refactor: improve config validation in precise-prefix-cache-scorer

- Extract hardcoded subscription timeout to named constant
- Add validation for pod discovery configuration
- Validate socket port range when discoverPods is enabled

This prevents runtime panics from invalid configuration and makes
the timeout value more maintainable.

Author: lisperz

pkg/plugins/scorer/precise_prefix_cache.go

@@ -27,6 +27,10 @@ import (
 const (
 	// PrecisePrefixCachePluginType is the type-name of the PrecisePrefixCacheScorer plugin.
 	PrecisePrefixCachePluginType = "precise-prefix-cache-scorer"
+
+	// defaultSubscriptionTimeout defines how long to keep inactive endpoint
+	// subscriptions before removing them from the KV-events pool.
+	defaultSubscriptionTimeout = 10 * time.Minute
 )
 
 // PrecisePrefixCachePluginConfig holds the configuration for the
@@ -94,6 +98,18 @@ func New(ctx context.Context, config PrecisePrefixCachePluginConfig) (*PrecisePr
 		config.TokenProcessorConfig = kvblock.DefaultTokenProcessorConfig()
 	}
 
+	// Validate pod discovery configuration
+	if config.KVEventsConfig != nil && config.KVEventsConfig.DiscoverPods {
+		if config.KVEventsConfig.PodDiscoveryConfig == nil {
+			return nil, errors.New("podDiscoveryConfig is required when discoverPods is enabled")
+		}
+		if config.KVEventsConfig.PodDiscoveryConfig.SocketPort <= 0 ||
+			config.KVEventsConfig.PodDiscoveryConfig.SocketPort > 65535 {
+			return nil, fmt.Errorf("invalid socket port: must be between 1 and 65535, got %d",
+				config.KVEventsConfig.PodDiscoveryConfig.SocketPort)
+		}
+	}
+
 	tokenProcessor := kvblock.NewChunkedTokenDatabase(config.TokenProcessorConfig)
 
 	// initialize the indexer
@@ -114,9 +130,8 @@ func New(ctx context.Context, config PrecisePrefixCachePluginConfig) (*PrecisePr
 	// initialize the subscribers cache only if endpoint discovery is enabled
 	if config.KVEventsConfig.DiscoverPods {
 		// initialize the subscribers TTL cache
-		subscriptionTimeout := 10 * time.Minute
 		subscribersCache = ttlcache.New[string, struct{}](
-			ttlcache.WithTTL[string, struct{}](subscriptionTimeout),
+			ttlcache.WithTTL[string, struct{}](defaultSubscriptionTimeout),
 		)
 		subscribersCache.OnEviction(func(ctx context.Context, reason ttlcache.EvictionReason,
 			item *ttlcache.Item[string, struct{}],
@@ -125,7 +140,7 @@ func New(ctx context.Context, config PrecisePrefixCachePluginConfig) (*PrecisePr
 				subscribersManager.RemoveSubscriber(ctx, item.Key())
 			}
 		})
-		go cleanCachePeriodically(ctx, subscribersCache, subscriptionTimeout)
+		go cleanCachePeriodically(ctx, subscribersCache, defaultSubscriptionTimeout)
 	}
 	if config.KVEventsConfig.ZMQEndpoint != "" {
 		// setup local subscriber to support global socket mode

pkg/plugins/scorer/precise_prefix_cache_validation_test.go

@@ -0,0 +1,105 @@
+package scorer
+
+import (
+	"context"
+	"testing"
+
+	"github.com/llm-d/llm-d-kv-cache/pkg/kvcache"
+	"github.com/llm-d/llm-d-kv-cache/pkg/kvevents"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestNew_PodDiscoveryValidation(t *testing.T) {
+	ctx := context.Background()
+
+	tests := []struct {
+		name        string
+		config      PrecisePrefixCachePluginConfig
+		expectError bool
+		errorMsg    string
+	}{
+		{
+			name: "valid config with pod discovery disabled",
+			config: PrecisePrefixCachePluginConfig{
+				IndexerConfig: &kvcache.Config{},
+				KVEventsConfig: &kvevents.Config{
+					DiscoverPods: false,
+				},
+			},
+			expectError: false,
+		},
+		{
+			name: "missing podDiscoveryConfig when discoverPods enabled",
+			config: PrecisePrefixCachePluginConfig{
+				IndexerConfig: &kvcache.Config{},
+				KVEventsConfig: &kvevents.Config{
+					DiscoverPods:        true,
+					PodDiscoveryConfig:  nil,
+				},
+			},
+			expectError: true,
+			errorMsg:    "podDiscoveryConfig is required when discoverPods is enabled",
+		},
+		{
+			name: "invalid socket port - zero",
+			config: PrecisePrefixCachePluginConfig{
+				IndexerConfig: &kvcache.Config{},
+				KVEventsConfig: &kvevents.Config{
+					DiscoverPods: true,
+					PodDiscoveryConfig: &kvevents.PodDiscoveryConfig{
+						SocketPort: 0,
+					},
+				},
+			},
+			expectError: true,
+			errorMsg:    "invalid socket port: must be between 1 and 65535, got 0",
+		},
+		{
+			name: "invalid socket port - negative",
+			config: PrecisePrefixCachePluginConfig{
+				IndexerConfig: &kvcache.Config{},
+				KVEventsConfig: &kvevents.Config{
+					DiscoverPods: true,
+					PodDiscoveryConfig: &kvevents.PodDiscoveryConfig{
+						SocketPort: -1,
+					},
+				},
+			},
+			expectError: true,
+			errorMsg:    "invalid socket port: must be between 1 and 65535, got -1",
+		},
+		{
+			name: "invalid socket port - too large",
+			config: PrecisePrefixCachePluginConfig{
+				IndexerConfig: &kvcache.Config{},
+				KVEventsConfig: &kvevents.Config{
+					DiscoverPods: true,
+					PodDiscoveryConfig: &kvevents.PodDiscoveryConfig{
+						SocketPort: 65536,
+					},
+				},
+			},
+			expectError: true,
+			errorMsg:    "invalid socket port: must be between 1 and 65535, got 65536",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			_, err := New(ctx, tt.config)
+
+			if tt.expectError {
+				require.Error(t, err)
+				assert.Contains(t, err.Error(), tt.errorMsg)
+			} else {
+				// Note: This will still fail due to missing tokenizer config,
+				// but it should pass the pod discovery validation
+				if err != nil {
+					assert.NotContains(t, err.Error(), "podDiscoveryConfig")
+					assert.NotContains(t, err.Error(), "socket port")
+				}
+			}
+		})
+	}
+}