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RE: Interop issue: Proposal for fixing lock token provision

From: Clemm, Geoff <gclemm@rational.com>
Date: Fri, 27 Sep 2002 09:42:21 -0400
Message-ID: <3906C56A7BD1F54593344C05BD1374B1085A9376@SUS-MA1IT01>
To: "'Webdav WG'" <w3c-dist-auth@w3c.org>
Could someone post what exactly were the interoperability problems
that were found?  As far as I can tell, the If header is a superior
way of handling the locking scenarios than the alternatives being

In particular, I do not find the "separation of concerns" argument
convincing, since issue #3 (detecting when you have an
invalid lock token) is exactly the reason why a single header
is used both to check state and demonstrate possession of the
required token (i.e. I believe the concerns are inherently linked).

In particular, I do not support #2, because it leads a client to
perform updates against resources that it has lost its lock on.
Why would a client ever want to do that, instead of reacquiring
a lock?  A key benefit of locks as currently defined is that they
solve the lost update problem for servers that cannot provide etags,
but updating a resource for which you have lost your lock 
opens you up to the lost update problem.

Note: If lengthy If headers has proven to be a problem, I am
happy to allow a "," to separate If clauses, so that
you can submit multiple If headers in one request.


-----Original Message-----
From: Jason Crawford [mailto:nn683849@smallcue.com]

This thread seemed to get overlooked, so I want to get discussion going on

On Sunday, 09/15/2002 at 11:31 MST, "Lisa Dusseault" wrote:
> At this week's Interop event, as at last year's, many interoperability
> problems were found with scenarios involving change methods where a lock
> token is required.  A long, animated, exciting conversation was held to
> finally achieve  consensus among attendees on goals for a new way to
> supply lock tokens to servers.
> GOALS for Lock Token Provision
> ------------------------------
> 1. Clients should be able to provide lock tokens in conditional requests
> that cause the request to fail if the token does not still match the
> state. This goal is currently met by the If header, but this goal must
> continue to be met by any new solution.
> 2. Clients should ALSO be able to provide multiple unqualified lock
> tokens in order to prove that they have those tokens and can do write
> requests legally, in a way that does not impose conditions on the
> success of the request. This mechanism should not use or affect the
> Lock-Token header which is required in UNLOCK to specify a single lock
> token to remove or refresh. This mechanism should be capable of
> supporting many values.
> 3. Servers should be able to inform clients when lock tokens being used
> in any way are no longer valid.   This helps clients keep their
> understanding of the server's state up-to-date.

I basically agree with (1) and (2).  I value keeping the server driven
of tokens seperate from client driven consistancy checks.  Hopefully this
simplify the If: header semantics.

(3) is new to me.  I'd like to hear more discussion on it.  Perhaps as a

> Discussions on how to solve
> ---------------------------
> 1. Already solved by If header. Only slight clarifications needed to
> improve basic interoperability of this header (see below).


> 2. The mechanism to provide multiple tokens could easily be a new
> header. The syntax should involve comma-separated values, because then
> lines can be split across multiple instances of the header according to
> RFC2616 header rules.

OK.  I can see how that can be implemented without breaking compatibility.

> 3. A new response header or two could allow servers to return invalid or
> unnecessary lock tokens.  This should be a response header so that the
> information can easily be marshaled even on responses that already
> contain a body. Again, the response header syntax should be
> comma-separated.

I'd like to hear more about the requirement for this.

> Slight changes to existing definitions
> --------------------------------------
> - The existing Lock-Token header is used to specify a single lock token,
> in methods that must operate on a single lock.  It is used on UNLOCK to
> remove a lock.  The LOCK refresh request should ALSO use this header
> (and the If header should continue to be supported by servers in order
> to handle existing clients).  This includes the clarification that LOCK
> refresh can only be used to refresh a single lock.  That's a good thing,
> because the Timeout header only exists once per request too.

OK with me.

>  - An untagged token in the IF header should apply ONLY to the resource
> named in the Request-URI.  The original definition is that they apply to
> any resources "affected" by the request. This has turned out to be too
> ambiguous and arduous to determine.  Also most lock tokens only apply to
> one resource, not the entire set of resources "affected" by a request
> like MOVE/COPY. Since any token in the IF header can be tagged with a
> URL in order to make it explicit what resource the token refers to, we
> can make the untagged token equally explicit without removing any client
> functionality in the If header.


So what do other people have to say?


Phone: 914-784-7569
Received on Friday, 27 September 2002 09:42:55 UTC

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