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。
[email protected]:~/TMP$ python code1.py 2011-08-29 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 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：
[email protected]:~/TMP$ python code2.py 2011-08-29 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 : 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：
[email protected]:~$ netcat 127.0.0.1 9999test 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: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 mail Aug 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 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。
codego.net代码节选