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Submitting lock tokens without a validity check

From: Clemm, Geoff <gclemm@rational.com>
Date: Wed, 20 Nov 2002 22:51:31 -0500
Message-ID: <E4F2D33B98DF7E4880884B9F0E6FDEE20108128C@SUS-MA1IT01>
To: "'Webdav WG'" <w3c-dist-auth@w3c.org>
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 22:52:03 UTC

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