[#122] Add versioning cache

Signed-off-by: Denis Kirillov <denis@nspcc.ru>

api/cache/system.go

@@ -0,0 +1,56 @@
+package cache
+
+import (
+	"time"
+
+	"github.com/nspcc-dev/neofs-api-go/pkg/object"
+
+	"github.com/bluele/gcache"
+)
+
+type (
+	// SystemCache provides interface for lru cache for objects.
+	SystemCache interface {
+		Get(key string) *object.Object
+		Put(key string, obj *object.Object) error
+		Delete(key string) bool
+	}
+
+	// systemCache contains cache with objects and lifetime of cache entries.
+	systemCache struct {
+		cache    gcache.Cache
+		lifetime time.Duration
+	}
+)
+
+// NewSystemCache creates an object of SystemCache.
+func NewSystemCache(cacheSize int, lifetime time.Duration) SystemCache {
+	gc := gcache.New(cacheSize).LRU().Build()
+
+	return &systemCache{cache: gc, lifetime: lifetime}
+}
+
+// Get returns cached object.
+func (o *systemCache) Get(key string) *object.Object {
+	entry, err := o.cache.Get(key)
+	if err != nil {
+		return nil
+	}
+
+	result, ok := entry.(*object.Object)
+	if !ok {
+		return nil
+	}
+
+	return result
+}
+
+// Put puts an object to cache.
+func (o *systemCache) Put(key string, obj *object.Object) error {
+	return o.cache.SetWithExpire(key, obj, o.lifetime)
+}
+
+// Delete deletes an object from cache.
+func (o *systemCache) Delete(key string) bool {
+	return o.cache.Remove(key)
+}