ROS service通信机制中，客户端编程实例

ROS (Robot Operating System) 中的服务(service)是一种异步的消息传递模式，用于处理特定任务并返回结果。服务通信由客户端和服务端两部分组成。下面是一个简单的ROS服务客户端编程实例，假设我们有一个名为`add_two_numbers`的服务，它接受两个整数并返回它们的和。

**服务定义** (通常在`server.py`文件):

import rclpy
from rclpy.node import Node
from std_msgs.msg import Int32

class AddNumbersService(Node):
    def __init__(self):
        super().__init__('add_two_numbers_service')
        self.service = self.create_service(Int32, 'add_two_numbers', self.add_two_numbers_callback)

    def add_two_numbers_callback(self, request, response):
        result = request.data1 + request.data2
        response.sum = result
        return response

def main(args=None):
    rclpy.init(args=args)
    node = AddNumbersService()
    rclpy.spin(node)
    node.destroy_node()
    rclpy.shutdown()

if __name__ == '__main__':
    main()

**客户端编程** (通常在`client.py`文件):

import rclpy
from rclpy.node import Node
from add_two_numbers_service.srv import AddTwoNumbers

class ClientNode(Node):
    def __init__(self):
        super().__init__('client_node')
        self.add_service = self.create_client(AddTwoNumbers, 'add_two_numbers')

    def call_add_service(self, num1, num2):
        future = self.add_service.call_async({'data1': num1, 'data2': num2})
        while rclpy.ok() and not future.done():
            self.get_logger().info('Waiting for server...')
            rclpy.spin_once(self, timeout_sec=0.1)
        if not future.done():
            self.get_logger().error('Service call failed!')
            return None
        else:
            result = future.result()
            return result.sum

def main(args=None):
    rclpy.init(args=args)
    client = ClientNode()
    sum_result = client.call_add_service(4, 5)
    if sum_result is not None:
        client.get_logger().info(f'The sum of {num1} and {num2} is: {sum_result}')
    rclpy.shutdown()

if __name__ == '__main__':
    main()

当你运行`client.py`时，它会连接到`server.py`中定义的服务，并发送请求计算两个数字之和。如果服务正常运行，它将返回响应。