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Date:	Wed, 16 Sep 2009 10:50:54 +0100
From:	Dave Korn <dave DOT korn DOT cygwin AT googlemail DOT com>
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Subject:	Re: setup.exe: Determine Geographically closest mirror programmatically
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Dr. Christoph Gille wrote:
>> Closest mirror?  I'm not sure what you mean by this.  'setup.exe' does
>> not require this as a setting.  Actually, there is no such concept.  You
>> need to specify a mirror to work with but you can do that with '-s'.
> 
> With each superfluous click I lose a user, so it would be best if setup.exe
> would be run within http://3d-alignment.eu/  without user interaction.

  You could very simply compile a custom version of setup.exe for your users
which had a different URL for the mirrors list, pointing to a custom list on
your own server that only had one entry on it for 3d-alignment.eu.  (You could
even take advantage of the opportunity to replace the public key embedded in
it with one that you could use for signing on your own server; otherwise your
users will need to run setup.exe using the -X command-line flag to ignore
security, or you'd need to distribute a key file to all your users somehow.)

> I am not a network specialist, but I see two possibilities how I could
> determine the closest cygwin mirror:
> 
> (I) I could compare the IP numbers  of all mirrors to the IP number of the
> client and make a guess of the geographically closest site. I would use the
> site where the first digits of the IP match best and I would then probe a
> short file to check whether the mirror is indeed working.
> 
> (II) This is what I am currently using to determine the fastest database
> mirror for 3D-structures: I fetch a tiny probe file from each database
> mirror and take the one with the shortest respond time. This method is more
> simple  but as there are that many cygwin mirrors, I am not sure whether I
> would run into problems.

  Just as one further possibility, there's a bit of scripting on the page at
the cygwin website about how to setup your own package server that uses a
utility called 'netselect' to determine which is the fastest server in the
mirrors list:

    http://sourceware.org/cygwin-apps/package-server.html

  You might (or perhaps might not) find it adaptable to suit your purposes.

> When I have the mirror I would set it with the command line option of
> setup.exe. I think this would work and could be done easily. Do you have
> other ideas?

  If you wanted to be really cool, the URL that points to the alternative
mirrors list on your own server can in fact be a CGI script of some kind that
selects a geographically-nearest server based on the client's browser request
headers, and returns a dynamically generated mirrors.lst with one entry
customised just for that user.

> Could you please tell me the URL of the file with the cygwin mirror list?

  http://cygwin.com/mirrors.lst

  In the setup.exe source code, this is defined in IDS_MIRROR_LST in res.rc.

    cheers,
      DaveK

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