R57: FIFO eviction; keep fresh replay JTIs in cache

review_r57_shard_eviction_test.go

@@ -0,0 +1,53 @@
+package traefikoidc
+
+import (
+	"fmt"
+	"testing"
+	"time"
+)
+
+// TestShardedCacheFIFOEvictionRetainsNewest guards against the pre-fix eviction
+// policy in evictFromShardLocked, which (a) over-evicted by +10 per Set at
+// capacity (each shard sat ~9 slots under its cap) and (b) deleted entries in
+// random Go map-iteration order, so a just-written, still-valid-TTL entry
+// (e.g. a fresh replay-protection JTI) could be dropped immediately —
+// truncating the replay window.
+func TestShardedCacheFIFOEvictionRetainsNewest(t *testing.T) {
+	cache := NewShardedCache(4, 400) // maxPerShard = 100
+
+	// Collect 100 filler keys + 1 trigger key that all hash into ONE shard,
+	// giving deterministic control over capacity pressure.
+	var shard *cacheShard
+	fillers := make([]string, 0, 100)
+	var trigger string
+	for i := 0; len(fillers) < 100 || trigger == ""; i++ {
+		k := fmt.Sprintf("key-%d", i)
+		s := cache.getShard(k)
+		if shard == nil {
+			shard = s
+			continue
+		}
+		if s == shard {
+			if len(fillers) < 100 {
+				fillers = append(fillers, k)
+			} else if trigger == "" {
+				trigger = k
+			}
+		}
+	}
+
+	for _, k := range fillers {
+		cache.Set(k, true, time.Minute)
+	}
+
+	// This write hits the shard at capacity: it must evict the OLDEST and
+	// place the newcomer, keeping the shard full.
+	cache.Set(trigger, true, time.Minute)
+
+	if !cache.Exists(trigger) {
+		t.Fatalf("capacity-triggering write evicted the just-written newest entry (random over-eviction)")
+	}
+	if n := cache.Size(); n != 100 {
+		t.Fatalf("shard size = %d, want 100 (old code over-evicted below capacity)", n)
+	}
+}