Started working on jump service feature

[Kaju-Bubanja]

I would like to implement Expose jump services on the Player from #696. I checked how it was done for the set_rate service #767, but the whole package is quite complex and I'm not sure how rosbag2_cpp interacts with rosbag2_transport. I'm not sure if one can be seen as the backend and the other as the frontend and if I should expose the jump service in rosbag2_transport, like the others or if it should reside in rosbag2_cpp like I did now. I currently can't get it to build, but before investing more time, I would be thankful for some advice, if this is the correct package to add the service.

[emersonknapp]

I'm not sure if one can be seen as the backend and the other as the frontend

rosbag2_cpp is the generic rosbag2 C++ API, it doesn't interact with "communications", it only deals with the "bag" portion. rosbag2_transport is the package that has Publishers and Subscribers, and manages actual "transport" of messages.

if I should expose the jump service in rosbag2_transport, like the others

Yes, this service should be with the others, for a cohesive design. It is not good practice to split up related functionality into different places - if we migrate it, it would all be at once.

In this case, though, the service belongs to the Player, which owns a PlayerClock that controls time. So, the service to interact with this clock will also live on the Player in rosbag2_transport.

Additionally, ROS 2 Services are a "transport"/"communications" concept, which we want to keep isolated to the rosbag2_transport package

[MichaelOrlov]

@Kaju-Bubanja @emersonknapp Unfortunately Player::jump(..) API have not yet fully implemented and I am afraid it will be a blocker for relevant service implementation.

[emersonknapp]

I'll close this for now as stale until the relevant underlying features are ready to expose