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Subject DO NOT REPLY [Bug 39727] Incorrect ETag on gzip:ed content
Date Fri, 13 Feb 2009 02:42:14 GMT

--- Comment #32 from Henrik Nordstrom <>  2009-02-12 18:42:13 PST
Deleting the ETag+Content-Location is safe with respect to caches even if very
suboptimal in terms of HTTP performance and cache validation robustness. It's
highly undesireable, but still better than sending out the same ETag or
Content-Location on incompatible respones.

Sending responses with an ETag and/or Content-Location which MAY be shared by
an incompatible response for the same URL makes a true mess for caches. This
applies to both 200 and 304 responses. The mess gets injected by the processing
of 304 responses which may make incompatible but identified equal content
migrate between different requeests.

And yes, Roy is absolutely right. HTTP is not well suited for on-the-fly
content recoding. You can't both eat the cake and keep it unless you do a lot
of effort, far beyond the recoding itself. To anyone external from the server
it SHOULD look like the recoding is in fact done statically with different
representations stored on the server (i.e. page.html and page.html.gz) as
negotiated by mod_negotiate, That means unique ETags and unique
Content-Location, plus the If-* conditions working properly for all

Not impossible, but not easy either.

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