ros 自定义服务（service）数据类型

假设工作文件夹在~/catkin_ws/src/learning_service下

第一步，创建一个srv文件夹

$ mkdir srv

第2步，定义自定义数据类型，在srv文件夹下创建.srv文件，假设定义一个Person.

$ cd srv
$ vi Person.srv

Person里面包含他的名字，年龄，性别，注意service要有request和response,
"- --"上面的部分是request, 下面是response

string name
uint8 age
uint8 sex

uint8 unknown = 0
uint8 male = 1
uint8 female = 2
---
string result

第3步， 编译message
首先需要添加依赖
（1）在learning_service下的package.xml中加入如下部分

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

（2）在learning_service下的CMakeLists.txt中加入如下部分

find_package(catkin REQUIRED COMPONENTS
  geometry_msgs
  roscpp
  rospy
  std_msgs
  turtlesim
  message_generation  #added
)
....

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

################################################
## Declare ROS dynamic reconfigure parameters ##
################################################
....

catkin_package(
#  INCLUDE_DIRS include
#  LIBRARIES learning_service
   CATKIN_DEPENDS geometry_msgs roscpp rospy std_msgs turtlesim message_runtime #注释取消掉，加上message_runtime
#  DEPENDS system_lib
)

（3）编译

$ cd ~/catkin_ws
$ catkin_make

可以看到编译出来的文件

$ cd ~/catkin_ws/devel/include/learning_service
$ ls
Person.h  PersonRequest.h  PersonResponse.h

其中Person.h包含了PersonRequest和PersonResponse, 用的时候只需要include Person.h

第4步， client端代码
进入src文件夹

$ cd ~/catkin_ws/src/learning_service/src
$ vi person_client.cpp

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

int main(int argc, char** argv) {
   ros::init(argc, argv, "person_client");

   ros::NodeHandle node;

   //发现/show_person服务后，创建client, 连接/show_person的服务
   ros::service::waitForService("/show_person");
   ros::ServiceClient person_client = node.serviceClient<learning_service::Person>("/show_person");

   //初始化请求数据
   learning_service::Person srv;
   srv.request.name = "Tom";
   srv.request.age = 20;
   srv.request.sex = learning_service::Person::Request::male;

   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);

   ROS_INFO("Show person result: %s", srv.response.result.c_str());

   return 0;
}

可以看到，只需要include Person.h, Person的数据类型是learning_service::Person,
它有request和response两个部分，person_client.call(srv)调用时，它会发送出数据消息，并等待server的response,
等到response之后，输出srv.response.result, 注意ROS_INFO string类型的数据时，要转为c_str()

第5步， server端代码

$ cd ~/catkin_ws/src/learning_service/src
$ vi person_server.cpp

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

bool personCallback(learning_service::Person::Request &req,
                    learning_service::Person::Response &res) {
   ROS_INFO("Person: name:%s age:%d sex:%d", req.name.c_str(), req.age, req.sex);
   res.result = "OK";
   return true;
}

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

   ros::NodeHandle n;

   ros::ServiceServer person_service = n.advertiseService("/show_person", personCallback);

   ROS_INFO("Ready to show person information");
   ros::spin();

   return 0;
}

service名为"/show_person", ros::spin()是无限循环，一直等client发来的request,
一旦有request, 就进入回调函数personCallback, 它的参数一个是request, 一个是response。

第6步，编译cpp文件
（1）在CMakeLists.txt中加入如下部分

#added-S
add_executable(person_server src/person_server.cpp)
target_link_libraries(person_server ${catkin_LIBRARIES}) 
add_dependencies(person_server ${PROJECT_NAME}_gencpp)

add_executable(person_client src/person_client.cpp)
target_link_libraries(person_client ${catkin_LIBRARIES})
add_dependencies(person_client ${PROJECT_NAME}_gencpp)
#added-E
#############
## Install ##
#############

（2）编译

$ cd ~/catkin_ws
$ catkin_make
$ source devel/setup.bash

最后一步，运行

先运行server

$ rosrun learning_service person_server 
[ INFO] [1642040930.719064479]: Ready to show person information

再运行client

$ rosrun learning_service person_client 
[ INFO] [1642040973.332175599]: Call service to show person [name:Tom, age:20, sex:1]
[ INFO] [1642040973.334280244]: Show person result: OK

这时server端由于进入了回调函数，会出现如下信息

[ INFO] [1642040973.334187292]: Person: name:Tom age:20 sex:1

参考《古月居 ros》