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Date: Wed, 15 Jun 2011 10:43:23 +1000
Subject: Re: Question regarding DNS resolution in urllib2
From: Chris Angelico <rosuav@gmail.com>
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Xref: x330-a1.tempe.blueboxinc.net comp.lang.python:7656

On Wed, Jun 15, 2011 at 4:34 AM, saurabh verma <nitw.saurabh@gmail.com> wro=
te:
> hi ,
>
> I trying to use urllib2 in my script , but the problem is lets say a doma=
ins resolves to multiple IPs , If the URL is served by plain http , I can a=
dd =93Host: domain=94 header and check whether all IPs are returning proper=
 responses or not , but in case of https , I have to trust on my local mach=
ines dns resolver and I can=92t apply host header in the request .

Regarding Host: headers, experimentation showed that urllib2 did
indeed send one (I tested using Python 2.7.1 on Windows, talking to a
snooping HTTPS server running on a Linux box beside me - source code
available if you're curious, but it's not Python).

>>> import urllib2
>>> req=3Durllib2.Request(url=3D'https://mirlemont/')
>>> f=3Durllib2.urlopen(req)
>>> f.read()
'Hello, world!'

Meanwhile the snoop server reports:

conn =3D Protocols.HTTP.Server.Request("GET" "/")
GET / HTTP/1.1
Accept-Encoding: identity
Host: mirlemont
Connection: close
User-Agent: Python-urllib/2.7

(Yes, my computer's name is Mirlemont. What's yours'? :) )

You could control the selection of IP address using a hosts file. In
Unix, that's /etc/hosts; in Windows,
c:\windows\system32\drivers\etc\hosts; in OS/2, c:\mptn\etc\hosts;
etc. The urllib2 resolver should respect that.

Chris Angelico