Bug report

• Operating System:
  • ubuntu20.04
• Installation type:
  • source build
• Version or commit hash:
  • ros2/ros2@c059de9
• DDS implementation:
  • Fast-RTPS
• Client library (if applicable):
  • rclcpp

once node is created, there are built-in services to access parameters. there seems to be inconsistent behavior for these services between describe_parameters / get_parameter_types and get_parameters. describe_parameters / get_parameter_types services return empty if request include non-exist parameter name. on the other hand get_parameters always returns the same size with request which includes non-exist parameter name.

Steps to reproduce issue

• describe_parameters

root@5c7a784cba7f:~/ros2_ws/colcon_ws# ros2 service call /talker/describe_parameters rcl_interfaces/srv/DescribeParameters "names: [use_sim_time, not_exist]"
waiting for service to become available...
requester: making request: rcl_interfaces.srv.DescribeParameters_Request(names=['use_sim_time', 'not_exist'])

response:
rcl_interfaces.srv.DescribeParameters_Response(descriptors=[])

-> empty since there is undeclared parameter non_exist. (it prints WARN message on server that failed to describe non_exist)

• get_parameter_types

root@5c7a784cba7f:~/ros2_ws/colcon_ws# ros2 service call /talker/get_parameter_types rcl_interfaces/srv/GetParameterTypes "names: [use_sim_time, not_exist]"
waiting for service to become available...
requester: making request: rcl_interfaces.srv.GetParameterTypes_Request(names=['use_sim_time', 'not_exist'])

response:
rcl_interfaces.srv.GetParameterTypes_Response(types=[])

-> empty since there is undeclared parameter non_exist. (it prints WARN message on server that failed to get type non_exist)

• get_parameters

root@5c7a784cba7f:~/ros2_ws/colcon_ws# ros2 service call /talker/get_parameters rcl_interfaces/srv/GetParameters "names: [use_sim_time, not_exist]"
requester: making request: rcl_interfaces.srv.GetParameters_Request(names=['use_sim_time', 'not_exist'])

response:
rcl_interfaces.srv.GetParameters_Response(values=[rcl_interfaces.msg.ParameterValue(type=1, bool_value=False, integer_value=0, double_value=0.0, string_value='', byte_array_value=[], bool_array_value=[], integer_array_value=[], double_array_value=[], string_array_value=[]), rcl_interfaces.msg.ParameterValue(type=0, bool_value=False, integer_value=0, double_value=0.0, string_value='', byte_array_value=[], bool_array_value=[], integer_array_value=[], double_array_value=[], string_array_value=[])])

-> return default Parameter for non_exist request.

Expected behavior

I think it would be nice to have consistent behavior based on NodeParameters::allow_undeclared_(default false)

Actual behavior

behavior is inconsistent.

Additional information

further more, there is not even consistent with rclpy. if we use rclpy and provided built-in parameter services,

• get_parameters returns the same size with request, it will return default ParameterValue for non_exist. (same with rclcpp)
• describe_parameters returns the same size with request, it will return default ParameterDescriptor for for non_exist.
• get_parameter_types returns the same size with request, it will return default type = 0 for for non_exist.