[#209] pkg/object: Support splitID field in SDK library

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

pkg/object/raw.go

@@ -110,6 +110,11 @@ func (o *RawObject) SetChildren(v ...*ID) {
 	o.setChildren(v...)
 }
 
+// SetSplitID sets split identifier for the split object.
+func (o *RawObject) SetSplitID(v []byte) {
+	o.setSplitID(v)
+}
+
 // SetParentID sets identifier of the parent object.
 func (o *RawObject) SetParentID(v *ID) {
 	o.setParentID(v)

pkg/object/raw_test.go

@@ -5,6 +5,7 @@ import (
 	"crypto/sha256"
 	"testing"
 
+	"github.com/google/uuid"
 	"github.com/nspcc-dev/neofs-api-go/pkg"
 	"github.com/nspcc-dev/neofs-api-go/pkg/container"
 	"github.com/nspcc-dev/neofs-api-go/pkg/owner"
@@ -190,6 +191,19 @@ func TestRawObject_SetChildren(t *testing.T) {
 	require.Equal(t, []*ID{id1, id2}, obj.Children())
 }
 
+func TestRawObject_SetSplitID(t *testing.T) {
+	obj := NewRaw()
+
+	require.Nil(t, obj.SplitID())
+
+	splitID, err := uuid.New().MarshalBinary()
+	require.NoError(t, err)
+
+	obj.SetSplitID(splitID)
+
+	require.Equal(t, obj.SplitID(), splitID)
+}
+
 func TestRawObject_SetParent(t *testing.T) {
 	obj := NewRaw()
 

pkg/object/rw.go

@@ -251,6 +251,21 @@ func (o *rwObject) setChildren(v ...*ID) {
 	})
 }
 
+// SplitID return split identity of split object. If object is not split
+// returns nil.
+func (o *rwObject) SplitID() []byte {
+	return (*object.Object)(o).
+		GetHeader().
+		GetSplit().
+		GetSplitID()
+}
+
+func (o *rwObject) setSplitID(id []byte) {
+	o.setSplitFields(func(split *object.SplitHeader) {
+		split.SetSplitID(id)
+	})
+}
+
 // ParentID returns identifier of the parent object.
 func (o *rwObject) ParentID() *ID {
 	return NewIDFromV2(