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RE: Bindings, Locks, and MOVE

From: Kevin Wiggen <wiggs@wiggenout.com>
Date: Tue, 14 Sep 1999 11:11:48 -0700
To: "Slein, Judith A" <JSlein@crt.xerox.com>, "'Yaron Goland (Exchange)'" <yarong@exchange.microsoft.com>, <jamsden@us.ibm.com>, <w3c-dist-auth@w3.org>
Message-ID: <LNBBKDGPNJMOJNOBHLLMKEGCCCAA.wiggs@wiggenout.com>


My thoughts on the following subject, and some random thoughts...

1)  Xythos does have cross-server communication planned.  We have a hook for
it, some code written, but need to build a version that works with
proxy-servers etc.  This being said, I agree that cross-server MOVE is hard.
For all the reasons stated earlier plus other things such as keeping
permissions on a file constant across servers (especially if they are across
corporate barriers and users/groups do not exist on both servers.  I will
agree with the statements that cross-server MOVE should be out-of-scope for
Webdav, and should just return an error.  Clients can still issue a COPY,
then DELETE if they want.

Xythos will implement cross-server COPY.

2)  I am fine with the lock-token being MOVED with a resource.  If we can
get away with saying cross-server MOVE is not supported, then the individual
servers simply need to make a way of keeping locks on their own server.  I
believe this is how we should proceed.  It sounds like we are cutting out a
bunch of functionality, but I think it will take a whole set of working
groups to get cross-server MOVE to work correctly in all cases anyway, so we
might as well punt now.

3)  I believe (with I think most other people), that the language
surrounding the use of write-lock, should remain a MUST.

4)  I would then like to take Judith's original note on locks and work
though the scenarios to make sure we are all not missing anything...

I now assume that locks are locking the resource not the URI.

A resource is being MOVEd.  The locks are on that resource and / or its
destination, not the collections that contain them.

1. The source resource is locked, but the destination is not.
MOVE /a/b to /x/y, where /a/b is locked  but /a/ is not and /x/y is not.

<KW> /a/b moves to /x/y and remains locked with the same lock-token it had
before.  The only Lock Token mentioned still exists and remains on the
resource it was locking.</KW>

2. The source resource is not locked, but the destination is.
MOVE /a/b to /x/y, where /a/b is not locked and /x/ is not locked, but /x/y
is locked

<KW> This one gets a little weird.  I assume that we can delete /x/y since
we have the lock on it.  This delete removes the lock from the system.  When
/a/b is moved to /x/y, it still is not locked.

As a user, I might expect that /a/b (which is now /x/y) has the /x/y lock,
but I have always thought (from a user's perspective) that a merge would
happen and not a delete followed by a write.  But the fact that the lock is
removed from the system, does make the rest of the scenarios work
nicely</KW>

3. Both are locked, but with separate locks.
MOVE /a/b to /x/y, where /a/b has lock L1 and /x/y has lock L2, but neither
/a/ nor /x/ is locked.

<KW> This will remove L2 from the system, and the new /x/y is still locked
by L1.</KW>

A resource is being MOVEd.  The locks are Depth: infinity locks on the
collections that contain either the source or the destination location.

4. The source collection is locked, but the destination collection is not
MOVE /a/b to /x/y, where /a/ is locked, but /x/ is not and /x/y is not.

<KW> Since the lock on /a/b comes from /a, the lock is not kept on its move.
/a remains locked, but the new resource /x/y loses the lock it had on it.
</KW>

5. The source collection is not locked, but the destination collection is.
MOVE /a/b to /x/y, where /a/ is not locked and /a/b is not locked, but /x/
is locked.

<KW> The original /x/y is removed, and the lock on that resource is removed.
/a/b is then moved there, and picks up the lock from its new parent /x/</KW>

6. Both are locked, but with separate locks.
MOVE /a/b to /x/y, where /a/ has lock L1 and /b/ has lock L2.

<KW> /x/y is removed and its resource is no longer locked by L2.  /a/b is
removed from /a's lock, and the resource is added to the L2 lock space.</KW>

One lock is at the collection level, the other at the resource level.

7. The source resource is locked, and the destination collection is locked
with a different token
MOVE /a/b to /x/y, where /a/b has lock L1, /a/ is not locked, and /x/ has
lock L2.

<KW> I believe this must FAIL.  A user cannot have 2 locks on the same
resource, and therefore needs to remove one of them before the MOVE can
happen.</KW>

8. The source collection is locked, the destination resource (not its
collection) is locked with a different token
MOVE /a/b to /x/y, where /a/ has lock L1, /x/ is not locked, and /x/y has
lock L2.

<KW> Strangely enough (to the user), this succeeds.  The lock L2 is removed
from the system during the DELETE phase of the move, /a/b is then moved.  It
is removed from /a's L1 and no lock now exists on the new /x/y </KW>

For the following cases, should the MOVE succeed or fail? If it succeeds,
what should the lock state be afterwards?

9. The source resource was locked through one mapping, and a MOVE is
attempted through a different mapping.
9a. /a/b and /c/d map to R. /a/ is locked. MOVE /c/d to /x/y.

<KW> Since locks are on resources, if the correct lock-token is passed, I
say this succeeds.  The new /x/y is still locked via /a's lock because the
binding for /a/b still exists.  In order to do something to the new /x/y you
need to pass the correct lock-token.</KW>

9b. /a/b and /c/d map to R. /a/ is not locked, but /a/b is. MOVE /c/d to
/x/y.

<KW> Again the MOVE succeeds if the token for R is given, the resource is
still locked and bound to /a/b and the new /x/y </KW>

10. The destination resource was locked through one mapping, and a MOVE is
attempted through a different mapping.
10a. /w/x and /y/z map to R. /w/ is locked. MOVE /a/b to /y/z.

<KW> If correct lock token for R is given (If header with a tagged list of
/y/z and the correct token) the move completes.  Since /w is locking the
resource R, it continues to do so, but /y/z no longer maps to R so it is not
locked anymore </KW>

10b. /w/x and /y/z map to R. /w/ is not locked, but /w/x is. MOVE /a/b to
/y/z.

<KW> If the correct lock-token for R is passed (through the correct IF
header and tagged list), the MOVE succeeds.  When it is done, /w/x is still
locking R, and the new /y/z is no longer locked as it now points to a new
resource R2. </KW>

Kevin
Received on Tuesday, 14 September 1999 14:13:44 GMT

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