Originally, We have two applications communication with TCP/IP, and both of them are implemented by C++. The messages between them are custom message type.

Now the client program will be changed to web application based on nodejs and the communication between them will be changed to message bus such as rabbitmq

So the message type between them should be changed.

JSON comes to my mind first, however the custom messages are too complicated, which are defined by template and inheritance. It seems that convert the custom message to JSON is not a good option. Am I right?

class Address {
    int network;
    int addressType;
    //...
};

class MsgType{
    unsigned char   msgSeq;
    unsigned int    msgLen;
    //...
};

class Message{
    Address destination;
    Address source;
    MsgType msgType;

    //...
};

template <typename T, int RESPONSE_TYPE>
class ResponseMessage : public Message{
    //...
}

typedef struct{
    int number;
    int type;
}ConfigResp;

class CfgResp : public ResponseMessage<ConfigResp, CONFIG_REQUEST>
{
    //...
}

Protocol Buffers is another option for me to do that. What should I do?
redefine the custom message into protocol buffer? no no

Here is my solution: Just wrap the whole original custom message (binary type) into protocol buffer as one message in the server side, then decode the custom message(binary type) in client side. Is that possible?