structure_needs_at_least_one_member Verbosity with std_msgs/msg/Empty

[IanTheEngineer]

Bug report

When dealing with std_msgs.msg.Empty messages, there's a repeated field output from the ros2cli: structure_needs_at_least_one_member=0. This appears on both publisher and subscriber sides.

Required Info:

• Operating System:
  • Ubuntu 18.04
• Installation type:
  • ROS Buildfarm Debian binaries
• Version:
  • ROS Dashing
• DDS implementation:
  • Fast-RTPS
• Client library:
  • rclpy

Steps to reproduce issue:

Terminal 1

$ ros2 topic pub /my_empty_topic std_msgs/msg/Empty
publisher: beginning loop
publishing #1: std_msgs.msg.Empty(structure_needs_at_least_one_member=0)

publishing #2: std_msgs.msg.Empty(structure_needs_at_least_one_member=0)

publishing #3: std_msgs.msg.Empty(structure_needs_at_least_one_member=0)

publishing #4: std_msgs.msg.Empty(structure_needs_at_least_one_member=0)

publishing #5: std_msgs.msg.Empty(structure_needs_at_least_one_member=0)

Terminal 2

$ ros2 topic echo /my_empty_topic
structure_needs_at_least_one_member: 0
---
structure_needs_at_least_one_member: 0
---
structure_needs_at_least_one_member: 0
---
structure_needs_at_least_one_member: 0
---
structure_needs_at_least_one_member: 0

Expected behavior

The same as ROS1, just output the three dashes:

$ rostopic echo /my_empty_topic

---

---

Actual behavior

Extra structure_needs_at_least_one_member=0 per publish

[IanTheEngineer]

@dirk-thomas well done on the swift fix 👍