[#1634] meta: Add epoch state

It allows performing expiration checks on the stored objects.

Signed-off-by: Pavel Karpy <carpawell@nspcc.ru>

pkg/local_object_storage/metabase/db.go

@@ -24,6 +24,13 @@ type matcher struct {
 	matchBucket func(*bbolt.Bucket, string, string, func([]byte, []byte) error) error
 }
 
+// EpochState is an interface that provides access to the
+// current epoch number.
+type EpochState interface {
+	// CurrentEpoch must return current epoch height.
+	CurrentEpoch() uint64
+}
+
 // DB represents local metabase of storage node.
 type DB struct {
 	*cfg
@@ -50,6 +57,8 @@ type cfg struct {
 	info Info
 
 	log *logger.Logger
+
+	epochState EpochState
 }
 
 func defaultCfg() *cfg {
@@ -71,6 +80,10 @@ func New(opts ...Option) *DB {
 		opts[i](c)
 	}
 
+	if c.epochState == nil {
+		panic("metabase: epoch state is not specified")
+	}
+
 	return &DB{
 		cfg: c,
 		matchers: map[object.SearchMatchType]matcher{
@@ -311,3 +324,10 @@ func WithMaxBatchDelay(d time.Duration) Option {
 		}
 	}
 }
+
+// WithEpochState return option to specify a source of current epoch height.
+func WithEpochState(s EpochState) Option {
+	return func(c *cfg) {
+		c.epochState = s
+	}
+}