python network programming tutorial

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关于网络编程以及socket 等一些概念和函数介绍就不再重复了，这里示例性用python 编写客户端和服务器端。

一、最简单的客户端流程：

1. Create a socket
2. Connect to remote server
3. Send some data
4. Receive a reply

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#Socket client example in python

import socket
#for sockets

import sys
#for exit

import struct

import time

#create an INET, STREAMing socket

try:

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

except socket.error:

print
'Failed to create socket'

sys.exit()

print
'Socket Created'

host =
'www.google.com';

port =
;

try:

remote_ip = socket.gethostbyname( host )

except socket.gaierror:

#could not resolve

print
'Hostname could not be resolved. Exiting'

sys.exit()

#Connect to remote server
s.connect((remote_ip , port))

print
'Socket Connected to ' + host +
' on ip ' + remote_ip

#Send some data to remote server
message =
"GET / HTTP/1.1\r\n\r\n"

try :

#Set the whole string
s.sendall(message)

except socket.error:

#Send failed

print
'Send failed'

sys.exit()

print
'Message send successfully'

def recv_timeout(the_socket,timeout=
):

#make socket non blocking
the_socket.setblocking(
)

#total data partwise in an array
total_data=[];

data=
'';

#beginning time
begin=time.time()

while
:

#if you got some data, then break after timeout

if total_data
and time.time()-begin > timeout:

break

#if you got no data at all, wait a little longer, twice the timeout

elif time.time()-begin > timeout*
:

break

#recv something

try:

data = the_socket.recv(
)

if data:

total_data.
append(data)

#change the beginning time for measurement
begin=time.time()

else:

#sleep for sometime to indicate a gap
time.sleep(
.
)

except:

pass

#join all parts to make final string

return
''.
join(total_data)

#get reply and print

print recv_timeout(s)

#Close the socket
s.
close()

需要注意的是也许http 响应数据比较大，要经过多次才能完整接收，设置socket 非阻塞，设定timeout，最后join 数据；因为我们并不知道具体数据到底多大，故不能这样使用 data. s.recv(4096 , socket.MSG_WAITALL); 如果最后一次来的数据不够4096，那么将一直阻塞。输出如下：

二、最简单的服务器端流程：

1. Open a socket
2. Bind to a address(and port).
3. Listen for incoming connections.
4. Accept connections
5. Read/Send

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import socket

import sys

HOST =
''
# Symbolic name meaning all available interfaces
PORT =

# 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[
]) +
' Message ' + msg[
]

sys.exit()

print
'Socket bind complete'

s.listen(
)

print
'Socket now listening'

#now keep talking with the client

while
:

#wait to accept a connection - blocking call
conn, addr = s.accept()

print
'Connected with ' + addr[
] +
':' +
str(addr[
])

data = conn.recv(
)

reply =
'OK...' + data

if
not data:

break

conn.sendall(reply)

conn.
close()

s.
close()

三、上述程序的缺点是每个连接上来就回应一次就不再搭理了，显然不可取，用多线程改进如下：

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import socket

import sys

from thread
import *

HOST =
''
# Symbolic name meaning all available interfaces
PORT =

# 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[
]) +
' Message ' + msg[
]

sys.exit()

print
'Socket bind complete'

#Start listening on socket
s.listen(
)

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(
)

reply =
'OK...' + data

if
not data:

break

conn.sendall(reply)

#came out of loop
conn.
close()

#now keep talking with the client

while
:

#wait to accept a connection - blocking call
conn, addr = s.accept()

print
'Connected with ' + addr[
] +
':' +
str(addr[
])

#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()

即每accept 返回一个连接，就创建一个线程对其服务。

启动server，然后开两个窗口telnet 上去，如下：

四、接下来，我们再用select 来实现，函数原型如下：

read_sockets,write_sockets,error_sockets = select(read_fds , write_fds, except_fds [, timeout]);

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#Socket server in python using select function

import socket, select

#Function to broadcast chat messages to all connected clients

def broadcast_data(sock, message):

#Do not send the message to master socket and the client who has send us the message

for socket
in CONNECTION_LIST:

if socket != server_socket
and socket != sock:

try:

socket.send(message)

except:

#broken socket connection may be, chat client pressed ctrl+c for example
socket.
close()

CONNECTION_LIST.
remove(socket)

if __name__ ==
"__main__":

CONNECTION_LIST = []
#list of socket clients
RECV_BUFFER =

#Advisable to keep it as an exponent of 2
PORT =

server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

#this has no effect, why?
server_socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR,
)

server_socket.bind((
"0.0.0.0", PORT))

server_socket.listen(
)

#Add server socket to the list of readable connections
CONNECTION_LIST.
append(server_socket)

print
"Chat server started on port " +
str(PORT)

while
:

#Get the list sockets which are ready to be read through select
read_sockets, write_sockets, error_sockets = select.select(CONNECTION_LIST, [], [])

for sock
in read_sockets:

#New connection

if sock == server_socket:

#handle the case in which there is a new connection recieved through server_socket
sockfd, addr = server_socket.accept()

CONNECTION_LIST.
append(sockfd)

print
"Client (%s, %s) connected" % addr

#Some incoming message from a client

else:

#Data recieved from client, process it

try:

#In windows, sometimes when a Tcp program closes abruptly

#a "Connection reset by peer" exception will be thrown
data = sock.recv(RECV_BUFFER)

#echo back the client message

if data:

sock.send(
'Ok...' + data)

#client disconnected, so remove from socket list

except:

broadcast_data(sock,
"Client (%s, %s) is offline" % addr)

print
"Client (%s, %s) is offline" % addr

sock.
close()

CONNECTION_LIST.
remove(sock)

continue

server_socket.
close()

五、最后使用poll 来实现，如下：

launcelot.py

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#!/usr/bin/env python
#coding=utf-8
#Constants and routines for supporting a certain network conversation.

import sys, socket

PORT =

qa = ((
'What is your name?',
'My name is Sir Launcelot of Camelot.'),

(
'What is your quest?',
'To seek the Holy Grail.'),

(
'What is your favorite color?',
'Blue.'))

qadict =
dict(qa)

def recv_until(sock, suffix):

message =
''

while
not message.
endswith(suffix):

data = sock.recv(
)

if
not data:

raise
EOFError(
'socket closed before we saw %r' % suffix)

message += data

return message

def setup():

if
len(sys.argv) !=
:

print >>sys.stderr,
'usage: %s interface' % sys.argv[
]

exit(
)

interface = sys.argv[
]

sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR,
)

sock.bind((interface, PORT))

sock.listen(
)

print
'Ready and listening at %r port %d' % (interface, PORT)

return sock

poll_server.py

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# An event-driven approach to serving several clients with poll().

import launcelot

import select

listen_sock = launcelot.setup()

sockets = {listen_sock.
fileno():listen_sock}

requests = {}

responses = {}

poll = select.poll()

poll.register(listen_sock, select.POLLIN)

while
True:

for fd, event
in poll.poll():

sock = sockets[fd]

#Removed closed sockets from our list.

if event & (select.POLLHUP | select.POLLERR | select.POLLNVAL):

poll.unregister(fd)

del sockets[fd]

requests.
pop(sock,
None)

responses.
pop(sock,
None)

#Accept connections from new sockets.

elif sock
is listen_sock:

newsock, sockname = sock.accept()

newsock.setblocking(
False)

fd = newsock.
fileno()

sockets[fd] = newsock

poll.register(fd, select.POLLIN)

requests[newsock] =
''

#Collect incoming data until it forms a question.

elif event & select.POLLIN:

data = sock.recv(
)

if
not data:
#end of file
sock.
close()
# make POLLNVAL happen next time

continue

requests[sock] += data.
replace(
'\r\n',
'')

if
'?'
in requests[sock]:

question = requests.
pop(sock)

answer =
dict(launcelot.qa)[question]

poll.modify(sock, select.POLLOUT)

responses[sock] = answer

#Send out pieces of each reply until they are all sent

elif event & select.POLLOUT:

response = responses.
pop(sock)

n = sock.send(response)

if n <
len(response):

responses[sock] = response[n:]

else:

poll.modify(sock, select.POLLIN)

requests[sock] =
''