關鍵術語

服務檔案(.srv)：服務檔案的副檔名是.srv，本質上是一個txt檔案，開發者可以在建立的服務檔案中自定義需要的服務格式，由於服務欄位中的欄位型別是來自其他功能包，因此需要在package.xml檔案及CMakeLists.txt檔案中包含定義了欄位型別的功能包，服務檔案由兩個部分組成。分別時請求和響應，兩者通過---間隔開來.

建立工作空間(workspace)

mkdir -p ~/catkin_ws/src
cd ~/catkin_ws/src
catkin_init_workspace
cd ..
catkin_make

建立功能包(package)

cd
 
 ~/catkin_ws/src
catkin_create_pkg custom_srv_service roscpp std_msgs message_generation message_runtime
cd ..
catkin_make

向功能包新增自定義服務檔案(.srv)

roscd custom_srv_service
mkdir srv && cd srv
gedit custom_srv.srv

輸入如下的內容：

int64 a
int64 b

---
int64 sum

修改CMakeLists.txt檔案

cmake_minimum_required
 
(VERSION 2.8.3)
project(custom_srv_service)
find_package(catkin REQUIRED COMPONENTS
  roscpp
  std_msgs
  message_generation
)
add_service_files(
  FILES
  custom_srv.srv
)
generate_messages(
  DEPENDENCIES
  std_msgs
)
catkin_package(
  LIBRARIES custom_srv_service
  CATKIN_DEPENDS
)
include_directories
 
(
  ${catkin_INCLUDE_DIRS}
)

構建生成服務型別標頭檔案

cd ~/catkin_ws
catkin_make

檢查生成的自定義的服務型別是否正確：

$ rossrv show custom_srv_service/custom_srv
int64 a
int64 b
---
int64 sum

根據輸出的結果可知，輸出與定義完全一致.

建立服務伺服器(server)節點

#include "ros/ros.h"
#include "custom_srv_service/custom_srv.h"

bool add(custom_srv_service::custom_srv::Request  &req,
         custom_srv_service::custom_srv::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)
{
  ros::init(argc, argv, "custom_srv_server");

  ros::NodeHandle nh;
  ros::ServiceServer service = nh.advertiseService("add_two_ints", add);

  ROS_INFO("Ready to add two ints!");
  ros::spin();

  return 0;
}

建立服務客戶端(client)節點

#include "ros/ros.h"
#include "custom_srv_service/custom_srv.h"
#include <cstdlib>

int main(int argc, char **argv)
{
  ros::init(argc, argv, "custom_srv_client");
  if (argc != 3){
    ROS_INFO("usage: rosrun package_name executable_name arguments");
    return 1;
  }

  ros::NodeHandle nh;
  ros::ServiceClient client = nh.serviceClient<custom_srv_service::custom_srv>("add_two_ints");

  custom_srv_service::custom_srv srv;
  srv.request.a = atol(argv[1]);
  srv.request.b = atol(argv[2]);

  if (client.call(srv)){
    ROS_INFO("with the given [%ld] and [%ld],the sum is: [%ld]", srv.request.a, srv.request.b, (long int)srv.response.sum);
  }
  else{
    ROS_ERROR("Failed to call service: add_two_ints");
    return 1;
  }
  return 0;
}

修改CMakeLists.txt檔案

cmake_minimum_required(VERSION 2.8.3)
project(custom_srv_service)
find_package(catkin REQUIRED COMPONENTS
  roscpp
  std_msgs
  message_generation
)
add_service_files(
  FILES
  custom_srv.srv
)
generate_messages(
  DEPENDENCIES
  std_msgs
)
catkin_package(
  LIBRARIES custom_srv_service
  CATKIN_DEPENDS
)
include_directories(
  ${catkin_INCLUDE_DIRS}
)

#下面是新增加的內容
add_executable(custom_srv_server src/custom_srv_server.cpp)
add_executable(custom_srv_client src/custom_srv_client.cpp)
add_dependencies(custom_srv_server ${${PROJECT_NAME}_EXPORTED_TARGETS} ${catkin_EXPORTED_TARGETS})
add_dependencies(custom_srv_client ${${PROJECT_NAME}_EXPORTED_TARGETS} ${catkin_EXPORTED_TARGETS})
target_link_libraries(custom_srv_server ${catkin_LIBRARIES})
target_link_libraries(custom_srv_client ${catkin_LIBRARIES})

構建功能包，執行自定義服務的節點程式

執行服務伺服器節點程式

rosrun custom_srv_service custom_srv_server

執行服務客戶端節點程式

rosrun custom_srv_service custom_srv_client 12 23

至此，編寫基於服務的節點程式就此完成了.
Enjoy It!