How to set up launch arguments for multiple topics?

[khaiyichin]

Description

This is more of a question, but I couldn't seem to find any pointers on how to do it. Essentially I'm trying to create a launch file that allows the user to specify the topics as arguments to the launch file. I wasn't sure if this was a launch question, but I figured it might be helpful to have a rosbag2 targeted answer.

To Reproduce

Minimum example:

# rosbag_record.launch.py
launch_arg_rosbag_topics = DeclareLaunchArgument('topics', default_value='-a')

process_rosbag_record = ExecuteProcess(
      cmd=['ros2', 'bag', 'record', LaunchConfiguration('topics')],
)

return LaunchDescription([
    launch_arg_rosbag_topics,
    process_rosbag_record
])

In the terminal,

# terminal
$ ros2 launch ./rosbag_record.launch.py topics:='/cmd_vel /odom /odom_gt /velodyne_points /tf /tf_static'

gives the following error:

[ros2-1] [ERROR] [1614037748.512620668] [rosbag2_transport]: Failed to expand topic name /cmd_vel /odom /odom_gt /velodyne_points /tf /tf_static with error: topic name is invalid, at /tmp/binarydeb/ros-foxy-rcl-1.1.10/src/rcl/expand_topic_name.c:73

And after killing it I get the following message, which seems to indicate that the evaluated command should be correct, and I was able to verify by copy and pasting it (i.e., ros2 bag record /cmd_vel /odom /odom_gt /velodyne_points /tf /tf_static).

[ERROR] [ros2-1]: process has died [pid 257759, exit code 2, cmd 'ros2 bag record /cmd_vel /odom /odom_gt /velodyne_points /tf /tf_static'].

System (please complete the following information)

• OS: Ubuntu Focal
• ROS 2 Distro: Foxy

[emersonknapp]

This question may be better suited to ROS Answers

[emersonknapp]

To add some more context on this - the commandline is being interpreted as a request to record a single topic named "/cmd_vel /odom /odom_gt /velodyne_points /tf /tf_static" - which is not a valid topic name because it contains spaces. The ExecuteProcess args need to be a list. This is described in ros2/launch#263

Until that issue is solved, you can solve this using shell=True as is described in the above issue. E.g.

from launch import LaunchDescription
from launch.actions import DeclareLaunchArgument
from launch.actions import ExecuteProcess
from launch.substitutions import LaunchConfiguration

def generate_launch_description():
    return LaunchDescription([
        DeclareLaunchArgument('topics', default_value=['-a'], description='Topics to record'),
        ExecuteProcess(cmd=['ros2', 'bag', 'record', LaunchConfiguration('topics')], shell=True),
    ])

I'll close this issue given there is nothing to do in rosbag2 for this.