Apply suggestions from code review

lib/netext/grpcext/conn.go

@@ -154,23 +154,11 @@ func (c *Conn) Invoke(
 	}
 
 	if resp != nil {
-		// (rogchap) there is a lot of marshaling/unmarshaling here, but if we just pass the dynamic message
-		// the default Marshaller would be used, which would strip any zero/default values from the JSON.
-		// eg. given this message:
-		// message Point {
-		//    double x = 1;
-		// 	  double y = 2;
-		// 	  double z = 3;
-		// }
-		// and a value like this:
-		// msg := Point{X: 6, Y: 4, Z: 0}
-		// would result in JSON output:
-		// {"x":6,"y":4}
-		// rather than the desired:
-		// {"x":6,"y":4,"z":0}
-		raw, _ := marshaler.Marshal(resp)
-		var msg interface{}
-		_ = json.Unmarshal(raw, &msg)
+		msg, err := convert(marshaler, resp)
+		if err != nil {
+			return nil, fmt.Errorf("unable to convert response object to JSON: %w", err)
+		}
+
 		response.Message = msg
 	}
 	return &response, nil

lib/netext/grpcext/stream.go

@@ -35,7 +35,7 @@ func (s *Stream) ReceiveConverted() (interface{}, error) {
 		return nil, err
 	}
 
-	msg, errConv := s.convert(raw)
+	msg, errConv := convert(s.marshaler, raw)
 	if errConv != nil {
 		return nil, errConv
 	}
@@ -68,8 +68,8 @@ func (s *Stream) receive() (*dynamicpb.Message, error) {
 //
 //	message Point {
 //	   double x = 1;
-//		  double y = 2;
-//		  double z = 3;
+//		double y = 2;
+//		double z = 3;
 //	}
 //
 // and a value like this:
@@ -78,10 +78,10 @@ func (s *Stream) receive() (*dynamicpb.Message, error) {
 // {"x":6,"y":4}
 // rather than the desired:
 // {"x":6,"y":4,"z":0}
-func (s *Stream) convert(msg *dynamicpb.Message) (interface{}, error) {
+func convert(marshaler protojson.MarshalOptions, msg *dynamicpb.Message) (interface{}, error) {
 	// TODO(olegbespalov): add the test that checks that message is not nil
 
-	raw, err := s.marshaler.Marshal(msg)
+	raw, err := marshaler.Marshal(msg)
 	if err != nil {
 		return nil, fmt.Errorf("failed to marshal the message: %w", err)
 	}