twisted入门

http://outofmemory.cn/code-snippet/4624/python-twisted-example

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

翻译自: http://www.wallix.org/2011/08/30/getting-started-with-twisted/

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