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Re: salt in version probes
From: David Fifield <david () bamsoftware com>
Date: Tue, 3 May 2011 08:36:31 -0700

On Tue, May 03, 2011 at 05:38:54PM +0300, Toni Ruottu wrote:
These probes are probably fine, but I don't want to add them without any
matchlines. It's kind of a minimum barrier to entry to try a new probe
against a known server and add a match for it. (And ideally, try it
against two different servers, and get distinguishable responses.) I
notice that some of the stun-br responses contain the string
"Vovida\.org\x200\.96\", which looks like a nice server name and version
number for http://www.voip-info.org/wiki/view/Vovida.org+STUN+server. So
if you can test that, we'll add the probe.

I think it is impossible to do a regexp that would match the fields
accurately because they have length prefixes, and the regexp would
need to take into account that the fields might be in different
orders, and skip fields. On the other hand we may just have the regexp
look for string "Vovida.org", but in theory this string might exist in
some field with wrong type. I suppose we are okay with that?

We match fields with length prefixes all the time. For example, see the
AFP matches. Just use . or .. for the prefix and [\w._-]+ for the
version number part, and it usually works fine.

Yes, conceivably the fields might come in different orders, but if they
do, it means a different server or different version (at least a
different configuration), so it's fine to assume a static ordering in
each match line. Consider that the same ordering problem exists with our
thousands of HTTP match lines.

David Fifield
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