Python下的twisted框架入门指引

什么是twisted？

twisted是一个用python语言写的事件驱动的网络框架，他支持很多种协议，包括udp,tcp,tls和其他应用层协议，比如http，smtp，nntm，irc，xmpp/jabber。 非常好的一点是twisted实现和很多应用层的协议，开发人员可以直接只用这些协议的实现。其实要修改twisted的ssh服务器端实现非常简单。很多时候，开发人员需要实现protocol类。

一个twisted程序由reactor发起的主循环和一些回调函数组成。当事件发生了，比如一个client连接到了server，这时候服务器端的事件会被触发执行。
用twisted写一个简单的tcp服务器

下面的代码是一个tcpserver，这个server记录客户端发来的数据信息。

==== code1.py ====
import sys
from twisted.internet.protocol import serverfactory
from twisted.protocols.basic import linereceiver
from twisted.python import log
from twisted.internet import reactor

class cmdprotocol(linereceiver):

  delimiter = '\n'

  def connectionmade(self):
    self.client_ip = self.transport.getpeer()[1]
    log.msg("client connection from %s" % self.client_ip)
    if len(self.factory.clients) >= self.factory.clients_max:
      log.msg("too many connections. bye !")
      self.client_ip = none
      self.transport.loseconnection()
    else:
      self.factory.clients.append(self.client_ip)

  def connectionlost(self, reason):
    log.msg('lost client connection. reason: %s' % reason)
    if self.client_ip:
      self.factory.clients.remove(self.client_ip)

  def linereceived(self, line):
    log.msg('cmd received from %s : %s' % (self.client_ip, line))

class myfactory(serverfactory):

  protocol = cmdprotocol

  def __init__(self, clients_max=10):
    self.clients_max = clients_max
    self.clients = []

log.startlogging(sys.stdout)
reactor.listentcp(9999, myfactory(2))
reactor.run()

下面的代码至关重要：

from twisted.internet import reactor
reactor.run()

这两行代码会启动reator的主循环。

在上面的代码中我们创建了"serverfactory"类，这个工厂类负责返回“cmdprotocol”的实例。 每一个连接都由实例化的“cmdprotocol”实例来做处理。 twisted的reactor会在tcp连接上后自动创建cmdprotocol的实例。如你所见，protocol类的方法都对应着一种事件处理。

当client连上server之后会触发“connectionmade"方法，在这个方法中你可以做一些鉴权之类的操作，也可以限制客户端的连接总数。每一个protocol的实例都有一个工厂的引用，使用self.factory可以访问所在的工厂实例。

上面实现的”cmdprotocol“是twisted.protocols.basic.linereceiver的子类，linereceiver类会将客户端发送的数据按照换行符分隔，每到一个换行符都会触发linereceived方法。稍后我们可以增强linereceived来解析命令。

twisted实现了自己的日志系统，这里我们配置将日志输出到stdout

当执行reactor.listentcp时我们将工厂绑定到了9999端口开始监听。

user@lab:~/tmp$ python code1.py
2011-08-29 13:32:32+0200 [-] log opened.
2011-08-29 13:32:32+0200 [-] __main__.myfactory starting on 9999
2011-08-29 13:32:32+0200 [-] starting factory <__main__.myfactory instance at 0x227e320
2011-08-29 13:32:35+0200 [__main__.myfactory] client connection from 127.0.0.1
2011-08-29 13:32:38+0200 [cmdprotocol,0,127.0.0.1] cmd received from 127.0.0.1 : hello server

使用twisted来调用外部进程

下面我们给前面的server添加一个命令，通过这个命令可以读取/var/log/syslog的内容

import sys
import os

from twisted.internet.protocol import serverfactory, processprotocol
from twisted.protocols.basic import linereceiver
from twisted.python import log
from twisted.internet import reactor

class tailprotocol(processprotocol):
  def __init__(self, write_callback):
    self.write = write_callback

  def outreceived(self, data):
    self.write("begin lastlog\n")
    data = [line for line in data.split('\n') if not line.startswith('==')]
    for d in data:
      self.write(d + '\n')
    self.write("end lastlog\n")

  def processended(self, reason):
    if reason.value.exitcode != 0:
      log.msg(reason)

class cmdprotocol(linereceiver):

  delimiter = '\n'

  def processcmd(self, line):
    if line.startswith('lastlog'):
      tailprotocol = tailprotocol(self.transport.write)
      reactor.spawnprocess(tailprotocol, '/usr/bin/tail', args=['/usr/bin/tail', '-10', '/var/log/syslog'])
    elif line.startswith('exit'):
      self.transport.loseconnection()
    else:
      self.transport.write('command not found.\n')

  def connectionmade(self):
    self.client_ip = self.transport.getpeer()[1]
    log.msg("client connection from %s" % self.client_ip)
    if len(self.factory.clients) >= self.factory.clients_max:
      log.msg("too many connections. bye !")
      self.client_ip = none
      self.transport.loseconnection()
    else:
      self.factory.clients.append(self.client_ip)

  def connectionlost(self, reason):
    log.msg('lost client connection. reason: %s' % reason)
    if self.client_ip:
      self.factory.clients.remove(self.client_ip)

  def linereceived(self, line):
    log.msg('cmd received from %s : %s' % (self.client_ip, line))
    self.processcmd(line)

class myfactory(serverfactory):

  protocol = cmdprotocol

  def __init__(self, clients_max=10):
    self.clients_max = clients_max
    self.clients = []

log.startlogging(sys.stdout)
reactor.listentcp(9999, myfactory(2))
reactor.run()

在上面的代码中，没从客户端接收到一行内容后会执行processcmd方法，如果收到的一行内容是exit命令，那么服务器端会断开连接，如果收到的是lastlog，我们要吐出一个子进程来执行tail命令，并将tail命令的输出重定向到客户端。这里我们需要实现processprotocol类，需要重写该类的processended方法和outreceived方法。在tail命令有输出时会执行outreceived方法，当进程退出时会执行processended方法。

如下是执行结果样例：

user@lab:~/tmp$ python code2.py
2011-08-29 15:13:38+0200 [-] log opened.
2011-08-29 15:13:38+0200 [-] __main__.myfactory starting on 9999
2011-08-29 15:13:38+0200 [-] starting factory <__main__.myfactory instance at 0x1a5a3f8>
2011-08-29 15:13:47+0200 [__main__.myfactory] client connection from 127.0.0.1
2011-08-29 15:13:58+0200 [cmdprotocol,0,127.0.0.1] cmd received from 127.0.0.1 : test
2011-08-29 15:14:02+0200 [cmdprotocol,0,127.0.0.1] cmd received from 127.0.0.1 : lastlog
2011-08-29 15:14:05+0200 [cmdprotocol,0,127.0.0.1] cmd received from 127.0.0.1 : exit
2011-08-29 15:14:05+0200 [cmdprotocol,0,127.0.0.1] lost client connection. reason: [failure instance: traceback (failure with no frames): <class 'twisted.internet.error.connectiondone'>: connection was closed cleanly.

可以使用下面的命令作为客户端发起命令：

user@lab:~$ netcat 127.0.0.1 9999
test
command not found.
lastlog
begin lastlog
aug 29 15:02:03 lab ssmtp[5919]: unable to locate mail
aug 29 15:02:03 lab ssmtp[5919]: cannot open mail:25
aug 29 15:02:03 lab cron[4945]: (cron) error (grandchild #4947 failed with exit status 1)
aug 29 15:02:03 lab ssmtp[5922]: unable to locate mail
aug 29 15:02:03 lab ssmtp[5922]: cannot open mail:25
aug 29 15:02:03 lab cron[4945]: (logcheck) mail (mailed 1 byte of output; but got status 0x0001, #012)
aug 29 15:05:01 lab cron[5925]: (root) cmd (command -v debian-sa1 > /dev/null && debian-sa1 1 1)
aug 29 15:10:01 lab cron[5930]: (root) cmd (test -x /usr/lib/atsar/atsa1 && /usr/lib/atsar/atsa1)
aug 29 15:10:01 lab cron[5928]: (cron) error (grandchild #5930 failed with exit status 1)
aug 29 15:13:21 lab pulseaudio[3361]: ratelimit.c: 387 events suppressed

 
end lastlog
exit

使用deferred对象

reactor是一个循环，这个循环在等待事件的发生。 这里的事件可以是数据库操作，也可以是长时间的计算操作。 只要这些操作可以返回一个deferred对象。deferred对象可以自动得在事件发生时触发回调函数。reactor会block当前代码的执行。

现在我们要使用defferred对象来计算sha1哈希。

import sys
import os
import hashlib

from twisted.internet.protocol import serverfactory, processprotocol
from twisted.protocols.basic import linereceiver
from twisted.python import log
from twisted.internet import reactor, threads

class tailprotocol(processprotocol):
  def __init__(self, write_callback):
    self.write = write_callback

  def outreceived(self, data):
    self.write("begin lastlog\n")
    data = [line for line in data.split('\n') if not line.startswith('==')]
    for d in data:
      self.write(d + '\n')
    self.write("end lastlog\n")

  def processended(self, reason):
    if reason.value.exitcode != 0:
      log.msg(reason)

class hashcompute(object):
  def __init__(self, path, write_callback):
    self.path = path
    self.write = write_callback

  def blockingmethod(self):
    os.path.isfile(self.path)
    data = file(self.path).read()
    # uncomment to add more delay
    # import time
    # time.sleep(10)
    return hashlib.sha1(data).hexdigest()

  def compute(self):
    d = threads.defertothread(self.blockingmethod)
    d.addcallback(self.ret)
    d.adderrback(self.err)

  def ret(self, hdata):
    self.write("file hash is : %s\n" % hdata)

  def err(self, failure):
    self.write("an error occured : %s\n" % failure.geterrormessage())

class cmdprotocol(linereceiver):

  delimiter = '\n'

  def processcmd(self, line):
    if line.startswith('lastlog'):
      tailprotocol = tailprotocol(self.transport.write)
      reactor.spawnprocess(tailprotocol, '/usr/bin/tail', args=['/usr/bin/tail', '-10', '/var/log/syslog'])
    elif line.startswith('comphash'):
      try:
        useless, path = line.split(' ')
      except:
        self.transport.write('please provide a path.\n')
        return
      hc = hashcompute(path, self.transport.write)
      hc.compute()
    elif line.startswith('exit'):
      self.transport.loseconnection()
    else:
      self.transport.write('command not found.\n')

  def connectionmade(self):
    self.client_ip = self.transport.getpeer()[1]
    log.msg("client connection from %s" % self.client_ip)
    if len(self.factory.clients) >= self.factory.clients_max:
      log.msg("too many connections. bye !")
      self.client_ip = none
      self.transport.loseconnection()
    else:
      self.factory.clients.append(self.client_ip)

  def connectionlost(self, reason):
    log.msg('lost client connection. reason: %s' % reason)
    if self.client_ip:
      self.factory.clients.remove(self.client_ip)

  def linereceived(self, line):
    log.msg('cmd received from %s : %s' % (self.client_ip, line))
    self.processcmd(line)

class myfactory(serverfactory):

  protocol = cmdprotocol

  def __init__(self, clients_max=10):
    self.clients_max = clients_max
    self.clients = []

log.startlogging(sys.stdout)
reactor.listentcp(9999, myfactory(2))
reactor.run()

blockingmethod从文件系统读取一个文件计算sha1，这里我们使用twisted的defertothread方法，这个方法返回一个deferred对象。这里的deferred对象是调用后马上就返回了，这样主进程就可以继续执行处理其他的事件。当传给defertothread的方法执行完毕后会马上触发其回调函数。如果执行中出错，blockingmethod方法会抛出异常。如果成功执行会通过hdata的ret返回计算的结果。
推荐的twisted阅读资料

http://twistedmatrix.com/documents/current/core/howto/defer.html http://twistedmatrix.com/documents/current/core/howto/process.html http://twistedmatrix.com/documents/current/core/howto/servers.html

api文档：

http://twistedmatrix.com/documents/current/api/twisted.html