How to create an interface package

Create a separate package for message and service definitions, for easier dependency management later on. This package does not need any dependencies, since it won’t have any program code. So the first pkg create command does not have any dependencies. However, some changes need to be done to the package.xml and CMakeLists.txt files.

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

Open package.xml and add between <buildtool_depend> and <test_depend>:

<build_depend>rosidl_default_generators</build_depend>
<exec_depend>rosidl_default_runtime</exec_depend>
<member_of_group>rosidl_interface_packages</member_of_group>

Edit CMakeLists.txt like this:

• Remove # Default to C99 section.
• Remove if(BUILD_TESTING) block.
• Add to # find dependencies section:
  • find_package(rosidl_default_generators REQUIRED)

Add file to msg folder, e. g. SomeStatus.msg:

int64 some_int_value
bool is_ready
string debug_message

Add to CMakeLists.txt, after # find dependencies section:

rosidl_generate_interfaces(${PROJECT_NAME}
  "msg/SomeStatus.msg"
)

Build the package:

cd /root/of/project
colcon build --packages-select my_interfaces

Verify that it’s there:

source ~/.bashrc
ros2 interface show my_interfaces/msg/SomeStatus