Initialize the DNS cache at plugin init time

No need for a lazily-created cache and sync.Once.

Author: jedisct1

dnscrypt-proxy/monitoring_ui.go

@@ -710,9 +710,9 @@ func (mc *MetricsCollector) collectCacheStats(cacheHitRatio float64, cacheHits,
 	stats["neg_max_ttl"] = mc.proxy.cacheNegMaxTTL
 	stats["neg_min_ttl"] = mc.proxy.cacheNegMinTTL
 
-	if cachedResponses.cache != nil {
-		stats["entries"] = cachedResponses.cache.Len()
-		stats["capacity"] = cachedResponses.cache.Capacity()
+	if cachedResponses != nil {
+		stats["entries"] = cachedResponses.Len()
+		stats["capacity"] = cachedResponses.Capacity()
 	}
 
 	return stats

dnscrypt-proxy/plugin_cache.go

@@ -4,7 +4,6 @@ import (
 	"crypto/sha512"
 	"encoding/binary"
 	"fmt"
-	"sync"
 	"time"
 
 	"codeberg.org/miekg/dns"
@@ -18,12 +17,20 @@ type CachedResponse struct {
 	msg        *dns.Msg
 }
 
-type CachedResponses struct {
-	cache     *sievecache.ShardedSieveCache[[32]byte, CachedResponse]
-	cacheOnce sync.Once
-}
+// cachedResponses is created once, before any goroutine that reads it exists
+var cachedResponses *sievecache.ShardedSieveCache[[32]byte, CachedResponse]
 
-var cachedResponses CachedResponses
+func initCachedResponses(cacheSize int) error {
+	if cachedResponses != nil {
+		return nil
+	}
+	cache, err := sievecache.NewSharded[[32]byte, CachedResponse](cacheSize)
+	if err != nil {
+		return fmt.Errorf("failed to initialize the cache: %w", err)
+	}
+	cachedResponses = cache
+	return nil
+}
 
 func computeCacheKey(pluginsState *PluginsState, msg *dns.Msg) [32]byte {
 	question := msg.Question[0]
@@ -57,7 +64,7 @@ func (plugin *PluginCache) Description() string {
 }
 
 func (plugin *PluginCache) Init(proxy *Proxy) error {
-	return nil
+	return initCachedResponses(proxy.cacheSize)
 }
 
 func (plugin *PluginCache) Drop() error {
@@ -69,12 +76,11 @@ func (plugin *PluginCache) Reload() error {
 }
 
 func (plugin *PluginCache) Eval(pluginsState *PluginsState, msg *dns.Msg) error {
-	cacheKey := computeCacheKey(pluginsState, msg)
-
-	if cachedResponses.cache == nil {
+	if cachedResponses == nil {
 		return nil
 	}
-	cached, ok := cachedResponses.cache.Get(cacheKey)
+	cacheKey := computeCacheKey(pluginsState, msg)
+	cached, ok := cachedResponses.Get(cacheKey)
 	if !ok {
 		return nil
 	}
@@ -113,7 +119,7 @@ func (plugin *PluginCacheResponse) Description() string {
 }
 
 func (plugin *PluginCacheResponse) Init(proxy *Proxy) error {
-	return nil
+	return initCachedResponses(proxy.cacheSize)
 }
 
 func (plugin *PluginCacheResponse) Drop() error {
@@ -131,6 +137,9 @@ func (plugin *PluginCacheResponse) Eval(pluginsState *PluginsState, msg *dns.Msg
 	if msg.Truncated {
 		return nil
 	}
+	if cachedResponses == nil {
+		return nil
+	}
 	cacheKey := computeCacheKey(pluginsState, msg)
 	ttl := getMinTTL(
 		msg,
@@ -139,26 +148,11 @@ func (plugin *PluginCacheResponse) Eval(pluginsState *PluginsState, msg *dns.Msg
 		pluginsState.cacheNegMinTTL,
 		pluginsState.cacheNegMaxTTL,
 	)
-	cachedResponse := CachedResponse{
-		expiration: time.Now().Add(ttl),
-		msg:        cloneMsg(msg),
-	}
-	var cacheInitError error
-	cachedResponses.cacheOnce.Do(func() {
-		cache, err := sievecache.NewSharded[[32]byte, CachedResponse](pluginsState.cacheSize)
-		if err != nil {
-			cacheInitError = err
-		} else {
-			cachedResponses.cache = cache
-		}
-	})
-	if cacheInitError != nil {
-		return fmt.Errorf("failed to initialize the cache: %w", cacheInitError)
-	}
-	if cachedResponses.cache != nil {
-		cachedResponses.cache.Insert(cacheKey, cachedResponse)
-	}
-	updateTTL(msg, cachedResponse.expiration)
+	expiration := time.Now().Add(ttl)
+	cachedMsg := cloneMsg(msg)
+	cachedMsg.Question = nil
+	cachedResponses.Insert(cacheKey, CachedResponse{expiration: expiration, msg: cachedMsg})
+	updateTTL(msg, expiration)
 
 	return nil
 }

dnscrypt-proxy/plugins.go

@@ -82,7 +82,6 @@ type PluginsState struct {
 	timeout                          time.Duration
 	returnCode                       PluginsReturnCode
 	maxPayloadSize                   int
-	cacheSize                        int
 	originalMaxPayloadSize           int
 	maxUnencryptedUDPSafePayloadSize int
 	rejectTTL                        uint32
@@ -255,7 +254,6 @@ func NewPluginsState(
 		maxPayloadSize:                   MaxDNSUDPPacketSize - ResponseOverhead,
 		clientProto:                      clientProto,
 		clientAddr:                       clientAddr,
-		cacheSize:                        proxy.cacheSize,
 		cacheNegMinTTL:                   proxy.cacheNegMinTTL,
 		cacheNegMaxTTL:                   proxy.cacheNegMaxTTL,
 		cacheMinTTL:                      proxy.cacheMinTTL,