How is the native protobuf support implemented?

[chizhangsysu]

Hi, I was trying to understand which changes to the ROS source codes make it possible to directly publishing a protobuf object.

In vanilla ROS, gencpp will provide template specializations for the MD5Sum<T> struct and the Serializer<T> struct, when generating the header file for a .msg file, so that the message object can be serialized and published.

However, when the message class comes from a .proto file instead of the .msg file, what changes make the protobuf object serializable using the ROS publisher? Could you explain what has been done here if possible?

Thanks,
Chi