Rename to be specifically immutable, panic if we try to mutate a cache entry

common/basecomponent/base.go

@@ -54,12 +54,12 @@ type BaseDendrite struct {
 	tracerCloser  io.Closer
 
 	// APIMux should be used to register new public matrix api endpoints
-	APIMux        *mux.Router
-	httpClient    *http.Client
-	Cfg           *config.Dendrite
-	Cache         caching.Cache
-	KafkaConsumer sarama.Consumer
-	KafkaProducer sarama.SyncProducer
+	APIMux         *mux.Router
+	httpClient     *http.Client
+	Cfg            *config.Dendrite
+	ImmutableCache caching.ImmutableCache
+	KafkaConsumer  sarama.Consumer
+	KafkaProducer  sarama.SyncProducer
 }
 
 const HTTPServerTimeout = time.Minute * 5
@@ -85,20 +85,20 @@ func NewBaseDendrite(cfg *config.Dendrite, componentName string) *BaseDendrite {
 		kafkaConsumer, kafkaProducer = setupKafka(cfg)
 	}
 
-	cache, err := caching.NewInMemoryLRUCache()
+	cache, err := caching.NewImmutableInMemoryLRUCache()
 	if err != nil {
 		logrus.WithError(err).Warnf("Failed to create cache")
 	}
 
 	return &BaseDendrite{
-		componentName: componentName,
-		tracerCloser:  closer,
-		Cfg:           cfg,
-		Cache:         cache,
-		APIMux:        mux.NewRouter().UseEncodedPath(),
-		httpClient:    &http.Client{Timeout: HTTPClientTimeout},
-		KafkaConsumer: kafkaConsumer,
-		KafkaProducer: kafkaProducer,
+		componentName:  componentName,
+		tracerCloser:   closer,
+		Cfg:            cfg,
+		ImmutableCache: cache,
+		APIMux:         mux.NewRouter().UseEncodedPath(),
+		httpClient:     &http.Client{Timeout: HTTPClientTimeout},
+		KafkaConsumer:  kafkaConsumer,
+		KafkaProducer:  kafkaProducer,
 	}
 }
 
@@ -132,7 +132,7 @@ func (b *BaseDendrite) CreateHTTPRoomserverAPIs() (
 	if err != nil {
 		logrus.WithError(err).Panic("NewRoomserverInputAPIHTTP failed", b.httpClient)
 	}
-	query, err := roomserverAPI.NewRoomserverQueryAPIHTTP(b.Cfg.RoomServerURL(), b.httpClient, b.Cache)
+	query, err := roomserverAPI.NewRoomserverQueryAPIHTTP(b.Cfg.RoomServerURL(), b.httpClient, b.ImmutableCache)
 	if err != nil {
 		logrus.WithError(err).Panic("NewRoomserverQueryAPIHTTP failed", b.httpClient)
 	}

common/caching/immutablecache.go

@@ -3,10 +3,11 @@ package caching
 import "github.com/matrix-org/gomatrixserverlib"
 
 const (
-	MaxRoomVersionCacheEntries = 128
+	RoomVersionCachingEnabled  = true
+	RoomVersionMaxCacheEntries = 128
 )
 
-type Cache interface {
+type ImmutableCache interface {
 	GetRoomVersion(roomId string) (gomatrixserverlib.RoomVersion, bool)
 	StoreRoomVersion(roomId string, roomVersion gomatrixserverlib.RoomVersion)
 }

common/caching/immutableinmemorylru.go

@@ -0,0 +1,47 @@
+package caching
+
+import (
+	lru "github.com/hashicorp/golang-lru"
+	"github.com/matrix-org/gomatrixserverlib"
+)
+
+type ImmutableInMemoryLRUCache struct {
+	roomVersions *lru.Cache
+}
+
+func NewImmutableInMemoryLRUCache() (*ImmutableInMemoryLRUCache, error) {
+	roomVersionCache, rvErr := lru.New(RoomVersionMaxCacheEntries)
+	if rvErr != nil {
+		return nil, rvErr
+	}
+	return &ImmutableInMemoryLRUCache{
+		roomVersions: roomVersionCache,
+	}, nil
+}
+
+func checkForInvalidMutation(cache *lru.Cache, key string, value interface{}) {
+	if peek, ok := cache.Peek(key); ok && peek != value {
+		panic("invalid use of immutable cache tries to mutate existing value")
+	}
+}
+
+func (c *ImmutableInMemoryLRUCache) GetRoomVersion(roomID string) (gomatrixserverlib.RoomVersion, bool) {
+	if c == nil || !RoomVersionCachingEnabled {
+		return "", false
+	}
+	val, found := c.roomVersions.Get(roomID)
+	if found && val != nil {
+		if roomVersion, ok := val.(gomatrixserverlib.RoomVersion); ok {
+			return roomVersion, true
+		}
+	}
+	return "", false
+}
+
+func (c *ImmutableInMemoryLRUCache) StoreRoomVersion(roomID string, roomVersion gomatrixserverlib.RoomVersion) {
+	if c == nil || !RoomVersionCachingEnabled {
+		return
+	}
+	checkForInvalidMutation(c.roomVersions, roomID, roomVersion)
+	c.roomVersions.Add(roomID, roomVersion)
+}

common/caching/inmemorylru.go

@@ -1,40 +0,0 @@
-package caching
-
-import (
-	lru "github.com/hashicorp/golang-lru"
-	"github.com/matrix-org/gomatrixserverlib"
-)
-
-type InMemoryLRUCache struct {
-	roomVersions *lru.Cache
-}
-
-func NewInMemoryLRUCache() (*InMemoryLRUCache, error) {
-	roomVersionCache, rvErr := lru.New(MaxRoomVersionCacheEntries)
-	if rvErr != nil {
-		return nil, rvErr
-	}
-	return &InMemoryLRUCache{
-		roomVersions: roomVersionCache,
-	}, nil
-}
-
-func (c *InMemoryLRUCache) GetRoomVersion(roomID string) (gomatrixserverlib.RoomVersion, bool) {
-	if c == nil {
-		return "", false
-	}
-	val, found := c.roomVersions.Get(roomID)
-	if found && val != nil {
-		if roomVersion, ok := val.(gomatrixserverlib.RoomVersion); ok {
-			return roomVersion, true
-		}
-	}
-	return "", false
-}
-
-func (c *InMemoryLRUCache) StoreRoomVersion(roomID string, roomVersion gomatrixserverlib.RoomVersion) {
-	if c == nil {
-		return
-	}
-	c.roomVersions.Add(roomID, roomVersion)
-}

roomserver/api/query.go

@@ -412,7 +412,7 @@ const RoomserverQueryRoomVersionForRoomPath = "/api/roomserver/queryRoomVersionF
 
 // NewRoomserverQueryAPIHTTP creates a RoomserverQueryAPI implemented by talking to a HTTP POST API.
 // If httpClient is nil an error is returned
-func NewRoomserverQueryAPIHTTP(roomserverURL string, httpClient *http.Client, cache caching.Cache) (RoomserverQueryAPI, error) {
+func NewRoomserverQueryAPIHTTP(roomserverURL string, httpClient *http.Client, cache caching.ImmutableCache) (RoomserverQueryAPI, error) {
 	if httpClient == nil {
 		return nil, errors.New("NewRoomserverQueryAPIHTTP: httpClient is <nil>")
 	}
@@ -420,9 +420,9 @@ func NewRoomserverQueryAPIHTTP(roomserverURL string, httpClient *http.Client, ca
 }
 
 type httpRoomserverQueryAPI struct {
-	roomserverURL string
-	httpClient    *http.Client
-	cache         caching.Cache
+	roomserverURL  string
+	httpClient     *http.Client
+	immutableCache caching.ImmutableCache
 }
 
 // QueryLatestEventsAndState implements RoomserverQueryAPI
@@ -587,7 +587,7 @@ func (h *httpRoomserverQueryAPI) QueryRoomVersionForRoom(
 	request *QueryRoomVersionForRoomRequest,
 	response *QueryRoomVersionForRoomResponse,
 ) error {
-	if roomVersion, ok := h.cache.GetRoomVersion(request.RoomID); ok {
+	if roomVersion, ok := h.immutableCache.GetRoomVersion(request.RoomID); ok {
 		response.RoomVersion = roomVersion
 		return nil
 	}
@@ -598,7 +598,7 @@ func (h *httpRoomserverQueryAPI) QueryRoomVersionForRoom(
 	apiURL := h.roomserverURL + RoomserverQueryRoomVersionForRoomPath
 	err := commonHTTP.PostJSON(ctx, span, h.httpClient, apiURL, request, response)
 	if err == nil {
-		h.cache.StoreRoomVersion(request.RoomID, response.RoomVersion)
+		h.immutableCache.StoreRoomVersion(request.RoomID, response.RoomVersion)
 	}
 	return err
 }

roomserver/query/query.go

@@ -98,8 +98,8 @@ type RoomserverQueryAPIDatabase interface {
 
 // RoomserverQueryAPI is an implementation of api.RoomserverQueryAPI
 type RoomserverQueryAPI struct {
-	DB    RoomserverQueryAPIDatabase
-	Cache caching.Cache
+	DB             RoomserverQueryAPIDatabase
+	ImmutableCache caching.ImmutableCache
 }
 
 // QueryLatestEventsAndState implements api.RoomserverQueryAPI
@@ -898,7 +898,7 @@ func (r *RoomserverQueryAPI) QueryRoomVersionForRoom(
 	request *api.QueryRoomVersionForRoomRequest,
 	response *api.QueryRoomVersionForRoomResponse,
 ) error {
-	if roomVersion, ok := r.Cache.GetRoomVersion(request.RoomID); ok {
+	if roomVersion, ok := r.ImmutableCache.GetRoomVersion(request.RoomID); ok {
 		response.RoomVersion = roomVersion
 		return nil
 	}
@@ -908,7 +908,7 @@ func (r *RoomserverQueryAPI) QueryRoomVersionForRoom(
 		return err
 	}
 	response.RoomVersion = roomVersion
-	r.Cache.StoreRoomVersion(request.RoomID, response.RoomVersion)
+	r.ImmutableCache.StoreRoomVersion(request.RoomID, response.RoomVersion)
 	return nil
 }
 

roomserver/roomserver.go

@@ -49,8 +49,8 @@ func SetupRoomServerComponent(
 	inputAPI.SetupHTTP(http.DefaultServeMux)
 
 	queryAPI := query.RoomserverQueryAPI{
-		DB:    roomserverDB,
-		Cache: base.Cache,
+		DB:             roomserverDB,
+		ImmutableCache: base.ImmutableCache,
 	}
 
 	queryAPI.SetupHTTP(http.DefaultServeMux)