Extended MKCOL for Web Distributed Authoring and Versioning (WebDAV)

Network Working Group                                           C. Daboo
Request for Comments: 5689                                    Apple Inc.
Updates: 4791, 4918                                       September 2009
Category: Standards Track


  Extended MKCOL for Web Distributed Authoring and Versioning (WebDAV)

Abstract

   This specification extends the Web Distributed Authoring and
   Versioning (WebDAV) MKCOL (Make Collection) method to allow
   collections of arbitrary resourcetype to be created and to allow
   properties to be set at the same time.

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions Used in This Document  . . . . . . . . . . . . . .  3
   3.  WebDAV Extended MKCOL  . . . . . . . . . . . . . . . . . . . .  4
     3.1.  Extended MKCOL Support . . . . . . . . . . . . . . . . . .  5
       3.1.1.  Example: Using OPTIONS for the Discovery of
               Support for Extended MKCOL . . . . . . . . . . . . . .  5
     3.2.  Status Codes . . . . . . . . . . . . . . . . . . . . . . .  5
     3.3.  Additional Precondition for Extended MKCOL . . . . . . . .  5
     3.4.  Example: Successful Extended MKCOL Request . . . . . . . .  6
     3.5.  Example: Unsuccessful Extended MKCOL Request . . . . . . .  6
   4.  Using Extended MKCOL as an Alternative for MKxxx Methods . . .  8
     4.1.  MKCALENDAR Alternative . . . . . . . . . . . . . . . . . .  8
       4.1.1.  Example: Using MKCOL Instead of MKCALENDAR . . . . . .  8
   5.  XML Element Definitions  . . . . . . . . . . . . . . . . . . . 10
     5.1.  mkcol XML Element  . . . . . . . . . . . . . . . . . . . . 10
     5.2.  mkcol-response XML Element . . . . . . . . . . . . . . . . 10
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   7.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 11
   8.  Normative References . . . . . . . . . . . . . . . . . . . . . 11

1.  Introduction

   WebDAV [RFC4918] defines the HTTP [RFC2616] method MKCOL.  This
   method is used to create WebDAV collections on the server.  However,
   several WebDAV-based specifications (e.g., CalDAV [RFC4791]) define
   "special" collections -- ones that are identified by additional
   values in the DAV:resourcetype property assigned to the collection
   resource or by other means.  These "special" collections are created
   by new methods (e.g., MKCALENDAR).  The addition of a new MKxxx
   method for each new "special" collection adds to server complexity
   and is detrimental to overall reliability due to the need to make
   sure intermediaries are aware of these methods.

   This specification defines an extension to the WebDAV MKCOL method
   that adds a request body allowing a client to specify WebDAV
   properties to be set on the newly created collection or resource.  In
   particular, the DAV:resourcetype property can be used to create a
   "special" collection; alternatively, other properties can be used to
   create a "special" resource.  This avoids the need to invent new
   MKxxx methods.

2.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

   This document uses XML DTD fragments (Section 3.2 of
   [W3C.REC-xml-20081126]) as a purely notational convention.  WebDAV
   request and response bodies cannot be validated by a DTD due to the
   specific extensibility rules defined in Section 17 of [RFC4918] and
   due to the fact that all XML elements defined by this specification
   use the XML namespace name "DAV:".  In particular:

   1.  Element names use the "DAV:" namespace.

   2.  Element ordering is irrelevant unless explicitly stated.

   3.  Extension elements (elements not already defined as valid child
       elements) may be added anywhere, except when explicitly stated
       otherwise.

   4.  Extension attributes (attributes not already defined as valid for
       this element) may be added anywhere, except when explicitly
       stated otherwise.

   When an XML element type in the "DAV:" namespace is referenced in
   this document outside of the context of an XML fragment, the string
   "DAV:" will be prefixed to the element type.

   This document inherits, and sometimes extends, DTD productions from
   Section 14 of [RFC4918].

3.  WebDAV Extended MKCOL

   The WebDAV MKCOL request is extended to allow the inclusion of a
   request body.  The request body is an XML document containing a
   single DAV:mkcol XML element as the root element.  The Content-Type
   request header MUST be set appropriately for an XML body (e.g., set
   to "text/xml" or "application/xml").  XML-typed bodies for an MKCOL
   request that do not have DAV:mkcol as the root element are reserved
   for future usage.

   One or more DAV:set XML elements may be included in the DAV:mkcol XML
   element to allow setting properties on the collection as it is
   created.  In particular, to create a collection of a particular type,
   the DAV:resourcetype XML element MUST be included in a DAV:set XML
   element and MUST specify the expected resource type elements for the
   new resource, which MUST include the DAV:collection element that
   needs to be present for any WebDAV collection.

   As per the PROPPATCH method (Section 9.2 of [RFC4918]), servers MUST
   process any DAV:set instructions in document order (an exception to
   the normal rule that ordering is irrelevant).  If any one instruction
   fails to execute successfully, all instructions MUST fail (i.e.,
   either all succeed or all fail).  Thus, if any error occurs during
   processing, all executed instructions MUST be undone and a proper
   error result returned.  Failure to set a property value on the
   collection MUST result in a failure of the overall MKCOL request --
   i.e., the collection is not created.

   The response to an extended MKCOL request MUST be an XML document
   containing a single DAV:mkcol-response XML element, which MUST
   contain DAV:propstat XML elements with the status of each property
   when the request fails due to a failure to set one or more of the
   properties specified in the request body.  The server MAY return a
   response body in the case where the request is successful, indicating
   success for setting each property specified in the request body.
   When an empty response body is returned with a success request status
   code, the client can assume that all properties were set.

   In all other respects, the behavior of the extended MKCOL request
   follows that of the standard MKCOL request.

3.1.  Extended MKCOL Support

   A server supporting the features described in this document MUST
   include "extended-mkcol" as a field in the DAV response header from
   an OPTIONS request on any URI that supports use of the extended MKCOL
   method.

3.1.1.  Example: Using OPTIONS for the Discovery of Support for Extended
        MKCOL

   >> Request <<

   OPTIONS /addressbooks/users/ HTTP/1.1
   Host: addressbook.example.com

   >> Response <<

   HTTP/1.1 200 OK
   Allow: OPTIONS, GET, HEAD, POST, PUT, DELETE, TRACE, COPY, MOVE
   Allow: MKCOL, PROPFIND, PROPPATCH, LOCK, UNLOCK, REPORT, ACL
   DAV: 1, 2, 3, access-control, extended-mkcol
   Date: Sat, 11 Nov 2006 09:32:12 GMT
   Content-Length: 0

3.2.  Status Codes

   As per Section 9.3.1 of [RFC4918].

3.3.  Additional Precondition for Extended MKCOL

   WebDAV ([RFC4918], Section 16) defines preconditions and
   postconditions for request behavior.  This specification adds the
   following precondition for the extended MKCOL request.

   Name:  valid-resourcetype

   Namespace:  DAV:

   Use with:  Typically 403 (Forbidden)

   Purpose:  (precondition) -- The server MUST support the specified
      resourcetype value for the specified collection.

3.4.  Example: Successful Extended MKCOL Request

   This example shows how the extended MKCOL request is used to create a
   collection of a fictitious type "special-resource".  The response
   body is empty as the request completed successfully.

   >> Request <<

   MKCOL /home/special/ HTTP/1.1
   Host: special.example.com
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <D:mkcol xmlns:D="DAV:"
                 xmlns:E="http://example.com/ns/">
     <D:set>
       <D:prop>
         <D:resourcetype>
           <D:collection/>
           <E:special-resource/>
         </D:resourcetype>
         <D:displayname>Special Resource</D:displayname>
       </D:prop>
     </D:set>
   </D:mkcol>

   >> Response <<

   HTTP/1.1 201 Created
   Cache-Control: no-cache
   Date: Sat, 11 Nov 2006 09:32:12 GMT

3.5.  Example: Unsuccessful Extended MKCOL Request

   This example shows an attempt to use the extended MKCOL request to
   create a collection of a fictitious type "special-resource", which is
   not actually supported by the server.  The response body shows that
   an error occurred specifically with the DAV:resourcetype property.

   >> Request <<

   MKCOL /home/special/ HTTP/1.1
   Host: special.example.com
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <D:mkcol xmlns:D="DAV:"
                 xmlns:E="http://example.com/ns/">
     <D:set>
       <D:prop>
         <D:resourcetype>
           <D:collection/>
           <E:special-resource/>
         </D:resourcetype>
         <D:displayname>Special Resource</D:displayname>
       </D:prop>
     </D:set>
   </D:mkcol>

   >> Response <<

   HTTP/1.1 403 Forbidden
   Cache-Control: no-cache
   Date: Sat, 11 Nov 2006 09:32:12 GMT
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <D:mkcol-response xmlns:D="DAV:">
     <D:propstat>
       <D:prop>
         <D:resourcetype/>
       </D:prop>
       <D:status>HTTP/1.1 403 Forbidden</D:status>
       <D:error><D:valid-resourcetype /></D:error>
       <D:responsedescription>Resource type is not
       supported by this server</D:responsedescription>
     </D:propstat>
     <D:propstat>
       <D:prop>
         <D:displayname/>
       </D:prop>
       <D:status>HTTP/1.1 424 Failed Dependency</D:status>
     </D:propstat>
   </D:mkcol-response>

4.  Using Extended MKCOL as an Alternative for MKxxx Methods

   One of the goals of this extension is to eliminate the need for other
   extensions to define their own variant of MKCOL to create the special
   collections they need.  This extension can be used as an alternative
   to existing MKxxx methods in other extensions as detailed below.  If
   a server supports this extension and the other extension listed, then
   the server MUST support use of the extended MKCOL method to achieve
   the same result as the MKxxx method of the other extension.

4.1.  MKCALENDAR Alternative

   CalDAV defines the MKCALENDAR method to create a calendar collection
   as well as to set properties during creation (Section 5.3.1 of
   [RFC4791]).

   The extended MKCOL method can be used instead by specifying both DAV:
   collection and CALDAV:calendar-collection XML elements in the DAV:
   resourcetype property, set during the extended MKCOL request.

4.1.1.  Example: Using MKCOL Instead of MKCALENDAR

   The first example below shows an MKCALENDAR request containing a
   CALDAV:mkcalendar XML element in the request body and returning a
   CALDAV:mkcalendar-response XML element in the response body.

   >> MKCALENDAR Request <<

   MKCALENDAR /home/lisa/calendars/events/ HTTP/1.1
   Host: calendar.example.com
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <C:mkcalendar xmlns:D="DAV:"
                 xmlns:C="urn:ietf:params:xml:ns:caldav">
     <D:set>
       <D:prop>
         <D:displayname>Lisa's Events</D:displayname>
       </D:prop>
     </D:set>
   </C:mkcalendar>
   >> MKCALENDAR Response <<

   HTTP/1.1 201 Created
   Cache-Control: no-cache
   Date: Sat, 11 Nov 2006 09:32:12 GMT
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <C:mkcalendar-response xmlns:D="DAV:"
                 xmlns:C="urn:ietf:params:xml:ns:caldav">
     <D:propstat>
       <D:prop>
         <D:displayname/>
       </D:prop>
       <D:status>HTTP/1.1 200 OK</D:status>
     </D:propstat>
   </C:mkcalendar-response>

   The second example shows the equivalent extended MKCOL request with
   the same request and response XML elements.

   >> MKCOL Request <<

   MKCOL /home/lisa/calendars/events/ HTTP/1.1
   Host: calendar.example.com
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <D:mkcol xmlns:D="DAV:"
                 xmlns:C="urn:ietf:params:xml:ns:caldav">
     <D:set>
       <D:prop>
         <D:resourcetype>
           <D:collection/>
           <C:calendar/>
         </D:resourcetype>
         <D:displayname>Lisa's Events</D:displayname>
       </D:prop>
     </D:set>
   </D:mkcol>
   >> MKCOL Response <<

   HTTP/1.1 201 Created
   Cache-Control: no-cache
   Date: Sat, 11 Nov 2006 09:32:12 GMT
   Content-Type: application/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <D:mkcol-response xmlns:D="DAV:"
                 xmlns:C="urn:ietf:params:xml:ns:caldav">
     <D:propstat>
       <D:prop>
         <D:resourcetype/>
         <D:displayname/>
       </D:prop>
       <D:status>HTTP/1.1 200 OK</D:status>
     </D:propstat>
   </D:mkcol-response>

5.  XML Element Definitions

5.1.  mkcol XML Element

   Name:  mkcol

   Namespace:  DAV:

   Purpose:  Used in a request to specify properties to be set in an
      extended MKCOL request, as well as any additional information
      needed when creating the resource.

   Description:  This XML element is a container for the information
      required to modify the properties on a collection resource as it
      is created in an extended MKCOL request.

   Definition:

       <!ELEMENT mkcol (set+)>

5.2.  mkcol-response XML Element

   Name:  mkcol-response

   Namespace:  DAV:

   Purpose:  Used in a response to indicate the status of properties
      that were set or failed to be set during an extended MKCOL
      request.

   Description:  This XML element is a container for the information
      returned about a resource that has been created in an extended
      MKCOL request.

   Definition:

       <!ELEMENT mkcol-response (propstat+)>

6.  Security Considerations

   This extension does not introduce any new security concerns beyond
   those already described in HTTP [RFC2616] and WebDAV [RFC4918].

7.  Acknowledgments

   Thanks to Bernard Desruisseaux, Mike Douglass, Alexey Melnikov,
   Julian Reschke, and Simon Vaillancourt.


8.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
              Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
              Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

   [RFC4791]  Daboo, C., Desruisseaux, B., and L. Dusseault,
              "Calendaring Extensions to WebDAV (CalDAV)", RFC 4791,
              March 2007.

   [RFC4918]  Dusseault, L., "HTTP Extensions for Web Distributed
              Authoring and Versioning (WebDAV)", RFC 4918, June 2007.

   [W3C.REC-xml-20081126]
              Maler, E., Yergeau, F., Paoli, J., Bray, T., and C.
              Sperberg-McQueen, "Extensible Markup Language (XML) 1.0
              (Fifth Edition)", World Wide Web Consortium
              Recommendation REC-xml-20081126, November 2008,
              <http://www.w3.org/TR/2008/REC-xml-20081126>.

Author's Address

   Cyrus Daboo
   Apple Inc.
   1 Infinite Loop
   Cupertino, CA  95014
   USA

   EMail: cyrus@daboo.name
   URI:   http://www.apple.com/