客户端Client的编程实现

这一节实现一个请求创建海龟的服务

创建功能包

在catkin_ws/src中创建功能包

catkin_create_pkg learning_service roscpp rospy std_msgs geometry_msgs turtlesim

实现一个客户端

• 初始化ROS节点
• 创建一个Client实例
• 发布服务请求
• 等待Server处理之后的应答结果

/**
 * 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service
    ros::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;
};

修改CMakeLists.txt

• 设置需要编译的代码和生成的可执行文件
• 设置链接库

add_executable(turtle_spawn src/turtle_spawn.cpp)
target_link_libraries(turtle_spawn ${catkin_LIBRARIES})

编译运行

同之前一样编译后打开roscore
运行rosrun turtlesim turtlesim_node
再运行rosrun learning_service turtle_spawn

服务端Server的编程实现

实现一个服务器步骤

• 初始化ROS节点
• 创建Server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，并反馈给应答数据
  下面实现一个服务器实例，目的是实现一个服务器，在接受到请求时之后发出回应，然后发布者发布消息令海龟动起来。

#!/usr/bin/env python
# -*- coding: utf-8 -*-
# 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()

修改CMakeLists.txt

add_executable(turtle_command_server src/turtle_command_server.cpp)
target_link_libraries(turtle_command_server ${catkin_LIBRARIES})

编译运行

• 编译：catkin_make
• roscore
• rosrun turtlesim turtlesim_node
• rosrun learning_service
• turtle_command_server

• rosservice call /turtle_command "{}"