Feature request

Feature description

This feature is a subset of the functionality now described in REP-2011 ros-infrastructure/rep#358

1. Provide an equivalent of the ROS 1 message hashsum to detect message definition mismatches across topics.
2. Provide a way to discover and communicate the definition of message types from remote topics at runtime.

Use Cases

• Record and store definitions for messages in rosbag2 for inspection of bags on systems that may not have message definitions installed, or whose local definitions of messages may have evolved since recording
• Inspect messages in off-host visualization tools - such as RViz, Foxglove Studio, and Webviz, for plotting or printing of message contents

Implementation considerations

Reference spec in REP-2011 ros-infrastructure/rep#358

TODO

Based on current state of REP-2011 design and implementation discussion, this list will keep up to date

• Finalize REP-2011 design (for this feature subset)
  • Update Type Version Hash to use SHA-256, and details updates based on design discussion wjwwood/rep#7
  • Update RIHS version and string details wjwwood/rep#8
• TypeDescription interfaces for representing and communicating type info
  • new package and interfaces for describing other types rcl_interfaces#146
• Type Hash
  • Hash type description at code generation time
    • Install python3-jsonschema as Linux build requirement ci#695
    • Add jsonschema to pip installs for windows cookbook ros-infrastructure/ros2-cookbooks#52
    • Add jsonschema to windows install requirements ros2_documentation#3356
    • Type hash in interface codegen (rep2011) rosidl#722
  • Hash TypeDescriptions at runtime
    • Add SHA256 utility implementation rcutils#408
    • Calculate type hash from TypeDescription (rep2011) rcl#1027
  • Expose type hashes to typesupport
    • Expose type hash to typesupport structs (rep2011) rosidl_typesupport_fastrtps#95
    • Expose type hash on typesupports (rep2011) rosidl#729
    • Type hashes in typesupport (rep2011) rosidl_typesupport#135
    • Type hashes on typesupport (rep2011) rosidl_typesupport_fastrtps#98
  • Distribute type hashes during discovery
    • Add type hash to rmw_topic_endpoint_info_t (rep2011) rmw#348
    • Type hash in GraphCache, user_data encoding tools rmw_dds_common#70
    • Type hash distribution in discovery (rep2011) rmw_fastrtps#671
    • Type hash distribution in discovery (rep2011) rmw_cyclonedds#437
    • Type hash distribution during discovery (rep2011) rmw_connextdds#104
• Type Description and Raw Sources code generation
  • Copied type_description_interfaces structs (rep2011) rosidl#732
  • Type Description Codegen and Typesupport (rep2011) rosidl#727
  • Extend TypeDescription codegen with referenced type inclusion, disable option, raw sources emersonknapp/rosidl#10
  • Type Description Nested Support rosidl_typesupport#141
  • Type Description Nested Support rosidl_typesupport_fastrtps#101
  • Use get_type_hash_func on typesupports (rep2011) rmw_fastrtps#680
  • Use get_type_hash_func on typesupports (rep2011) rmw_connextdds#113
  • Use get_type_hash_func on typesupports (rep2011) rmw_cyclonedds#448
  • Use get_type_hash_func on typesupports (rep2011) rcl#1053
• (For Iron Freeze) Type Description distribution
  • Add GetTypeDescription.srv (rep2011) rcl_interfaces#153
  • Add enable_type_description_service node option - API only (rep2011) rcl#1060
  • Stub type hash value line in TopicEndpointInfo string rclpy#1110
  • Expect type hash cli output in test ros2cli#822
  • Add type_hash to cpp TopicEndpointInfo rclcpp#2137

Post-Iron Followups (to be backported to Iron)

• Type Hash Distribution (get_type_description service)
  • C core
    • Add ~/get_type_description service (rep2011) rcl#1052
  • C++ client exposure
    • Add new node interface TypeDescriptionsInterface to provide GetTypeDescription service rclcpp#2224
    • new builtin parameter: fix test expectations system_tests#520
  • Python client exposure
    • GetTypeDescription service rclpy#1139
    • Fix tests with new service and param present ros2cli#838
• CLI access to type description / hash
  • ros2node: Add verb get_type_description (rep2011) ros2cli#817
  • Include type hash in topic endpoint info (rep2011) rclpy#1104
  • Add marshalling functions for rclpy.type_hash.TypeHash (rep2011) ros2cli#816

Related Issues

ros2/rosbag2#782