Feature request: disable loopback

[Timple]

In ros1 we used to use the socketcan bridge to convert the canbusses to can_msgs/Frame ros messages. All messages we put on /to_canbus were never on the /from_canbus topic.

However, for ROS2 this package is recommended it seems.

Now we do see all messages we send on the /to_canbus back on the /from_canbus topic. Not only led this to (solvable) issues, but this actually almost doubles the frequency of the /from_canbus topic. And (thus) doubles the handling effort on the subscribing nodes as these messages need to be discarded.

Is there a way to get the 'old' behavior back?

[Timple]

This could be implemented by adding

// Check if it's a TX frame
if (frame.can_id & (CAN_ERR_TX_TIMEOUT | CAN_ERR_CRTL_TX_WARNING | CAN_ERR_CRTL_TX_PASSIVE))
{
  // This is a TX frame, ignore it
  continue;
}

After the read here: https://github.com/autowarefoundation/ros2_socketcan/blob/d25a55528eb7b27ab3c22c1b888a7276ae4af6f9/ros2_socketcan/src/socket_can_receiver.cpp#L140C48-L140C53

Would such a PR be accepted if not made optional? As I can't think of a usecase where anyone wants this. As they also could subscribe to the /to_can_bus_topic topic.

[tonynajjar]

I'm also interested by this!

[JWhitleyWork]

I'm working on a more detailed implementation of this feature.