DDS: Added subscriber support

[arshPratap]

Aims to provide a subscriber support for the current DDS functionality in Ardupilot.
Note : based on the changes made in PR #23586
Current Scenario :

Special thanks to @Ryanf55 for initiating the said work on his branch

[srmainwaring]

Hi @arshPratap, this is looking good!

It can be rebased on master now that #23586 is merged (I found it easier to cherry pick db8b632 onto master than try and rebase the old UDP transport commits).

I worked through your example and have a couple of suggested changes to get a working test:

• Add the IDL for sensor_msgs/Joy
• Update the topic table and topic name.
• Add a registration entry.

This branch has the edits: https://github.com/srmainwaring/ardupilot/tree/arsh/ddsAddSubscriber-rebased

Run the example as usual and publish data with:

ros2 topic pub /ap/joy sensor_msgs/Joy "axes: [0.1, 0.2, 0.3, 0.4]"

and monitor in MAVProxy

[arshPratap]

@srmainwaring thanks for the edits ..have rebased accordingly !

[Ryanf55]

Please update the commit messages to all be compliant with standards, and feel free to squash them. The merge conflict commit yet doesn't have AP_DDS prefix, nor does it need to be part of the history since it's a rebase-style repo. Thanks for getting this updated!

[Ryanf55]

ros2 topic pub /ap/joy sensor_msgs/Joy "axes: [0.1, 0.2, 0.3, 0.4]"

I tested with the above process, it works. Then, with an empty array:

LGTM. Just finish up the last touches, and I'm happy to approve.

[arshPratap]

@Ryanf55 thanks for the suggestions ! Have made the required changes

[Ryanf55]

Hey the build was failing due to style failing. I ran ./Tools/CodeStyle/ardupilot-astyle.sh libraries/AP_DDS/*.cpp libraries/AP_DDS/*.h to fix it. Overall, the PR appears to work. Great work. Approved

[arshPratap]

rebased to master... @Ryanf55 @srmainwaring thanks for all your suggestions

[Ryanf55]

With the latest changes, it does not compile.

In file included from ../../libraries/AP_DDS/AP_DDS_Client.cpp:9:
../../libraries/AP_DDS/AP_DDS_Client.cpp: In static member function ‘static void AP_DDS_Client::on_topic(uxrSession*, uxrObjectId, uint16_t, uxrStreamId, ucdrBuffer*, uint16_t, void*)’:
../../libraries/AP_DDS/AP_DDS_Client.cpp:424:29: error: request for member ‘axes’ in ‘topic’, which is of pointer type ‘sensor_msgs_msg_Joy*’ (maybe you meant to use ‘->’ ?)
  424 |                       topic.axes[0], topic.axes[1], topic.axes[2], topic.axes[3]);
      |                             ^~~~
../../libraries/GCS_MAVLink/GCS.h:1312:86: note: in definition of macro ‘GCS_SEND_TEXT’
 1312 | #define GCS_SEND_TEXT(severity, format, args...) gcs().send_text(severity, format, ##args)

Can you reproduce this on your side?

[arshPratap]

@Ryanf55 should work now . Just rebased and pushed the latest changes and have run the astyle script for the necessary files.

[Ryanf55]

Excellent work getting all the changes folded in. I've verified, LGTM. Marked merge on CI pass. Thanks for the contribution!

[peterbarker]

Merged, thanks!