LifecycleNode: how to manage errors?

[Myzhar]

I'm trying to understand how to correctly manage errors in a LifecycleNode.
From what I understood currently the on_error callback is called in two cases:

1. when a transition callback returns lifecycle_msgs::msg::Transition::TRANSITION_CALLBACK_ERROR
2. when an uncaught exception is thrown inside a transition callback

But according to ROS2 design page the node should be able to enter in error processing transition also from ACTIVE state.

Now I have two problems:

1. Understand who generated the error that called on_error since the only argument of the on_error callback is const rclcpp_lifecycle::State& previous_state
2. Understand how to trigger an error from ACTIVE state (for example from a thread acquiring data from a device, when the device disconnects)

I think that the lifecycle demo should have an example of on_error callback together with the other.

[dirk-thomas]

Duplicate of https://answers.ros.org/question/302178/ros2-managed-node-triggering-an-error-from-primary-state/