Add stable marshal for owner id

Signed-off-by: Alex Vanin <alexey@nspcc.ru>

refs/v2/marshal.go

@@ -0,0 +1,49 @@
+package v2
+
+import (
+	"encoding/binary"
+	"math/bits"
+)
+
+func (m *OwnerID) StableMarshal(buf []byte) ([]byte, error) {
+	if m == nil {
+		return []byte{}, nil
+	}
+
+	if buf == nil {
+		buf = make([]byte, m.StableSize())
+	}
+
+	var (
+		i, n, offset int
+	)
+
+	// Write key field.
+
+	buf[i] = 0x0A // id:0x1 << 3 | wiretype:0x2
+	offset = binary.PutUvarint(buf[i+1:], uint64(len(m.Value)))
+	n = copy(buf[i+1+offset:], m.Value)
+	i += 1 + offset + n
+
+	return buf, nil
+}
+
+func (m *OwnerID) StableSize() int {
+	if m == nil {
+		return 0
+	}
+
+	var (
+		ln, size int
+	)
+
+	ln = len(m.Value)                        // size of key field
+	size += 1 + uvarIntSize(uint64(ln)) + ln // wiretype + size of string + string
+
+	return size
+}
+
+// uvarIntSize returns length of varint byte sequence for uint64 value 'x'.
+func uvarIntSize(x uint64) int {
+	return (bits.Len64(x|1) + 6) / 7
+}

refs/v2/marshal_test.go

@@ -0,0 +1,44 @@
+package v2
+
+import (
+	"crypto/rand"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestOwnerID_StableMarshal(t *testing.T) {
+	owner := make([]byte, 25)
+	_, err := rand.Read(owner)
+	require.NoError(t, err)
+
+	expectedOwner := new(OwnerID)
+	expectedOwner.Value = owner
+
+	gotOwner := new(OwnerID)
+
+	t.Run("small buffer", func(t *testing.T) {
+		_, err = expectedOwner.StableMarshal(make([]byte, 1))
+		require.Error(t, err)
+	})
+
+	t.Run("empty owner", func(t *testing.T) {
+		data, err := new(OwnerID).StableMarshal(nil)
+		require.NoError(t, err)
+
+		err = gotOwner.Unmarshal(data)
+		require.NoError(t, err)
+
+		require.Len(t, gotOwner.Value, 0)
+	})
+
+	t.Run("non empty owner", func(t *testing.T) {
+		data, err := expectedOwner.StableMarshal(nil)
+		require.NoError(t, err)
+
+		err = gotOwner.Unmarshal(data)
+		require.NoError(t, err)
+
+		require.Equal(t, expectedOwner, gotOwner)
+	})
+}