Question

I have been creating an async server socket that sends and recives xml using twisted.

The application works great! but because my main objective was to embed it in an init.d script and make it run in the background i decided to transform it in a “twisted application” in order to run it using twistd

# from twisted.internet import reactor
from twisted.internet.protocol import ServerFactory
from twisted.protocols.basic import LineOnlyReceiver
from twisted.application import internet, service

from xml.etree import ElementTree as ET

from aMuleClass import amulecmd

class DialogueProtocol(LineOnlyReceiver):
    def connectionMade(self):
        print "Connected: %s" % self.transport.getPeer().host
def lineReceived(self, line):
    parsed= ET.XML(line)
    if parsed.attrib['type'] == 'request':
        if parsed.attrib['prompt'] == 'results':
            self.transport.write(self.factory.mule.results())
        elif parsed.attrib['prompt'] == 'downloads':
            self.transport.write(self.factory.mule.downloads())
        else:
            print "Invalid request: %s\n" % line
    else:
        query= parsed.attrib['value']
        if parsed.attrib['type'] == 'search':
            print "must search for %s" % query
            self.factory.mule.search(query)
        elif parsed.attrib['type'] == 'cancel':
            print "must cancel %s" % query
            self.factory.mule.command("cancel %s" % query)
        elif parsed.attrib['type'] == 'download':
            print "must download %s" % query
            self.factory.mule.command("download %s" % query)

class DialogueProtocolFactory(ServerFactory):
def __init__(self):
    self.protocol= DialogueProtocol
    self.mule= amulecmd()

def main():
factory= DialogueProtocolFactory()
port = 14000
#
daemon= internet.TCPServer(port, factory)
application= service.Application("aMuleSocket")
#
daemon.setServiceParent(application)

if __name__ == '__main__':
main()

Running this with “twistd -noy file” (debug) works PERFECTLY.
The problem is when i want to background my script! (“twistd -y file”) the socket dosent respond and the log gets filled with errors from pexpect, which is imported in my amulecmd class…
pexpect communicates with a terminal-prompt application and returns the answers to the socket..

logfile:

2010/02/17 19:54 +0200 [-] Log opened.
2010/02/17 19:54 +0200 [-] twistd 2.5.0 (/usr/bin/python 2.5.2) starting up
2010/02/17 19:54 +0200 [-] reactor class: <class          'twisted.internet.selectreactor.SelectReactor'>
2010/02/17 19:54 +0200 [-] Loading aMuleSocket.tac...
2010/02/17 19:54 +0200 [-] Starting parent
2010/02/17 19:54 +0200 [-] Loaded.
2010/02/17 19:54 +0200 [-] __builtin__.DialogueProtocolFactory starting on 2000
2010/02/17 19:54 +0200 [-] Starting factory <__builtin__.DialogueProtocolFactory instance at 0x82dbd8c>
2010/02/17 19:54 +0200 [__builtin__.DialogueProtocolFactory] Connected: 192.168.0.2
2010/02/17 19:54 +0200 [DialogueProtocol,0,192.168.0.2] Unhandled Error
Traceback (most recent call last):
File "/usr/lib/python2.5/site-packages/twisted/python/log.py", line 48, in      callWithLogger
 return callWithContext({"system": lp}, func, *args, **kw)
File "/usr/lib/python2.5/site-packages/twisted/python/log.py", line 33, in callWithContext
 return context.call({ILogContext: newCtx}, func, *args, **kw)
File "/usr/lib/python2.5/site-packages/twisted/python/context.py", line 59, in callWithContext
 return self.currentContext().callWithContext(ctx, func, *args, **kw)
File "/usr/lib/python2.5/site-packages/twisted/python/context.py", line 37, in callWithContext
 return func(*args,**kw)
--- <exception caught here> ---
File "/usr/lib/python2.5/site-packages/twisted/internet/selectreactor.py", line 139, in _doReadOrWrite
 why = getattr(selectable, method)()
File "/usr/lib/python2.5/site-packages/twisted/internet/tcp.py", line 362, in doRead
 return self.protocol.dataReceived(data)
File "/usr/lib/python2.5/site-packages/twisted/protocols/basic.py", line 149, in dataReceived
 self.lineReceived(line)
File "aMuleSocket.tac", line 19, in lineReceived
 self.transport.write(self.factory.mule.downloads())
File "/home/hecyra/amule_scripts/amule-remote-read-only/server/aMuleClass.py", line 60, in downloads
 list= self.command('show DL').splitlines()
File "/home/hecyra/amule_scripts/amule-remote-read-only/server/aMuleClass.py", line 42, in command
 self.prompt()
File "/home/hecyra/amule_scripts/amule-remote-read-only/server/aMuleClass.py", line 27, in prompt
 self.process.expect('aMulecmd')
File "/usr/lib/python2.5/site-packages/pexpect.py", line 1064, in expect
 return self.expect_list(compiled_pattern_list, timeout, searchwindowsize)
File "/usr/lib/python2.5/site-packages/pexpect.py", line 1116, in expect_list
 c = self.read_nonblocking (self.maxread, timeout)
File "/usr/lib/python2.5/site-packages/pexpect.py", line 656, in read_nonblocking
 if not self.isalive():
File "/usr/lib/python2.5/site-packages/pexpect.py", line 914, in isalive
raise ExceptionPexpect ('isalive() encountered condition where "terminated" is 0, but   there was no child process. Did someone else call waitpid() on our process?')
pexpect.ExceptionPexpect: isalive() encountered condition where "terminated" is 0,            but there was no child process. Did someone else call waitpid() on our process?

What could it be?? all i need is to background this script 🙁 looked easy

Answer 1

You’re spawning a child process before daemonizing. After daemonizing that child is now a child of init, and not a child of your daemon.

You need to subclass from twisted.application.service import Service and spawn the child process in startService, which will be called after daemonizing.

Á La: Twisted network client with multiprocessing workers?

Edit: implementation

I can’t test this entirely as I don’t have your amulecmd, but try something more like this:

#!/usr/bin/env python
# vim:ai:et:ts=2:sw=2:bg=dark
from twisted.internet import protocol
from twisted.protocols.basic import LineOnlyReceiver
from twisted.application import service


from xml.etree import ElementTree as ET

from aMuleClass import amulecmd

class DialogueProtocol(LineOnlyReceiver):
  def connectionMade(self):
    print "Connected: %s" % self.transport.getPeer().host
  def lineReceived(self, line):
    parsed= ET.XML(line)
    if parsed.attrib['type'] == 'request':
      if parsed.attrib['prompt'] == 'results':
        self.transport.write(self.factory.mule.results())
      elif parsed.attrib['prompt'] == 'downloads':
        self.transport.write(self.factory.mule.downloads())
      else:
        print "Invalid request: %s\n" % line
    else:
      query= parsed.attrib['value']
      if parsed.attrib['type'] == 'search':
        print "must search for %s" % query
        self.factory.mule.search(query)
      elif parsed.attrib['type'] == 'cancel':
        print "must cancel %s" % query
        self.factory.mule.command("cancel %s" % query)
      elif parsed.attrib['type'] == 'download':
        print "must download %s" % query
        self.factory.mule.command("download %s" % query)

class MyService(service.Service):
  def __init__(self,port=14000):
    self.port = port
  def startService(self):
    self.factory = protocol.Factory()
    self.factory.protocol = DialogueProtocol
    from twisted.internet import reactor
    reactor.callWhenRunning(self.startListening)
  def startListening(self):
    self.factory.mule = amulecmd()
    from twisted.internet import reactor
    self.listener = reactor.listenTCP(self.port,self.factory)
    print "Started listening"
  def stopService(self):
    self.listener.stopListening()

if __name__ == '__main__':
  pass
else:
  application = service.Application("aMuleSocket")
  services = service.IServiceCollection(application)
  MyService().setServiceParent(services)