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RE: Submitting lock tokens without a validity check

From: Clemm, Geoff <gclemm@rational.com>
Date: Wed, 20 Nov 2002 23:14:35 -0500
Message-ID: <E4F2D33B98DF7E4880884B9F0E6FDEE201081290@SUS-MA1IT01>
To: "'Webdav WG'" <w3c-dist-auth@w3c.org>
Oops: "to avoid lock protection" should read "to avoid lost updates".


-----Original Message-----
From: Clemm, Geoff [mailto:gclemm@Rational.Com]
Sent: Wednesday, November 20, 2002 10:52 PM
To: 'Webdav WG'
Subject: Submitting lock tokens without a validity check

One of the topics discussed at this weeks WebDAV working group meeting 
was how to provide a mechanism that would allow a client to submit a 
set of lock tokens without a validity check (i.e. the request could 
succeed even if some or all of those lock tokens have expired). 
Note that a client needs to submit an If header with etags with such 
a request, to avoid lock protection. 

There are currently two alternative proposals for this (the semantics 
of these two proposals are identical, so this is a marshalling question): 

Proposal One: Extend the If header so that it can take a comma 
separated list of arguments (and therefore can be split into multiple 
If statements).  To submit a set of lock tokens without a validity 
check, the following pattern would be used: 

  If: urlA (tokenA [etagA]) (Not tokenA [etagA]) 
  If: urlB (tokenB [etagA]) (Not tokenB [etagB]) 

Proposal Two: Add a new header for a comma separated list of lock 
tokens that indicate possession of the lock token but do not cause the 
request to fail if they are invalid (I neglected to write down the 
proposed name, so I'll just call it New-Header).  Since the etag list 
can be long when the client holds a large number of locks, the 
extension defined in alternative one is also required, to handle the 
possibly large number of etags.  The pattern of usage for this 
proposal would be: 
  New-Header: tokenA 
  If: urlA ([etagA]) 
  New-Header: tokenB 
  If: urlB ([etagB]) 

Advantage of proposal 1: 
- It does not require defining an extra header. 

Advantage of proposal 2: 
- It requires 40% fewer strings per resource (3 non-constant strings 
instead of 5 non-constant strings).  Lisa: You calculated that 
proposal one requires four times as many non-constant strings ... how 
did you get that number? 

I believe that it is not appropriate to add a new header to the protocol 
just to decrease the header length for this particular use case by 40%. 

I am particularly disinclined to optimize this kind of request, 
because I believe that it is significantly simpler for a client to 
use a standard If header, and if locks have expired, the request 
fails, the client deletes from its state those expired locks, and then 
resubmits the request, replacing the expired locks with etags.  This 
allows the client to just issue very simple If header requests, 
i.e. if the lock token for urlA is still valid but the lock token for 
urlB has expired: 

If: urlA (tokenA) 
If: urlB ([etagB]) 

Received on Wednesday, 20 November 2002 23:15:09 UTC

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