[Gen-art] Gen-ART review of draft-daboo-webdav-sync-07

[<[e-mail]>]

Hi Peter,

Yes, the new -07 of this draft is fine, as it resolves issues [1] and [2] as agreed
with the authors, and also resolves issue [3] by changing RFC 5842 from a normative
reference to an informative reference. That change is fine with me, as the references
to RFC 5842 are all for examples that explain some of the synchronization functionality
- it is not necessary to implement any of the requests listed as being specified in
RFC 5842 in order to implement the synchronization functionality.

Thanks,
--David

> -----Original Message-----
> From: Peter Saint-Andre [mailto:[e-mail]]
> Sent: Thursday, January 19, 2012 11:53 AM
> To: Black, David
> Cc: [e-mail]; [e-mail]; [e-mail]; [e-mail]
> Subject: Re: Gen-ART review of draft-daboo-webdav-sync-06
> 
> Hi David,
> 
> The text changes that Cyrus proposed have been incorporated into a
> revised I-D:
> 
> http://tools.ietf.org/rfcdiff?url2=draft-daboo-webdav-sync-07
> 
> Please let us know if the new version accurately reflects your
> discussion with the authors.
> 
> Thanks!
> 
> Peter
> 
> On 1/2/12 12:55 PM, [e-mail] wrote:
> > Hi Cyrus,
> >
> > The proposed changes for the two major issues look good to me:
> >
> > [1] I'm pleased that the concern about adding elements turned out to be a wording issue.
> >
> > [2] Your proposed new text is fine - it provides adequate notice/warning about possible
> > collection inconsistency, so I'm ok with not providing pseudo-code.
> >
> > I'll leave the Downref issue ([3]) for you and Peter to work out with the IESG, and I'm
> > fine with continued use of your name in the examples if that's common practice.
> >
> > Thanks,
> > --David
> >
> >> -----Original Message-----
> >> From: Cyrus Daboo [mailto:[e-mail]]
> >> Sent: Monday, January 02, 2012 2:44 PM
> >> To: Black, David; [e-mail]; [e-mail]; [e-mail]
> >> Cc: [e-mail]
> >> Subject: Re: Gen-ART review of draft-daboo-webdav-sync-06
> >>
> >> Hi David,
> >> Thank you for your review. Comments inline:
> >>
> >> --On December 27, 2011 11:07:49 PM -0500 [e-mail] wrote:
> >>
> >>> [1] -Major- Section 3.5 does not appear to cover the case reporting added
> >>> elements on a subsequent synchronization.  The problem may be that the
> >>> word "changed" as used in Section 3.5.1 is assumed to cover adding an
> >>> element - if so, that's not a good assumption, and the addition case
> >>> should be explicitly called out in the title and body of Section 3.5.1.
> >>
> >> The first sentence of 3.5.1 is:
> >>
> >>     A member URL MUST be reported as changed if it has been mapped as a
> >>     member of the target collection since the request sync-token was
> >>     generated.
> >>
> >> The term "mapped" implies creation/addition of a new resource in this case.
> >> That may not be obvious to anyone who is not intimately familiar with
> >> WebDAV terminology here, so I propose changing that to:
> >>
> >>     A member URL MUST be reported as changed if it has been newly mapped as
> >>     a member of the target collection since the request sync-token was
> >>     generated (e.g., when a new resource has been created as a child of the
> >>     collection).
> >>
> >>> [2] -Major- The operations to retrieve changed members of a collection
> >>> are not atomic wrt the operation that obtains a report on what has
> >>> changed; collection changes can occur between retrieving the report and
> >>> retrieving the changed elements or while retrieving the changed elements.
> >>> For this reason, simply obtaining a change report and then retrieving the
> >>> elements that have changed according to the report may not result in a
> >>> consistent (e.g., as of a point in time) copy of a collection.  I believe
> >>> that this absence of atomicity is a WebDAV "feature", as opposed to a
> >>> "bug", but I believe that this behavior and what to do about it should be
> >>> discussed in the draft.  I suggest the following, possibly to the end of
> >>> section 3.1
> >>>
> >>> i) Add a sentence or two to warn that obtaining a change report and then
> >>> retrieving the changed elements may not result in a consistent local
> >>> version of the collection if nothing else is done because changes may
> >>> have occurred in the interim.
> >>>
> >>> ii Add a discussion of how to ensure that a local copy of the collection
> >>> is consistent. The basic idea is to re-presented the sync token for that
> >>> copy to the server after the changed elements have been retrieved; the
> >>> local copy is consistent if the server reports that there have been no
> >>> changes.  Some pseudo-code may help, e.g.:
> >>>
> >>> 	GetSyncCollectionReport(in token, out newtoken, out report);
> >>> 	while (ReportHasChangedItems(report) {
> >>> 		GetChangedItems(report)
> >>> 		token = newtoken;
> >>> 		GetSyncCollectionReport(in token, out newtoken, out report);
> >>> 	}
> >>>
> >>> Actual code should include a counter that counts the number of iterations
> >>> of the while loop and exits with an error if the number of iterations
> >>> exceeds some limit; that error exit implies that the collection is
> >>> (currently) changing too rapidly to obtain a consistent local version.
> >>
> >> Good point. I agree that this deserves some additional text to clarify this
> >> situation. However, I would rather not go into too much detail of how
> >> clients "re-sync" in cases like this as there are a bunch of different ways
> >> that could happen each of which depends on exactly what the client is
> >> trying to do (e.g., in a lot of cases clients will be doing two-way syncs
> >> so will need to reconcile server and local changes within the loop you
> >> propose above - the details of that are not in scope for this
> >> specification). What I propose is the addition of the following paragraph
> >> to the end of Section 3.1:
> >>
> >>     Typically, a client will use the synchronization report to retrieve the
> >>     list of changes, and will follow that with requests to retrieve the
> >>     content of changed resources. It is possible that additional changes to
> >>     the collection could occur between the time of the synchronization
> >>     report and resource content retrieval, which could result in an
> >>     inconsistent view of the collection. When clients use this method of
> >>     synchronization, they need to be aware that such additional changes
> >>     could occur, and track them through normal means (e.g., differences
> >>     between the ETag values returned in the synchronization report and
> >>     those returned when actually fetching resource content), conditional
> >>     requests as described in Section 5, or repeating the synchronization
> >>     process until no changes are returned.
> >>
> >>> [3] -Minor- idnits 2.12.12  reports a Downref to RFC 5842.  Please
> >>> consult your Area Director (Peter Saint-Andre) to determine what to do
> >>> about this Downref (it requires attention, but may not require changes to
> >>> the draft).
> >>
> >> Working with IESG on this one.
> >>
> >>> Nit: I suggest not using the author's own name (cyrusdaboo) in the
> >>> examples.  Someone may copy the code from the resulting RFC.
> >>
> >> This has been common practice in most of the other CalDAV/CardDAV RFCs I
> >> have worked on and has not been the source of any problems, so I would
> >> rather leave this unchanged. If there is an official IETF policy on using
> >> "real names" in examples, then I would be happy to change to follow that,
> >> but I am not aware of anything like that.
> >>
> >>> Nit: idnits 2.12.12 reports that draft-ietf-vcarddav-carddav has been
> >>> published as RFC 6352; the RFC Editor will correct this if a new version
> >>> of the draft is not required for other reasons.
> >>
> >> Fixed in my working copy.
> >>
> >>
> >> --
> >> Cyrus Daboo
> >>
> >
>