add ros2 param

[dirk-thomas]

• list outputs the names of all parameters, either for all nodes or a node passed as an argument
• get outputs the value of a specific parameter, the type information can be suppressed
• set sets a parameter, the type is being determined by guessing the primitive types, no array types atm
• delete removed a specific parameter (at least it should but it seems that the service doesn't work for that use case).

[sloretz]

Partial review. I used get and list so far and they seem to work fine.

[sloretz]

Looks like there are a few debug print statements. Use the node's logger for debug messages instead?

[dirk-thomas]

I removed the debug output in 55a5948.

[mikaelarguedas]

Tested this along ros2/rclcpp#489 and it works great 👍
(I haven't tested with many requests queued up, only one a a time)

I pushed a few nitpicks, feel free to revert them if they're not appropriate.

A few questions that come to mind:

• Could we add the option to provide the type explicitly ?
  • e.g. if I want to pass to a string parameter a value that can be converted to another type ("0", "True", "42.42"...)
• Is there something in the API preventing to set the array types ? or was it just to keep the scope reasonable?

[dirk-thomas]

• Could we add the option to provide the type explicitly ?
• Is there something in the API preventing to set the array types ? or was it just to keep the scope reasonable?

Additional feature can be added anytime. You could add it to this PR right now or keep it for a future PR. I just wanted to get a first version of this verb in to be able to use / test the parameters more easily.

[mikaelarguedas]

Additional feature can be added anytime. You could add it to this PR right now or keep it for a future PR. I just wanted to get a first version of this verb in to be able to use / test the parameters more easily.

Follow up is fine by me 👍 it's great to have a first version of this verb out!
I just wanted to make sure that there was not a technical blocker for implementing all parameter types in the other verbs, I didn't mean to appear requesting additional features in this PR :).

[mikaelarguedas]

lgtm, thanks for pounding on this 👍

[wjwwood]

Retroactive summary for this feature:

add ros2 param

Purpose / Use Cases (Why implement this feature?)

This was implemented to provide a way to set and get parameters of ROS nodes which have parameters and a parameter service (allowing parameters to be set/checked via ROS).

Design (How does it work?)

It provides a new "command" to the ros2 command line tool called param which has a variety of "verbs" that do different things like list, set, get, and delete.
These verbs operate on remote nodes using the ROS parameter interface, see: https://design.ros2.org/articles/ros_parameters.html

Inputs / Outputs / API (How to use it?)

The usage of the tool is documented in the help text with ros2 param -h.

There is a "public" API which implements the actions the tool can take (used internally by the tool), see:

ros2cli/ros2param/ros2param/api/__init__.py

Line 1 in 211fc16

# Copyright 2018 Open Source Robotics Foundation, Inc.