[#253] container: Implement marshalers on UsedSpaceAnnouncement structure

Implement Unmarshal method on UsedSpaceAnnouncement v2 message. Implement
Marshal/Unmarshal methods on cross-version UsedSpaceAnnouncement type.

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

pkg/container/announcement.go

@@ -55,3 +55,23 @@ func (a *UsedSpaceAnnouncement) SetUsedSpace(value uint64) {
 func (a *UsedSpaceAnnouncement) ToV2() *container.UsedSpaceAnnouncement {
 	return (*container.UsedSpaceAnnouncement)(a)
 }
+
+// Marshal marshals UsedSpaceAnnouncement into a protobuf binary form.
+//
+// Buffer is allocated when the argument is empty.
+// Otherwise, the first buffer is used.
+func (a *UsedSpaceAnnouncement) Marshal(b ...[]byte) ([]byte, error) {
+	var buf []byte
+	if len(b) > 0 {
+		buf = b[0]
+	}
+
+	return a.ToV2().
+		StableMarshal(buf)
+}
+
+// Unmarshal unmarshals protobuf binary representation of UsedSpaceAnnouncement.
+func (a *UsedSpaceAnnouncement) Unmarshal(data []byte) error {
+	return a.ToV2().
+		Unmarshal(data)
+}

pkg/container/announcement_test.go

@@ -1,6 +1,7 @@
 package container_test
 
 import (
+	"crypto/sha256"
 	"testing"
 
 	"github.com/nspcc-dev/neofs-api-go/pkg/container"
@@ -47,3 +48,24 @@ func TestAnnouncement(t *testing.T) {
 		require.Equal(t, container.NewIDFromV2(newCID), newA.ContainerID())
 	})
 }
+
+func TestUsedSpaceEncoding(t *testing.T) {
+	a := container.NewAnnouncement()
+	a.SetUsedSpace(13)
+	a.SetEpoch(666)
+
+	id := container.NewID()
+	id.SetSHA256([sha256.Size]byte{1, 2, 3})
+
+	a.SetContainerID(id)
+
+	t.Run("binary", func(t *testing.T) {
+		data, err := a.Marshal()
+		require.NoError(t, err)
+
+		a2 := container.NewAnnouncement()
+		require.NoError(t, a2.Unmarshal(data))
+
+		require.Equal(t, a, a2)
+	})
+}