How to use a c++ type (struct) in inet packet definition

Question

I want to create an inet packet and the packet content needs to be of c++ type struct which is defined outside the message file. I have done this earlier to define a .msg file derived from cMessages in OMNeT like this:

cplusplus{{
       #include "util/DataTypes/StateDataTypes.h" 
}};

struct StateWithCovariance;

message WirelessMsg
{
   StateWithCovariance VehicleLocation; 
}

Now I am working with simu5g and want to send the same msg content as an inet packet. I know the inet Packet data structure builds on top of the data structure chunks. Thus I followed how it's done in inet and when I try to create the packet I can't use the same above format to define the packet because then

cplusplus{{
     #include "inet/common/INETDefs"
     #include "inet/common/packet/chunk/chunk"
}}
class WirelessAppPacket extends inet::FieldsChunk
{
   simtime_t payloadTimestamp;
   StateWithCovariance VehicleLocation;
}

wouldn't work and gives me the error:

modules/communication/NR/App/WirelessAppPacket.msg:34: Error: 'WirelessAppPacket': unknown base class 'inet::FieldsChunk', 
available classes' (inet::StateWithCovariance:1)' ,'(omnetpp::cMessage:4)', '(omnetpp::cNamedObject:5)','(omnetpp::cObject:3)','(omnetpp::cOwnedObject:4)','(omnetpp::cPacket:4)'

if I give it as

import inet.common.INETDefs;
import inet.common.packet.chunk.Chunk;

class WirelessAppPacket extends inet::FieldsChunk
{
   simtime_t payloadTimestamp;
   StateWithCovariance VehicleLocation;
}

it wouldn't give any error with regards to chunks, if I change the message complier to --msg6 in project properties as follows

MSGC:=$(MSGC) --msg6

But it gives me an error with respect to the data type definition as:

modules/communication/NR/App/WirelessAppPacket.msg:28: Error: Type declarations are not needed with imports, try invoking the message compiler in legacy (4.x) mode using the --msg4 option
modules/communication/NR/App/WirelessAppPacket.msg:32: Error: unknown type 'StateWithCovariance' for field 'VehicleLocation' in 'WirelessAppPacket'

The entire code I used look like this

import inet.common.INETDefs;
import inet.common.packet.chunk.Chunk;

cplusplus{{
   #include "util/DataTypes/StateDataTypes.h" 
   #include "modules/vehicle/CommunicationCoordinator.h"   
}};

struct StateWithCovariance;
class WirelessAppPacket extends inet::FieldsChunk
{
   simtime_t payloadTimestamp;
   StateWithCovariance VehicleLocation;
}

If I change the message compiler to --msg4 then I can't define my packet from chunk base class in INET framework and with --msg6 I can't use the data type I want to use.

Is there a way to rectify this issue?

I use OMNeT++ version 5.6.2, INET version 4.2.2 and Simu5G version 1.1.0

Answer 1

This thread explains what to do. Basically you need to change the line

struct StateWithCovariance;

from your last code snippet into

struct StateWithCovariance {
   @existingClass;
}

This works with the --msg6 message compiler, so that you can still import INET classes.