[caldav] WebDAv collection sync: last issue

Cyrus Daboo <cyrus@daboo.name> Mon, 07 June 2010 15:18 UTC

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Date: Mon, 07 Jun 2010 09:57:09 -0400
From: Cyrus Daboo <cyrus@daboo.name>
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Cc: caldav@ietf.org, vcarddav@ietf.org
Subject: [caldav] WebDAv collection sync: last issue
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Hi folks,
The latest WebDAV collection sync draft is here: 
<https://datatracker.ietf.org/doc/draft-daboo-webdav-sync/>;. We believe we 
are close to done with this and would like to submit to the IESG soon. 
However, there is one open issue that we need feedback from implementors on.

The question is whether collection resources that are immediate children of 
the collection being targeted for the REPORT should be reported as 
"modified" if any of their child resources (depth infinity) are modified.

Key points:

1) We have deliberately scoped the REPORT defined in this draft to be 
Depth:1 only - i.e. it will only report changes to immediate children. 
Depth:infinity change reporting was ruled out at this time (though 
eventually we would expect to see it defined if there is interest).

2) The first real implementations of this REPORT are being done for CalDAV 
and CardDAV servers where typically calendar/addressbook collections only 
have immediate child resources and not collections - so the draft as 
currently written is fine. (BTW there are already several client and server 
implementations of this draft that have been tested at various interops). 
However, my concern is that more "general" WebDAV servers may wish to do 
reporting of changes to immediate child collections to allow clients to 
progressively sync an entire hierarchy.

3) Reporting changes to immediate child collections requires any change at 
depth:infinity within those collections to "bubble up" - i.e. a change with 
a collection changes its DAV:sync-token and the properties of all its 
parent collections. This potentially places a big performance burden on the 
server - particularly if it were to choose to support the REPORT on the 
root resource. In reality servers would probably limit the scope of the 
report to a reasonable "sub-hierarchy" set (e.g. CalDAV and CardDAV servers 
would only support the REPORT on calendar or address book home collections 
and not on any parents of those).

-- 
Cyrus Daboo