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From Henrik Nordstrom <>
Subject Re: Wrong etag sent with mod_deflate
Date Fri, 08 Dec 2006 14:39:49 GMT
fre 2006-12-08 klockan 14:47 +0100 skrev Justin Erenkrantz:

> mod_deflate is certainly not creating a new resource

It is creating a new HTTP entity. Not a new object on your server, but
still a new unique HTTP entity with different characteristics from the
identity encoding.

If we were talking about transfer-encoding then you would be correct as
it only alter the encoding for transfer purposes and not the HTTP entity
as such, but this is content-encoding. Content encoding is a property of
the response entity.

The main reason why things get blurred is because the creation of this
entity is done on the fly instead of creating a new resource on the
server like HTTP expects. As result you need to be very careful with the
ETag and Content-Location headers.

Not modifying ETag (including just making it weak) says that the
identity and gzip encodings is semantically equivalent, and can be
exchanged freely. In other words says it's fine to send gzip encoding to
all clients (which we all know it's not).

Not modifying/removing Content-Location is less harmful but will cause
cache bouncing, as each time the cache sees a new response entity for a
given URI any older ones with the same Content-Location will get removed
from the cache.


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