Support for DDS on_inconsistent_topic topic listener callback

[clalancette]

Is there an already existing issue for this?

• I have searched the existing issues

Expected behavior

DDS 1.4, 2.2.4.3 allows for an "inconsistent topic" callback to be called when a topic with the same name but different characteristics is detected.

In Fast-DDS, this callback can be set using the Topic Listener class https://github.com/eProsima/Fast-DDS/blob/master/include/fastdds/dds/topic/TopicListener.hpp . However, nothing in the implementation will ever call that callback. That was determined both through code inspection, and also through empirical testing using https://github.com/clalancette/dds_experimentation/tree/clalancette/cleanups/fastdds/HelloWorldExample .

It would be great if Fast-DDS would finish up support for this so we can get these callbacks at the ROS 2 layer.

Current behavior

The on_inconsistent_topic callback can be registered, but will never be called.

Steps to reproduce

1. Clone https://github.com/clalancette/dds_experimentation/tree/clalancette/cleanups/fastdds/HelloWorldExample (first time)
2. Build the example with mkdir build ; cd build ; cmake .. -DV1TYPE=T1 -DV2TYPE=T1 -DV3TYPE=T1 ; make
3. Run the Subscriber: ./HelloWorldSubscriber v1
4. Clone https://github.com/clalancette/dds_experimentation/tree/clalancette/cleanups/fastdds/HelloWorldExample (second time)
5. Build the example with mkdir build ; cd build ; cmake .. -DV1TYPE=T3 -DV2TYPE=T1 -DV3TYPE=T1 ; make
6. Run the Publisher: ./HelloWorldPublisher v1

Fast DDS version/commit

Commit bffc876

Platform/Architecture

Ubuntu Focal 20.04 amd64

Transport layer

UDPv4

Additional context

Related to ros2/ros2#1361

XML configuration file

No response

Relevant log output

No response

Network traffic capture

No response

[EduPonz]

Hi @clalancette , as documented here, as of Fast DDS v2.9.0, on_inconsistent_topic functionality is not yet implemented. Therefore, I'm converting this issue into a discussion on the channel appropriate for feature requests. We will plan internally how to support this feature in Fast DDS for future releases.

Thanks!

[clalancette]

Related to ros2/ros2#1361

[MiguelCompany]

@clalancette I have a PoC you can test on this branch

[clalancette]

I gave it a quick whirl, but I think Fast-DDS is doing something different than Connext here.

In particular, what I did was to build a ROS 2 workspace twice; once unmodified, and once with the effort field of https://github.com/ros2/demos/blob/rolling/pendulum_msgs/msg/JointState.msg changed to a string. Then I ran the following under Connext:

Terminal 1:

RMW_IMPLEMENTATION=rmw_connextdds ros2 topic pub /chatter pendulum_msgs/msg/JointState '{position: 0, velocity: 0, effort: 0}'
publisher: beginning loop
publishing #1: pendulum_msgs.msg.JointState(position=0.0, velocity=0.0, effort=0.0)
...

Terminal 2:

RMW_IMPLEMENTATION=rmw_connextdds ros2 topic echo /chatter pendulum_msgs/msg/JointState
[WARN] [1678975432.330708363] [_ros2cli_3752035]: Incompatible type on topic '/chatter', no messages will be sent to it.

That's what I expect to happen.

I then rebuilt the workspaces with the feature/inconsistent_topic_status/poc branch for Fast-DDS, and it is still transferring data as far as I can tell:

Terminal 1:

RMW_IMPLEMENTATION=rmw_fastrtps_cpp ros2 topic pub /chatter pendulum_msgs/msg/JointState '{position: 0, velocity: 0, effort: 0}'
publisher: beginning loop
publishing #1: pendulum_msgs.msg.JointState(position=0.0, velocity=0.0, effort=0.0)
...

Terminal 2:

RMW_IMPLEMENTATION=rmw_fastrtps_cpp ros2 topic echo /chatter pendulum_msgs/msg/JointState
position: 0.0
velocity: 0.0
effort: ''
---
...

Any thoughts on what might be going on here?

[MiguelCompany]

@clalancette Fast DDS is not sending type information on the discovery by default (yet), so you should check with different type names.

[clalancette]

@clalancette Fast DDS is not sending type information on the discovery by default (yet), so you should check with different type names.

Ah, thanks for the hint. Indeed, with using different type names, this works all the way through rmw_fastrtps_cpp and all the way to rclpy. Great works, thanks for this.