[#2068] blobovnicza: Add Exists method

Signed-off-by: Evgenii Stratonikov <evgeniy@morphbits.ru>

pkg/local_object_storage/blobovnicza/exists.go

@@ -0,0 +1,29 @@
+package blobovnicza
+
+import (
+	oid "github.com/nspcc-dev/neofs-sdk-go/object/id"
+	"go.etcd.io/bbolt"
+)
+
+// Exists check if object with the specified address is stored in b.
+func (b *Blobovnicza) Exists(addr oid.Address) (bool, error) {
+	var (
+		exists  bool
+		addrKey = addressKey(addr)
+	)
+
+	err := b.boltDB.View(func(tx *bbolt.Tx) error {
+		return tx.ForEach(func(_ []byte, buck *bbolt.Bucket) error {
+			exists = buck.Get(addrKey) != nil
+			if exists {
+				return errInterruptForEach
+			}
+			return nil
+		})
+	})
+
+	if err == errInterruptForEach {
+		err = nil
+	}
+	return exists, err
+}