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Re: Feedback on the ping="" attribute (ISSUE-1)

From: Mark Baker <distobj@acm.org>
Date: Tue, 6 Nov 2007 23:51:30 -0500
Message-ID: <e9dffd640711062051o66b70853nfd295688ac47277d@mail.gmail.com>
To: "Ian Hickson" <ian@hixie.ch>
Cc: "Julian Reschke" <julian.reschke@gmx.de>, "HTML WG List" <public-html@w3.org>

On 11/6/07, Ian Hickson <ian@hixie.ch> wrote:
> > Ok.  The closest thing to a definition that Roy's cited, AFAIK, can be
> > found here;
> >
> > http://lists.w3.org/Archives/Public/www-tag/2002Apr/0207.html
> >
> > But again, the word can be used in many contexts, including both the
> > contexts that are of importance here: message and implementation.  So
> > I'm not sure that will help.
> The above e-mail seems to imply that a message in HTTP is "safe" if it
> causes no loss of property for the user (with a loose definition of
> property here).

No, what Roy cited there was just a subject-independent definition of
safety.  When applied to the server implementation, it would mean what
you describe.  But as HTTP is a protocol, that's not what it means.

> Note, though, that it seems that the danger is not in doing "safe" things
> with "unsafe" methods, but with doing "unsafe" things with "safe" methods.
> That is, doing "unsafe" work (work which can cause loss of property) is
> bad when you're using GET or HEAD -- but doing "safe" work as part of a
> message with "POST" is harmless. As far as I can tell.

None of what you describe there is "bad".  If a server wants to change
something when it receives a GET, it is completely free to do so.
What it cannot do though, is blame the user for that change because
they didn't ask for it (as the message the user agent sent was safe).

> On the other hand, if we agree that "idempotent" means "has no important
> side-effects" (for anyone), then clearly ping="" is not idempotent, and
> so we have to have a non-idempotent method.

That sounds like "safe".  "idempotent", for a message, means that any
series of identical messages means the same as just one.

> Does that make sense?

It still seems we're talking past each other.  I'm all out of ways to
explain my position though, so hopefully others will have better luck.

Mark Baker.  Ottawa, Ontario, CANADA.         http://www.markbaker.ca
Coactus; Web-inspired integration strategies  http://www.coactus.com
Received on Wednesday, 7 November 2007 04:51:44 UTC

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