[users@httpd] Coordinating ETag policies for mirror networks

[Anthony Bryan <an...@gmail.com>]

Hi,

I work on Metalink, which tries to make downloads more reliable by
describing mirrors and checksums for download programs. One way to do
this is with Metalink/XML, another is with the Link header, Instance
Digests, and ETags [1].

It seems like it would be nice to be able to have ETag policies
coordinated across the mirror network, that is have them based on the
same attributes on all mirrors. We want them based on the file (size,
date modified, or checksum etc) and not server-unique filesystem
metadata. Then we could use If-Match to detect early on if the files
were the same.

http://httpd.apache.org/docs/2.2/mod/core.html#fileetag says the default is

	FileETag INode MTime Size

where we probably want

	FileETag MTime Size

I'm wondering why INode needs to be in there? If the default was the
second (assuming that's correct) and that's how Apache behaved when
installed, then all the mirrors would share the same ETag and you can
do neat things with that.

The problem is, it's hard to get mirrors to make changes (Fedora,
openSUSE, but I'm sure it's most open source mirror networks). Some
mirrors just silently mirror don't even know to do anything else. I
know the Apache mirrors had trouble getting in sync with the
instructions on http://www.apache.org/info/how-to-mirror.html

-- 
(( Anthony Bryan ... Metalink [ http://www.metalinker.org ]
  )) Easier, More Reliable, Self Healing Downloads

[1]
http://tools.ietf.org/html/draft-bryan-metalinkhttp

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