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From Henrik Nordstrom <>
Subject Re: Wrong etag sent with mod_deflate
Date Fri, 08 Dec 2006 14:26:42 GMT
fre 2006-12-08 klockan 14:40 +0100 skrev Justin Erenkrantz:

> Uh, no, they *are* semantically equivalent - but, yes, not
> syntactically (bit-for-bit) equivalent.  You inflate the response and
> you get exactly what the ETag originally represented.

To entities is only semantically equivalent if they can be interchanged
freely at the HTTP level with no semantic difference in the end-user

identiy and gzip encoding can not be said to bidirectionally have the
same semantic meaning as a gzip encoded entity is pure rubbish to a
recipient not understanding gzip. No more than a Swedish translation of
a document could be said to be semantically equivalent to a Greek
translation of the same document.

Content-Encoding is a case of unidirectional semantic equivalence where
the identity encoding can be substituted for the gzip encoding with kept
semantics, but for ETag bidirectional semantic equivalence is required
which is not fulfilled as gzip encoding can not be substituted for
identity encoding without risking a significant semantic difference to
the recipient.

The only real difference of a weak etag compared to a strong one is that
the weak one does not guarantee octet equality. All other restrictions
apply. Plus a bunch of protocol restrictions where weak etags is not
allowed to be used.


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