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Re: REPOST (was: HTTP working group status & issues)

From: Roy T. Fielding <fielding@liege.ICS.UCI.EDU>
Date: Wed, 02 Oct 1996 19:35:13 -0700
To: Foteos Macrides <MACRIDES@sci.wfbr.edu>
Cc: http-wg%cuckoo.hpl.hp.com@hplb.hpl.hp.com
Message-Id: <9610021935.aa01631@paris.ics.uci.edu>
>>Thus, introducing a `Redo-Safe: yes' header would make more sense
>>than `Idempotent: yes'.
> 
> 	The concept of "safe" is subject to a variety of interpetations,
> in contrast to "idempotent", which can be defined precisely.  We can
> define a POST as "idempotent" if it "resulted solely in a retrieval, or
> only in side effects for which the UA will not be held responsible" to
> cover the above -- which is how it already is used *in practice* -- a
> FORM with METHOD=GET could (and at many sites does 8-) cause a counter
> change on submission, but is considered idempotent by current standards.

Nope, that is the definition of "safe methods" -- idempotent is a
mathematical term having to do with repeating the method not changing
the result.  Re-read sections 9.1.1 (Safe Methods) and 9.1.2
(Idempotent Methods) of the HTTP/1.1 spec, since we are
going to get hopelessly confused if you keep swapping the meaning.
I can say that with certainty, since the reason both are defined in
the spec is because people got hopelessly confused by it every time
this WG has discussed the issue last year.

 ...Roy T. Fielding
    Department of Information & Computer Science    (fielding@ics.uci.edu)
    University of California, Irvine, CA 92697-3425    fax:+1(714)824-4056
    http://www.ics.uci.edu/~fielding/
Received on Wednesday, 2 October 1996 19:50:29 EDT

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