Inspecting services (:program:`ros2 service`) ============================================= :program:`ROS2` has a tool to help us inspect services. It is just as helpful as the tools for topics. .. code:: console ros2 service -h which outputs the detailed information of the tool, as shown below. In particular, the highlighted fields are used quite frequently in practice. .. code-block:: console :emphasize-lines: 11,15 usage: ros2 service [-h] [--include-hidden-services] Call `ros2 service -h` for more detailed usage. ... Various service related sub-commands options: -h, --help show this help message and exit --include-hidden-services Consider hidden services as well Commands: call Call a service echo Echo a service find Output a list of available services of a given type info Print information about a service list Output a list of available services type Output a service's type Call `ros2 service -h` for more detailed usage. Start a service server ---------------------- Similar to the discussion about topics, it is good to be able to test service servers without having to develop a complete service client. Let's start by running the service server we created just now. .. warning:: Be sure to terminate the Nodes we used in the past section before proceeding (e.g. with :kbd:`CTRL+C`), otherwise, the output will look different from what is described here. .. code:: console ros2 run python_package_that_uses_the_services add_points_service_server_node Getting all services with :program:`ros2 service list` ------------------------------------------------------ To see all currently active services, we run .. code:: console ros2 service list which, in this case, outputs .. code-block:: console :emphasize-lines: 1 /add_points /add_points_service_server/describe_parameters /add_points_service_server/get_parameter_types /add_points_service_server/get_parameters /add_points_service_server/get_type_description /add_points_service_server/list_parameters /add_points_service_server/set_parameters /add_points_service_server/set_parameters_atomically To everyone's surprise, there are a lot of services beyond the one we created. We can address those when we talk about ROS2 parameters, for now, we ignore them. Testing your service servers with ros2 service call --------------------------------------------------- Like the discussion about topics, ROS2 has a tool to call a service from the terminal, called :program:`ros2 service call`. The service must be specified and an instance of its request must be written using :abbr:`YAML (YAML Ain't Markup Language)`. Back to our example, we can do .. code-block:: console ros2 service call /add_points \ package_with_interfaces/srv/AddPoints \ '{ a: { x: 10, y: 11, z: 12 }, b: { x: -10, y: -10, z: 22 } }' which results in .. code-block:: console requester: making request: package_with_interfaces.srv.AddPoints_Request(a=geometry_msgs.msg.Point(x=10.0, y=11.0, z=12.0), b=geometry_msgs.msg.Point(x=-10.0, y=-10.0, z=22.0)) response: package_with_interfaces.srv.AddPoints_Response(result=geometry_msgs.msg.Point(x=0.0, y=1.0, z=34.0)) Testing your service clients ---------------------------- To the best of my knowledge, there is no tool inside :program:`ros2 service` to allow us to experiment with service clients. For service clients the only way to test them is to make a minimal service server to interact with them. We've already done that, so this topic ends here. How about :program:`ros2 service echo` -------------------------------------- .. versionadded:: Jazzy Added this section. .. seealso:: - `Official tutorial on service introspection `_ - https://github.com/ros2/demos/blob/rolling/demo_nodes_py/demo_nodes_py/services/introspection.py .. admonition:: We'll be working in these files .. code-block:: console :emphasize-lines: 5,7 python_package_that_uses_the_services |-- package.xml |-- python_package_that_uses_the_services | |-- __init__.py | |-- add_points_service_client_introspection_node.py | |-- add_points_service_client_node.py | |-- add_points_service_server_introspection_node.py | `-- add_points_service_server_node.py |-- resource | `-- python_package_that_uses_the_services |-- setup.cfg |-- setup.py `-- test |-- test_copyright.py |-- test_flake8.py `-- test_pep257.py It might be good to know of the existence of *service introspection*. Although it seems to work the documentation might be ongoing, according to this discussion: https://github.com/ros-infrastructure/rep/pull/360. After proper configuration of the server and client, :program:`ros2 service echo` allows us to look at what information is being exchanged between participants. It helps not having to add endless ``print`` functions throughout the code that hurt performance. In the folder :file:`~/ros2_tutorial_workspace/src/python_package_that_uses_the_services/python_package_that_uses_the_services` we add the following two files. Note that we are using inheritance from the previously written :code:`AddPointsServiceClientNode` and :code:`AddPointsServiceServerNode` to minimize code replication. .. tab-set:: .. tab-item:: Introspection Client For the :code:`Node` with the service client, we must use the :code:`configure_introspection` method. The argument requires a :code:`service_event_qos_profile` and a :code:`introspection_state`. The quality-of-service profile is within the same scope as the quality-of-service for messages and has a similar meaning. The :code:`introspection_state` defines how much of the service can be introspected. Less information can be made accessible if that is necessary. :download:`add_points_service_client_introspection_node.py <../../ros2_tutorial_workspace/src/python_package_that_uses_the_services/python_package_that_uses_the_services/add_points_service_client_introspection_node.py>` .. literalinclude:: ../../ros2_tutorial_workspace/src/python_package_that_uses_the_services/python_package_that_uses_the_services/add_points_service_client_introspection_node.py :language: python :linenos: :lines: 24- :emphasize-lines: 4,5,12-16 .. tab-item:: Introspection Server The service server has the same syntax and requirements to activate introspection as the service client. :download:`add_points_service_server_introspection_node.py <../../ros2_tutorial_workspace/src/python_package_that_uses_the_services/python_package_that_uses_the_services/add_points_service_server_introspection_node.py>` .. literalinclude:: ../../ros2_tutorial_workspace/src/python_package_that_uses_the_services/python_package_that_uses_the_services/add_points_service_server_introspection_node.py :language: python :linenos: :lines: 24- :emphasize-lines: 4,5,12-16 Build and source ---------------- Before we proceed, let us build and source once. .. include:: the_canonical_build_command.rst Finally the :program:`ros2 service echo` ---------------------------------------- To be able to use :program:`ros2 service echo`, we must be sure that the service server and :program:`ros2 service echo` are active before the service client requests the service we want to inspect the entire exchange. It might be a bit of a handful, but we will need three (properly sourced) terminals. In this order. .. tab-set:: .. tab-item:: (1) service server .. code-block:: console ros2 run python_package_that_uses_the_services add_points_service_server_introspection_node .. tab-item:: (2) ros2 service echo .. code-block:: console ros2 service echo /add_points .. tab-item:: (3) service client .. code-block:: console ros2 run python_package_that_uses_the_services add_points_service_client_introspection_node Each program will have it's own output, shown below. For the purposes of this section we can focus on the output of :program:`ros2 service echo`. The other two outputs repeat what we have seen in the previous session, further guaranteeing that the introspection works without affecting the overall behavior of the nodes too much. .. tab-set:: .. tab-item:: ros2 service echo output As you can see, we will receive a profoundly detailed output showing all aspects of the service, including the request sent, an acknowledgement of what was received, what was replied, and the acknowledgement of the reply! .. code-block:: console info: event_type: REQUEST_SENT stamp: sec: 1761419221 nanosec: 796638805 client_gid: - 1 - 15 - 235 - 125 - 217 - 40 - 45 - 142 - 0 - 0 - 0 - 0 - 0 - 0 - 20 - 3 sequence_number: 1 request: - a: x: 104.79864813644902 y: 422.844185397337 z: 0.0 b: x: 531.6723658565676 y: 761.3967957778456 z: 357.29827376582836 response: [] --- info: event_type: REQUEST_RECEIVED stamp: sec: 1761419221 nanosec: 800073888 client_gid: - 1 - 15 - 235 - 125 - 217 - 40 - 45 - 142 - 0 - 0 - 0 - 0 - 0 - 0 - 19 - 4 sequence_number: 1 request: - a: x: 104.79864813644902 y: 422.844185397337 z: 0.0 b: x: 531.6723658565676 y: 761.3967957778456 z: 357.29827376582836 response: [] --- info: event_type: RESPONSE_SENT stamp: sec: 1761419221 nanosec: 801308763 client_gid: - 1 - 15 - 235 - 125 - 217 - 40 - 45 - 142 - 0 - 0 - 0 - 0 - 0 - 0 - 19 - 4 sequence_number: 1 request: [] response: - result: x: 636.4710139930166 y: 1184.2409811751827 z: 357.29827376582836 --- info: event_type: RESPONSE_RECEIVED stamp: sec: 1761419221 nanosec: 801765763 client_gid: - 1 - 15 - 235 - 125 - 217 - 40 - 45 - 142 - 0 - 0 - 0 - 0 - 0 - 0 - 20 - 3 sequence_number: 1 request: [] response: - result: x: 636.4710139930166 y: 1184.2409811751827 z: 357.29827376582836 --- .. tab-item:: service client output For the service client, the output is the same as with the service client without introspection. .. code-block:: console [INFO] [1761419221.816188138] [add_points_service_client]: The result was (636.4710139930166, 1184.2409811751827, 357.29827376582836) .. tab-item:: service server output Nothing is output in the service server, because our service server is not supposed to output anything to the screen.