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RE: Interop issue: Proposal for fixing lock token provision

From: Jason Crawford <nn683849@smallcue.com>
Date: Thu, 10 Oct 2002 00:26:46 -0400
To: "Clemm, Geoff" <gclemm@Rational.Com>
Cc: "'Webdav WG'" <w3c-dist-auth@w3c.org>
Message-ID: <OF403139AE.735174C3-ON85256C4D.0052D0FA@us.ibm.com>

On Wednesday, 10/09/2002 at 08:28 AST, "Clemm, Geoff" wrote:
>    From: Jason Crawford [mailto:nn683849@smallcue.com] 
> 
>    >    And ALL tag list productions would be evaluated, so that even 
>    >    if the server didn't think it was relevant, it still would be 
>    >    checked.  So for example I can do a GET on a resource with an 
>    >    IF: header and the IF: header would be checked despite the 
>    >    server thinking it is unnecessary to check for locks on a GET 
>    >    request.  Does this sound fine? 
>    > 
>    > If a server knows that no condition specifiable in an If can 
>    > cause a GET to fail, then it can skip the If check.  But if it is 
>    > not absolutely sure, then yes, it has to check the If header. 
> 
>    I don't understand that answer.  It sounds like you're saying 
>    that it's up to the server to decide what clauses should be 
>    checked.   Could you explain more? 
> 
> My answer was poorly worded.  I meant to say that if the server can 
> tell just by scanning the If header that it doesn't apply to the GET, 
> then it can skip the If header.  For example, if the If is a tagged 
> list, and the tag did not identify the request-URL, since a GET only 
> applies to the request-URL, it can ignore that If header. 

Wow.  I wouldn't have expected this as an answer.  It sounds
like the purpose of the If: header becomes for the server to
verify what it wants to.  That seems 
like a signficant change in philosophy from 2518.  2518 seems
to spend a lot of time talking about If: header and all it's
details but not about how it's used to submit lock tokens.  It's use
for lock token submission seems to simply be an afterthought.  It even
says the following when  it begins to talk about the If; header.

   The If header is intended to have similar functionality to the If-
   Match header defined in section 14.24 of [RFC2616].  However the If 
   header is intended for use with any URI which represents state 
   information, referred to as a state token, about a resource as well 
   as ETags.  A typical example of a state token is a lock token, and 
   lock tokens are the only state tokens defined in this specification. 

And I've taken this opening statement, and the fact that it never talks
about lock token submission in this section, to mean that the primary 
purpose of the If: header was for a client to verify various aspects
of server state (like If-Match) before doing an operation.  I'm not saying
that you're wrong to want to specify what you just have, but it seems 
to me that you are suggesting is a change in purpose/philosophy
because the client can no longer really fully use it for verifying
server state.    I want to bring
attention to that to be sure that's what you really want.

I'm going to stray a bit and say a bit about 2518 and say what I've
said above in a different way...

Above I outlined what I thought the *primary* purpose of the If:
header was in 2518.   But there are stray comments in the 2518
that make the If; header's purpose confused.  We've fixed one
of those in 2518bis.  But 2518bis still has the statement that the
server will only check the assertions on the URL's it chooses.
With that statement, the semantics and purpose of the If; header 
gets confusing.   It's like the server saying, 
   "you can ask me questions, but I'll only answer the one's 
   I want, and I'll only cooperate with your request if you ask 
   all the questions I want you to ask me."
It (2518) just doesn't make sense.  It makes it hard for us
and readers to figure out how to fill in gaps in the spec.  There
is no guiding philosophy and purpose.  It's difficult to build on 
that.


The proposal by Lisa and the interop folks, which I tried to
clearly guess at and describe, does fix this.  It provides
a clear purpose and semantics for the headers.  And it does 
a good job achieving compatibility.

As an alternative to that proposal, I think it's possible that 
you can achieve much of that by saying that the client can 
submit assertions against whatever resource it likes in 
the If: header, and the server will evaluate all of the If: header, 
and the server does also require that the client ask a few 
particular questions against particular resources.  It's not 
as simple as Lisa's solution, but it's at least an improvement 
over 2518. 

But if you say that the server only evalutes some of 
what the client submits, then you might as well abandon 
what appeared to be the primary purpose of 
the If: header in 2518.   If we do that, we should be 
aware the we're doing that and make sure we're 
comfortable with that.


> 
>    >    And what is "modifying"? A PUT/PROPPATCH to an ordinary 
>    >    resouce modifies it. 
>    > 
>    > Yes, in this case, I think we can clearly state that only the 
>    > lock on the resource specified by the request-URL must be 
>    > submitted. 
> 
>    The request URL?  I guess that's okay.  I had actually proposed the 
>    root of the lock rather than the request URL.  I think lower in 
>    this note you also said it should be the root of the lock. 
> 
> Parsing problem (:-).  I meant: "the lock on (the resource specified by 
> the request-URL) must be submitted", not "(the lock on the resource) 
> specified by the request-URL must be submitted". 

I think you didn't understand my question... 

A (depth) lock can lock 
many resources. Which locked resource/URL should be specified when 
submitting the lock token?   You've suggested both (1) the root and (2) 
the
request resource.  Another option
is to just submit it  on the resource whose being locked poses an
impediment, but there can be zillions of those in the case of operations
like the 2518-style DELETE in the presence of depth locks.  That leaves 
the first two options and I think only (1) can work universally.

> I could go either way, but I'd probably be inclined to not say 
> anything special about the NOT.  This means that putting a NOT 
> around a lock token is guaranteed to fail (i.e. because either it 
> is locked with that token, so the NOT fails, or it is not locked 
> with that token, so it is an invalid lock token, and it fails). 
> Alternatively, we could say that it is only a submission of the 
> lock token if it does not appear in a NOT, but all that buys the 
> client is the ability to have a request succeed only if the 
> resource is not locked by a particular lock token, which seems 
> like a pretty pointless semantics to support.  But I'm happy 
> to do it either way. 

I suspect that's the best approach. 

So I'd say...

All of the If; header is evaluated, 
and the token(s) in question must be "mentioned".  And I suspect we need
resolve on what resource it should be mentioned.    I'm voting tor the 
resource
that is the root of the lock. 

Am I nutz?  :-)

J.


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Received on Thursday, 10 October 2002 00:27:50 GMT

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