[#840] metabase: Distinguish objects with tombstones and GC marks

Each object from graveyard has tombstone or GC mark. If object has
tombstone, metabase should return `ErrAlreadyRemoved` on object requests.
This is the case when user clearly removed the object from container. GC
marks are used for physical removal which can appear even if object is still
presented in container (Control service, Policer job, etc.). In this case
metabase should return 404 error on object requests.

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

pkg/local_object_storage/metabase/exists.go

@@ -1,6 +1,7 @@
 package meta
 
 import (
+	"bytes"
 	"errors"
 	"fmt"
 
@@ -62,7 +63,10 @@ func (db *DB) Exists(prm *ExistsPrm) (res *ExistsRes, err error) {
 
 func (db *DB) exists(tx *bbolt.Tx, addr *objectSDK.Address) (exists bool, err error) {
 	// check graveyard first
-	if inGraveyard(tx, addr) {
+	switch inGraveyard(tx, addr) {
+	case 1:
+		return false, object.ErrNotFound
+	case 2:
 		return false, object.ErrAlreadyRemoved
 	}
 
@@ -92,16 +96,26 @@ func (db *DB) exists(tx *bbolt.Tx, addr *objectSDK.Address) (exists bool, err er
 	return inBucket(tx, storageGroupBucketName(addr.ContainerID()), objKey), nil
 }
 
-// inGraveyard returns true if object was marked as removed.
+// inGraveyard returns:
-func inGraveyard(tx *bbolt.Tx, addr *objectSDK.Address) bool {
+//  * 0 if object is not in graveyard;
+//  * 1 if object is in graveyard with GC mark;
+//  * 2 if object is in graveyard with tombstone.
+func inGraveyard(tx *bbolt.Tx, addr *objectSDK.Address) uint8 {
 	graveyard := tx.Bucket(graveyardBucketName)
 	if graveyard == nil {
-		return false
+		return 0
 	}
 
-	tombstone := graveyard.Get(addressKey(addr))
+	val := graveyard.Get(addressKey(addr))
+	if val == nil {
+		return 0
+	}
 
-	return len(tombstone) != 0
+	if bytes.Equal(val, []byte(inhumeGCMarkValue)) {
+		return 1
+	}
+
+	return 2
 }
 
 // inBucket checks if key <key> is present in bucket <name>.

pkg/local_object_storage/metabase/get.go

@@ -85,8 +85,13 @@ func (db *DB) get(tx *bbolt.Tx, addr *objectSDK.Address, checkGraveyard, raw boo
 	key := objectKey(addr.ObjectID())
 	cid := addr.ContainerID()
 
-	if checkGraveyard && inGraveyard(tx, addr) {
+	if checkGraveyard {
-		return nil, object.ErrAlreadyRemoved
+		switch inGraveyard(tx, addr) {
+		case 1:
+			return nil, object.ErrNotFound
+		case 2:
+			return nil, object.ErrAlreadyRemoved
+		}
 	}
 
 	// check in primary index

pkg/local_object_storage/metabase/get_test.go

@@ -94,6 +94,20 @@ func TestDB_Get(t *testing.T) {
 		require.NoError(t, err)
 		require.True(t, binaryEqual(child.CutPayload().Object(), newChild))
 	})
+
+	t.Run("get removed object", func(t *testing.T) {
+		obj := generateAddress()
+		ts := generateAddress()
+
+		require.NoError(t, meta.Inhume(db, obj, ts))
+		_, err := meta.Get(db, obj)
+		require.ErrorIs(t, err, object.ErrAlreadyRemoved)
+
+		obj = generateAddress()
+		require.NoError(t, meta.Inhume(db, obj, nil))
+		_, err = meta.Get(db, obj)
+		require.ErrorIs(t, err, object.ErrNotFound)
+	})
 }
 
 // binary equal is used when object contains empty lists in the structure and

pkg/local_object_storage/metabase/select.go

@@ -134,7 +134,7 @@ func (db *DB) selectObjects(tx *bbolt.Tx, cid *cid.ID, fs object.SearchFilters)
 			return nil, err
 		}
 
-		if inGraveyard(tx, addr) {
+		if inGraveyard(tx, addr) > 0 {
 			continue // ignore removed objects
 		}