Support Connext key fields

[superware]

Hello,

I have a working ROS2 foxy ecosystem running Connext and came to the point where I need Connext key fields support. I'm looking for the simplest way to modify ROS2 or rmw_connextdds and allow the underlaying Connext RMW to have some of the fields defined as keys.

Most of the related rmw implementation seem to be in rmw_connext_dynamic_cpp/src/utility_templates.hpp which in conjunction with DDS_StructMember.is_key seems technically possible but I don't have the necessary architectural knowledge to workaround.

Any help will be greatly appreciated.

[clalancette]

There is no current plan to work on this. This is actually a pretty complicated feature request, so if you were interested in pursuing it please start by opening a design document REP on https://github.com/ros-infrastructure/rep .

For now I'll put this on the backlog.

[superware]

I'm not referring to ROS support for key fields, but rather to somehow add the is_key bit in Connext RMW typesupport. Which issues would rise in ROS if the RMW will internally handle keyed topics?