First message(s) published by diagnostic updater have empty hardware_id

[wentasah]

Even if updater.setHardwareID() is called before updater.add(), the first published message has hardware_id empty. Only the messages published later from the timer callback have hardware_id set.

The consequence of this behaviour is that tools like foxglove or ros2_console_tools can show one diagnostic entry twice, each with different status. See the screenshot below:

This happens in Jazzy, but from looking at the source code, the it's likely the same in newer distros.

This can be reproduced as follows:

1. In one terminal run:

   ros2 topic echo /diagnostics --filter 'm.status[0].name == "diagnostic_updater_example: Function updater"' | grep hardware_id```
   

2. In the second terminal run:

   ros2 run diagnostic_updater example
   

Received output:

  hardware_id: ''
  hardware_id: ''
  hardware_id: ''
  hardware_id: ''
  hardware_id: Device-27-46
  hardware_id: Device-27-46
  hardware_id: Device-27-46
  hardware_id: Device-27-46

Expected output:

  hardware_id: Device-27-46
  hardware_id: Device-27-46
  hardware_id: Device-27-46
  hardware_id: Device-27-46
  hardware_id: Device-27-46
  hardware_id: Device-27-46
  hardware_id: Device-27-46
  hardware_id: Device-27-46

The fix is probably simple. I just don't have time right now to prepare and test it.

Received output (without grep filtering)

For completeness, the full output without filtering the hardware_id is below.

header:
  stamp:
    sec: 1788283543
    nanosec: 462839642
  frame_id: ''
status:
- level: "\0"
  name: 'diagnostic_updater_example: Function updater'
  message: Node starting up
  hardware_id: ''
  values: []
---
header:
  stamp:
    sec: 1788283543
    nanosec: 462852992
  frame_id: ''
status:
- level: "\0"
  name: 'diagnostic_updater_example: Function updater'
  message: Doing important initialization stuff.
  hardware_id: ''
  values: []
- level: "\0"
  name: 'diagnostic_updater_example: Method updater'
  message: Doing important initialization stuff.
  hardware_id: ''
  values: []
- level: "\0"
  name: 'diagnostic_updater_example: Bound check'
  message: Doing important initialization stuff.
  hardware_id: ''
  values: []
---
header:
  stamp:
    sec: 1788283543
    nanosec: 963490803
  frame_id: ''
status:
- level: "\x02"
  name: 'diagnostic_updater_example: Function updater'
  message: Buckle your seat belt. Launch in 0.000000 seconds!
  hardware_id: Device-27-46
  values:
  - key: Diagnostic Name
    value: dummy
  - key: Time to Launch
    value: '0'
  - key: Geeky thing to say
    value: The square of the time to launch 0.000000 is 0.000000
- level: "\x01"
  name: 'diagnostic_updater_example: Method updater'
  message: This is a silly updater.
  hardware_id: Device-27-46
  values:
  - key: Stupidicity of this updater
    value: '1000'
- level: "\x02"
  name: 'diagnostic_updater_example: Bound check'
  message: Too low
  hardware_id: Device-27-46
  values:
  - key: Low-Side Margin
    value: '-5'
  - key: Top-Side Margin
    value: '10'
- level: "\x02"
  name: 'diagnostic_updater_example: topic1 topic status'
  message: No events recorded.; Too low
  hardware_id: Device-27-46
  values:
  - key: Events in window
    value: '0'
  - key: Events since startup
    value: '0'
  - key: Duration of window (s)
    value: '0.000190'
  - key: Actual frequency (Hz)
    value: '0.000000'
  - key: Minimum acceptable frequency (Hz)
    value: '0.450000'
  - key: Maximum acceptable frequency (Hz)
    value: '2.200000'
  - key: Low-Side Margin
    value: '-5'
---