- Open a new terminal and source the workspace
cd ~/ros2_helloworld_ws
source install/local_setup.bash- Create a new package for the service files
cd src
ros2 pkg create --build-type ament_cmake ros2_calculator_interfaces- Create extra folders for use with services
cd ros2_calculator_interfaces/
mkdir srv- Create a file for the 'process two numbers' service
touch srv/ProcessTwoNums.srv- Open VSCode within the working directory
code .6a. Paste the following into srv/ProcessTwoNums.srv
int64 a
int64 b
int64 op
---
int64 result
- Paste the following in
CMakeLists.txt, just below the# find_package(<dependency> REQUIRED)line.
find_package(rosidl_default_generators REQUIRED)
rosidl_generate_interfaces(${PROJECT_NAME}
"srv/ProcessTwoNums.srv"
)
Your final file should look like this:
cmake_minimum_required(VERSION 3.8)
project(ros2_calculator_interfaces)
if(CMAKE_COMPILER_IS_GNUCXX OR CMAKE_CXX_COMPILER_ID MATCHES "Clang")
add_compile_options(-Wall -Wextra -Wpedantic)
endif()
# find dependencies
find_package(ament_cmake REQUIRED)
# uncomment the following section in order to fill in
# further dependencies manually.
# find_package(<dependency> REQUIRED)
find_package(rosidl_default_generators REQUIRED)
rosidl_generate_interfaces(${PROJECT_NAME}
"srv/ProcessTwoNums.srv"
)
if(BUILD_TESTING)
find_package(ament_lint_auto REQUIRED)
# the following line skips the linter which checks for copyrights
# comment the line when a copyright and license is added to all source files
set(ament_cmake_copyright_FOUND TRUE)
# the following line skips cpplint (only works in a git repo)
# comment the line when this package is in a git repo and when
# a copyright and license is added to all source files
set(ament_cmake_cpplint_FOUND TRUE)
ament_lint_auto_find_test_dependencies()
endif()
ament_package()- Paste the following in
package.xml, just below the<buildtool_depend>ament_cmake</buildtool_depend>line.
<buildtool_depend>rosidl_default_generators</buildtool_depend>
<exec_depend>rosidl_default_runtime</exec_depend>
<member_of_group>rosidl_interface_packages</member_of_group>
Your final file should look like this:
<?xml version="1.0"?>
<?xml-model href="http://download.ros.org/schema/package_format3.xsd" schematypens="http://www.w3.org/2001/XMLSchema"?>
<package format="3">
<name>ros2_calculator_interfaces</name>
<version>0.0.0</version>
<description>TODO: Package description</description>
<maintainer email="ros2@todo.todo">ros2</maintainer>
<license>TODO: License declaration</license>
<buildtool_depend>ament_cmake</buildtool_depend>
<buildtool_depend>rosidl_default_generators</buildtool_depend>
<exec_depend>rosidl_default_runtime</exec_depend>
<member_of_group>rosidl_interface_packages</member_of_group>
<test_depend>ament_lint_auto</test_depend>
<test_depend>ament_lint_common</test_depend>
<export>
<build_type>ament_cmake</build_type>
</export>
</package>- Build the interface package you've just made
cd ~/ros2_helloworld_ws
colcon build --packages-select ros2_calculator_interfaces- In another terminal, verify that the services are correctly compiled (in a new terminal).
cd ~/ros2_helloworld_ws
source install/local_setup.bash
ros2 interface show ros2_calculator_interfaces/srv/ProcessTwoNums
- Create a new package for the calculator project
cd src
ros2 pkg create --build-type ament_python ros2_calculator- Create two files, one for the calculator node and one for consumer node.
cd ros2_calculator
touch ros2_calculator/calculator_node.py
touch ros2_calculator/consumer_node.py- Open VSCode within the working directory
code .- In
calculator_node.py, copy and paste the following template code.
from ros2_calculator_interfaces.srv import ProcessTwoNums
import rclpy
from rclpy.node import Node
class CalculatorServiceNode(Node):
def __init__(self):
super().__init__('calculator_service')
self.srv = self.create_service(ProcessTwoNums, 'process_two_nums', self.process_two_nums_callback)
def process_two_nums_callback(self, request, response):
self.get_logger().info(f'Received numbers: {request.a} & {request.b} with operator {request.op}')
# TODO: Implement logic
def main(args=None):
rclpy.init(args=args)
calculator_service_node = CalculatorServiceNode()
rclpy.spin(calculator_service_node)
rclpy.shutdown()
if __name__ == '__main__':
main()- In
consumer_node.py, copy and paste the following code.
from ros2_calculator_interfaces.srv import ProcessTwoNums
import sys
import rclpy
from rclpy.node import Node
class ConsumerNode(Node):
def __init__(self):
super().__init__('consumer_node')
self.cli = self.create_client(ProcessTwoNums, 'process_two_nums')
while not self.cli.wait_for_service(timeout_sec=1.0):
self.get_logger().info('Service not available, waiting again...')
self.req = ProcessTwoNums.Request()
def send_request(self, a, b, op):
self.req.a = a
self.req.b = b
self.req.op = op
self.future = self.cli.call_async(self.req)
def main(args=None):
rclpy.init(args=args)
a = int(sys.argv[1])
b = int(sys.argv[2])
op = int(sys.argv[3])
consumer_node = ConsumerNode()
consumer_node.send_request(a, b, op)
while rclpy.ok():
rclpy.spin_once(consumer_node)
if consumer_node.future.done():
try:
response = consumer_node.future.result()
except Exception as e:
consumer_node.get_logger().info('Service call failed %r' % (e,))
else:
consumer_node.get_logger().info(f'Input: (a = {consumer_node.req.a}, b = {consumer_node.req.b}, op = {consumer_node.req.op})')
consumer_node.get_logger().info(f'Output: {response.result}')
break
consumer_node.destroy_node()
rclpy.shutdown()
if __name__ == '__main__':
main()- Run the service node.
python3 ros2_calculator/calculator_node.py- In a new terminal, run the client node. Substitute , and with the corresponding nodes.
python3 ros2_calculator/consumer_node.py 1 1 1