ROS service communication programming

1 ROS-Service Communication programming

1.1 Service model

• Client client （person_client） Release request （Request） Send information to the service .
• Sever Server side （person_sever） Received request and data content , In the initial response to it （Response）
• service service （show_person）
  Pictured ：
  

1.2 Basic steps

• 1、 Create feature packs and compile
• 2、 Definition srv file
• 3、 modify package.xml file
• 4、 modify CMakeList.txt file
• 5、 Programming
• 6、 Compile operation

1.3 The detailed steps

1.3.1 Create feature packs and compile

• 1、 Enter the workspace src in .

cd ~/catkin_ws/src/

• 2、 Create Feature Pack

[email protected]:~/catkin_ws/src$ catkin_create_pkg learning_sevice roscpp rospy std_msgs geometry_msgs turtlesim
Created file learning_sevice/package.xml
Created file learning_sevice/CMakeLists.txt
Created folder learning_sevice/include/learning_sevice
Created folder learning_sevice/src
Successfully created files in /home/ubuntu/catkin_ws/src/learning_sevice. Please adjust the values in package.xml.

• 3、 Compile workspace
• You can edit it and compile it . Those who dislike trouble can skip .

[email protected]:~/catkin_ws$ cd ~/catkin_ws/
[email protected]:~/catkin_ws$ catkin_make

1.3.2 Definition srv file

• 1、 Open the function package path , Create folders and files

[email protected]:~/catkin_ws/src$ cd ~/catkin_ws/src/learning_sevice/
[email protected]:~/catkin_ws/src/learning_sevice$ mkdir srv
[email protected]:~/catkin_ws/src/learning_sevice$ cd srv/
[email protected]:~/catkin_ws/src/learning_sevice/srv$ ls
[email protected]:~/catkin_ws/src/learning_sevice/srv$ touch Person.srv
[email protected]:~/catkin_ws/src/learning_sevice/srv$ ls
Person.srv

• 2、 To write srv file

[email protected]:~/catkin_ws/src/learning_sevice/srv$ gedit Person.srv 

• Write the following

string name
uint8 age
uint8 sex

uint8 unknow = 0
uint8 male = 1
uint8 female = 2

---
string result

• The top of which is Request Definition of the type of , Here is Response The type definitions of are separated by three horizontal lines .

1.3.3 modify package.xml file

• 1、 Enter the corresponding file path , Open file

[email protected]:~/catkin_ws/src/learning_sevice/srv$ cd ../
[email protected]:~/catkin_ws/src/learning_sevice$ ls
CMakeLists.txt  include  package.xml  src  srv
[email protected]:~/catkin_ws/src/learning_sevice$ gedit package.xml 

• 2、 Enter the following , Save and exit

<build_depend>message_generation</build_depend>
<exec_depend>message_runtime</exec_depend>

1.3.4 modify CMakeList.txt file

• 1、 Open the corresponding file path and open the file

[email protected]:~/catkin_ws/src/learning_sevice$ gedit package.xml 
[email protected]:~/catkin_ws/src/learning_sevice$ gedit CMakeLists.txt

• 2、 newly added message_generation Dependency package

find_package(catkin REQUIRED COMPONENTS
...
  message_generation
)

• 3、 Add compilation dependency and execution dependency

add_service_files(FILES Person.srv)
generate_messages(DEPENDENCIES std_msgs)

• 4、 Open the function package required for compilation

catkin_package(
# INCLUDE_DIRS include
# LIBRARIES learning_sevice
  CATKIN_DEPENDS geometry_msgs roscpp rospy std_msgs turtlesim message_runtime
# DEPENDS system_lib
)

• 5、 Compile the , Check if there is any problem with the addition . Confident people can skip .

[email protected]:~/catkin_ws$ cd ~/catkin_ws/
[email protected]:~/catkin_ws$ catkin_make

1.3.5 Programming

• 1、 stay learning_sevice The next path src Create files and write person_server.cpp Program

//  The header file 
#include <ros/ros.h>
#include "learning_service/Person.h"

// service Callback function , Input parameters req, Output parameters res
bool personCallback(learning_service::Person::Request  &req,
         			learning_service::Person::Response &res)
{
    
    //  Display request data 
    ROS_INFO("Person: name:%s age:%d sex:%d", req.name.c_str(), req.age, req.sex);
	//  Set feedback data 
	res.result = "OK";
    return true;
}

int main(int argc, char **argv)
{
    
    // ROS Node initialization 
    ros::init(argc, argv, "person_server");

    //  Create node handle 
    ros::NodeHandle n;

    //  Create a file called /show_person Of server, Register callback function personCallback
    ros::ServiceServer person_service = n.advertiseService("/show_person", personCallback);

    //  Loop waiting for callback function 
    ROS_INFO("Ready to show person informtion.");
    ros::spin();

    return 0;
}

• 2、 stay learning_sevice The next path src Create files and write person_client.cpp Program

#include <ros/ros.h>
#include "learning_service/Person.h"

int main(int argc, char** argv)
{
    
    //  initialization ROS node 
	ros::init(argc, argv, "person_client");
    //  Create node handle 
	ros::NodeHandle node;
	
    //  Find out /spawn After service , Create a service client , The connection name is /spawn Of service
	ros::service::waitForService("/show_person");
	ros::ServiceClient person_client = node.serviceClient<learning_service::Person>("/show_person");

    //  initialization learning_service::Person Request data for 
	learning_service::Person srv;
	srv.request.name = "Tom";
	srv.request.age  = 20;
	srv.request.sex  = learning_service::Person::Request::male;

    //  Request service call 
	ROS_INFO("Call service to show person[name:%s, age:%d, sex:%d]", 
			 srv.request.name.c_str(), srv.request.age, srv.request.sex);

	person_client.call(srv);
	//  Display the service call result 
	ROS_INFO("Show person result : %s", srv.response.result.c_str());
	return 0;
};

1.3.6 Compile operation

[email protected]:~/catkin_ws$ cd ~/catkin_ws/
[email protected]:~/catkin_ws$ catkin_make