[Twisted-Python] Handeling unresolved DNS queries?

Jesper Taxbøl jesper at taxboel.dk
Mon Oct 26 17:34:50 EDT 2009

First of all. Thanx for the help!!! The internet is just fantastic!!

I like the wrapper approach.

I had not thought of that approach myself. Sounds very reasonable. -So I
started wrapping Resolver, but got stuck pretty fast. I get a problem saying

'NoneType' object has no attribute 'addCallback'

"addCallback" seems to be implemented in defer.py, but im unsure on how to
handle that in the wrapper?

Kind regards


As a side question: In my old hack approach, which I have had almost
working, I have had problems constructing valid DNS answers. Wold you happen
to know what requirements there is to the returning package, to be accepted.

I made some attempts by using pickle to capture live packages, but have a
hard time tweaking other values than the address. Ideally I would like to
pass on a very short TTL, so the client would not be bothered by fake DNS
when I turn the system off.

As you might have guessed, Im building a gateway system for a small set of
apartments. Requirements are:

invalid domains should go to a shop
valid domains should be redirected to the shop if the client have not paid,
except if the query is for paypal.

2009/10/25 <exarkun at twistedmatrix.com>

> On 24 Oct, 08:04 pm, jesper at taxboel.dk wrote:
> >Im looking at the common.py and I feel a bit confused about how to wrap
> >a
> >resolver.
> >
> >Would'nt a subclass achieve the same thing. I would only need to
> >implement
> >the changed functions in the subclass.
> >
> >I guess my problem is that I dont exactly know how to write a wrapper
> >in
> >python.
> There's nothing special to it.  Just do the obvious thing:
>    class SomeWrapper:
>        def __init__(self, wrapee):
>            self.wrapee = wrapee
>        def someMethod(self, args):
>            do something with self.wrapee.someMethod and args
> common.py will show you all the methods that a resolver is expected to
> have.  Subclassing ResolverBase might help, though it's unfortunate that
> it works by demultiplexing everything to "_lookup", a private method
> that Twisted's compatibility policy doesn't guarantee will continue to
> operate as it presently does.
> Wrapping (ie "containment" or "has-a") is just an alternative
> implementation strategy to subclassing (ie "inheritance" or "is-a").
> Generally it's a better approach for various reasons, none of which are
> really specific to Twisted.
> Jean-Paul
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