目标:创建和运行服务和客户端节点使用C++.
背景
当一个节点使用服务通信时,客户端节点发送请求数据,服务节点响应请求。请求和响应的结构文件为.srv。
下面的例子是:一个节点请求两个整数求和,另外一个节点响应这个结果。
任务
1、创建一个包
ros2 pkg create --build-type ament_cmake cpp_srvcli --dependencies rclcpp example_interfaces
example_interfaces包包含了文件.srv,里面的内容如下
int64 a int64 b --- int64 sum
上两行为请求的内容,下面一行为响应。
1.1 更新package.xml
由于在创建包的时候,使用了--dependencies,所以不需要再package.xml和CMakeLists.txt中再添加。
2、实现服务节点
创建文件:add_two_ints_server.cpp
#include "rclcpp/rclcpp.hpp" #include "example_interfaces/srv/add_two_ints.hpp" #include <memory> void add(const std::shared_ptr<example_interfaces::srv::AddTwoInts::Request> request, std::shared_ptr<example_interfaces::srv::AddTwoInts::Response> response) { response->sum = request->a + request->b; RCLCPP_INFO(rclcpp::get_logger("rclcpp"), "Incoming request\na: %ld" " b: %ld", request->a, request->b); RCLCPP_INFO(rclcpp::get_logger("rclcpp"), "sending back response: [%ld]", (long int)response->sum); } int main(int argc, char **argv) { rclcpp::init(argc, argv); std::shared_ptr<rclcpp::Node> node = rclcpp::Node::make_shared("add_two_ints_server"); rclcpp::Service<example_interfaces::srv::AddTwoInts>::SharedPtr service = node->create_service<example_interfaces::srv::AddTwoInts>("add_two_ints", &add); RCLCPP_INFO(rclcpp::get_logger("rclcpp"), "Ready to add two ints."); rclcpp::spin(node); rclcpp::shutdown(); }
3、实现客户端节点
#include <rclcpp/rclcpp.hpp> #include "example_interfaces/srv/add_two_ints.hpp" #include <chrono> #include <cstdlib> #include <memory> using namespace std::chrono_literals; int main(int argc, char **argv) { rclcpp::init(argc, argv); if(argc != 3) { RCLCPP_INFO(rclcpp::get_logger("rclcpp"), "usage: add_two_ints_client X Y"); return 1; } //创建一个节点并初始化客户端 std::shared_ptr<rclcpp::Node> node = rclcpp::Node::make_shared("add_two_ints_client"); rclcpp::Client<example_interfaces::srv::AddTwoInts>::SharedPtr client = node->create_client<example_interfaces::srv::AddTwoInts>("add_two_ints"); //请求被创建,定义在.srv文件中 auto request = std::make_shared<example_interfaces::srv::AddTwoInts::Request>(); request->a = atoll(argv[1]); request->b = atoll(argv[2]); //while的loop给客户端1s的时间在网络上搜索,找不到就等待 while(!client->wait_for_service(1s)) { //如果客户端被取消就退出 if(!rclcpp::ok()) { RCLCPP_ERROR(rclcpp::get_logger("rclcpp"), "Interrupted while waiting for the serrvice.Exiting."); return 0; } RCLCPP_INFO(rclcpp::get_logger("rclcpp"), "service not available, waiting again ..."); } auto result = client->async_send_request(request); //wait for the result if(rclcpp::spin_until_future_complete(node, result) == rclcpp::FutureReturnCode::SUCCESS) { RCLCPP_INFO(rclcpp::get_logger("rclcpp"), "Sum: %ld", result.get()->sum); } else { RCLCPP_ERROR(rclcpp::get_logger("rclcpp"), "Failed to call service and_two_ints"); } rclcpp::shutdown(); return 0; }
4、运行
ros2 run cpp_srvcli server ros2 run cpp_srvcli client 5 9
总结
创建了两个节点来请求和响应数据通过service服务。将一些依赖和二进制添加 到了CMakeLists.txt中以便能够编译和运行。
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