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RE: Issue: WRITE_DAV_PROP

From: Jim Whitehead <ejw@cse.ucsc.edu>
Date: Mon, 16 Apr 2001 12:24:17 -0700
To: "John Glavin" <john@riverfrontsoftware.com>, "WebDAV WG" <w3c-dist-auth@w3.org>
Message-ID: <AMEPKEBLDJJCCDEJHAMICELMCMAA.ejw@cse.ucsc.edu>
John Glavin writes:
> I agree about the "getlastmodified" property.  I would love to be able to
> set this so that file synchronization software will work properly.  My
> product maps a network drive to a DAV server and unless I can set the
> "getlastmodified" property file synch software won't work right.  I only
> know of one server that allows this now, it would be nice if this could be
> standardized.

Hmm, it's not at all obvious to me why writing to getlastmodified helps
synchronization. Naively I would think the synchronization algorithm on
resource R would be:

- retrieve getlastmodified and getetag properties on R
- IF local copy of R unchanged AND ((getlastmodified > R file timestamp) OR
(getetag != stored value of R's etag from when it was originally
downloaded)) THEN get file from server & update cached etag value ELSE leave
local copy of R unchanged (it is the latest version)
- IF local copy of R is changed THEN
  - IF (getlastmodified > value of getlastmodified from last download of the
resource) OR (getetag != stored value of R's etag from when it was
originally downloaded) THEN note a conflict, since the file has been updated
on the client and the server
  - ELSE write the client file to the server, since the client file has been
changed, and the server file hasn't


I don't ever see a case here where changing the value of getlastmodified
helps. When writing the client file to the server using PUT, the server
automatically updates getlastmodified.

This synch algorithm does assume that two pieces of metadata are stored for
each resource, on the client side:

- value of getlastmodified from the last download of the resource
- value of getetag from the last download of the resource

- Jim
Received on Monday, 16 April 2001 15:25:55 GMT

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