使用Python的Twisted框架编写简单的网络客户端

Protocol
  和服务器一样，也是通过该类来实现。先看一个简短的例程：

from twisted.internet.protocol import Protocol
from sys import stdout

class Echo(Protocol):
  def dataReceived(self, data):
    stdout.write(data)

在本程序中，只是简单的将获得的数据输出到标准输出中来显示,还有很多其他的事件没有作出任何响应,下面
有一个回应其他事件的例子:

from twisted.internet.protocol import Protocol

class WelcomeMessage(Protocol):
  def connectionMade(self):
    self.transport.write("Hello server, I am the client!/r/n")
    self.transport.loseConnection()

本协议连接到服务器,发送了一个问候消息,然后关闭了连接。
connectionMade事件通常被用在建立连接的事件发生时触发。关闭连接的时候会触发connectionLost事件函数

(Simple, single-use clients)简单的单用户客户端
  在许多情况下，protocol仅仅是需要连接服务器一次，并且代码仅仅是要获得一个protocol连接的实例。在
这样的情况下，twisted.internet.protocol.ClientCreator提供了一个恰当的API

from twisted.internet import reactor
from twisted.internet.protocol import Protocol, ClientCreator

class Greeter(Protocol):
  def sendMessage(self, msg):
    self.transport.write("MESSAGE %s/n" % msg)

def gotProtocol(p):
  p.sendMessage("Hello")
  reactor.callLater(1, p.sendMessage, "This is sent in a second")
  reactor.callLater(2, p.transport.loseConnection)

c = ClientCreator(reactor, Greeter)
c.connectTCP("localhost", 1234).addCallback(gotProtocol)

ClientFactory(客户工厂)
  ClientFactory负责创建Protocol，并且返回相关事件的连接状态。这样就允许它去做像连接发生错误然后
重新连接的事情。这里有一个ClientFactory的简单例子使用Echo协议并且打印当前的连接状态

from twisted.internet.protocol import Protocol, ClientFactory
from sys import stdout

class Echo(Protocol):
  def dataReceived(self, data):
    stdout.write(data)

class EchoClientFactory(ClientFactory):
  def startedConnecting(self, connector):
    print 'Started to connect.'
  
  def buildProtocol(self, addr):
    print 'Connected.'
    return Echo()
  
  def clientConnectionLost(self, connector, reason):
    print 'Lost connection. Reason:', reason
  
  def clientConnectionFailed(self, connector, reason):
    print 'Connection failed. Reason:', reason

要想将EchoClientFactory连接到服务器，可以使用下面代码：

from twisted.internet import reactor
reactor.connectTCP(host, port, EchoClientFactory())
reactor.run()

注意：clientConnectionFailed是在Connection不能被建立的时候调用，clientConnectionLost是在连接关闭的时候被调用，两个是有区别的。

Reconnection(重新连接)
  许多时候，客户端连接可能由于网络错误经常被断开。一个重新建立连接的方法是在连接断开的时候调用

connector.connect()方法。

from twisted.internet.protocol import ClientFactory

class EchoClientFactory(ClientFactory):
  def clientConnectionLost(self, connector, reason):
    connector.connect()

   connector是connection和protocol之间的一个接口被作为第一个参数传递给clientConnectionLost，

factory能调用connector.connect()方法重新进行连接
   然而，许多程序在连接失败和连接断开进行重新连接的时候使用ReconnectingClientFactory函数代替这个

函数，并且不断的尝试重新连接。这里有一个Echo Protocol使用ReconnectingClientFactory的例子：

from twisted.internet.protocol import Protocol, ReconnectingClientFactory
from sys import stdout

class Echo(Protocol):
  def dataReceived(self, data):
    stdout.write(data)

class EchoClientFactory(ReconnectingClientFactory):
  def startedConnecting(self, connector):
    print 'Started to connect.'

  def buildProtocol(self, addr):
    print 'Connected.'
    print 'Resetting reconnection delay'
    self.resetDelay()
    return Echo()

  def clientConnectionLost(self, connector, reason):
    print 'Lost connection. Reason:', reason
    ReconnectingClientFactory.clientConnectionLost(self, connector, reason)

  def clientConnectionFailed(self, connector, reason):
    print 'Connection failed. Reason:', reason
    ReconnectingClientFactory.clientConnectionFailed(self, connector,reason)

A Higher-Level Example: ircLogBot
上面的所有例子都非常简单，下面是一个比较复杂的例子来自于doc/examples目录

# twisted imports
from twisted.words.protocols import irc
from twisted.internet import reactor, protocol
from twisted.python import log

# system imports
import time, sys


class MessageLogger:
  """
  An independent logger class (because separation of application
  and protocol logic is a good thing).
  """
  def __init__(self, file):
    self.file = file

  def log(self, message):
    """Write a message to the file."""
    timestamp = time.strftime("[%H:%M:%S]", time.localtime(time.time()))
    self.file.write('%s %s/n' % (timestamp, message))
    self.file.flush()

  def close(self):
    self.file.close()


class LogBot(irc.IRCClient):
  """A logging IRC bot."""

  nickname = "twistedbot"

  def connectionMade(self):
    irc.IRCClient.connectionMade(self)
    self.logger = MessageLogger(open(self.factory.filename, "a"))
    self.logger.log("[connected at %s]" %
            time.asctime(time.localtime(time.time())))

  def connectionLost(self, reason):
    irc.IRCClient.connectionLost(self, reason)
    self.logger.log("[disconnected at %s]" %
            time.asctime(time.localtime(time.time())))
    self.logger.close()


  # callbacks for events

  def signedOn(self):
    """Called when bot has succesfully signed on to server."""
    self.join(self.factory.channel)

  def joined(self, channel):
    """This will get called when the bot joins the channel."""
    self.logger.log("[I have joined %s]" % channel)

  def privmsg(self, user, channel, msg):
    """This will get called when the bot receives a message."""
    user = user.split('!', 1)[0]
    self.logger.log("<%s> %s" % (user, msg))

    # Check to see if they're sending me a private message
    if channel == self.nickname:
      msg = "It isn't nice to whisper! Play nice with the group."
      self.msg(user, msg)
      return

    # Otherwise check to see if it is a message directed at me
    if msg.startswith(self.nickname + ":"):
      msg = "%s: I am a log bot" % user
      self.msg(channel, msg)
      self.logger.log("<%s> %s" % (self.nickname, msg))

  def action(self, user, channel, msg):
    """This will get called when the bot sees someone do an action."""
    user = user.split('!', 1)[0]
    self.logger.log("* %s %s" % (user, msg))

  # irc callbacks

  def irc_NICK(self, prefix, params):
    """Called when an IRC user changes their nickname."""
    old_nick = prefix.split('!')[0]
    new_nick = params[0]
    self.logger.log("%s is now known as %s" % (old_nick, new_nick))


class LogBotFactory(protocol.ClientFactory):
  """A factory for LogBots.

  A new protocol instance will be created each time we connect to the server.
  """

  # the class of the protocol to build when new connection is made
  protocol = LogBot

  def __init__(self, channel, filename):
    self.channel = channel
    self.filename = filename

  def clientConnectionLost(self, connector, reason):
    """If we get disconnected, reconnect to se