[Twisted-Python] Beginner's question about names and callbacks

Adan Broderick broder79 at gmail.com
Tue Jan 27 20:19:17 EST 2009

Fantastic, that is exactly what I was looking for.  Thank you very much for
helping me.

On Mon, Jan 26, 2009 at 1:46 AM, Tim Allen <screwtape at froup.com> wrote:

> On Mon, Jan 26, 2009 at 01:06:37AM -0500, Adan Broderick wrote:
> > I'm trying to write a program that will call my own function whenever a
> > query to a nameserver times out. I have figured out how to run the DNS
> > server. And I also know how to use filterAnswers(). But how do I catch
> the
> > "Failure: twisted.names.error.DNSQueryTimeoutError:" messages by adding
> code
> > to the resolver I've constructed?
> I'm not familiar with twisted.names, but looking at the source to
> client.Resolver, it seems that something winds up calling _lookup() with
> a timeout, which passes it off to the queryUDP() and sets up the basic
> result handling. If queryUDP() returns a result, it goes to filterAnswers,
> which checks for truncation and re-sends with queryTCP().
> Since the actual deferreds that deal with the timeouts are returned from
> queryUDP() and queryTCP(), it looks like you should be overriding those
> methods and capturing the results instead. Something like this:
> class MyResolver(client.Resolver):
>    def _handle_query_timeout(self, fail):
>        fail.trap(DNSQueryTimeoutError)
>        print "Got an error:", fail.getErrorMessage()
>    def queryUDP(self, *args, **kwargs):
>        d = client.Resolver.queryUDP(self, *args, **kwargs)
>        d.addErrback(self._handle_query_timeout)
>        return d
>    def queryTCP(self, *args, **kwargs):
>        d = client.Resolver.queryTCP(self, *args, **kwargs)
>        d.addErrback(self._handle_query_timeout)
>        return d
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