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
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