Getting started with twisted framework in Python

What is twisted?

twisted is an event-driven networking framework written in python. It supports many protocols, including UDP, TCP, TLS and other application layer protocols, such as HTTP, SMTP, NNTM, IRC, XMPP/Jabber. A very good point is that twisted implementation and many application layer protocols, developers can directly use only the implementation of these protocols. In fact, it is very simple to modify the SSH server-side implementation of Twisted. Many times, developers need to implement the protocol class.

A Twisted program consists of the main loop initiated by the reactor and some callback functions. When an event occurs, such as a client connecting to the server, the server-side event will be triggered and executed.
Write a simple TCP server with Twisted

The following code is a TCPServer, which records the data information sent by the client.


==== 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()


below The code is crucial: the two lines of code

from twisted.internet import reactor
reactor.run()


will start the main loop of the reactor.

In the above code we created the "ServerFactory" class which is responsible for returning an instance of "CmdProtocol". Each connection is handled by an instantiated "CmdProtocol" instance. Twisted's reactor will automatically create an instance of CmdProtocol after the TCP connection is made. As you can see, the methods of the protocol class all correspond to an event handler.

When the client connects to the server, the "connectionMade" method will be triggered. In this method, you can do some operations such as authentication, and you can also limit the total number of connections of the client. Each instance of the protocol has a reference to the factory, and the factory instance where it is located can be accessed using self.factory.

The "CmdProtocol" implemented above is a subclass of twisted.protocols.basic.LineReceiver. The LineReceiver class separates the data sent by the client according to newlines, and the lineReceived method is triggered for each newline. Later we can enhance LineReceived to parse commands.

Twisted implements its own logging system. Here we configure the log output to stdout

. When executing reactor.listenTCP, we bind the factory to port 9999 to start listening.





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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


uses Twisted to call an external process

Let 's add a command to the previous server, through which you can read / Contents of var/log/syslog


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()


In the above code, the processCmd method will be executed after a line of content is not received from the client. If a line of content is received If it is the exit command, the server will disconnect. If the lastlog is received, we need to spit out a subprocess to execute the tail command and redirect the output of the tail command to the client. Here we need to implement the ProcessProtocol class, and we need to override the processEnded method and outReceived method of this class. The outReceived method is executed when the tail command has output, and the processEnded method is executed when the process exits.

The following is a sample execution result:





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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：





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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


Using the Deferred object

reactor is a loop, this loop is waiting for the event to happen. The events here can be database operations or long computing operations. As long as these operations can return a Deferred object. Deferred objects can automatically trigger callback functions when events occur. reactor blocks the execution of the current code.

Now we are going to use the Defferred object to calculate the SHA1 hash.





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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 reads a file from the file system to calculate SHA1, here we use twisted deferToThread method, this method returns a Deferred object. The Deferred object here is returned immediately after the call, so that the main process can continue to process other events. When the method passed to deferToThread is executed, its callback function will be triggered immediately. If an error occurs during execution, the blockingMethod method will throw an exception. If the execution is successful, the result of the calculation will be returned through the ret of hdata.
Recommended twisted reading

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 documentation:

http://twistedmatrix.com/documents/current/api/twisted.html