[Twisted-Python] t.n.c.lookupAddress returns DNSNameError for hostnames w/ no A record

byr sa byrsa at sinkhole.me
Tue Apr 2 11:40:12 EDT 2013

On Tue, Apr 2, 2013 at 5:03 AM, <exarkun at twistedmatrix.com> wrote:

> Hi byrsa,
> The behavior you're describing does sound wrong.  However, I wasn't able
> to reproduce it locally.  Running your example, I get [] for
> megaupload.com, not an error.  Perhaps there is a tricky DNS server
> involved somewhere that is changing the response unexpectedly?  I
> suggest using something like tcpdump or wireshark to take a look at the
> actual traffic and perhaps produce a more deterministic demonstration of
> the problem.
You are correct! I was running the code on a Linux machine and the 'dig'
command on my Macbook. The answers were different. At least I know the code
is working!

> Regarding how you should detect certain errors, though, Failure just
> wraps normal exceptions, so you can use `isinstance` to check for them
> instead of checking by name.  Failure also provides some APIs that wrap
> up isinstance to provide some more commonly useful behavior - see
> Failure.check and Failure.trap.
'isinstance' was my initial thought, as well. I'll have to re-visit that.
Thanks for the pointer.

> And regarding determining error from a Message, you can use the rCode
> attribute to get the raw server response code as an integer.  The values
> and their meanings are defined in the DNS RFC and there are symbolic
> constants in twisted.names.dns - eg OK, ENAME, ESERVER, etc.
That doesn't sound too bad.

> Hope this helps,
> Jean-Paul
Your feedback has been immensely helpful, thanks a lot, Jean-Paul!

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://twistedmatrix.com/pipermail/twisted-python/attachments/20130402/af0415ff/attachment-0001.htm 

More information about the Twisted-Python mailing list