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Re: Does idempotence include the response codes?

From: Nicolas Mailhot <nicolas.mailhot@laposte.net>
Date: Wed, 16 Oct 2013 11:52:49 +0200
Message-ID: <a3a44bd26848044a5d3c706905742064.squirrel@arekh.dyndns.org>
To: "Nicolas Mailhot" <nicolas.mailhot@laposte.net>
Cc: "Willy Tarreau" <w@1wt.eu>, "cowwoc" <cowwoc@bbs.darktech.org>, "Martin Thomson" <martin.thomson@gmail.com>, "Mark Nottingham" <mnot@mnot.net>, "Julian Reschke" <julian.reschke@gmx.de>, "HTTP Working Group" <ietf-http-wg@w3.org>

Le Mer 16 octobre 2013 11:47, Nicolas Mailhot a écrit :
> Le Mer 16 octobre 2013 06:00, Willy Tarreau a écrit :
>> The main idea behind idempotence is to know whether or not a client can
>> safely resend a request that failed because of network errors. For
>> example,
>> sending a request over an established connection may result in an error
>> if
>> the server decided to close at the same time. But the client has no way
>> to
>> know if the request was considered or not, so it must resend it. If the
>> previous request was correctly processed, the second one may return an
>> error, but it's the client's job to handle this. I can give you an
>> example
>> here with unix commands :
> I'm not sure I agree with the example, I've seen cases where idempotence
> is a much stronger property.
> For example, since GET is idempotent, that means a malware checker service
> can replay (before or after the browser) get requests to check if the
> result is dangerous or not. And it does not affect the result the browser
> will receive on its own GET.
> If you say mv is an example of idempotence, that means all the broken
> websites that transform GETs into implicit POSTs are right, since the
> first GET destroys the result the following GET could expect.
> IMHO idempotence means a replay of the same command will give the same
> result, baring errors, website reorganisations, and data changes (when the
> request exposes some dynamic data store)

Or to put it more succinctly an idempotent method must not trigger by
itself a state change server-side. Is that clear and short enough for

Nicolas Mailhot
Received on Wednesday, 16 October 2013 09:53:18 UTC

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