Add RoomInfo cache, remove RoomServerRoomNIDsCache (#1646)

* Add RoomInfo cache, remove RoomServerRoomNID cache, ensure caches are thread-safe

* Don't panic if the roomInfo isn't known yet

* LRU package is already threadsafe

* Use RoomInfo cache to find room version if possible in Events()

* Adding comments about RoomInfoCache safety

4 files changed, 57 insertions, 32 deletions

diff --git a/internal/caching/cache_roominfo.go b/internal/caching/cache_roominfo.go
new file mode 100644
index 00000000..f32d6ba9
--- /dev/null
+++ b/internal/caching/cache_roominfo.go
@@ -0,0 +1,45 @@
+package caching
+
+import (
+	"github.com/matrix-org/dendrite/roomserver/types"
+)
+
+// WARNING: This cache is mutable because it's entirely possible that
+// the IsStub or StateSnaphotNID fields can change, even though the
+// room version and room NID fields will not. This is only safe because
+// the RoomInfoCache is used ONLY within the roomserver and because it
+// will be kept up-to-date by the latest events updater. It MUST NOT be
+// used from other components as we currently have no way to invalidate
+// the cache in downstream components.
+
+const (
+	RoomInfoCacheName       = "roominfo"
+	RoomInfoCacheMaxEntries = 1024
+	RoomInfoCacheMutable    = true
+)
+
+// RoomInfosCache contains the subset of functions needed for
+// a room Info cache. It must only be used from the roomserver only
+// It is not safe for use from other components.
+type RoomInfoCache interface {
+	GetRoomInfo(roomID string) (roomInfo types.RoomInfo, ok bool)
+	StoreRoomInfo(roomID string, roomInfo types.RoomInfo)
+}
+
+// GetRoomInfo must only be called from the roomserver only. It is not
+// safe for use from other components.
+func (c Caches) GetRoomInfo(roomID string) (types.RoomInfo, bool) {
+	val, found := c.RoomInfos.Get(roomID)
+	if found && val != nil {
+		if roomInfo, ok := val.(types.RoomInfo); ok {
+			return roomInfo, true
+		}
+	}
+	return types.RoomInfo{}, false
+}
+
+// StoreRoomInfo must only be called from the roomserver only. It is not
+// safe for use from other components.
+func (c Caches) StoreRoomInfo(roomID string, roomInfo types.RoomInfo) {
+	c.RoomInfos.Set(roomID, roomInfo)
+}
diff --git a/internal/caching/cache_roomservernids.go b/internal/caching/cache_roomservernids.go
index cac59549..bf4fe85e 100644
--- a/internal/caching/cache_roomservernids.go
+++ b/internal/caching/cache_roomservernids.go
@@ -15,10 +15,6 @@ const (
 	RoomServerEventTypeNIDsCacheMaxEntries = 64
 	RoomServerEventTypeNIDsCacheMutable    = false
 
-	RoomServerRoomNIDsCacheName       = "roomserver_room_nids"
-	RoomServerRoomNIDsCacheMaxEntries = 1024
-	RoomServerRoomNIDsCacheMutable    = false
-
 	RoomServerRoomIDsCacheName       = "roomserver_room_ids"
 	RoomServerRoomIDsCacheMaxEntries = 1024
 	RoomServerRoomIDsCacheMutable    = false
@@ -27,6 +23,7 @@ const (
 type RoomServerCaches interface {
 	RoomServerNIDsCache
 	RoomVersionCache
+	RoomInfoCache
 }
 
 // RoomServerNIDsCache contains the subset of functions needed for
@@ -38,9 +35,6 @@ type RoomServerNIDsCache interface {
 	GetRoomServerEventTypeNID(eventType string) (types.EventTypeNID, bool)
 	StoreRoomServerEventTypeNID(eventType string, nid types.EventTypeNID)
 
-	GetRoomServerRoomNID(roomID string) (types.RoomNID, bool)
-	StoreRoomServerRoomNID(roomID string, nid types.RoomNID)
-
 	GetRoomServerRoomID(roomNID types.RoomNID) (string, bool)
 	StoreRoomServerRoomID(roomNID types.RoomNID, roomID string)
 }
@@ -73,21 +67,6 @@ func (c Caches) StoreRoomServerEventTypeNID(eventType string, nid types.EventTyp
 	c.RoomServerEventTypeNIDs.Set(eventType, nid)
 }
 
-func (c Caches) GetRoomServerRoomNID(roomID string) (types.RoomNID, bool) {
-	val, found := c.RoomServerRoomNIDs.Get(roomID)
-	if found && val != nil {
-		if roomNID, ok := val.(types.RoomNID); ok {
-			return roomNID, true
-		}
-	}
-	return 0, false
-}
-
-func (c Caches) StoreRoomServerRoomNID(roomID string, roomNID types.RoomNID) {
-	c.RoomServerRoomNIDs.Set(roomID, roomNID)
-	c.RoomServerRoomIDs.Set(strconv.Itoa(int(roomNID)), roomID)
-}
-
 func (c Caches) GetRoomServerRoomID(roomNID types.RoomNID) (string, bool) {
 	val, found := c.RoomServerRoomIDs.Get(strconv.Itoa(int(roomNID)))
 	if found && val != nil {
@@ -99,5 +78,5 @@ func (c Caches) GetRoomServerRoomID(roomNID types.RoomNID) (string, bool) {
 }
 
 func (c Caches) StoreRoomServerRoomID(roomNID types.RoomNID, roomID string) {
-	c.StoreRoomServerRoomNID(roomID, roomNID)
+	c.RoomServerRoomIDs.Set(strconv.Itoa(int(roomNID)), roomID)
 }
diff --git a/internal/caching/caches.go b/internal/caching/caches.go
index e7b7f550..f04d05d4 100644
--- a/internal/caching/caches.go
+++ b/internal/caching/caches.go
@@ -10,6 +10,7 @@ type Caches struct {
 	RoomServerEventTypeNIDs Cache // RoomServerNIDsCache
 	RoomServerRoomNIDs      Cache // RoomServerNIDsCache
 	RoomServerRoomIDs       Cache // RoomServerNIDsCache
+	RoomInfos               Cache // RoomInfoCache
 	FederationEvents        Cache // FederationEventsCache
 }
 
diff --git a/internal/caching/impl_inmemorylru.go b/internal/caching/impl_inmemorylru.go
index f05e8f3c..cf05a8b5 100644
--- a/internal/caching/impl_inmemorylru.go
+++ b/internal/caching/impl_inmemorylru.go
@@ -45,19 +45,19 @@ func NewInMemoryLRUCache(enablePrometheus bool) (*Caches, error) {
 	if err != nil {
 		return nil, err
 	}
-	roomServerRoomNIDs, err := NewInMemoryLRUCachePartition(
-		RoomServerRoomNIDsCacheName,
-		RoomServerRoomNIDsCacheMutable,
-		RoomServerRoomNIDsCacheMaxEntries,
+	roomServerRoomIDs, err := NewInMemoryLRUCachePartition(
+		RoomServerRoomIDsCacheName,
+		RoomServerRoomIDsCacheMutable,
+		RoomServerRoomIDsCacheMaxEntries,
 		enablePrometheus,
 	)
 	if err != nil {
 		return nil, err
 	}
-	roomServerRoomIDs, err := NewInMemoryLRUCachePartition(
-		RoomServerRoomIDsCacheName,
-		RoomServerRoomIDsCacheMutable,
-		RoomServerRoomIDsCacheMaxEntries,
+	roomInfos, err := NewInMemoryLRUCachePartition(
+		RoomInfoCacheName,
+		RoomInfoCacheMutable,
+		RoomInfoCacheMaxEntries,
 		enablePrometheus,
 	)
 	if err != nil {
@@ -77,8 +77,8 @@ func NewInMemoryLRUCache(enablePrometheus bool) (*Caches, error) {
 		ServerKeys:              serverKeys,
 		RoomServerStateKeyNIDs:  roomServerStateKeyNIDs,
 		RoomServerEventTypeNIDs: roomServerEventTypeNIDs,
-		RoomServerRoomNIDs:      roomServerRoomNIDs,
 		RoomServerRoomIDs:       roomServerRoomIDs,
+		RoomInfos:               roomInfos,
 		FederationEvents:        federationEvents,
 	}, nil
 }