[#132] sdk/object: Implement useful methods and function

Implement method to get address of the object. Implement method to copy the
object w/o payload. Implement function of object deserialization.

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

pkg/object/object.go

@@ -77,6 +77,19 @@ func (o *Object) Verify() error {
 	return nil
 }
 
+// Address returns address of the object.
+func (o *Object) Address() *Address {
+	if o != nil {
+		return &Address{
+			cid: o.cid,
+			oid: o.id,
+		}
+	}
+
+	return nil
+}
+
+// GetPayload returns object payload bytes.
 func (o *Object) GetPayload() []byte {
 	if o != nil {
 		return o.payload
@@ -85,6 +98,25 @@ func (o *Object) GetPayload() []byte {
 	return nil
 }
 
+// CutPayload copies object fields w/o payload.
+func (o *Object) CutPayload() *Object {
+	if o != nil {
+		return &Object{
+			rwObject: rwObject{
+				fin:             o.fin,
+				id:              o.id,
+				key:             o.key,
+				sig:             o.sig,
+				cid:             o.cid,
+				ownerID:         o.ownerID,
+				payloadChecksum: o.payloadChecksum,
+			},
+		}
+	}
+
+	return nil
+}
+
 // ToV2 converts object to v2 Object message.
 func (o *Object) ToV2() *object.Object {
 	obj, _ := o.rwObject.ToV2(nil)
@@ -210,3 +242,13 @@ func FromV2(oV2 *object.Object) (*Object, error) {
 		},
 	}, nil
 }
+
+// FromBytes restores Object from a binary representation.
+func FromBytes(data []byte) (*Object, error) {
+	oV2 := new(object.Object)
+	if err := oV2.StableUnmarshal(data); err != nil {
+		return nil, errors.Wrap(err, "could not unmarshal object")
+	}
+
+	return FromV2(oV2)
+}