Python Socket 网络编程 (服务器端编程)

时间:2022-08-19 08:23:50

服务器端主要做以下工作:

  • 打开 socket
  • 绑定到特定的地址以及端口上
  • 监听连接
  • 建立连接
  • 接收/发送数据

上面已经介绍了如何创建 socket 了,下面一步是绑定。

绑定 socket

函数 bind 可以用来将 socket 绑定到特定的地址和端口上,它需要一个 sockaddr_in 结构作为参数:

import socket
import sys HOST = '' # Symbolic name meaning all available interfaces
PORT = 8888 # Arbitrary non-privileged port s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
print 'Socket created' try:
s.bind((HOST, PORT))
except socket.error , msg:
print 'Bind failed. Error Code : ' + str(msg[0]) + ' Message ' + msg[1]
sys.exit() print 'Socket bind complete'

绑定完成之后,接下来就是监听连接了。

监听连接

函数 listen 可以将 socket 置于监听模式:

s.listen(10)
print 'Socket now listening'

该函数带有一个参数称为 backlog,用来控制连接的个数。如果设为 10,那么有 10 个连接正在等待处理,此时第 11 个请求过来时将会被拒绝。

接收连接

当有客户端向服务器发送连接请求时,服务器会接收连接:

#wait to accept a connection - blocking call
conn, addr = s.accept() #display client information
print 'Connected with ' + addr[0] + ':' + str(addr[1]) '''
Socket created
Socket bind complete
Socket now listening
'''

此时,该程序在 8888 端口上等待请求的到来。不要关掉这个程序,让它一直运行,现在客户端可以通过该端口连接到 socket。我们用 telnet 客户端来测试,打开一个终端,输入 telnet localhost 8888

$ telnet localhost 8888
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
Connection closed by foreign host.

这时服务端输出会显示:

$ python server.py
Socket created
Socket bind complete
Socket now listening
Connected with 127.0.0.1:59954

我们观察到客户端已经连接上服务器了。在建立连接之后,我们可以用来与客户端进行通信。下面例子演示的是,服务器建立连接之后,接收客户端发送来的数据,并立即将数据发送回去,下面是完整的服务端程序:

import socket
import sys HOST = '' # Symbolic name meaning all available interfaces
PORT = 8888 # Arbitrary non-privileged port s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
print 'Socket created' try:
s.bind((HOST, PORT))
except socket.error , msg:
print 'Bind failed. Error Code : ' + str(msg[0]) + ' Message ' + msg[1]
sys.exit() print 'Socket bind complete' s.listen(10)
print 'Socket now listening' #wait to accept a connection - blocking call
conn, addr = s.accept() print 'Connected with ' + addr[0] + ':' + str(addr[1]) #now keep talking with the client
data = conn.recv(1024)
conn.sendall(data) conn.close()
s.close()

在一个终端中运行这个程序,打开另一个终端,使用 telnet 连接服务器,随便输入字符串,你会看到:

$ telnet localhost 8888
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
happy
happy
Connection closed by foreign host.

客户端(telnet)接收了服务器的响应。

我们在完成一次响应之后服务器立即断开了连接,而像 www.google.com 这样的服务器总是一直等待接收连接的。我们需要将上面的服务器程序改造成一直运行,最简单的办法是将 accept 放到一个循环中,那么就可以一直接收连接了。

保持服务

我们可以将代码改成这样让服务器一直工作:

import socket
import sys HOST = '' # Symbolic name meaning all available interfaces
PORT = 5000 # Arbitrary non-privileged port s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
print 'Socket created' try:
s.bind((HOST, PORT))
except socket.error , msg:
print 'Bind failed. Error Code : ' + str(msg[0]) + ' Message ' + msg[1]
sys.exit() print 'Socket bind complete' s.listen(10)
print 'Socket now listening' #now keep talking with the client
while 1:
#wait to accept a connection - blocking call
conn, addr = s.accept()
print 'Connected with ' + addr[0] + ':' + str(addr[1]) data = conn.recv(1024)
reply = 'OK...' + data
if not data:
break conn.sendall(reply) conn.close()
s.close()

现在在一个终端下运行上面的服务器程序,再开启三个终端,分别用 telnet 去连接,如果一个终端连接之后不输入数据其他终端是没办法进行连接的,而且每个终端只能服务一次就断开连接。这从代码上也是可以看出来的。

这显然也不是我们想要的,我们希望多个客户端可以随时建立连接,而且每个客户端可以跟服务器进行多次通信,这该怎么修改呢?

处理连接

为了处理每个连接,我们需要将处理的程序与主程序的接收连接分开。一种方法可以使用线程来实现,主服务程序接收连接,创建一个线程来处理该连接的通信,然后服务器回到接收其他连接的逻辑上来。

import socket
import sys
from thread import * HOST = '' # Symbolic name meaning all available interfaces
PORT = 8888 # Arbitrary non-privileged port s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
print 'Socket created' #Bind socket to local host and port
try:
s.bind((HOST, PORT))
except socket.error , msg:
print 'Bind failed. Error Code : ' + str(msg[0]) + ' Message ' + msg[1]
sys.exit() print 'Socket bind complete' #Start listening on socket
s.listen(10)
print 'Socket now listening' #Function for handling connections. This will be used to create threads
def clientthread(conn):
#Sending message to connected client
conn.send('Welcome to the server. Type something and hit enter\n') #send only takes string #infinite loop so that function do not terminate and thread do not end.
while True: #Receiving from client
data = conn.recv(1024)
reply = 'OK...' + data
if not data:
break conn.sendall(reply) #came out of loop
conn.close() #now keep talking with the client
while 1:
#wait to accept a connection - blocking call
conn, addr = s.accept()
print 'Connected with ' + addr[0] + ':' + str(addr[1]) #start new thread takes 1st argument as a function name to be run, second is the tuple of arguments to the function.
start_new_thread(clientthread ,(conn,)) s.close()

再次运行上面的程序,打开三个终端来与主服务器建立 telnet 连接,这时候三个客户端可以随时接入,而且每个客户端可以与主服务器进行多次通信。

telnet 终端下可能输出如下:

$ telnet localhost 8888
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
Welcome to the server. Type something and hit enter
hi
OK...hi
asd
OK...asd
cv
OK...cv

要结束 telnet 的连接,按下 Ctrl-] 键,再输入 close 命令。

服务器终端的输出可能是这样的:

$ python server.py
Socket created
Socket bind complete
Socket now listening
Connected with 127.0.0.1:60730
Connected with 127.0.0.1:60731