机器人操作系统ROS（13）：service of service和client

service和client的C++和Python实现方式。

• 10、先建立消息msg和服务srv基础

rosmsg/rossrv/roscp可用于生成msg和srv文件，msg文件描述message，srv文件描述request/response服务。
msg文件有可能包括header，header由时间戳和坐标组成，例如：
Header header
string child_frame_id
geometry_msgs/PoseWithCovariance pose
geometry_msgs/TwistWithCovariance twist
srv文件也类似于msg文件，包括由’—‘分开的request和response两部分，例如：
int64 A
int64 B
—
int64 Sum
10.1、建立一个简单的msg文件：
$ cd ~/catkin_ws/src/beginner_tutorials
$ mkdir msg
$ echo “int64 num” > msg/Num.msg
1.2、修改package.xml文件，由于build时候需要”message_generation”，运行时候需要 “message_runtime”，所以要在package.xml文件中添加这两者：
<build_depend>message_generation</build_depend>
<run_depend>message_runtime</run_depend>
1.3、修改CMakeLists.txt，在find_package call中添加message_generation的依赖：
catkin_package(
roscpp
rospy
std_msgs
message_generation
…)
1.4、修改CMakeLists.txt，添加运行时的依赖：
catkin_package(
# INCLUDE_DIRS include
# LIBRARIES beginner_tutorials
CATKIN_DEPENDS roscpp rospy std_msgs message_runtime
# DEPENDS system_lib
)
1.5、修改CMakeLists.txt，添加一下代码块：
add_message_files(
FILES
Num.msg
)
1.6、编辑generate_
generate_messages(
DEPENDENCIES
std_msgs
)
1.7、验证：
$ rosmsg show beginner_tutorials/Num
/int64 num

2、建立一个简单的srv文件，功能是返回两个数的和：
$ roscd beginner_tutorials
$ mkdir srv
$ vi AddTwoInts.srv
int64 a
int64 b
—
int64 sum
2.2、如果有必要，修改package.xml文件，添加这build和runtime时候的消息：
<build_depend>message_generation</build_depend>
<run_depend>message_runtime</run_depend>
2.3、如果必要，修改CMakeLists.txt，在find_package call中添加message_generation的依赖：
catkin_package(
roscpp
rospy
std_msgs
message_generation
…)
2.4、修改CMakeLists.txt，添加一下代码块：
add_service_files(
FILES
AddTwoInts.srv
)
2.5、可以检查：
$ rossrv show AddTwoInts
int64 a
int64 b
—
int64 sum

• 14、service 和client（C++）

1、建立service的node：
$ cd ~/catkin_ws/src/beginner_tutorials/src
$ vi add_two_ints_server.cpp
#include “ros/ros.h”
#include “beginner_tutorials/AddTwoInts.h”//由以前AddTwoInts.srv生成的头文件
bool add(beginner_tutorials::AddTwoInts::Request  &req,beginner_tutorials::AddTwoInts::Response &res) { //提供的服务，request和response的类型由AddTwoInts.srv文件定义，返回类型是boolean。
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, “add_two_ints_server”);
ros::NodeHandle n;
ros::ServiceServer service = n.advertiseService(“add_two_ints”, add);//服务建立，并广播
ROS_INFO(“Ready to add two ints.”);
ros::spin();
return 0;
}
2、vi add_two_ints_client.cpp，建立client的node：
#include “ros/ros.h”
#include “beginner_tutorials/AddTwoInts.h”
#include <cstdlib>
int main(int argc, char **argv) {
ros::init(argc, argv, “add_two_ints_client”);
if (argc != 3) {
ROS_INFO(“usage: add_two_ints_client X Y”);
return 1;
}
ros::NodeHandle n;
ros::ServiceClient client = n.serviceClient<beginner_tutorials::AddTwoInts>(“add_two_ints”); //建立ros::ServiceClient对象，用于后面调用服务
beginner_tutorials::AddTwoInts srv; //实例化这个类
srv.request.a = atoll(argv[1]);
srv.request.b = atoll(argv[2]);
if (client.call(srv)) //调用服务
ROS_INFO(“Sum: %ld”, (long int)srv.response.sum);
else {
ROS_ERROR(“Failed to call service add_two_ints”);
return 1;
}
return 0;
}
3、如果必要，修改CMakeLists.txt：
add_executable(add_two_ints_server src/add_two_ints_server.cpp)
target_link_libraries(add_two_ints_server ${catkin_LIBRARIES})
add_dependencies(add_two_ints_server beginner_tutorials_gencpp)
add_executable(add_two_ints_client src/add_two_ints_client.cpp)
target_link_libraries(add_two_ints_client ${catkin_LIBRARIES})
add_dependencies(add_two_ints_client beginner_tutorials_gencpp)
4、build：
$ cd ~/catkin_ws
$ catkin_make
4、测试
运行service
$ rosrun beginner_tutorials add_two_ints_server
[ INFO] [1465192131.709699255]: Ready to add two ints.
…
运行client
$ rosrun beginner_tutorials add_two_ints_client 1 3
[ INFO] [1465192219.751503941]: request: x=1, y=3
[ INFO] [1465192219.751688678]: sending back response: [4]
…

• 15、service 和client（Python）

1、建立service的node：
$ cd ~/catkin_ws/src/beginner_tutorials/scripts
$ nano add_two_ints_server.py
#!/usr/bin/env python
from beginner_tutorials.srv import *
import rospy

def handle_add_two_ints(req):
print “Returning [%s + %s = %s]”%(req.a, req.b, (req.a + req.b))
return AddTwoIntsResponse(req.a + req.b)

def add_two_ints_server():
rospy.init_node(‘add_two_ints_server’)
s = rospy.Service(‘add_two_ints’, AddTwoInts, handle_add_two_ints) #name，type，func_handler with AddTwoIntsRequest
print “Ready to add two ints.” #keeps your code from exiting until the service is shutdown.
rospy.spin()

if __name__ == “__main__”:
add_two_ints_server()

2、建立cilnet的node：
$ nano add_two_ints_client.py
#!/usr/bin/env python
import sys
import rospy
from beginner_tutorials.srv import *

def add_two_ints_client(x, y):
rospy.wait_for_service(‘add_two_ints’) # one way of calling services, blocks until the service named add_two_ints is available
try:
add_two_ints = rospy.ServiceProxy(‘add_two_ints’, AddTwoInts)
resp1 = add_two_ints(x, y)
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__”:
if len(sys.argv) == 3:
x = int(sys.argv[1])
y = int(sys.argv[2])
else:
print usage()
sys.exit(1)
print “Requesting %s+%s”%(x, y)
print “%s + %s = %s”%(x, y, add_two_ints_client(x, y))

3、测试
加权限：
$ chmod +x add_two_ints_server.py
$ chmod +x add_two_ints_client.py
build：
$ cd ~/catkin_ws
$ catkin_make
刷新：
$ source ~/.bashrc
运行：
$ rosrun beginner_tutorials add_two_ints_server.py
…
$ rosrun beginner_tutorials add_two_ints_client.py 4 5
…