Feature request

Related to #1928 (comment)

Feature description

• A generic application server that people can use to build their specific autonomy applications.
  • It loads and executes BT and provides an interface as an action server.
  • This makes it easy to provide an action with a user-defined BT.
• A module for mapping from BT to Action (like BtActionNode mapping from Action to BT::ActionNodeBase)
• It is similar to BtNavigator, but it applies to general actions.

Implementation considerations

plan A: template

• class name: BtApplicationServer
• Inherit: nav2_util::LifecycleNode
• Template arg: Action type (ActionT)
• Key functions:
  • Create action server (nav2_util::SimpleActionServer<ActionT>)
  • Load BT from file specified by goal
  • Provide the interfaces below
    • on_initialize_blackboard: Initialize blackboard (ex. Set goals)
    • on_bt_loop; Publish feedback by action server
    • on_bt_shutdown: Return result by action server
• Constraints:
  • ActionT::Goal must have string bt_xml_filename

plan B: generic action

• Inherit: nav2_util::LifecycleNode
• Key functions:
  • Create action server (nav2_util::SimpleActionServer<PerformTask>)
  • Load BT from file specified by goal
  • Provide generic feedback and result.
• Constraints:
  • PerformTask::Goal must have string bt_xml_filename
  • PerformTask::Goal must have something like Something[] ports

plan A vs. plan B

• plan A
  • The user implements a BT, and extend BtApplicationServer<ActionT> to create their own application classes and implement some methods.
  • Custom feedbacks and results can be handled.
• plan B
  • The user implements a BT only.