) / 2;
+        assert_eq!(cache.get(ip(1)), expected);
+    }
+
+    #[test]
+    fn multiple_decay_periods() {
+        let mut cache = saturated_penalty_cache();
+        let raw = cache.entries[&ip(1)].srtt_ms;
+        cache.set_updated_at(ip(1), age(DECAY_AFTER_SECS * 4 + 1));
+        let mut expected = raw;
+        for _ in 0..4 {
+            expected = (expected + INITIAL_SRTT_MS) / 2;
+        }
+        assert_eq!(cache.get(ip(1)), expected);
+    }
+
+    #[test]
+    fn decay_caps_at_8_periods() {
+        // 9 periods and 100 periods should produce the same result (capped at 8)
+        let mut cache_a = saturated_penalty_cache();
+        let mut cache_b = saturated_penalty_cache();
+        cache_a.set_updated_at(ip(1), age(DECAY_AFTER_SECS * 9 + 1));
+        cache_b.set_updated_at(ip(1), age(DECAY_AFTER_SECS * 100));
+        assert_eq!(cache_a.get(ip(1)), cache_b.get(ip(1)));
+    }
+
+    #[test]
+    fn decay_converges_toward_initial() {
+        let mut cache = saturated_penalty_cache();
+        cache.set_updated_at(ip(1), age(DECAY_AFTER_SECS * 100));
+        let decayed = cache.get(ip(1));
+        let diff = decayed.abs_diff(INITIAL_SRTT_MS);
+        assert!(
+            diff < 25,
+            "expected near INITIAL_SRTT_MS, got {} (diff={})",
+            decayed,
+            diff
+        );
+    }
+
+    #[test]
+    fn record_rtt_applies_decay_before_ewma() {
+        let mut cache = saturated_penalty_cache();
+        cache.set_updated_at(ip(1), age(DECAY_AFTER_SECS * 8));
+        cache.record_rtt(ip(1), 50, false);
+        let srtt = cache.get(ip(1));
+        // Without decay-before-EWMA, result would be ~(5000*7+50)/8 ≈ 4381
+        assert!(srtt < 500, "expected decay before EWMA, got srtt={}", srtt);
+    }
+
+    #[test]
+    fn decay_reranks_stale_failures() {
+        let mut cache = saturated_penalty_cache();
+        for _ in 0..30 {
+            cache.record_rtt(ip(2), 300, false);
+        }
+        let mut addrs = vec![sock(1), sock(2)];
+        cache.sort_by_rtt(&mut addrs);
+        assert_eq!(addrs, vec![sock(2), sock(1)]);
+
+        // Age server 1 so it decays toward INITIAL (200ms) — below server 2's 300ms
+        cache.set_updated_at(ip(1), age(DECAY_AFTER_SECS * 100));
+        let mut addrs = vec![sock(1), sock(2)];
+        cache.sort_by_rtt(&mut addrs);
+        assert_eq!(addrs, vec![sock(1), sock(2)]);
+    }
+
     #[test]
     fn eviction_removes_oldest() {
         let mut cache = SrttCache::new(true);