Topic

• Name (ex: /number_count)
• msg definition (ex: example_interfaces/msg/Int64)

Service

• Name (ex: /reset_number_count)
• srv definition (ex: example_interfaces/srv/SetBool)
  • Request: msg
  • Response: msg

Built-in-types

index.ros.org/doc/ros2/Concepts/About-ROS-Interfaces/

Example msg, srv

https://github.com/ros2/example_interfaces

common interfaces

https://github.com/ros2/common_interfaces

You can use other msg’s type for your service, too.

Let build own msg!

ros2 pkg create hexa_robot_interfaces
cd hexa_robot_interfaces
rm -rf include/
rm -rf src/
mkdir msg

In package.xml, add 3 lines (functionality to build and use your interfaces)