Service creation and operation example of ROS

Reference resources
ROS Official website Wiki— establish ROS Messages and services
ROS Official website Wiki— Write simple services and clients （C++）
ROS Official website Wiki— Verify simple services and clients

In front of
ROS Logical view of
ROS Working space for

The sample code is intuitive , Go straight to the code

Definition of service message

First, enter the created package

$ roscd beginner_tutorials
$ mkdir srv

Define the service file

Define service messages srv file ``, The content is as follows ,--- Above is request (Request) Content ,--- The following is the response (Response) Content .

int64 A
int64 B
---
int64 Sum

This file is available from rospy_tutorials Copy

# roscp [package_name] [file_to_copy_path] [copy_path]
$ roscp rospy_tutorials AddTwoInts.srv srv/AddTwoInts.srv

Set up srv File compilation information

stay packages.xml Add the configuration

  <build_depend>message_generation</build_depend> #  Compile time dependent Libraries 
  <exec_depend>message_runtime</exec_depend>      #  Runtime dependent Libraries 

stay CMakeLists.txt Make the following settings in

#  add to ROS Dependency Library 
find_package(catkin REQUIRED COMPONENTS
   roscpp
   rospy
   std_msgs		#  Standard information , Basic data supported by the system , Such as int,float,...
   message_generation #  take *.srv The file to C++/Python Code 
                      #  stay  packages.xml  Has added 
)

#  Add just written *.srv file 
add_service_files(
   FILES
   AddTwoInts.srv
)

View the generated srv Information

# rossrv show <service type>
$ rossrv show beginner_tutorials/AddTwoInts

Publisher code

#include "ros/ros.h" // ROS  System header file 
#include "beginner_tutorials/AddTwoInts.h" //  The code generated by the previous service definition 

//  Callback function 
bool add(beginner_tutorials::AddTwoInts::Request  &req,
         beginner_tutorials::AddTwoInts::Response &res)
{
    
  res.sum = req.a + req.b;
  ROS_INFO("request: x=%ld, y=%ld", (long int)req.a, (long int)req.b);
  ROS_INFO("sending back response: [%ld]", (long int)res.sum);
  return true;
}

int main(int argc, char **argv)
{
    
  //  Parameters 1、2： Command line arguments 
  //  Parameters 3： The node name , Node names cannot conflict ！！！
  ros::init(argc, argv, "add_two_ints_server");
  
  // ROS  System handle 
  //  The first to apply for resources , The last handle destroys all requested resources 
  ros::NodeHandle n;
  
  //  Create a "add_two_ints" Service for , The callback function is "add(...)"
  ros::ServiceServer service = n.advertiseService("add_two_ints", add);
  ROS_INFO("Ready to add two ints.");
  
  //  Loop response request , until ros::ok() return false
  ros::spin();

  return 0;
}

Client code

#include "ros/ros.h"
#include "beginner_tutorials/AddTwoInts.h" //  The code generated by the previous service definition 
#include <cstdlib>

int main(int argc, char **argv)
{
    
  ros::init(argc, argv, "add_two_ints_client");
  if (argc != 3)
  {
    
    ROS_INFO("usage: add_two_ints_client X Y");
    return 1;
  }

  ros::NodeHandle n;

  //  establish client End , The message type of the publish request is "beginner_tutorials::AddTwoInts"
  //  The service to be requested is named "add_two_ints", See the server code above 
  ros::ServiceClient client = n.serviceClient<beginner_tutorials::AddTwoInts>("add_two_ints");
  
  //  Create message object , And fill in the data 
  beginner_tutorials::AddTwoInts srv;
  srv.request.a = atoll(argv[1]);
  srv.request.b = atoll(argv[2]);
  
  //  Request service 
  if (client.call(srv))
  {
    
    ROS_INFO("Sum: %ld", (long int)srv.response.sum);
  }
  else
  {
    
    ROS_ERROR("Failed to call service add_two_ints");
    return 1;
  }

  return 0;
}

Building a node

edit beginner_tutorials Inside CMakeLists.txt file , The file is located in ~/catkin_ws/src/beginner_tutorials/CMakeLists.txt.

add_executable(add_two_ints_server src/add_two_ints_server.cpp)
target_link_libraries(add_two_ints_server ${catkin_LIBRARIES})
add_dependencies(add_two_ints_server beginner_tutorials_gencpp)

add_executable(add_two_ints_client src/add_two_ints_client.cpp)
target_link_libraries(add_two_ints_client ${catkin_LIBRARIES})
add_dependencies(add_two_ints_client beginner_tutorials_gencpp)

Built executable add_two_ints_server and add_two_ints_client By default, it is placed in the package directory devel In the space , namely ~/catkin_ws/devel/lib/<package name>.
You can directly call to generate an executable file , You can also use rosrun To call .

Inspection node

Operation service

$ rosrun beginner_tutorials add_two_ints_server     # (C++)

Running client

$ rosrun beginner_tutorials add_two_ints_client 1 3     # (C++)

Running results

Requesting 1+3
1 + 3 = 4