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Re: Subprocess puzzle and two questions

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On Thu, Nov 15, 2012 at 3:20 AM, Roy Smith <roy@panix.com> wrote:
> I wrote:
>>> Oh, my.  You're using DNS as a replacement for ping?  Fair enough.  In
>>> that case, all you really care about is that you can connect to port 53
>>> on the server...
>>>
>>> s = socket.socket()
>>> s.connect(('8.8.8.8', 53))
>
> In article <mailman.3684.1352904008.27098.python-list@python.org>,
> Chris Angelico  <rosuav@gmail.com> wrote:
>>That assumes that (a) the remote server supports TCP for DNS
>
> This is true.  I honestly don't know what percentage of DNS servers
> out there only support UDP.  The two I tried (Google's 8.8.8.8, and my
> Apple TimeCapsule) both supported TCP, but that's hardly a
> representitive sample.

I don't know either, all I know is that DNSReport recommends
supporting TCP, and none of my DNS servers ever fail that check.

>> and (b) that connection time for TCP is comparable to
>> ping or an actual DNS lookup.
>
> My first thought to solve both of these is that it shouldn't be too
> hard to hand-craft a minimal DNS query and send it over UDP.  Then, I
> hunted around a bit and found that somebody had already done that, in
> spades.  Take a look at http://www.dnspython.org; it might be exactly
> what's needed here.

Yeah, that sounds like a good option. I'm slightly surprised that
there's no way with the Python stdlib to point a DNS query at a
specific server, but dnspython might be the solution. On the flip
side, dnspython is dauntingly large; it looks like a full
implementation of DNS, but I don't see a simple entrypoint that wraps
it all up into a simple function that can be bracketed with
time.time() calls (granted, I only skimmed the docs VERY quickly). So
it may be simpler to hand-craft an outgoing UDP packet once, save it
as a string literal, send that, and just wait for any response. That
eliminates all DNS protocolling and just times the round trip.

ChrisA

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Subprocess puzzle and two questions wrw@mac.com - 2012-11-13 22:34 -0500
  Re: Subprocess puzzle and two questions Roy Smith <roy@panix.com> - 2012-11-13 23:41 -0500
    Re: Subprocess puzzle and two questions William Ray Wing <wrw@mac.com> - 2012-11-14 00:03 -0500
      Re: Subprocess puzzle and two questions Roy Smith <roy@panix.com> - 2012-11-14 09:22 -0500
        Re: Subprocess puzzle and two questions Chris Angelico <rosuav@gmail.com> - 2012-11-15 01:40 +1100
          Re: Subprocess puzzle and two questions roy@panix.com (Roy Smith) - 2012-11-14 11:20 -0500
            Re: Subprocess puzzle and two questions Chris Angelico <rosuav@gmail.com> - 2012-11-15 08:54 +1100
              Re: Subprocess puzzle and two questions Roy Smith <roy@panix.com> - 2012-11-14 20:49 -0500
                Re: Subprocess puzzle and two questions Chris Angelico <rosuav@gmail.com> - 2012-11-15 13:04 +1100
                Re: Subprocess puzzle and two questions Roy Smith <roy@panix.com> - 2012-11-14 21:10 -0500
                Re: Subprocess puzzle and two questions Chris Angelico <rosuav@gmail.com> - 2012-11-15 13:21 +1100
                Re: Subprocess puzzle and two questions Dave Angel <d@davea.name> - 2012-11-14 21:55 -0500
                Re: Subprocess puzzle and two questions Kushal Kumaran <kushal.kumaran+python@gmail.com> - 2012-11-15 10:23 +0530
                Re: Subprocess puzzle and two questions Nobody <nobody@nowhere.com> - 2012-11-15 22:54 +0000
                Re: Subprocess puzzle and two questions Roy Smith <roy@panix.com> - 2012-11-15 20:07 -0500
                Re: Subprocess puzzle and two questions Nobody <nobody@nowhere.com> - 2012-11-17 00:17 +0000
              DNS from Python (was Re: Subprocess puzzle and two questions) aahz@pythoncraft.com (Aahz) - 2012-11-14 21:42 -0800
        Re: Subprocess puzzle and two questions wrw@mac.com - 2012-11-14 09:37 -0500
  Re: Subprocess puzzle and two questions Tim Roberts <timr@probo.com> - 2012-11-13 23:17 -0800

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