ROS学习笔记7_服务端Server

 在上图所示的模型中，Client作为请求的发送端，Server端接收Client发送的指令，并且完成topic指令的发送。其中请求的信息类型是std_srvs::Trigger类，同时返回一个Response，说明是否成功。

服务器端代码实现。

#include<ros/ros.h>
#include<geometry_msgs/Twist.h>
#include<std_srvs/Trigger.h>

//will be used later when publish a topic
ros::Publisher turtle_vel_pub;
//as a flag to show if the turtle is moving or not
bool pubCommand = false;


//service callback function
bool commandCallback(std_srvs::Trigger::Request &req, std_srvs::Trigger::Response &res)
{
	pubCommand = !pubCommand;
	
	//display the request data
	ROS_INFO("Publish turtle velocity command [%s]", pubCommand==true?"Yes":"No");
	
	//set the callback data
	res.success = true;
	res.message = "Change turtle command state!";
	
	return true;
}



int main(int argc, char **argv)
{
	//initiate ros node
	ros::init(argc, argv, "turtle_command_server");
	
	//create node handle
	ros::NodeHandle n;
	
	//create a server named /turtle_command, register the command callback function
	ros::ServiceServer command_service = n.advertiseService("/turtle_command", commandCallback);
	
	//create a Publisher, publish a topic named /turtle1/cmd_vel, message type is geometry_msgs::Twist, queue length is 10
	turtle_vel_pub = n.advertise<geometry_msgs::Twist>("/turtle1/cmd_vel", 10);
	
	ROS_INFO("Ready to receive turtle command.");
	
	//set the frequency of loop
	ros::Rate loop_rate(10);
	
	while(ros::ok())
	{
		//look at queue of callback function once
		ros::spinOnce();
		
		//if the flag is true, publish the velosity command
		if(pubCommand)
		{
			geometry_msgs::Twist vel_msg;
			vel_msg.linear.x = 0.5;
			vel_msgs.angular.z = 0.2;
			turtle_vel_pub.publish(vel_msg);
		}
		
		//delay by setting
		loop_rate.sleep();
	}

	return 0;

}

修改CMakeList.txt，添加编译规则。

add_executable(turtle_command_server src/turtle_command_server.cpp)
target_link_libraries(turtle_command_server ${catkin_LIBRARIES})

 返回catkin_ws目录下进行编译。之后启动海龟仿真节点和服务器节点

rosrun turtlesim turtlesim_node
rosrun learning_service turtle_command_server
rosservice call /turtle_command "{}"

rosservice call来发送/turtle_command请求，每次请求都改变当前的运动状态。