Support MCAP files with IDL schema encoding

[amacneil]

I downloaded a ROS 2 db3 file from Autoware here.

I tried to convert it to MCAP using mcap convert. I ran this inside a docker container with the message definitions available:

$ docker run --rm -it -v ~/Desktop/bags:/bags ghcr.io/autowarefoundation/autoware-universe:humble-latest-prebuilt

root@b89cf3a30f2a:/autoware# curl -fsSL -o /usr/local/bin/mcap https://github.com/foxglove/mcap/releases/latest/download/mcap-linux-arm64
root@b89cf3a30f2a:/autoware# chmod +x /usr/local/bin/mcap

root@b89cf3a30f2a:/autoware# cd /bags/autoware
root@b89cf3a30f2a:/bags/autoware# mcap convert sample.db3 sample.mcap
failed to convert file: failed to find schema for autoware_auto_vehicle_msgs/msg/ControlModeReport: schema not found

It turns out that these schemas are specified using .idl instead of .msg:

root@b89cf3a30f2a:/bags/autoware# find / | grep -i ControlModeReport
/autoware/build/autoware_auto_vehicle_msgs/ament_cmake_core/stamps/ControlModeReport.idl.stamp
/autoware/src/core/external/autoware_auto_msgs/autoware_auto_vehicle_msgs/msg/ControlModeReport.idl
/autoware/install/autoware_auto_vehicle_msgs/share/autoware_auto_vehicle_msgs/msg/ControlModeReport.idl

.idl is supported by ROS 2 as an alternative to .msg.

mcap convert doesn't appear to support db3 files with .idl message definitions, and the MCAP spec appendix doesn't document a way to store these.

Even if mcap convert supported .idl schemas, Foxglove Studio apparently does not support rendering them.

Pre-requisites:

• mcap convert should support db3 files with IDL schemas mcap#496

Related:

• Add support for IDL messages ros-tooling/rosbag2_storage_mcap#43