[Service Introspection] Support echo verb for ros2 service cli

[deepanshubansal01]

Related to the proposed service introspection REP (ros-infrastructure/rep#360)

This PR implements the cli for echoing service events.
ros2 service echo /name_of_service

Depends on ros2/rosidl_runtime_py#17 for deserializing bytes type data and echoing contents to the user.

Connects to: ros2/ros2#1285

Signed-off-by: deepanshu deepanshubansal01@gmail.com

[ihasdapie]

I gave this a run and it's great to see a working prototype going. I would like to see this tool behave in a way consistent to ros2 topic echo, i.e. wait until the service is avaliable instead of exiting if unavaliable. This way we can keep a terminal with ros2 service echo open instead of having to scramble to run it once the service starts.

[deepanshubansal01]

I gave this a run and it's great to see a working prototype going. I would like to see this tool behave in a way consistent to ros2 topic echo, i.e. wait until the service is avaliable instead of exiting if unavaliable. This way we can keep a terminal with ros2 service echo open instead of having to scramble to run it once the service starts.

I see, makes sense. I guess right now the ros2 service echo behaves similar to the way ros2 topic echo works, I might be wrong though. The ros2 topic echo also exits if the topic name does not exist. For instance if you do ros2 topic echo /test it will exit if /test topic is not their. The reason is it needs the topic to be present to determine the topic type. However, you can provide the topic type along with topic name, making the echo to not exit even if the topic is not present.

This being said we can also wait for the service to be present, I just made it similar to ros2 topic for now. In order to make it wait for service we can set blocking == True by default here or provide an additional optional argument.

ros2cli/ros2service/ros2service/api/__init__.py

Line 40 in 02c9e93

def get_service_class(node, service, blocking=False, include_hidden_services=False):

The ros2 topic echo has blocking = False by default.

ros2cli/ros2topic/ros2topic/api/__init__.py

Line 97 in 02c9e93

def get_msg_class(node, topic, blocking=False, include_hidden_topics=False):

ros2cli/ros2topic/ros2topic/verb/echo.py

Lines 230 to 232 in 02c9e93

	if args.message_type is None:
	message_type = get_msg_class(
	node, args.topic_name, include_hidden_topics=True)

[adityapande-1995]

Could you expand this docstring to provide a short explanation and an example ? It would be nice if we could write a simple test / self contained example for this feature.

[jacobperron]

Yes, we should add a test to test_cli.py.

[ihasdapie]

@deepanshubansal01 I've pushed a commit which tidies up the code a bit and removes the serialization bit. I've also tided up the output.

Also, sorry for hijacking your branch. On a side note, if possible I'd like to close this PR and open up a new one so that we can have all of the PRs off a service_introspection branch which would make CI a little easier later.

[deepanshubansal01]

@deepanshubansal01 I've pushed a commit which tidies up the code a bit and removes the serialization bit. I've also tided up the output.

Also, sorry for hijacking your branch. On a side note, if possible I'd like to close this PR and open up a new one so that we can have all of the PRs off a service_introspection branch which would make CI a little easier later.

Sounds good to me. You can open a new PR, this PR also contains some changes related to unit tests which we can ignore in the new PR since they were in progress. Unit tests can be added in the new PR though.

[ihasdapie]

I opened #745. Closing in lieu of that PR.