Fix ros2 topic pub --stdin

[wentasah]

Description

Running the following command currently fails:

ros2 topic pub --stdin /test std_msgs/Bool <<< "{data: true}"

The error is:

Traceback (most recent call last):
  File "/python3.12-ros-jazzy-ros2cli-0.32.6-r1/bin/ros2", line 34, in <module>
    sys.exit(load_entry_point('ros2cli==0.32.6', 'console_scripts', 'ros2')())
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/ros-env/lib/python3.12/site-packages/ros2cli/cli.py", line 91, in main
    rc = extension.main(parser=parser, args=args)
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/ros-env/lib/python3.12/site-packages/ros2topic/command/topic.py", line 41, in main
    return extension.main(args=args)
           ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/ros-env/lib/python3.12/site-packages/ros2topic/verb/pub.py", line 117, in main
    return main(args)
           ^^^^^^^^^^
  File "/ros-env/lib/python3.12/site-packages/ros2topic/verb/pub.py", line 138, in main
    return publisher(
           ^^^^^^^^^^
  File "/ros-env/lib/python3.12/site-packages/ros2topic/verb/pub.py", line 174, in publisher
    if '^J' in values:
       ^^^^^^^^^^^^^^
TypeError: a bytes-like object is required, not 'str'

We fix it by decoding stdin to utf8 string to match the type of values passed via a command line argument.

Is this user-facing behavior change?

yes

Did you use Generative AI?

no

[fujitatomoya]

This allows subsequent code to work with a string instead of bytes, which is often necessary for text processing. test would be ideal to add somewhere like https://github.com/ros2/ros2cli/blob/rolling/ros2topic/test/test_echo_pub.py

[wentasah]

I'm trying to write the test, but I have no idea how to pass something to process stdin. I see there is a ProcessStdin event, which is handled by the ExecuteLocal action, but I din't find a way to generate the event from the test. And from looking at ExecuteLocal.__on_process_stdin, I doubt that it can do anything useful here. I also tried to follow the documentation, which says that ExecuteProcess passes many arguments to Popen, but it seems not to be the case for stdin.

Perhaps, I'd be able to write a test without the complex launch machinery by using plain Python's Popen. Would that be acceptable?