Modify the payload of a dynamic generated message

[Mihai Muraru]

Hi,

I have a plugin which has to modify at runtime the value of  field from a dynamic protobuf message. First in the constructor of my class I create a copy of the original message

  auto desc_set=gproto::FileDescriptorSet();

  if (!desc_set.ParseFromString(channel_info.description))

  {

    throw ExporterException("\"" + channel_info.description + "\" is no valid protobuf descriptor.");

  }

  std::string error;

  auto proto_msg = _proto_decoder.GetProtoMessageFromDescriptorSet(desc_set, StripProtoTopicInfo(channel_info.type), error);

  if (proto_msg != nullptr)

  {

    _proto_msg.reset(proto_msg);

  }

  else

  {

    throw ExporterException(error);

  }

  //create a copy of original message because later we have to parse the original message with const parameter

  auto new_desc_set = gproto::FileDescriptorSet();

  new_desc_set.ParseFromString(channel_info.description);

  _modified_msg = _proto_decoder.GetProtoMessageFromDescriptorSet(new_desc_set, StripProtoTopicInfo(channel_info.type), error);

 , then I populate the original message fields in a using

void ExporterChannel::SetData(Timestamp timestamp, const MetaData& meta_data, const std::string& payload)
....
_proto_msg->ParseFromString(payload)
....

 Then I parse the original message using a recursive function 

ParseProtobufMessage(_proto_msg.get(), _modified_msg, _proto_msg->GetTypeName());

by iterate in each field using   

auto refl = msg->GetReflection();
  std::vector<const gproto::FieldDescriptor*> field_descs;
  refl->ListFields(*msg, &field_descs);

 All is good until I get to repeated field.

refl->SetRepeatedFloat(new_msg, field_desc, index, refl->GetRepeatedFloat(*msg, field_desc, index)*signal.FactorValue.toFloat() + signal.OffsetValue.toFloat());

When I come back from the function and try to :

 _modified_msg->SerializeToString(&new_payload_);

  I get this Exception error:

in the header:

Can anyone tell me what i'm doing wrong?

Thanks in advance!

[Adam Cozzette]

My guess would be that there's a lifetime issue involving DynamicMessageFactory. The factory has to outlive any messages created from it via factory.GetPrototype(...)->New(). I would have to see more of the code to know for sure, though.

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[Mihai Muraru]

Hi Cozzette,

I've attached all files. Maybe it will help you to help me . Thank you! Remember that the problems is only with Repeated fields.

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[Mihai Muraru]

Hi all.

Problem solved. I have used Reflection->GetMutableMessage(_modified_msg, field_descriptor, index) to get a not const message which then I've passed it to the recursive function 

ParseProtobufMessage(_proto_msg.get(), _modified_msg, _proto_msg->GetTypeName());

Thanks!