python网络编程学习笔记(三)：socket网络服务器
1、TCP连接的建立方法
客户端在建立一个TCP连接时一般需要两步，而服务器的这个过程需要四步，具体见下面的比较。
| 步骤 | TCP客户端 | TCP服务器 |
| 第一步 | 建立socket对象 | 建立socket对象 |
| 第二步 | 调用connect()建立一个和服务器的连接 | 设置socket选项（可选） |
| 第三步 | 无 | 绑定到一个端口（也可以是一个指定的网卡） |
| 第四步 | 无 | 侦听连接 |
下面具体来讲这四步的建立方法：
第一步，建立socket对象：这里与客户端一样，依然是：
s=socket.socket(socket.AF_INET,socket.SOCK_STREAM)
第二步，设置和得到socket选项
python定义了setsockopt()和getsockopt()，一个是设置选项，一个是得到设置。这里主要使用setsockopt()，具体结构如下：
setsockopt(level,optname,value)
level定义了哪个选项将被使用。通常情况下是SOL_SOCKET，意思是正在使用的socket选项。它还可以通过设置一个特殊协议号码来设置协议选项，然而对于一个给定的操作系统，大多数协议选项都是明确的，所以为了简便，它们很少用于为移动设备设计的应用程序。
optname参数提供使用的特殊选项。关于可用选项的设置，会因为操作系统的不同而有少许不同。如果level选定了SOL_SOCKET，那么一些常用的选项见下表：
|
选项 |
意义 |
期望值 |
|
SO_BINDTODEVICE |
可以使socket只在某个特殊的网络接口（网卡）有效。也许不能是移动便携设备 |
一个字符串给出设备的名称或者一个空字符串返回默认值 |
|
SO_BROADCAST |
允许广播地址发送和接收信息包。只对UDP有效。如何发送和接收广播信息包 |
布尔型整数 |
|
SO_DONTROUTE |
禁止通过路由器和网关往外发送信息包。这主要是为了安全而用在以太网上UDP通信的一种方法。不管目的地址使用什么IP地址，都可以防止数据离开本地网络 |
布尔型整数 |
|
SO_KEEPALIVE |
可以使TCP通信的信息包保持连续性。这些信息包可以在没有信息传输的时候，使通信的双方确定连接是保持的 |
布尔型整数 |
|
SO_OOBINLINE |
可以把收到的不正常数据看成是正常的数据，也就是说会通过一个标准的对recv()的调用来接收这些数据 |
布尔型整数 |
|
SO_REUSEADDR |
当socket关闭后，本地端用于该socket的端口号立刻就可以被重用。通常来说，只有经过系统定义一段时间后，才能被重用。 |
布尔型整数 |
本节在学习时，用到了SO_REUSEADDR选项，具体写法是：
S.setsockopt(socket.SOL_SOCKET,socket.SO_REUSEADDR,1) 这里value设置为1，表示将SO_REUSEADDR标记为TRUE，操作系统会在服务器socket被关闭或服务器进程终止后马上释放该服务器的端口，否则操作系统会保留几分钟该端口。
下面的方法可以帮助给出该系统下python所支持的socket选项列表：
import socket
solist=[x for x in dir(socket) if x.startswith('SO_')]
solist.sort()
for x in solist:
Print x
第三步：绑定socket
绑定即为服务器要求一个端口号。
S.bind((host,port))，其中host为服务器ip，通常为空，也可以绑定到一个特定的ip地址。Port为端口号。
第四步：侦听连接。
利用listen()函数进行侦听连接。该函数只有一个参数，其指明了在服务器实际处理连接的时候，允许有多少个未决（等待）的连接在队列中等待。作为一个约定，很多人设置为5。如：s.listen(5)
2、简单的TCP服务器实例
这个建立一个简单的TCP服务器和客户端。
服务器端：TCP响应服务器，当与客户端建立连接后，服务器显示客户端ip和端口，同时将接收的客户端信息和'I get it!'传给客户端，此时等待输入一个新的信息传给客户端。
客户端：TCP客户端,首先输入服务器ip地址，然后输入信息，回车后会得到服务器返回信息，然后等待服务器向其发送信息后退出。
具体代码如下：
服务器端：tcpserver.py
# -*- coding: cp936 -*-
##tcp响应服务器，当与客户端建立连接后，服务器显示客户端ip和端口，同时将接收的客户端信息和'I get it!'传给客户端，此时等待输入一个新的信息传给客户端。
##@小五义
import socket,traceback
host=''
port=12345
s=socket.socket(socket.AF_INET,socket.SOCK_STREAM)
s.setsockopt(socket.SOL_SOCKET,socket.SO_REUSEADDR,1)
s.bind((host,port))
s.listen(1)
while 1:
try:
clientsock,clientaddr=s.accept()
except KeyboardInterrupt:
raise
except:
traceback.print_exc()
continue
try:
print "连接来自：",clientsock.getpeername()
while 1:
data=clientsock.recv(4096)
if not len(data):
break
print clientsock.getpeername()[0]+':'+str(data)
clientsock.sendall(data)
clientsock.sendall("\nI get it!\n")
t=raw_input('input the word:')
clientsock.sendall(t)
except (KeyboardInterrupt,SystemExit):
raise
except:
traceback.print_exc()
try:
clientsock.close()
except KeyboardInterrupt:
raise
except:
traceback.print_exc()
客户端：tcpclient.py
# -*- coding: cp936 -*-
##tcp客户端,首先输入服务器ip地址，然后输入信息，回车后会得到服务器返回信息，然后等待服务器向其发送信息后退出。
##@小五义
import socket,sys
port=12345
host=raw_input('输入服务器ip:')
data=raw_input('输入要发送的信息：')
s=socket.socket(socket.AF_INET,socket.SOCK_STREAM)
try:
s.connect((host,port))
except:
print '连接错误！'
s.send(data)
s.shutdown(1)
print '发送完成。'
while 1:
buf=s.recv(4096)
if not len(buf):
break
sys.stdout.write(buf)
执行结果：
客户端输入hello，服务器端输入ok，具体显示结果是：
服务器端：
连接来自：('127.0.0.1',1945)
127.0.0.1:hello
Input the world:ok
客户端：
输入服务器ip:127.0.0.1
输入要发送的信息：hello
发送完成。
hello
I get it!
ok
3、UDP服务器
UDP服务器建立与TCP相类似，具体比较如下：
|
步骤 |
UDP |
TCP |
|
第一步 |
建立socket对象 |
建立socket对象 |
|
第二步 |
设置socket选项 |
设置socket选项 |
|
第三步 |
绑定到一个端口 |
绑定到一个端口 |
|
第四步 |
Recvfrom() |
侦听连接listen |
这里利用UDP建立一个时间服务器。
代码如下：
服务器端;serverudp.py
# -*- coding: cp936 -*-
##UDP服务器端,客户端连接后，向其发送当前时间
##@小五义
import socket,traceback,time,struct
host=''
port=12345
s=socket.socket(socket.AF_INET,socket.SOCK_DGRAM)
s.setsockopt(socket.SOL_SOCKET,socket.SO_REUSEADDR,1)
s.bind((host,port))
while 1:
try:
message,address=s.recvfrom(8192)
secs=int(time.time())
reply=struct.pack("!I",secs)
s.sendto(reply,address)
except (KeyboardInterrupt,SystemExit):
raise
except:
traceback.print_exc()
客户端:clientudp.py
# -*- coding: cp936 -*-
##udp客户端,向服务器发送一个空字符后，得到服务器返回时间
##@小五义
import socket,sys,struct,time
host=raw_input('输入服务器地址：')
port=12345
s=socket.socket(socket.AF_INET,socket.SOCK_DGRAM)
s.sendto('',(host,port))
print "等待回复……"
buf=s.recvfrom(2048)[0]
if len(buf)!=4:
print "回复错误%d:%s"%(len(buf),buf)
sys.exit(1)
secs=struct.unpack("!I",buf)[0]
print time.ctime(int(secs))
运行结果：
首先运行服务器端，然后运行客户端。
C:\>python clientudp.py ##clientudp.py程序存放在在c盘下
输入服务器地址：127.0.0.1
等待回复……
Mon Aug 06 17:09:17 2012
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