[Bug] Cannot write ROS 2 Launch file as mandatory "--ros-args" not handled by Zenoh

[ciandonovan]

Describe the bug

I want to run Zenoh as a ROS 2 package in a container. However, ros2 run does not install an explicit signal handler for SIGTERM, and when run as PID1 in a container, a special case where the default disposition of those signals being changed from Terminate to Ignore applies. Further, if the container is initialized with a lightweight init manager such as tini, ros2 run will explicitly set the disposition of SIGINT to Ignore because it doesn't detect a controlling terminal.

I therefore want to create a simple launchfile that correctly handles these signals (notably SIGINT) and forwards them to its children. The launchfile will be configured explicitly with "emulate_tty=True" to trick Zenoh installing the SIGINT handler. The problem is that as far as I can tell, ROS 2 Launch will always append --ros-args to argv of the node its launching, and Zenoh doesn't like that.

Could Zenoh be modified to detect --ros-args and harmlessly ignore it? At least until there's possibly more ROS-specific functionality integrated in which care maybe reading the args might be useful.

To reproduce

zenoh_launch.py

from launch import LaunchDescription
from launch_ros.actions import Node

def generate_launch_description():
    return LaunchDescription([
        Node(
            package='zenoh_bridge_ros2dds',
            executable='zenoh_bridge_ros2dds',
            name='zenoh_bridge_ros2dds',
            emulate_tty=True,
        )
    ])

Error log:

[INFO] [launch]: Default logging verbosity is set to INFO
[INFO] [zenoh_bridge_ros2dds-1]: process started with pid [21470]
[zenoh_bridge_ros2dds-1] [2023-12-20T19:34:39Z INFO  zenoh_bridge_ros2dds] zenoh-bridge-ros2dds v0.1.0-dev built with rustc 1.70.0 (90c541806 2023-05-31) (built from a source tarball)
[zenoh_bridge_ros2dds-1] error: Found argument '--ros-args' which wasn't expected, or isn't valid in this context
[zenoh_bridge_ros2dds-1] 
[zenoh_bridge_ros2dds-1] 	If you tried to supply `--ros-args` as a value rather than a flag, use `-- --ros-args`
[zenoh_bridge_ros2dds-1] 
[zenoh_bridge_ros2dds-1] USAGE:
[zenoh_bridge_ros2dds-1]     zenoh_bridge_ros2dds [OPTIONS]
[zenoh_bridge_ros2dds-1] 
[zenoh_bridge_ros2dds-1] For more information try --help
[ERROR] [zenoh_bridge_ros2dds-1]: process has died [pid 21470, exit code 2, cmd '/opt/ros/overlay_ws/install/zenoh_bridge_ros2dds/lib/zenoh_bridge_ros2dds/zenoh_bridge_ros2dds -c /root/.zenoh/lab.json5 -- --ros-args'].
[zenoh_bridge_ros2dds-1] 

System info

• Platform: Official Open Source Robotics Foundation Docker image (Humble) running on Debian 12 host.
• CPU: AMD Ryzen Embedded V2718 with Radeon Graphics
• Zenoh verison/commit: 2c52d0b

[JEnoch]

It would indeed be nice is zenoh-bridge-ros2dds acts as a ROS 2 Node and supports all or at least a subset of ROS Command Line Args.

A first step would be to just log a "not supported ROS argument ... - ignored" warning for each one.
No warning will be logged in your case, according to your cmd line.

But strangely, when I try your zenoh_launch.py in my Humble env (not in container), it run this cmd line which is different than yours:

[ERROR] [zenoh_bridge_ros2dds-1]: process has died [pid 78745, exit code 2, cmd '/home/guest/eclipse-zenoh/zenoh-plugin-ros2dds/install/zenoh_bridge_ros2dds/lib/zenoh_bridge_ros2dds/zenoh_bridge_ros2dds --ros-args -r __node:=zenoh_bridge_ros2dds'].

So I think at least -r __node:=node_name should be supported and mapped to the ros2dds.nodename configuration.
I created #48 to address this.

[ciandonovan]

But strangely, when I try your zenoh_launch.py in my Humble env (not in container), it run this cmd line which is different than yours:

Looks like you're only getting the std output from ros_launch and not the nodes running underneath, is your logging verbosity set differently on your host install? (Mine is INFO) Were you running with emulate_tty=True so ros_launch would pass through the std output from the node?

[JEnoch]

I get roughly the same logs than you with "error" and "usage" messages.
But I was pointing to the command lines and especially to the ordering of arguments that differ between you:
cmd '/opt/ros/overlay_ws/install/zenoh_bridge_ros2dds/lib/zenoh_bridge_ros2dds/zenoh_bridge_ros2dds -c /root/.zenoh/lab.json5 -- --ros-args'
and me:
cmd '/home/guest/eclipse-zenoh/zenoh-plugin-ros2dds/install/zenoh_bridge_ros2dds/lib/zenoh_bridge_ros2dds/zenoh_bridge_ros2dds --ros-args -r __node:=zenoh_bridge_ros2dds'

I find yours quite strange because:

1. the -- appears before the --ros-args, while the spec says it shall be the other way around
2. you don't have a -r __node:=zenoh_bridge_ros2dds option while I have, despite I was using the same zenoh_launch.py with a Node description specifying the name= zenoh_bridge_ros2dds
3. I don't see the -c /root/.zenoh/lab.json5 arguments in your zenoh_launch.py. How do you set those ?

For a correct support of --ros-args I would need to understand what's the cause of those differences, and moreover what to expect as arguments.

[ciandonovan]

https://github.com/ciandonovan/ros2_zenoh_bridge

Here's a full reproducible example of my setup, running the latest zenoh-plugin-ros2dds main branch installed as a ROS package in a submodule.

I'm not sure how I added -c /root/.zenoh/lab.json5 before, I may have accidentally copied the wrong output before.
As of now, I think my output matches yours.

[JEnoch]

#48 is now complete. zenoh-bridge-ros2dds now supports --ros-args but only with -r __ns:=... or -r __node:=....
I tested with the podman example you provided.

I created #58 for an eventual support of remapping also for topics/services/actions names.

[JEnoch]

Fixed via #58