`ros2 action send_goal` shows incorrect goal UUID

Bug report

Required Info:

• Operating System:
  • Ubuntu 20.04
• Installation type:
  • sources
• Version or commit hash:
  • Galactic
• DDS implementation:
  • Fast-DDS
• Client library (if applicable):
  • rclpy

Steps to reproduce issue

Send a ROS 2 action goal from command line to an action server running in a C++ application.
The ROS 2 CLI prints a goal id when the goal is accepted.
Have the action server print the UUID of the goal using

rclcpp_action::to_string(goal_handle->get_goal_id())

Expected behavior

The UUID printed by the C++ action server and the UUID printed by the Python action client should match.

Actual behavior

The UUIDs are very similar but they do not match.
For example, the CLI shows:

Goal accepted with ID: b10a7c4d52564eafa06962e25eefe297

while the C++ app shows

b1a7c4d52564eafa06962e25eefe297

Note how the two string representations are very similar, but different.

The same applies to many other goals. It looks like there are always a couple of extra/missing zeros in the Python representation.

Start with the ros2 action send_goal command and trace how the accepted goal UUID is formatted by the Python action client. Compare it with the UUID returned by rclcpp_action::to_string(goal_handle->get_goal_id()); done means both representations match for the same goal, including the reproduced example.