1 files changed, 73 insertions, 0 deletions
diff --git a/internal/caching/impl_inmemorylru.go b/internal/caching/impl_inmemorylru.go
new file mode 100644
index 00000000..f7901d2e
--- /dev/null
+++ b/internal/caching/impl_inmemorylru.go
@@ -0,0 +1,73 @@
+package caching
+
+import (
+	"fmt"
+
+	lru "github.com/hashicorp/golang-lru"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
+)
+
+func NewInMemoryLRUCache() (*Caches, error) {
+	roomVersions, err := NewInMemoryLRUCachePartition(
+		RoomVersionCacheName,
+		RoomVersionCacheMutable,
+		RoomVersionCacheMaxEntries,
+	)
+	if err != nil {
+		return nil, err
+	}
+	serverKeys, err := NewInMemoryLRUCachePartition(
+		ServerKeyCacheName,
+		ServerKeyCacheMutable,
+		ServerKeyCacheMaxEntries,
+	)
+	if err != nil {
+		return nil, err
+	}
+	return &Caches{
+		RoomVersions: roomVersions,
+		ServerKeys:   serverKeys,
+	}, nil
+}
+
+type InMemoryLRUCachePartition struct {
+	name       string
+	mutable    bool
+	maxEntries int
+	lru        *lru.Cache
+}
+
+func NewInMemoryLRUCachePartition(name string, mutable bool, maxEntries int) (*InMemoryLRUCachePartition, error) {
+	var err error
+	cache := InMemoryLRUCachePartition{
+		name:       name,
+		mutable:    mutable,
+		maxEntries: maxEntries,
+	}
+	cache.lru, err = lru.New(maxEntries)
+	if err != nil {
+		return nil, err
+	}
+	promauto.NewGaugeFunc(prometheus.GaugeOpts{
+		Namespace: "dendrite",
+		Subsystem: "caching_in_memory_lru",
+		Name:      name,
+	}, func() float64 {
+		return float64(cache.lru.Len())
+	})
+	return &cache, nil
+}
+
+func (c *InMemoryLRUCachePartition) Set(key string, value interface{}) {
+	if !c.mutable {
+		if peek, ok := c.lru.Peek(key); ok && peek != value {
+			panic(fmt.Sprintf("invalid use of immutable cache tries to mutate existing value of %q", key))
+		}
+	}
+	c.lru.Add(key, value)
+}
+
+func (c *InMemoryLRUCachePartition) Get(key string) (value interface{}, ok bool) {
+	return c.lru.Get(key)
+}