Re: [Twisted-Python] Some beginner questions about "twisted.names.client" and ".tac" environment

Dec. 18, 2005

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Jean-Paul Calderone wrote:
...
You want to tie your application logic to a Service subclass.  To start
with, I'd try something like this, in dns3.py:
The very same error :-(.

My code for "dns3.tac":

=====

from twisted.application import service

application = service.Application("DNS test")

import sys
sys.path=["."]+sys.path

from dns3 import DomainResolver
DomainResolver().setServiceParent(application)

=====

My code for "dns3.py":

=====

class resolucion(object) :
  def __init__(self,dominio) :
    global myResolver
    d = myResolver.lookupMailExchange(dominio,timeout=(1,))
    d.addCallbacks(self._cbMailExchange, self._ebMailExchange)
    self.dominio=dominio

  def _cbMailExchange(self,results):
    # Callback for MX query
    global aun_pendientes
    aun_pendientes-=1
    if not aun_pendientes :
      import time
      print "OK",time.time()-t
      #return
      from twisted.internet import reactor
      reactor.stop()
      return
    if not len(pendientes) :
      return

    resolucion(pendientes.pop())
    from twisted.names import dns
    for i in results[0] :
      n=i.payload.name
      tipo=i.payload.TYPE
      if tipo==dns.MX :
        return
        p=i.payload.preference
        print n,p,
        for j in results[2] :
          if n==j.name :
            print j.payload.dottedQuad(),"(%d)" %j.ttl
            break
        else :
          print "???"
      elif tipo==dns.CNAME :
        redirigidos.append((self.dominio,i.payload.name))

  def _ebMailExchange(self,failure):
    # Error callback for MX query
    global aun_pendientes
    aun_pendientes-=1
    if not aun_pendientes :
      import time
      print "ERROR",time.time()-t
      #return
      from twisted.internet import reactor
      reactor.stop()
      return
    if not len(pendientes) :
      return

    resolucion(pendientes.pop())
    print "XXX",self.dominio
    print 'Lookup failed:'
    failure.printTraceback()

from twisted.application import service

class DomainResolver(service.Service):
  def startService(self) :
    global pendientes,redirigidos,aun_pendientes,t,myResolver

    from twisted.names import client
    myResolver=client.Resolver(servers=[('127.0.0.1', 53)])

    import time
    t=time.time()

    pendientes=[]
    redirigidos=[]

    f=open("z1")
    for i in f :
      pendientes.append(i.split()[0])
    f.close()

    aun_pendientes=len(pendientes)

    concurrencia=1

    for i in pendientes[:concurrencia] :
      resolucion(i)

    pendientes=pendientes[concurrencia:]

=====
...
This will delay the execution of your startup code until twistd is
totally ready and the reactor is fully initialized.
Done, but not working :-(

[... DNS timeouts ...]
...
Okay, it sounds like you know what you're doing here :)
I like to think so };-)
...
I think the current caching resolver was a step in the wrong direction. 
A cache should probably *wrap* another resolver, not whatever weird
thing it is doing now.
I agree. Perhaps a subclass of the network DNS resolver could be fine.
So we could have a "client" class and a "cachingClient" one.

In any case, current code simply doesn't cache anything, but eats CPU
cycles.
...
If you write such a thing, it'd be great if you could submit it for
inclusion :)
I'm not familiar enough with Twisted internal, yet, to try.
Nevertheless, I would suggest an optional parameter in the caching
resolver constructor, pointing to a callable object to resolve misses.
Sort of. Code changes would be minimal...

[... about differenciatiing DNS misses from RR misses...]
...
I think flags like this are ugly hacks as well.  I completely agree that
subclass/override is not a great way to get this functionality, but I'd
like to think of a cleaner way to offer the new feature while still
maintaining backwards compatibility.
Keep me informed :-p
...
Try the service class I used above.  If you still see the exception, it
may indicate a bug in Twisted's UDP support.  If this case, could you
attach the new version of the whole program?  I'll take a closer look
and see if I can nail down the exact cause.
Not working. Same exception. Code posted.

Thanks a lot for your help, Jean Paul. Greatly appreciated.

- --
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