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Re: Mozilla and If-Modified-Since

From: Larry Masinter <masinter@parc.xerox.com>
Date: Fri, 14 Jun 1996 09:22:54 PDT
To: dmk@allegra.att.com
Cc: dan@spyglass.com, http-wg%cuckoo.hpl.hp.com@hplb.hpl.hp.com
Message-Id: <96Jun14.092259pdt.2733@golden.parc.xerox.com>
Re: "if-modified-since: tuesday, 24-Jan-95 00:24:37 GMT; length=116"
appearing to be dropped:

This was not a case of something "falling off the map", it was an
explicit choice to support entity tags instead.

A server is free to implement a kind of entity tag which contains both
modify date and length.

A cache can then just do "if-none-match" on the entity tag, without
knowing that the validator included the length.

If you want to build a _reliable_ web server for a file system that
allows random access to the files and also allows users to modify the
write dates, you should chose something other than date & length as
the cache validator. On the other hand, date is convenient, and
date+length a little more reliable, so some servers will choose to do
that.  By making the cache validator opaque (rather than explicitly
calling out date and length), we could allow many different kinds of
validators.

Because entity tags are used not only for cache validation but also
fresh variant selection, we wanted another name than "cache
validator", thus "entity tag".

Larry
Received on Friday, 14 June 1996 09:29:44 EDT

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