服务模型（客户端/服务器）

ruizi816 / 2023-08-02 / 原文

服务模型

创建功能包

cd ~/catkin_ws/src
catkin_create_pkg learning_service roscpp rospy std_msgs geometry_msgs turtlesim

客户端Client

如何实现一个客户端

初始化ROS节点；
创建一个Client实例；
发布服务请求数据；
等待Server处理之后的应答结果。

客户端代码

turtle_spqwn.cpp

点击查看代码

/**
 * 该例程将请求/spawn服务，服务数据类型turtlesim::Spawn
 */

#include <ros/ros.h>
#include <turtlesim/Spawn.h>

int main(int argc, char** argv)
{
    // 初始化ROS节点
	ros::init(argc, argv, "turtle_spawn");

    // 创建节点句柄
	ros::NodeHandle node;

    // 发现/spawn服务后，创建一个服务客户端，连接名为/spawn的service
	ros::service::waitForService("/spawn");
	ros::ServiceClient add_turtle = node.serviceClient<turtlesim::Spawn>("/spawn");

    // 初始化turtlesim::Spawn的请求数据
	turtlesim::Spawn srv;
	srv.request.x = 2.0;
	srv.request.y = 2.0;
	srv.request.name = "turtle2";

    // 请求服务调用
	ROS_INFO("Call service to spwan turtle[x:%0.6f, y:%0.6f, name:%s]", 
			 srv.request.x, srv.request.y, srv.request.name.c_str());

	add_turtle.call(srv);

	// 显示服务调用结果
	ROS_INFO("Spwan turtle successfully [name:%s]", srv.response.name.c_str());

	return 0;
};

在CmakeLists.txt中添加编译规则

在build中添加
add_executable(turtle_spawn src/turtle_spawn.cpp)
target_link_libraries(turtle_spawn ${catkin_LIBRARIES})

编译并且运行客户端

cd _/catkin_ws
catkin_make
source devel/setup.bash
roscore
rosrun turtlesim turtlesim_node
rosrun learning_service turtle_spawn

服务端Server

如何实现一个服务器

初始化ROS节点；
创建Server实例；
循环等待服务请求，进入回调函数；
在回调函数中完成服务功能的处理，并反馈应答数据。

创建服务器代码

turtle_command_server.cpp

点击查看代码


/**
 * 该例程将执行/turtle_command服务，服务数据类型std_srvs/Trigger
 */
 
#include <ros/ros.h>
#include <geometry_msgs/Twist.h>
#include <std_srvs/Trigger.h>

ros::Publisher turtle_vel_pub;
bool pubCommand = false;

// service回调函数，输入参数req，输出参数res
bool commandCallback(std_srvs::Trigger::Request  &req,
         			std_srvs::Trigger::Response &res)
{
	pubCommand = !pubCommand;

    // 显示请求数据
    ROS_INFO("Publish turtle velocity command [%s]", pubCommand==true?"Yes":"No");

	// 设置反馈数据
	res.success = true;
	res.message = "Change turtle command state!"

    return true;
}

int main(int argc, char **argv)
{
    // ROS节点初始化
    ros::init(argc, argv, "turtle_command_server");

    // 创建节点句柄
    ros::NodeHandle n;

    // 创建一个名为/turtle_command的server，注册回调函数commandCallback
    ros::ServiceServer command_service = n.advertiseService("/turtle_command", commandCallback);

	// 创建一个Publisher，发布名为/turtle1/cmd_vel的topic，消息类型为geometry_msgs::Twist，队列长度10
	turtle_vel_pub = n.advertise<geometry_msgs::Twist>("/turtle1/cmd_vel", 10);

    // 循环等待回调函数
    ROS_INFO("Ready to receive turtle command.");

	// 设置循环的频率
	ros::Rate loop_rate(10);

	while(ros::ok())
	{
		// 查看一次回调函数队列
    	ros::spinOnce();
		
		// 如果标志为true，则发布速度指令
		if(pubCommand)
		{
			geometry_msgs::Twist vel_msg;
			vel_msg.linear.x = 0.5;
			vel_msg.angular.z = 0.2;
			turtle_vel_pub.publish(vel_msg);
		}

		//按照循环频率延时
	    loop_rate.sleep();
	}

    return 0;
}

配置CMakeLists.txt中编译规则

在build中添加
add_executable(turtle_commans_server src/turtle_command_server.cpp)
target_link_libraries(turtle_command_server ${catkin_LIBRARIES})

编译并且运行服务器

cd ~/catkin_ws
catkin_make
source devel/setup.bash
roscore
rosrun turtlesim turtlesim_node
rosrun learning_service turtle_commans_server
rosservice call /turtle_commans"{}"