Topic Interception

For the general idea, refer to Controlling Callback Invocations.

The interception is done by remapping input topics using globally applied node-specific remapping rules. Node-specific rules are of the form nodename:before:=after (refer to the ROS 2 Design article on remapping). Note that those node-specific rules do not accept nodes in namespaces, meaning nodename containing forward slashes. An Issue about allowing node-FQNs for node-specific remapping rules exists since 2018. A proposed change to the design doc allowing this was rejected in 2020.

Node-specific remapping rules were chosen since that allows applying all remappings only once, before including the original launch file, like that:

Listing 5 Example launch file

def generate_launch_description():
    return LaunchDescription([
        *generate_remappings_from_config_file(
            "orchestrator",
            "sil_reconfig_launch_config.json"
        ),
        IncludeLaunchDescription(
            PythonLaunchDescriptionSource([
                PathJoinSubstitution([
                    FindPackageShare('platform_sil'),
                    'launch/sil.py'
                ])
            ])
        )
    ])

generate_remappings_from_config expands to a list of node-specific remapping rules.