Python下的twisted框架入门指引

什么是twisted？

twisted是一个用python/' target='_blank'>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 sysfrom twisted.internet.protocol import ServerFactoryfrom twisted.protocols.basic import LineReceiverfrom twisted.Python import logfrom twisted.internet import reactorclass 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 reactorreactor.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.py2011-08-29 13:32:32+0200 [-] Log opened.2011-08-29 13:32:32+0200 [-] __main__.MyFactory starting on 99992011-08-29 13:32:32+0200 [-] Starting factory <__main__.MyFactory instance at 0x227e3202011-08-29 13:32:35+0200 [__main__.MyFactory] Client connection from 127.0.0.12011-08-29 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 sysimport osfrom twisted.internet.protocol import ServerFactory, ProcessProtocolfrom twisted.protocols.basic import LineReceiverfrom twisted.python import logfrom twisted.internet import reactorclass 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.py2011-08-29 15:13:38+0200 [-] Log opened.2011-08-29 15:13:38+0200 [-] __main__.MyFactory starting on 99992011-08-29 15:13:38+0200 [-] Starting factory <__main__.MyFactory instance at 0x1a5a3f8>2011-08-29 15:13:47+0200 [__main__.MyFactory] Client connection from 127.0.0.12011-08-29 15:13:58+0200 [CmdProtocol,0,127.0.0.1] Cmd received from 127.0.0.1 : test2011-08-29 15:14:02+0200 [CmdProtocol,0,127.0.0.1] Cmd received from 127.0.0.1 : lastlog2011-08-29 15:14:05+0200 [CmdProtocol,0,127.0.0.1] Cmd received from 127.0.0.1 : exit2011-08-29 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 9999testCommand not found.lastlogBegin lastlogAug 29 15:02:03 lab sSMTP[5919]: Unable to locate mailAug 29 15:02:03 lab sSMTP[5919]: Cannot open mail:25Aug 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 mailAug 29 15:02:03 lab sSMTP[5922]: Cannot open mail:25Aug 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 lastlogexit

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 sysimport osimport hashlibfrom twisted.internet.protocol import ServerFactory, ProcessProtocolfrom twisted.protocols.basic import LineReceiverfrom twisted.python import logfrom twisted.internet import reactor, threadsclass 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