Feature Request: Service Introspection

[ottojo]

Feature request

Feature description

It would be useful to be able to use Service Introspection introduced in Jazzy with nav2 nodes (such as the costmap server). This requires some configuration for both the client and server, which is currently not enabled in nav2.

Implementation considerations

It has to be considered whether unconditionally enabling service introspection is a good idea. The tutorial in the ROS docs show how to introduce a parameter to enable or disable service introspection, it is unclear to me if it's expected to only turn this feature on during debugging, and if there are downsides to always enabling it.

[SteveMacenski]

The client side is easy, I think most all uses of service clients use our nav2_utils service client wrapper, so one spot should hit most if not all of them (but worth doing a quick grep to make sure of that).

The server side will be slightly more involved since I don't think we wrap anything there. I'm not sure if the right answer is to:

• create a nav2_util service server wrapper like the client; move all servers to use that
• create a nav2_util helper object that deals with these mechanics, getting the parameters, and setting it up that given a node and the server; after all servers are created, create this object and pass in the necessary inputs for it to be managed
• Better yet, contribute back to rclcpp by modifying create_service to handle this logic so that anyone creating a server can have this handled implicitly when a standardized parameter is set. I think you could do that with create_client too 😉
• Something else?

How do you think we should approach it?

I'd say leave it default off, but let users flip it on with a parameter.

[SteveMacenski]

@ottojo what do you think?

[mini-1235]

I can work on this if no one is on it :)

[SteveMacenski]

@mini-1235 please!

[mini-1235]

I'd say leave it default off, but let users flip it on with a parameter.

Where do you think we should put the parameter to flip this on, I haven't found a suitable place in nav2_params.yaml, also, do you think it is necessary to support dynamic configuration of this parameter?

[SteveMacenski]

I don't think a dynamic parameter should be supported here necessarily, but it could be. I'd put that out of scope for the first go at it; if someone else wants it later, they could contribute to it :-)

I think that parameter would need to be for each node. Like we have use_sim_time or transform_timeout, we could have another consistent parameter across all servers for service_introspection_mode or something similar that defaults to OFF. I think this is a big reason that having a nav2_util wrapper for the service server is important so we can create the service, get the parameter, and set it up before returning to the main application code. That way, a single implementation can be used in all places without alot of copy+pasting.

For instance, we could create a new nav2_util::create_service factory that uses rclcpp::create_service / Node::create_service and does the additional details. It could be implemented as either its own create service factory in a new utils file, or as a util itself as a member of the nav2_util::LifecycleNode, since all servers derive from that LifecycleNode class (actually, this is probably the best place to put it!)