Here's a detailed guide on creating a ROS2 service for calculating Fibonacci numbers, including defining a custom service interface, implementing a service server, and writing a service client.

Step 1: Create a Package for Custom Interfaces

First, ensure you have a ROS2 workspace set up. If not, create one:

mkdir -p ros2_ws/src
cd ros2_ws

Create a new package for your custom interfaces:

ros2 pkg create my_robot_interfaces --dependencies rclpy rosidl_default_generators

Navigate into the package:

cd src/my_robot_interfaces

Step 2: Define the Service Interface

1. Create a Service Interface File:

   • Navigate to the srv directory of your package. If it doesn't exist, create it:

     mkdir srv
     cd srv
     
     

   • Create a new file named Fibonacci.srv:

     touch Fibonacci.srv
     
     

   • Open Fibonacci.srv and define the service interface:

     int32 number
     ---
     int32 fibonacci_number
     
     

2. Update CMakeLists.txt:

   • Open the CMakeLists.txt file in the root of your package.

   • Add the following lines to include your service interface in the build process:

     find_package(rosidl_default_generators REQUIRED)
     rosidl_generate_interfaces(${PROJECT_NAME}
       "srv/Fibonacci.srv"
     )
     ament_export_dependencies(rosidl_default_runtime)
     
     

Step 3: Build the Package

1. Navigate Back to Your Workspace:

   cd ../../..
   
   

2. Build Your Workspace:

   colcon build --packages-select my_robot_interfaces
   
   

3. Source the Environment:

   source install/setup.bash
   
   

Step 4: Implement the Service Server

1. Create a New Package for the Server: If you haven't already, create a new package for your server node:

   ros2 pkg create my_pkg --dependencies rclpy my_robot_interfaces
   
   

2. Implement the Service Server:

   • Navigate to the src directory of your new package:

     cd src/my_pkg
     
     

   • Create a new Python file named fibonacci_server.py:

     touch fibonacci_server.py
     
     

   • Open fibonacci_server.py and implement the server:

     import rclpy
     from rclpy.node import Node
     from my_robot_interfaces.srv import Fibonacci
     
     def fibonacci(n):
         if n <= 0:
             return 0
         elif n == 1:
             return 1
         else:
             return fibonacci(n-1) + fibonacci(n-2)
     
     class FibonacciServer(Node):
         def __init__(self):
             super().__init__("fibonacci_server")
             self.fibonacci_service = self.create_service(
                 Fibonacci,  # Service interface
                 "fibonacci",  # Service name
                 self.fibonacci_callback  # Callback function
             )
             self.get_logger().info("Fibonacci Service started")
     
         def fibonacci_callback(self, request, response):
             response.fibonacci_number = fibonacci(request.number)
             self.get_logger().info(f"Fibonacci of {request.number} is {response.fibonacci_number}")
             return response
     
     def main(args=None):
         rclpy.init(args=args)
         node = FibonacciServer()
         rclpy.spin(node)
         rclpy.shutdown()
     
     if __name__ == "__main__":
         main()
     
     

3. Update setup.py:

   • Open the setup.py file in the root of your package.

   • Add the following line to include your server node in the package's entry points:

     entry_points={
         'console_scripts': [
             "fibonacci_server = my_pkg.fibonacci_server:main"
         ],
     },
     
     

Step 5: Build and Run the Server