Can't remap topic name and set hint at the same time;

[Ferenc Balint-Benczedi]

OS: Ubuntu 20.04
ROS: Galactic
Verions: 2.3.0-3 installed from Debian

I am trying to create a generic ROS2 node that subscribes to an image topic of a user's choice (through remapping of a topic name) and a user can in addition set the transport hint. Pretty straight forward, this is how image_saver from the image_view package used to work on ROS1

node->declare_parameter("transport", "raw");
std::string transport = node->get_parameter("transport").get_value<std::string>();     
image_sub_ = image_transport::create_subscription(
            &(*node), "image", std::bind(&MyClass::imageCallback, this, std::placeholders::_1), transport);

I run my node with ros2 run my_package my_node --ros-args -r image:=/my_image_topic/image_raw -p transport:=compressed but the output of ros2 node info my_node shows:

/my_node
  Subscribers:
    /image/compressed: sensor_msgs/msg/CompressedImage

If I don't set the parameter from the command line the remapping of the topic name works and I get:

/my_node
  Subscribers:
    /my_image_topic/image_raw: sensor_msgs/msg/Image

I have also tried doing this using TransportHints and creating the subscriber with it_.subscribe("image", 10, &MyClass::imageCallback, this, &hints); , and the overwriting the image_transport parameter; The first problem here is that this parameter from TransportHints is never declared, so I had to declare it from my node in order to overwrite it; But then the behavior is still the same; We can either remap the topic name or change the hint but not both at the same time;

I also tried this out with the image_saver node from image_view package on ROS2 and could not get that one to run either;

I suspect that this might be a bug somewhere in the code when resolving names of topics and parameters; My current workaround is to set both the topic name and the hint from parameters;

[Geoffrey Biggs]

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