ROS与Python入门教程-写简单服务端和客户端

ROS与Python入门教程-写简单服务端和客户端

说明

这一节介绍如何写服务端和客户端

定义srv服务

在beginner_tutorials,新建srv服务目录,新建AddTwoInts.srv文件

$ roscd beginner_tutorials
$ mkdir srv
$ cd srv
$ touch AddTwoInts.srv
$ rosed beginner_tutorials AddTwoInts.srv

srv文件分为请求和响应两部分，由'---'分隔。手工输入代码：

int64 A
int64 B
---
int64 Sum

打开文件rosed beginner_tutorials package.xml,增加依赖，

<build_depend>message_generation</build_depend>
<run_depend>message_runtime</run_depend>

打开文件rosed beginner_tutorials CMakeLists.txt,增加依赖,

# Do not just add this line to your CMakeLists.txt, modify the existing line
find_package(catkin REQUIRED COMPONENTS
  roscpp
  rospy
  std_msgs
 message_generation
)

在CMakeLists.txt文件，增加服务文件，取消#，并修改为

add_service_files(
   FILES
   AddTwoInts.srv
 )

在CMakeLists.txt文件，增加消息生成包，取消#，并修改为

generate_messages(
  DEPENDENCIES
  std_msgs
)

编译代码

$ cd ~/catkin_ws
$ catkin_make

检查服务

命令：

$ rossrv show beginner_tutorials/AddTwoInts

效果：

int64 a
int64 b
---
int64 sum

编写服务端节点

访问代码：

https://github.com/ros/ros_tutorials/blob/kinetic-devel/rospy_tutorials/005_add_two_ints/add_two_ints_server

在scripts目录新建add_two_ints_server.py文件

$ roscd beginner_tutorials/scripts
$ touch add_two_ints_server.py
$ chmod +x add_two_ints_server.py
$ rosed beginner_tutorials add_two_ints_server.py

手工输入如下代码：

#!/usr/bin/env python

NAME = 'add_two_ints_server'

# import the AddTwoInts service
from beginner_tutorials.srv import *
import rospy 

def add_two_ints(req):
    print("Returning [%s + %s = %s]" % (req.a, req.b, (req.a + req.b)))
    sum = req.a + req.b
    return AddTwoIntsResponse(sum)

def add_two_ints_server():
    rospy.init_node(NAME)
    s = rospy.Service('add_two_ints', AddTwoInts, add_two_ints)
    print "Ready to add Two Ints"
    # spin() keeps Python from exiting until node is shutdown
    rospy.spin()

if __name__ == "__main__":
    add_two_ints_server()

代码分析

代码：from beginner_tutorials.srv import *
分析：导入定义的服务
代码：s = rospy.Service('add_two_ints', AddTwoInts, add_two_ints)
分析：
- 定义服务节点名称，服务的类型，处理函数。
- 处理函数调用实例化的AddTwoIntsRequest接收请求和返回实例化的AddTwoIntsResponse
- 参考rospy.Service API
代码：return AddTwoIntsResponse(sum)
分析：AddTwoIntsResponse由服务生成的返回函数

编译代码

$ cd ~/catkin_ws/
$ catkin_make

测试代码

打开新终端，启动add_two_ints_server.py

$ rosrun beginner_tutorials add_two_ints_server.py

打开新终端，列出服务

$ rosservice list

/add_two_ints
/add_two_ints_server/get_loggers
/add_two_ints_server/set_logger_level
/rosout/get_loggers
/rosout/set_logger_level

查看服务参数类型

$ rosservice args /add_two_ints
A B

调用服务

$ rosservice call /add_two_ints 1 2
sum: 3

启动的服务端显示

$ rosrun beginner_tutorials add_two_ints_server.py 
Ready to add Two Ints
Returning [1 + 2 = 3]
Returning [1 + 4 = 5]
Returning [1 + 3 = 4]

编写客户端节点

访问代码：

https://github.com/ros/ros_tutorials/blob/kinetic-devel/rospy_tutorials/005_add_two_ints/add_two_ints_client

在scripts目录新建add_two_ints_client.py文件

$ roscd beginner_tutorials/scripts
$ touch add_two_ints_client.py
$ chmod +x add_two_ints_client.py
$ rosed beginner_tutorials add_two_ints_client.py

手工输入如下代码：

#!/usr/bin/env python

import sys
import os

import rospy

# imports the AddTwoInts service 
from rospy_tutorials.srv import *

## add two numbers using the add_two_ints service
## @param x int: first number to add
## @param y int: second number to add
def add_two_ints_client(x, y):

    # NOTE: you don't have to call rospy.init_node() to make calls against
    # a service. This is because service clients do not have to be
    # nodes.

    # block until the add_two_ints service is available
    # you can optionally specify a timeout
    rospy.wait_for_service('add_two_ints')
    
    try:
        # create a handle to the add_two_ints service
        add_two_ints = rospy.ServiceProxy('add_two_ints', AddTwoInts)
        
        print "Requesting %s+%s"%(x, y)
        
        # simplified style
        resp1 = add_two_ints(x, y)

        # formal style
        resp2 = add_two_ints.call(AddTwoIntsRequest(x, y))

        if not resp1.sum == (x + y):
            raise Exception("test failure, returned sum was %s"%resp1.sum)
        if not resp2.sum == (x + y):
            raise Exception("test failure, returned sum was %s"%resp2.sum)
        return resp1.sum
    except rospy.ServiceException, e:
        print "Service call failed: %s"%e

def usage():
    return "%s [x y]"%sys.argv[0]

if __name__ == "__main__":
    
    argv = rospy.myargv()
    if len(argv) == 1:
        import random
        x = random.randint(-50000, 50000)
        y = random.randint(-50000, 50000)
    elif len(argv) == 3:
        try:
            x = int(argv[1])
            y = int(argv[2])
        except:
            print usage()
            sys.exit(1)
    else:
        print usage()
        sys.exit(1)
    print "%s + %s = %s"%(x, y, add_two_ints_client(x, y))

代码分析

代码：rospy.wait_for_service('add_two_ints')
分析：等待接入服务节点，参考rospy.wait_for_service api
代码：add_two_ints = rospy.ServiceProxy('add_two_ints', AddTwoInts)
分析：创建服务的处理句柄，参考rospy.ServiceProxy api

编译代码

$ cd ~/catkin_ws/
$ catkin_make

测试代码

命令：

$ rosrun beginner_tutorials add_two_ints_client.py 4 5

效果：

Requesting 4+5
4 + 5 = 9

服务器输出

Returning [4 + 5 = 9]

制作launch文件

进入bringup目录，新建server_client.launch，用来启动add_two_ints_server.py

$ roscd beginner_tutorials/bringup
$ touch server_client.launch
$ rosed beginner_tutorials server_client.launch

手工输入如下代码：

<launch>
    <node name="server" pkg="beginner_tutorials" type="add_two_ints_server.py" />
</launch>

启动server_client.launch

命令：

$ roslaunch beginner_tutorials server_client.launch

效果：

started roslaunch server http://192.168.0.105:38839/

SUMMARY
========

PARAMETERS
 * /rosdistro: indigo
 * /rosversion: 1.11.16

NODES
  /
    service (beginner_tutorials/add_two_ints_server.py)

ROS_MASTER_URI=http://192.168.0.88:11311

core service [/rosout] found
process[service-1]: started with pid [32174]

运行客户端节点即可获得结果

$ rosrun beginner_tutorials add_two_ints_client.py 4 5

参考：

http://wiki.ros.org/rospy/Overview/Services
http://wiki.ros.org/srv

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