Proposal: extract ros2 interfaces from controller manager into a helper file

[Nibanovic]

extract ros2 pub/sub/services into a ros2_communication helper files.

Motivation:

In a project, we're wrapping controller_manager in a custom scheduler task, essentially re-writing the ros2_control_node

• Conceptual ambiguity: ros2_control_node is not a node, but an executable specific to the OS scheduler responsible for instantiating and running the controller_manager, which IS the node.
• Code Maintainability: controller_manager.cpp file is hitting 4k LoC, mixes core logic and ROS2 communicaiton (services, publishers, subscribers)

Proposed changes

We propose a simple refactoring with two main objectives:

1. Extract all ROS 2 interfaces and their callback implementations into a helper file ros2_communication.cpp/hpp which current controller_manager.hpp would include.

2. Rename the current ros2_control_node to ros2_control_executable to accurately reflect its function as a system entry point rather than a Node

Notes:

naming is are for discussion, of course

Food for thought, outside of scope of this suggestion:

We could push it a step further and make ControllerManager not inherit from Node at all, and place all ROS-related stuff into ControllerManagerNode class.

Then, as we do with ResourceManager, we'd pass in the necessary node interfaces to it:

• executor (already passed)
• parameters
• logger
• clock

Then the ControlNode would be responsible for ros2 communication, controller manager for controllers and resource manager for hardware.

[bmagyar]

I personally don't see much value in renaming this and it'd definitely break a lot of people's code when we remove the old one.