[#1483] metabase: Store version

The main problem is to distinguish the case of initial initialization
and update from version 0. We can't do this at `Open`, because of
`resync_metabase` flag. Thus, the following approach was taken:
1. During `Open` check whether the metabase was initialized.
2. Check for the version in `Init` or write the new one if the metabase
   is new.
3. Update version in `Reset`.

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

pkg/local_object_storage/metabase/version_test.go

@@ -0,0 +1,81 @@
+package meta
+
+import (
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+	"go.etcd.io/bbolt"
+)
+
+func TestVersion(t *testing.T) {
+	dir := t.TempDir()
+
+	newDB := func(t *testing.T) *DB {
+		return New(WithPath(filepath.Join(dir, t.Name())),
+			WithPermissions(0600))
+	}
+	check := func(t *testing.T, db *DB) {
+		require.NoError(t, db.boltDB.View(func(tx *bbolt.Tx) error {
+			b := tx.Bucket(shardInfoBucket)
+			if b == nil {
+				return errors.New("shard info bucket not found")
+			}
+			data := b.Get(versionKey)
+			if len(data) != 8 {
+				return errors.New("invalid version data")
+			}
+			if stored := binary.LittleEndian.Uint64(data); stored != version {
+				return fmt.Errorf("invalid version: %d != %d", stored, version)
+			}
+			return nil
+		}))
+	}
+	t.Run("simple", func(t *testing.T) {
+		db := newDB(t)
+		require.NoError(t, db.Open())
+		require.NoError(t, db.Init())
+		check(t, db)
+		require.NoError(t, db.Close())
+
+		t.Run("reopen", func(t *testing.T) {
+			require.NoError(t, db.Open())
+			require.NoError(t, db.Init())
+			check(t, db)
+			require.NoError(t, db.Close())
+		})
+	})
+	t.Run("old data", func(t *testing.T) {
+		db := newDB(t)
+		require.NoError(t, db.Open())
+		require.NoError(t, db.WriteShardID([]byte{1, 2, 3, 4}))
+		require.NoError(t, db.Close())
+
+		require.NoError(t, db.Open())
+		require.NoError(t, db.Init())
+		check(t, db)
+		require.NoError(t, db.Close())
+	})
+	t.Run("invalid version", func(t *testing.T) {
+		db := newDB(t)
+		require.NoError(t, db.Open())
+		require.NoError(t, db.boltDB.Update(func(tx *bbolt.Tx) error {
+			return updateVersion(tx, version+1)
+		}))
+		require.NoError(t, db.Close())
+
+		require.NoError(t, db.Open())
+		require.Error(t, db.Init())
+		require.NoError(t, db.Close())
+
+		t.Run("reset", func(t *testing.T) {
+			require.NoError(t, db.Open())
+			require.NoError(t, db.Reset())
+			check(t, db)
+			require.NoError(t, db.Close())
+		})
+	})
+}