7、客户端Client的编程实现

1. 创建功能包

cd ~/catkin_ws/src
catkin_create_pkg learning_service roscpp rospy std_msgs geometry_msgs
turtlesim

2. 创建客户端代码(C++) ——文件名为turtle_spawn.cpp

/***********************************************************************
Copyright 2020 GuYueHome (www.guyuehome.com).
***********************************************************************/
/**
* 该例程将请求/spawn服务,服务数据类型turtlesim::Spawn
*/
#include <ros/ros.h>
#include <turtlesim/Spawn.h>
int main(int argc, char** argv)
{
// 初始化ROS节点
ros::init(argc, argv, "turtle_spawn");
// 创建节点句柄
ros::NodeHandle node;
// 发现/spawn服务后,创建一个服务客户端,连接名为/spawn的serviceros::service::waitForService("/spawn");
ros::ServiceClient add_turtle = node.serviceClient<turtlesim::Spawn>
("/spawn");
// 初始化turtlesim::Spawn的请求数据
turtlesim::Spawn srv;
srv.request.x = 2.0;
srv.request.y = 2.0;
srv.request.name = "turtle2";
// 请求服务调用
ROS_INFO("Call service to spwan turtle[x:%0.6f, y:%0.6f, name:%s]",
srv.request.x, srv.request.y, srv.request.name.c_str());
add_turtle.call(srv);
// 显示服务调用结果
ROS_INFO("Spwan turtle successfully [name:%s]",
srv.response.name.c_str());
return 0;
};

总结上面的代码,实现一个客户端的步骤为:
初始化ROS节点
创建一个Client实例
发布服务请求数据
等待Server处理后的应答结果
python代码如下:

#!/usr/bin/env python
# -*- coding: utf-8 -*-
########################################################################
####
Copyright 2020 GuYueHome (www.guyuehome.com).
###
########################################################################
# 该例程将请求/spawn服务,服务数据类型turtlesim::Spawn
import sys
import rospy
from turtlesim.srv import Spawn
def turtle_spawn():
# ROS节点初始化
rospy.init_node('turtle_spawn')
# 发现/spawn服务后,创建一个服务客户端,连接名为/spawn的service


rospy.wait_for_service('/spawn')
try:
add_turtle = rospy.ServiceProxy('/spawn', Spawn)


# 请求服务调用,输入请求数据
response = add_turtle(2.0, 2.0, 0.0, "turtle2")return response.name
except rospy.ServiceException, e:
print "Service call failed: %s"%e
if __name__ == "__main__":
#服务调用并显示调用结果
print "Spwan turtle successfully [name:%s]" %(turtle_spawn())

3. 配置客户端代码编译规则
   设置需要的编译的代码和生成的可执行文件

add_executable(turtle_spawn src/turtle_spawn.cpp)

设置链接库

target_link_libraries(turtle_spawn ${catkin_LIBRARIES})

4. 编译并运行客户端

cd ~/catkin_ws
catkin_make
roscore
rosrun turtlesim turtlesim_node
rosrun learning_service turtle_spawn

运行结果如下,在坐标(2,2)处产生了一只新的乌龟。

8、服务端Server的编程实现

1. 创建服务器代码(C++) ——文件名为turtle_command_server.cpp

/***********************************************************************
Copyright 2020 GuYueHome (www.guyuehome.com).
***********************************************************************/
/**
* 该例程将执行/turtle_command服务,服务数据类型std_srvs/Trigger
*/
#include <ros/ros.h>
#include <geometry_msgs/Twist.h>
#include <std_srvs/Trigger.h>
ros::Publisher turtle_vel_pub;
bool pubCommand = false;
// service回调函数,输入参数req,输出参数res
bool commandCallback(std_srvs::Trigger::Request
&req,
std_srvs::Trigger::Response &res)
{
pubCommand = !pubCommand;
// 显示请求数据
ROS_INFO("Publish turtle velocity command [%s]",
pubCommand==true?"Yes":"No");
// 设置反馈数据
res.success = true;
res.message = "Change turtle command state!";
return true;
}
int main(int argc, char **argv)
{
// ROS节点初始化
ros::init(argc, argv, "turtle_command_server");
// 创建节点句柄
ros::NodeHandle n;
// 创建一个名为/turtle_command的server,注册回调函数commandCallback
ros::ServiceServer command_service =
n.advertiseService("/turtle_command", commandCallback);
// 创建一个Publisher,发布名为/turtle1/cmd_vel的topic,消息类型为
geometry_msgs::Twist,队列长度10
turtle_vel_pub = n.advertise<geometry_msgs::Twist>("/turtle1/cmd_vel",
10);
// 循环等待回调函数
ROS_INFO("Ready to receive turtle command.");
// 设置循环的频率
ros::Rate loop_rate(10);
while(ros::ok())
{// 查看一次回调函数队列
ros::spinOnce();
// 如果标志为true,则发布速度指令
if(pubCommand)
{
geometry_msgs::Twist vel_msg;
vel_msg.linear.x = 0.5;
vel_msg.angular.z = 0.2;
turtle_vel_pub.publish(vel_msg);
}
//按照循环频率延时
loop_rate.sleep();
}
return 0;
}

总结上面的代码,实现一个服务器的步骤为:
初始化ROS节点
创建Serveer实例
循环等待服务请求,进入回调函数
在回调函数中完成服务功能的处理,并反馈应答数据
python代码如下:

#!/usr/bin/env python
# -*- coding: utf-8 -*-
########################################################################
####
Copyright 2020 GuYueHome (www.guyuehome.com).
###
########################################################################
# 该例程将执行/turtle_command服务,服务数据类型std_srvs/Trigger
import rospy
import thread,time
from geometry_msgs.msg import Twist
from std_srvs.srv import Trigger, TriggerResponse
pubCommand = False;
turtle_vel_pub = rospy.Publisher('/turtle1/cmd_vel', Twist, queue_size=10)
def command_thread():
while True:
if pubCommand:
vel_msg = Twist()
vel_msg.linear.x = 0.5
vel_msg.angular.z = 0.2
turtle_vel_pub.publish(vel_msg)
time.sleep(0.1)
def commandCallback(req):global pubCommand
pubCommand = bool(1-pubCommand)
# 显示请求数据
rospy.loginfo("Publish turtle velocity command![%d]", pubCommand)
# 反馈数据
return TriggerResponse(1, "Change turtle command state!")
def turtle_command_server():
# ROS节点初始化
rospy.init_node('turtle_command_server')
# 创建一个名为/turtle_command的server,注册回调函数commandCallback
s = rospy.Service('/turtle_command', Trigger, commandCallback)
# 循环等待回调函数
print "Ready to receive turtle command."
thread.start_new_thread(command_thread, ())
rospy.spin()
if __name__ == "__main__":
turtle_command_server()

2. 配置服务器代码编译规则
   设置需要编译的代码和生成可执行文件

add_executable(turtle_command_server src/turtle_command_server.cpp)

设置链接库

target_link_libraries(turtle_command_server ${catkin_LIBRARIES})

3. 编译并运行服务器

cd ~/catkin_ws
catkin_make
roscore
rosrun turtlesim turtlesim_node
rosrun learning_service turtle_command_server
rosservice call /turtle_command "{}"

运行结果如下,可以发现可以通过客户端发送请求,然后达到控制海龟的运动和停止。

9、自定义服务数据

1. 自定义服务数据

定义srv文件

//在learning_service目录下创建srv文件夹
cd ~/catkin_ws/src/learning_topic
mkdir srv
//创建Penson.srv文件
touch Person.srv

创建好Person.srv文件后,在文件中写入以下内容:

string name
uint8 sex
uint8 age
uint8 unknown = 0
uint8 male = 1
uint8 female = 2
---
string result

在package.xml中添加功能包依赖

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

在CMakeLists.txt中添加编译选项

find_package( ...... message_generation)add_service_files(FILES Person.srv)
generate_messages(DEPENDENCIES std_msgs)
catkin_package(...... message_runtime)

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

catkin_package(…… message_runtime)

编译生成语言相关文件

cd ~/catkin_ws
catkin_make

2. 创建服务器代码(C++)——文件名为person_server.cpp

/***********************************************************************
Copyright 2020 GuYueHome (www.guyuehome.com).
***********************************************************************/
/**
* 该例程将执行/show_person服务,服务数据类型learning_service::Person
*/
#include <ros/ros.h>
#include "learning_service/Person.h"
// service回调函数,输入参数req,输出参数res
bool personCallback(learning_service::Person::Request
&req,
learning_service::Person::Response &res)
{// 显示请求数据
ROS_INFO("Person: name:%s
age:%d
sex:%d", req.name.c_str(), req.age,
req.sex);
// 设置反馈数据
res.result = "OK";
return true;
}
int main(int argc, char **argv)
{
// ROS节点初始化
ros::init(argc, argv, "person_server");
// 创建节点句柄
ros::NodeHandle n;
// 创建一个名为/show_person的server,注册回调函数personCallback
ros::ServiceServer person_service = n.advertiseService("/show_person",
personCallback);
// 循环等待回调函数
ROS_INFO("Ready to show person informtion.");
ros::spin();
return 0;
}

该部分和之前的步骤基本一致,这里不再进行总结。
python代码如下:

#!/usr/bin/env python
# -*- coding: utf-8 -*-
########################################################################
####
Copyright 2020 GuYueHome (www.guyuehome.com).
###
########################################################################
# 该例程将执行/show_person服务,服务数据类型learning_service::Person
import rospy
from learning_service.srv import Person, PersonResponse
def personCallback(req):
# 显示请求数据
rospy.loginfo("Person: name:%s
req.sex)
# 反馈数据
return PersonResponse("OK")
def person_server():
age:%d
sex:%d", req.name, req.age,# ROS节点初始化
rospy.init_node('person_server')
# 创建一个名为/show_person的server,注册回调函数personCallback
s = rospy.Service('/show_person', Person, personCallback)
# 循环等待回调函数
print "Ready to show person informtion."
rospy.spin()
if __name__ == "__main__":
person_server()

3. 创建客户端代码(C++)——文件名为person_client.cpp

/***********************************************************************
Copyright 2020 GuYueHome (www.guyuehome.com).
***********************************************************************/
/**
* 该例程将请求/show_person服务,服务数据类型learning_service::Person
*/
#include <ros/ros.h>
#include "learning_service/Person.h"
int main(int argc, char** argv)
{
// 初始化ROS节点
ros::init(argc, argv, "person_client");
// 创建节点句柄
ros::NodeHandle node;
// 发现/spawn服务后,创建一个服务客户端,连接名为/spawn的service
ros::service::waitForService("/show_person");
ros::ServiceClient person_client =
node.serviceClient<learning_service::Person>("/show_person");
// 初始化learning_service::Person的请求数据
learning_service::Person srv;
srv.request.name = "Tom";
srv.request.age = 20;
srv.request.sex = learning_service::Person::Request::male;
// 请求服务调用
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);
// 显示服务调用结果
ROS_INFO("Show person result : %s", srv.response.result.c_str());return 0;
};

python代码如下:

#!/usr/bin/env python
# -*- coding: utf-8 -*-
########################################################################
####
Copyright 2020 GuYueHome (www.guyuehome.com).
###
########################################################################
# 该例程将请求/show_person服务,服务数据类型learning_service::Person
import sys
import rospy
from learning_service.srv import Person, PersonRequest
def person_client():
# ROS节点初始化
rospy.init_node('person_client')
# 发现/spawn服务后,创建一个服务客户端,连接名为/spawn的service
rospy.wait_for_service('/show_person')
try:
person_client = rospy.ServiceProxy('/show_person', Person)
# 请求服务调用,输入请求数据
response = person_client("Tom", 20, PersonRequest.male)
return response.result
except rospy.ServiceException, e:
print "Service call failed: %s"%e
if __name__ == "__main__":
#服务调用并显示调用结果
print "Show person result : %s" %(person_client())

4. 配置服务器/客户端代码编译规则
   设置需要编译的代码和可执行文件
   设置链接库
   添加依赖项

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)

5. 编译并运行客户端和服务器

cd ~/catkin_ws
catkin_make
roscore
rosrun learning_service person_server
rosrun learning_service person_client

运行结果如下,可以发现每次客户端发送请求后,服务器做出响应。

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