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WebDav methods and idempotency

From: Mark Nottingham <mnot@mnot.net>
Date: Thu, 24 Feb 2005 21:38:00 -0800
Message-Id: <00e2ac1ef9bcade15ebed6e8af99e779@mnot.net>
To: w3c-dist-auth@w3.org

A couple of questions about WebDAV;

* The only mention of idempotency in any WebDAV RFC that I see is: 
"Responses from a MKCOL request MUST NOT be cached as MKCOL has 
non-idempotent semantics" in 2518, Section 8.3.2. Is it the case, then, 
that all other WebDAV-defined methods are in fact idempotent?

I could see MOVE as non-idempotent, IF the semantics of COPY are such 
that it's legal to COPY a null resource; i.e., the MOVE would first 
COPY the existant resource, then DELETE it, then on a subsequent 
request, would COPY the null resource. However, it isn't clear from a 
casual reading of 2518 as to whether COPY will fail (404?) if you try 
to point it at a null resource.

* How is MKCOL non-idempotent? I.e., how does performing MKCOL /foo 
five times have different side effects than performing it once? 2518 
says that "If the resource identified by the Request-URI is non-null 
then the MKCOL MUST fail." It seems that all MKCOLs after the first one 
will fail, thus bringing no new side-effects. I can certainly see how 
MKCOL could be involved in a non-idempotent sequence, but don't see how 
it is on its own; am I missing something, or should it be "MKCOL has 
side effects" instead of "MKCOL has non-idempotent semantics?"

Thanks,

--
Mark Nottingham     http://www.mnot.net/
Received on Friday, 25 February 2005 05:39:47 GMT

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