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From Nick Kew <>
Subject ETag and Content-Encoding
Date Wed, 03 Oct 2007 13:23:04 GMT

We have some controversy surrounding this bug, and bugzilla
has turned into a technical discussion that belongs here.

Fundamental question:  Does a weak ETag preclude (negotiated) 
changes to Content-Encoding?


Original bug: mod_deflate may compress/decompress content
but leave an existing ETag in place.

[ various discussion followed ]

Yesterday: I committed a fix to /trunk/, assuming it would
be uncontroversial.  The fix is that any existing ETag should
be made a weak ETag if mod_deflate either inflates or
deflates the contents.  Rationale: a weak ETag promises
equivalent but not byte-by-byte identical contents, and
that's exactly what you have with mod_deflate.

Henrik Nordstrom commented:

  "Not sufficient. The two versions is not semantically equivalen as one
  can not be exchanged for the other without breaking the protocol. In
  the context of If-None-Match the weak comparator is used in HTTP and
  there a strong ETag is equal to a weak ETag."

Further discussion followed.  I won't repost it here in full, but
since there clearly is an issue, it needs discussing here.

Cc: folks subscribed to the bug.

Nick Kew

Application Development with Apache - the Apache Modules Book

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