Fix #897 and shuffle directory around (#1054)

* Fix #897 and shuffle directory around

* Update find-lint

* goimports

Co-authored-by: Neil Alexander <neilalexander@users.noreply.github.com>

internal/caching/immutablecache.go

@@ -0,0 +1,17 @@
+package caching
+
+import (
+	"github.com/matrix-org/gomatrixserverlib"
+)
+
+const (
+	RoomVersionMaxCacheEntries = 1024
+	ServerKeysMaxCacheEntries  = 1024
+)
+
+type ImmutableCache interface {
+	GetRoomVersion(roomId string) (gomatrixserverlib.RoomVersion, bool)
+	StoreRoomVersion(roomId string, roomVersion gomatrixserverlib.RoomVersion)
+	GetServerKey(request gomatrixserverlib.PublicKeyLookupRequest) (gomatrixserverlib.PublicKeyLookupResult, bool)
+	StoreServerKey(request gomatrixserverlib.PublicKeyLookupRequest, response gomatrixserverlib.PublicKeyLookupResult)
+}

internal/caching/immutableinmemorylru.go

@@ -0,0 +1,95 @@
+package caching
+
+import (
+	"fmt"
+
+	lru "github.com/hashicorp/golang-lru"
+	"github.com/matrix-org/gomatrixserverlib"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
+)
+
+type ImmutableInMemoryLRUCache struct {
+	roomVersions *lru.Cache
+	serverKeys   *lru.Cache
+}
+
+func NewImmutableInMemoryLRUCache() (*ImmutableInMemoryLRUCache, error) {
+	roomVersionCache, rvErr := lru.New(RoomVersionMaxCacheEntries)
+	if rvErr != nil {
+		return nil, rvErr
+	}
+	serverKeysCache, rvErr := lru.New(ServerKeysMaxCacheEntries)
+	if rvErr != nil {
+		return nil, rvErr
+	}
+	cache := &ImmutableInMemoryLRUCache{
+		roomVersions: roomVersionCache,
+		serverKeys:   serverKeysCache,
+	}
+	cache.configureMetrics()
+	return cache, nil
+}
+
+func (c *ImmutableInMemoryLRUCache) configureMetrics() {
+	promauto.NewGaugeFunc(prometheus.GaugeOpts{
+		Namespace: "dendrite",
+		Subsystem: "caching",
+		Name:      "number_room_version_entries",
+		Help:      "The number of room version entries cached.",
+	}, func() float64 {
+		return float64(c.roomVersions.Len())
+	})
+
+	promauto.NewGaugeFunc(prometheus.GaugeOpts{
+		Namespace: "dendrite",
+		Subsystem: "caching",
+		Name:      "number_server_key_entries",
+		Help:      "The number of server key entries cached.",
+	}, func() float64 {
+		return float64(c.serverKeys.Len())
+	})
+}
+
+func checkForInvalidMutation(cache *lru.Cache, key string, value interface{}) {
+	if peek, ok := cache.Peek(key); ok && peek != value {
+		panic(fmt.Sprintf("invalid use of immutable cache tries to mutate existing value of %q", key))
+	}
+}
+
+func (c *ImmutableInMemoryLRUCache) GetRoomVersion(roomID string) (gomatrixserverlib.RoomVersion, bool) {
+	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) {
+	checkForInvalidMutation(c.roomVersions, roomID, roomVersion)
+	c.roomVersions.Add(roomID, roomVersion)
+}
+
+func (c *ImmutableInMemoryLRUCache) GetServerKey(
+	request gomatrixserverlib.PublicKeyLookupRequest,
+) (gomatrixserverlib.PublicKeyLookupResult, bool) {
+	key := fmt.Sprintf("%s/%s", request.ServerName, request.KeyID)
+	val, found := c.serverKeys.Get(key)
+	if found && val != nil {
+		if keyLookupResult, ok := val.(gomatrixserverlib.PublicKeyLookupResult); ok {
+			return keyLookupResult, true
+		}
+	}
+	return gomatrixserverlib.PublicKeyLookupResult{}, false
+}
+
+func (c *ImmutableInMemoryLRUCache) StoreServerKey(
+	request gomatrixserverlib.PublicKeyLookupRequest,
+	response gomatrixserverlib.PublicKeyLookupResult,
+) {
+	key := fmt.Sprintf("%s/%s", request.ServerName, request.KeyID)
+	checkForInvalidMutation(c.roomVersions, key, response)
+	c.serverKeys.Add(request, response)
+}