Subject: Re: Last Call: 'Calendaring Extensions to WebDAV (CalDAV)' to Proposed Standard (draft-dusseault-caldav)

From: Julian Reschke <[email-masked]>
Date: Mon, 31 Jul 2006 08:45:11 +0200

Hi,

below are last call comments, interleaved with the spec text.

Best regards, Julian

-- 

Section 1., para. 2:

     Discussion of this specification is taking place on the mailing list
     <http://lists.osafoundation.org/mailman/listinfo/ietf-caldav>.
     [[anchor2: Clarify that this paragraph should be removed upon
     publication --reschke]]

Section 1.2., para. 3:

     The XML declarations used in this document do not include namespace
     information.  Thus, implementers MUST NOT use these declarations as
     the only way to create valid CalDAV properties or to validate CalDAV
     XML element type. [[anchor5: "...MUST NOT use these declarations as
     the only way..." is extremly hard to understand; the presence of
     RFC2119 keywords make things worse in that the reader is confused to
     believe that a normative statement is being made.  As far as I can
     tell, all this wants to say is that the missing namespace needs to be
     taken into account.  Please clarify. --reschke]] Some of the
     declarations refer to XML elements defined by WebDAV
     [I-D.ietf-webdav-rfc2518bis] which use the "DAV:" namespace.
     Wherever such XML elements appear, they are explicitly prefixed with
     "DAV:" to avoid confusion.

Section 2., para. 5:

     o  MUST support transport over TLS [RFC2246] as defined in [RFC2818]
        (note that [RFC2246] has been obsoleted by [RFC4346]); [[anchor6:
        I assume that the down reference to RFC2818 (informational RFC) is
        intended; but what about the stuff with RFC2246?  Why doesn't spec
        refer to RFC4346 instead? --reschke]]

Section 3.1., para. 4:

     The CalDAV server or repository is the canonical location for
     calendar data and state information. [[anchor8: "server or
     repository": I think it would be good if the spec would choose one
     term and stick with it --reschke]] Both CalDAV servers and clients
     MUST ensure that the data is consistent and compliant. [[anchor9:
     What does it exactly mean for the data to be "consistent" and
     "compliant"?  If there's no exact definition for that then the "MUST"
     should go --reschke]] Clients may submit requests to change data or
     download data.  Clients may store calendar objects offline and
     attempt to synchronize at a later time.  However, clients MUST be
     prepared for calendar data on the server to change between the time
     of last synchronization and when attempting an update, as calendar
     collections may be shared and accessible via multiple clients.
     Entity tags and other features make this possible.

Section 5.2.4., para. 5:

     Description:  The CALDAV:supported-calendar-data property is used to
        specify the media type supported for the calendar object resources
        contained in a given calendar collection (e.g., iCalendar version
        2.0).  Any attempt by the client to store calendar object
        resources with a media type not listed in this property MUST
        result in an error, with the CALDAV:supported-calendar-data
        precondition (Section 5.3.2.1) being violated.  In the absence of
        this property the server MUST accept data with the media type
        "text/calendar" and iCalendar version 2.0, and clients can assume
        that. [[anchor15: What about other types in this case? --reschke]]

Section 5.3.1., para. 3:

     Clients SHOULD use the DAV:displayname property for a human-readable
     name of the calendar.  Clients can either specify the value of the
     DAV:displayname property in the request body of the MKCALENDAR
     request, or alternatively issue a PROPPATCH request to change the
     DAV:displayname property to the appropriate value immediately after
     issuing the MKCALENDAR request.  Clients SHOULD NOT set the DAV:
     displayname property to be the same as any other calendar collection
     at the same URI "level".  When displaying calendar collections to
     users, clients SHOULD check the DAV:displayname property and use that
     value as the name of the calendar.  In the event that the DAV:
     displayname property is empty, the client MAY use the last part of
     the calendar collection URI as the name, however that path segment
     may be "opaque" and not represent any meaningful human-readable text.
     [[anchor17: This seems to profile DAV:displayname as defined by
     RFC2518bis.  Furthermore it's not clear what happens when the client
     violates the constraint. --reschke]]

Section 5.3.4., para. 4:

     In the case where the data stored by a server as a result of a PUT
     request is not equivalent by octet equality to the submitted calendar
     object resource, the behavior of the ETag response header is not
     specified here, with the exception that a strong entity tag MUST NOT
     be returned in the response.  As a result, clients may need to
     retrieve the modified calendar object resource (and ETag) as a basis
     for further changes, rather than use the calendar object resource it
     had sent with the PUT request. [[anchor22: See comments on ietf-
     discuss mailing list. --reschke]]

Section 6.2.1., para. 4:

     Conformance:  This property MAY be defined in a principal resource.
        If defined, it MAY be protected and SHOULD NOT be returned by a
        PROPFIND DAV:allprop request (as defined in Section 14.2 of
        [I-D.ietf-webdav-rfc2518bis]).  Support for this property is
        RECOMMENDED. [[anchor24: Doesn't compute.  Is this a MAY
        (OPTIONAL) or a SHOULD (RECOMMENDED)? --reschke]]

Section 7.5., para. 1:

     Some calendaring REPORTs defined in this document allow partial
     retrieval of calendar object resources.  A CalDAV client MAY specify
     what information to return in the body of a calendaring REPORT
     request. [[anchor29: Why does this simple statement require RFC2219
     terminology?  Please don't over-use it.  In particular, please check
     that all "MAY" requirements really are needed for the purposes
     outlined in RFC2219. --reschke]]

Section 7.7.6., para. 1:

     In this example, the client requests the server to return the VEVENT
     component that has the UID property set to
     "[email-masked]". [[anchor37: Is whitespace
     significant here?  In which case the example below would be invalid.
     -reschke]]

Section 7.8., para. 4:

        The request body MUST be a CALDAV:calendar-multiget XML element
        (see Section 9.9).  If the Request-URI is a collection resource,
        then the DAV:href elements MUST refer to calendar object resources
        within that collection, and they MAY refer to calendar object
        resources at any depth within the collection.  As a result the
        "Depth" header MUST be ignored by the server and SHOULD NOT be
        sent by the client. [[anchor42: Bad idea.  Just stick with
        RFC3253/RFC3744 terminology (invalid depth values are rejected by
        the server, not ignored).  This leaves the possibilily to later
        define semantics for these values. --reschke]] If the Request-URI
        refers to a non-collection resource, then there MUST be a single
        DAV:href element that is equivalent to the Request-URI.

Section 8.4., para. 3:

     For calendar sharing and scheduling use cases, one might wish to find
     the calendar belonging to another user.  If the other user has a
     calendar in the same repository, that calendar can be found by using
     the principal namespace required by WebDAV ACL support.  For other
     cases, the authors have no universal solution but implementers can
     consider whether to use vCard [RFC2426] or LDAP [RFC2251] standards
     together with calendar attributes [RFC2739]. [[anchor55: LDAP
     reference is outdated. --reschke]]

Section 8.5.2., para. 1:

     CalDAV clients SHOULD support downloading of external attachments
     referenced by arbitrary URI schemes, by either processing them
     directly, or by passing the attachment URI to a suitable "helper
     application" for processing, if such an application exists.  CalDAV
     clients MUST support downloading of external attachments referenced
     by the "http" URI scheme, and MAY support downloading of external
     attachments referenced by the "https" URI scheme.  An external
     attachment could be: [[anchor59: Very confusing: MAY, SHOULD and MUST
     requirements for basically the same thing.  In particular, the MAY
     for "https" is bogus, because the spec just stated that the client
     SHOULD support arbitrary schemes. --reschke]]

Section 9.5., para. 7:

     Note:  The CALDAV:calendar-data XML element is specified in requests
        and responses inside the DAV:prop XML element as if it were a
        WebDAV property.  However, the CALDAV:calendar-data XML element is
        not a WebDAV property and as such it is not returned in PROPFIND
        responses nor used in PROPPATCH requests. [[anchor62: For this
        reason, I think a syntax where it can't be confused with a
        property whould be better. --reschke]]

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