Independent Submission K. Murchison Internet-Draft CMU Intended status: Standards Track January 12, 2015 Expires: July 16, 2015 Use of the Prefer Header Field in Web Distributed Authoring and Versioning (WebDAV) draft-murchison-webdav-prefer-08 Abstract This specification defines how the HTTP Prefer header field can be used by a WebDAV client to request that certain behaviors be employed by a server while constructing a response to a request. Editorial Note (To be removed by RFC Editor before publication) Please send comments to the Web Distributed Authoring and Versioning (WebDAV) mailing list at [1], which may be joined by sending a message with subject "subscribe" to [2]. This mailing list is archived at [3]. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on July 16, 2015. Copyright Notice Copyright (c) 2015 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents Murchison Expires July 16, 2015 [Page 1] Internet-Draft Prefer in WebDAV January 2015 (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Notational Conventions . . . . . . . . . . . . . . . . . 3 2. Reducing WebDAV Response Verbosity with "return=minimal" . . . . . . . . . . . . . . . . . . . . . . 3 2.1. Minimal PROPFIND Response . . . . . . . . . . . . . . . . 3 2.2. Minimal REPORT Response . . . . . . . . . . . . . . . . . 7 2.3. Minimal PROPPATCH Response . . . . . . . . . . . . . . . 11 2.4. Minimal MKCALENDAR / MKCOL Response . . . . . . . . . . . 13 3. Reducing WebDAV Round-Trips with "return=representation" . . . . . . . . . . . . . . . . . . . 15 4. The "depth-noroot" Processing Preference . . . . . . . . . . 22 5. Implementation Status . . . . . . . . . . . . . . . . . . . . 26 6. Security Considerations . . . . . . . . . . . . . . . . . . . 27 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 28 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 28 9.1. Normative References . . . . . . . . . . . . . . . . . . 28 9.2. Informative References . . . . . . . . . . . . . . . . . 29 9.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 30 Appendix A. The Brief and Extended Depth Request Header Fields . 30 Appendix B. Change Log (To be removed by RFC Editor before publication) . . . . . . . . . . . . . . . . . . . . 31 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 33 1. Introduction [RFC7240] defines the HTTP Prefer request header field and the "return=minimal" preference which indicates that a client wishes for the server to return a minimal response to a successful request, but states that what constitutes an appropriate minimal response is left solely to the discretion of the server. Section 2 of this specification defines precisely what is expected of a server when constructing minimal responses to successful WebDAV [RFC4918] requests. [RFC7240] also defines the "return=representaion" preference which indicates that a client wishes for the server to include an entity representing the current state of the resource in the response to a Murchison Expires July 16, 2015 [Page 2] Internet-Draft Prefer in WebDAV January 2015 successful request. Section 3 of this specification makes recommendations on when this preference should be used by clients and extends its applicability to 412 (Precondition Failed) [RFC7231] responses. Finally, Section 4 of this specifcation defines the "depth-noroot" preference that can be used with WebDAV methods that support the "Depth" header field.. 1.1. Notational Conventions 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 references XML element types in the "DAV:" [RFC4918] namespace outside of the context of an XML fragment. When doing so, the string "DAV:" will be prepended to the XML element type. 2. Reducing WebDAV Response Verbosity with "return=minimal" Some payload bodies in responses to WebDAV requests, such as 207 (Multi-Status) [RFC4918] responses, can be quite verbose or even unnecessary at times. This specification defines how the Prefer request header field, in conjunction with its "return=minimal" preference, can be used by clients to reduce the verbosity of such responses by requesting that the server omit those portions of the response that can be inferred by their absence. 2.1. Minimal PROPFIND Response When a PROPFIND [RFC4918] request contains a Prefer header field with a preference of "return=minimal", the server SHOULD omit all DAV:propstat XML elements containing a DAV:status XML element of value 404 (Not Found) [RFC7231] from the 207 (Multi-Status) response. If the omission of such a DAV:propstat element would result in a DAV:response XML element containing zero DAV:propstat elements, the server MUST substitute one of the following in its place: o a DAV:propstat element consisting of an empty DAV:prop element and a DAV:status element of value 200 (OK) [RFC7231] o a DAV:status element of value 200 (OK) Murchison Expires July 16, 2015 [Page 3] Internet-Draft Prefer in WebDAV January 2015 2.1.1. Example: Typical PROPFIND request/response This example tries to fetch an unknown property from a collection. >> Request << PROPFIND /container/ HTTP/1.1 Host: webdav.example.com Content-Type: application/xml; charset=utf-8 Content-Length: xxxx Murchison Expires July 16, 2015 [Page 4] Internet-Draft Prefer in WebDAV January 2015 >> Response << HTTP/1.1 207 Multi-Status Content-Type: application/xml; charset=utf-8 Content-Length: xxxx /container/ HTTP/1.1 200 OK HTTP/1.1 404 Not Found 2.1.2. Example: Minimal PROPFIND request/response This example tries to fetch an unknown property from a collection. Murchison Expires July 16, 2015 [Page 5] Internet-Draft Prefer in WebDAV January 2015 >> Request << PROPFIND /container/ HTTP/1.1 Host: webdav.example.com Content-Type: application/xml; charset=utf-8 Content-Length: xxxx Prefer: return=minimal >> Response << HTTP/1.1 207 Multi-Status Content-Type: application/xml; charset=utf-8 Content-Length: xxxx Preference-Applied: return=minimal /container/ HTTP/1.1 200 OK 2.1.3. Example: Minimal PROPFIND request/response with an empty DAV:propstat element This example tries to fetch an unknown property from a collection. Murchison Expires July 16, 2015 [Page 6] Internet-Draft Prefer in WebDAV January 2015 >> Request << PROPFIND /container/ HTTP/1.1 Host: webdav.example.com Content-Type: application/xml; charset=utf-8 Content-Length: xxxx Prefer: return=minimal >> Response << HTTP/1.1 207 Multi-Status Content-Type: application/xml; charset=utf-8 Content-Length: xxxx Preference-Applied: return=minimal /container/ HTTP/1.1 200 OK 2.2. Minimal REPORT Response When a REPORT [RFC3253] request, whose report type results in a 207 (Multi-Status) response, contains a Prefer header field with a preference of "return=minimal", the server SHOULD omit all DAV:propstat XML elements containing a DAV:status XML element of value 404 (Not Found) [RFC7231] from the 207 (Multi-Status) response. If the omission of such a DAV:propstat element would result in a DAV:response XML element containing zero DAV:propstat elements, the server MUST substitute one of the following in its place: Murchison Expires July 16, 2015 [Page 7] Internet-Draft Prefer in WebDAV January 2015 o a DAV:propstat element consisting of an empty DAV:prop element and a DAV:status element of value 200 (OK) [RFC7231] o a DAV:status element of value 200 (OK) 2.2.1. Example: Typical REPORT request/response This example tries to fetch an unknown property from several resources via the CALDAV:calendar-multiget [RFC4791] REPORT type. >> Request << REPORT /murch/work/ HTTP/1.1 Host: caldav.example.com Content-Type: application/xml; charset=utf-8 Content-Length: xxxx /murch/work/abc.ics /murch/work/qrs.ics /murch/work/xyz.ics Murchison Expires July 16, 2015 [Page 8] Internet-Draft Prefer in WebDAV January 2015 >> Response << HTTP/1.1 207 Multi-Status Content-Type: application/xml; charset=utf-8 Content-Length: xxxx /murch/work/abc.ics "jahsd823ru" HTTP/1.1 200 OK HTTP/1.1 404 Not Found /murch/work/qrs.ics HTTP/1.1 404 Not Found /murch/work/xyz.ics "p08ulkj" HTTP/1.1 200 OK HTTP/1.1 404 Not Found Murchison Expires July 16, 2015 [Page 9] Internet-Draft Prefer in WebDAV January 2015 2.2.2. Example: Minimal REPORT request/response This example tries to fetch an unknown property from several resources via the CALDAV:calendar-multiget [RFC4791] REPORT type. >> Request << REPORT /murch/work/ HTTP/1.1 Host: caldav.example.com Content-Type: application/xml; charset=utf-8 Content-Length: xxxx Prefer: return=minimal /murch/work/abc.ics /murch/work/qrs.ics /murch/work/xyz.ics Murchison Expires July 16, 2015 [Page 10] Internet-Draft Prefer in WebDAV January 2015 >> Response << HTTP/1.1 207 Multi-Status Content-Type: application/xml; charset=utf-8 Content-Length: xxxx Preference-Applied: return=minimal /murch/work/abc.ics "jahsd823ru" HTTP/1.1 200 OK /murch/work/qrs.ics HTTP/1.1 404 Not Found /murch/work/xyz.ics "p08ulkj" HTTP/1.1 200 OK 2.3. Minimal PROPPATCH Response When a PROPPATCH [RFC4918] request contains a Prefer header field with a preference of "return=minimal", and all instructions are processed successfully, the server SHOULD return one of the following responses rather than a 207 (Multi-Status) response: o 204 (No Content) [RFC7231] o 200 (OK) [RFC7231] (preferably with a zero-length message body) Murchison Expires July 16, 2015 [Page 11] Internet-Draft Prefer in WebDAV January 2015 2.3.1. Example: Typical PROPPATCH request/response >> Request << PROPPATCH /container/ HTTP/1.1 Host: webdav.example.com Content-Type: application/xml; charset=utf-8 Content-Length: xxxx My Container >> Response << HTTP/1.1 207 Multi-Status Content-Type: application/xml; charset=utf-8 Content-Length: xxxx /container/ HTTP/1.1 200 OK 2.3.2. Example: Minimal PROPPATCH request/response Murchison Expires July 16, 2015 [Page 12] Internet-Draft Prefer in WebDAV January 2015 >> Request << PROPPATCH /container/ HTTP/1.1 Host: webdav.example.com Content-Type: application/xml; charset=utf-8 Content-Length: xxxx Prefer: return=minimal My Container >> Response << HTTP/1.1 200 OK Content-Length: 0 Preference-Applied: return=minimal 2.4. Minimal MKCALENDAR / MKCOL Response Both the MKCALENDAR [RFC4791] and Extended MKCOL [RFC5689] specifications indicate that a server MAY return a message body in response to a successful request. This specification explicitly defines the intended behavior in the presence of the Prefer header field. When a MKCALENDAR or an Extended MKCOL request contains a Prefer header field with a preference of "return=minimal", and the collection is created with all requested properties being set successfully, the server SHOULD return a 201 (Created) [RFC7231] response with an empty (zero-length) message body. Note that the rationale for requiring that a minimal success response have an empty body is twofold: o [RFC4791] Section 5.3.1 states: "If a response body for a successful request is included, it MUST be a CALDAV:mkcalendar- response XML element." Murchison Expires July 16, 2015 [Page 13] Internet-Draft Prefer in WebDAV January 2015 o [RFC5689] Section 3 states: "When an empty response body is returned with a success request status code, the client can assume that all properties were set." 2.4.1. Example: Verbose MKCOL request/response >> Request << MKCOL /container/ HTTP/1.1 Host: webdav.example.com Content-Type: application/xml; charset=utf-8 Content-Length: xxxx My Container >> Response << HTTP/1.1 201 Created Cache-Control: no-cache Content-Type: application/xml; charset=utf-8 Content-Length: xxxx HTTP/1.1 200 OK 2.4.2. Example: Minimal MKCOL request/response Murchison Expires July 16, 2015 [Page 14] Internet-Draft Prefer in WebDAV January 2015 >> Request << MKCOL /container/ HTTP/1.1 Host: webdav.example.com Content-Type: application/xml; charset=utf-8 Content-Length: xxxx Prefer: return=minimal My Container >> Response << HTTP/1.1 201 Created Cache-Control: no-cache Content-Length: 0 Preference-Applied: return=minimal 3. Reducing WebDAV Round-Trips with "return=representation" The PUT, COPY, MOVE, [RFC4918] and POST [RFC5995] methods can be used to create or update a resource. In some instances, such as with CalDAV Scheduling [RFC6638], the created or updated resource representation may differ from the representation sent in the body of the request or referenced by the effective request URI. In cases where the client would normally issue a subsequent GET request to retrieve the current representation of the resource, the client SHOULD instead include a Prefer header field with the "return=representation" preference in the PUT, COPY, MOVE, or POST request. By doing this, the client can coalesce the create/update and retrieve operations into one round-trip rather than two. An additional benefit of using "return=representation" in such a request is that the client will know that any changes to the resource were produced by the server rather than a concurrent client, thus providing a level of atomicity to the operation. Murchison Expires July 16, 2015 [Page 15] Internet-Draft Prefer in WebDAV January 2015 Frequently, clients using a state-changing method such as those above will make them conditional by including either an If-Match or If- None-Match [RFC7232] header field in the request. If the specified condition evaluates to false, and the request includes a Prefer header field with the "return=representation" preference, the server SHOULD include an entity representing the current state of the resource in the resulting 412 (Precondition Failed) [RFC7231] response. 3.1. Example: Typical resource creation and retrieval via POST + GET Note that this request is not conditional because by using the POST [RFC5995] method the client lets the server choose the URI, thereby guaranteeing that it will not modify an existing resource. >> Request << POST /murch/work;add-member/ HTTP/1.1 Host: caldav.example.com Content-Type: text/calendar; charset=utf-8 Content-Length: xxxx BEGIN:VCALENDAR VERSION:2.0 PRODID:-//Example Corp.//CalDAV Client//EN BEGIN:VEVENT UID:CD87465FA SEQUENCE:0 DTSTAMP:20120602T185254Z DTSTART:20120602T160000Z DTEND:20120602T170000Z TRANSP:OPAQUE SUMMARY:Lunch ORGANIZER;CN="Ken Murchison":mailto:murch@example.com ATTENDEE;CN="Ken Murchison";CUTYPE=INDIVIDUAL;PARTSTAT=ACCEPTED: mailto:murch@example.com ATTENDEE;CN="John Doe";CUTYPE=INDIVIDUAL;PARTSTAT =NEEDS-ACTION;ROLE=REQ-PARTICIPANT;RSVP=TRUE:mailto:jdoe@ example.com END:VEVENT END:VCALENDAR Murchison Expires July 16, 2015 [Page 16] Internet-Draft Prefer in WebDAV January 2015 >> Response << HTTP/1.1 201 Created Location: /murch/work/abc.ics Content-Length: 0 Note that the server did not include any validator header fields (e.g ETag) in the response, signaling that the created representation differs from the representation sent in the body of the request. The client has to send a separate GET request to retrieve the current representation: >> Request << GET /murch/work/abc.ics HTTP/1.1 Host: caldav.example.com Murchison Expires July 16, 2015 [Page 17] Internet-Draft Prefer in WebDAV January 2015 >> Response << HTTP/1.1 200 OK Content-Type: text/calendar; charset=utf-8 Content-Length: xxxx ETag: "nahduyejc" Schedule-Tag: "jfd84hgbcn" BEGIN:VCALENDAR VERSION:2.0 PRODID:-//Example Corp.//CalDAV Server//EN BEGIN:VEVENT UID:CD87465FA SEQUENCE:0 DTSTAMP:20120602T185300Z DTSTART:20120602T160000Z DTEND:20120602T170000Z TRANSP:OPAQUE SUMMARY:Lunch ORGANIZER;CN="Ken Murchison":mailto:murch@example.com ATTENDEE;CN="Ken Murchison";CUTYPE=INDIVIDUAL;PARTSTAT=ACCEPTED: mailto:murch@example.com ATTENDEE;CN="John Doe";CUTYPE=INDIVIDUAL;PARTSTAT =NEEDS-ACTION;ROLE=REQ-PARTICIPANT;RSVP=TRUE;SCHEDULE-STATUS= 1.2:mailto:jdoe@example.com END:VEVENT END:VCALENDAR 3.2. Example: Streamlined resource creation and retrieval via POST Note that this request is not conditional because by using the POST [RFC5995] method the client lets the server choose the URI, thereby guaranteeing that it will not modify an existing resource. Murchison Expires July 16, 2015 [Page 18] Internet-Draft Prefer in WebDAV January 2015 >> Request << POST /murch/work;add-member/ HTTP/1.1 Host: caldav.example.com Content-Type: text/calendar; charset=utf-8 Content-Length: xxxx Prefer: return=representation BEGIN:VCALENDAR VERSION:2.0 PRODID:-//Example Corp.//CalDAV Client//EN BEGIN:VEVENT UID:CD87465FA SEQUENCE:0 DTSTAMP:20120602T185254Z DTSTART:20120602T160000Z DTEND:20120602T170000Z TRANSP:OPAQUE SUMMARY:Lunch ORGANIZER;CN="Ken Murchison":mailto:murch@example.com ATTENDEE;CN="Ken Murchison";CUTYPE=INDIVIDUAL;PARTSTAT=ACCEPTED: mailto:murch@example.com ATTENDEE;CN="John Doe";CUTYPE=INDIVIDUAL;PARTSTAT =NEEDS-ACTION;ROLE=REQ-PARTICIPANT;RSVP=TRUE:mailto:jdoe@ example.com END:VEVENT END:VCALENDAR Murchison Expires July 16, 2015 [Page 19] Internet-Draft Prefer in WebDAV January 2015 >> Response << HTTP/1.1 201 Created Location: /murch/work/abc.ics Content-Type: text/calendar; charset=utf-8 Content-Length: xxxx Content-Location: /murch/work/abc.ics ETag: "nahduyejc" Schedule-Tag: "jfd84hgbcn" Preference-Applied: return=representation BEGIN:VCALENDAR VERSION:2.0 PRODID:-//Example Corp.//CalDAV Server//EN BEGIN:VEVENT UID:CD87465FA SEQUENCE:0 DTSTAMP:20120602T185300Z DTSTART:20120602T160000Z DTEND:20120602T170000Z TRANSP:OPAQUE SUMMARY:Lunch ORGANIZER;CN="Ken Murchison":mailto:murch@example.com ATTENDEE;CN="Ken Murchison";CUTYPE=INDIVIDUAL;PARTSTAT=ACCEPTED: mailto:murch@example.com ATTENDEE;CN="John Doe";CUTYPE=INDIVIDUAL;PARTSTAT =NEEDS-ACTION;ROLE=REQ-PARTICIPANT;RSVP=TRUE;SCHEDULE-STATUS= 1.2:mailto:jdoe@example.com END:VEVENT END:VCALENDAR 3.3. Example: Typical conditional resource update failure and retrieval via PUT + GET >> Request << PUT /container/motd.txt HTTP/1.1 Host: dav.example.com Content-Type: text/plain Content-Length: xxxx If-Match: "asd973" Either write something worth reading or do something worth writing. Murchison Expires July 16, 2015 [Page 20] Internet-Draft Prefer in WebDAV January 2015 >> Response << HTTP/1.1 412 Precondition Failed Content-Length: 0 The resource has been modified by another user agent (ETag mismatch), therefore the client has to send a separate GET request to retrieve the current representation: >> Request << GET /container/motd.txt HTTP/1.1 Host: dav.example.com >> Response << HTTP/1.1 200 OK Content-Type: text/plain Content-Length: xxxx ETag: "789sdas" An investment in knowledge pays the best interest. 3.4. Example: Streamlined conditional resource update failure and retrieval via PUT >> Request << PUT /container/motd.txt HTTP/1.1 Host: dav.example.com Content-Type: text/plain Content-Length: xxxx If-Match: "asd973" Prefer: return=representation Either write something worth reading or do something worth writing. Murchison Expires July 16, 2015 [Page 21] Internet-Draft Prefer in WebDAV January 2015 >> Response << HTTP/1.1 412 Precondition Failed Content-Type: text/plain Content-Length: xxxx Content-Location: /container/motd.txt ETag: "789sdas" Preference-Applied: return=representation An investment in knowledge pays the best interest. 4. The "depth-noroot" Processing Preference The "depth-noroot" preference indicates that the client wishes for the server to exclude the target (root) resource from processing by the WebDAV method and only apply the WebDAV method to the target resource's subordinate resources. depth-noroot = "depth-noroot" This preference is only intended to be used with WebDAV methods whose definitions explicitly provide support for the Depth [RFC4918] header field. Furthermore, this preference only applies when the Depth header field has a value of "1" or "infinity" (either implicitly or explicitly). The "depth-noroot" preference MAY be used in conjunction with the "return=minimal" preference in a single request. 4.1. Example: Typical PROPFIND request/response with Depth:1 This example fetches the DAV:resourcetype [RFC4918] property for a collection and its child resources. Murchison Expires July 16, 2015 [Page 22] Internet-Draft Prefer in WebDAV January 2015 >> Request << PROPFIND /murch/ HTTP/1.1 Host: webdav.example.com Content-Type: text/xml Content-Length: xxx Depth: 1 >> Response << HTTP/1.1 207 Multi-Status Content-Type: application/xml; charset=utf-8 Content-Length: xxxx /murch/ HTTP/1.1 200 OK /murch/work/ HTTP/1.1 200 OK Murchison Expires July 16, 2015 [Page 23] Internet-Draft Prefer in WebDAV January 2015 /murch/home/ HTTP/1.1 200 OK /murch/foo.txt HTTP/1.1 200 OK 4.2. Example: PROPFIND request/response with Depth:1 and Prefer:depth- noroot This example fetches the DAV:resourcetype [RFC4918] property for just the child resources. >> Request << PROPFIND /murch/ HTTP/1.1 Host: webdav.example.com Content-Type: text/xml Content-Length: xxx Depth: 1 Prefer: depth-noroot Murchison Expires July 16, 2015 [Page 24] Internet-Draft Prefer in WebDAV January 2015 >> Response << HTTP/1.1 207 Multi-Status Content-Type: application/xml; charset=utf-8 Content-Length: xxxx Preference-Applied: depth-noroot /murch/work/ HTTP/1.1 200 OK /murch/home/ HTTP/1.1 200 OK /murch/foo.txt HTTP/1.1 200 OK Murchison Expires July 16, 2015 [Page 25] Internet-Draft Prefer in WebDAV January 2015 5. Implementation Status < RFC Editor: before publication please remove this section and the reference to [RFC6982] > This section records the status of known implementations of the protocol defined by this specification at the time of posting of this Internet-Draft, and is based on a proposal described in [RFC6982]. The description of implementations in this section is intended to assist the IETF in its decision processes in progressing drafts to RFCs. Please note that the listing of any individual implementation here does not imply endorsement by the IETF. Furthermore, no effort has been spent to verify the information presented here that was supplied by IETF contributors. This is not intended as, and must not be construed to be, a catalog of available implementations or their features. Readers are advised to note that other implementations may exist. According to [RFC6982], "this will allow reviewers and working groups to assign due consideration to documents that have the benefit of running code, which may serve as evidence of valuable experimentation and feedback that have made the implemented protocols more mature. It is up to the individual working groups to use this information as they see fit". 5.1. Cyrus The open source Cyrus [4] project is a highly scalable enterprise mail system which also supports calendaring and contacts. This beta level CalDAV/CardDAV implementation supports all of the preferences described in this document and successfully interoperates with the CalDAVTester and aCal client implementations described below. This implementation is freely distributable under a BSD style license from Computing Services at Carnegie Mellon University [5]. 5.2. Calendar and Contacts Server The open source Calendar and Contacts Server [6] project is a standards-compliant server implementing the CalDAV and CardDAV protocols. This production level implementation supports all of the preferences described in this document and successfully interoperates with the CalDAVTester client implementation described below. This implementation is freely distributable under the terms of the Apache License, Version 2.0 [7]. Murchison Expires July 16, 2015 [Page 26] Internet-Draft Prefer in WebDAV January 2015 5.3. Bedework Bedework [8] is an open-source enterprise calendar system that supports public, personal, and group calendaring. This production level implementation supports the "return=minimal" preference described in this document and successfully interoperates with the CalDAVTester client implementation described below. This implementation is freely distributable under the Jasig Licensing Policy [9]. 5.4. DAViCal DAViCal [10] is a server for calendar sharing using the CalDAV protocol. This production level implementation supports the "return=minimal" preference described in this document and successfully interoperates with the CalDAVTester client implementation described below. This implementation is Free Software [11] distributable under the General Public License [12]. 5.5. aCal aCal [13] is an open source calendar client for Android which uses the CalDAV standard for communication. This implementation makes some use of each of the preferences described in this document and successfully interoperates with the Cyrus server implementation described above. This implementation is freely distributable under the General Public License [14]. 5.6. CalDAVTester CalDAVTester [15] is an open source test and performance application designed to work with CalDAV and/or CardDAV servers and tests various aspects of their protocol handling as well as performance. This widely used implementation supports all of the preferences described in this document and successfully interoperates with the server implementations described above. This implementation is freely distributable under the terms of the Apache License, Version 2.0 [16]. 6. Security Considerations No new security considerations are introduced by use of the Prefer header field with WebDAV request methods, beyond those discussed in [RFC7240] and those already inherent in those methods. Murchison Expires July 16, 2015 [Page 27] Internet-Draft Prefer in WebDAV January 2015 7. IANA Considerations The following preference is to be added to the Preferences Registry defined in [RFC7240]. o Preference: depth-noroot o Description: The "depth-noroot" preference indicates that the client wishes for the server to exclude the target (root) resource from processing by the WebDAV method and only apply the WebDAV method to the target resource's subordinate resources. o Reference: Section 4 o Notes: This preference is only intended to be used with WebDAV methods whose definitions explicitly provide support for the "Depth" [RFC4918] header field. Furthermore, this preference only applies when the "Depth" header field has a value of "1" or "infinity" (either implicitly or explicitly). 8. Acknowledgements The author would like to thank the following individuals for contributing their ideas and support for writing this specification: Cyrus Daboo, Helge Hess, Andrew McMillan, Arnaud Quillaud, and Julian Reschke. The author would also like to thank the Calendaring and Scheduling Consortium for advice with this specification, and for organizing interoperability testing events to help refine it. 9. References 9.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3253] Clemm, G., Amsden, J., Ellison, T., Kaler, C., and J. Whitehead, "Versioning Extensions to WebDAV (Web Distributed Authoring and Versioning)", RFC 3253, March 2002. [RFC4791] Daboo, C., Desruisseaux, B., and L. Dusseault, "Calendaring Extensions to WebDAV (CalDAV)", RFC 4791, March 2007. Murchison Expires July 16, 2015 [Page 28] Internet-Draft Prefer in WebDAV January 2015 [RFC4918] Dusseault, L., "HTTP Extensions for Web Distributed Authoring and Versioning (WebDAV)", RFC 4918, June 2007. [RFC5689] Daboo, C., "Extended MKCOL for Web Distributed Authoring and Versioning (WebDAV)", RFC 5689, September 2009. [RFC5995] Reschke, J., "Using POST to Add Members to Web Distributed Authoring and Versioning (WebDAV) Collections", RFC 5995, September 2010. [RFC7231] Fielding, R. and J. Reschke, "Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content", RFC 7231, June 2014. [RFC7232] Fielding, R. and J. Reschke, "Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests", RFC 7232, June 2014. [RFC7240] Snell, J., "Prefer Header for HTTP", RFC 7240, June 2014. 9.2. Informative References [MSDN.aa493854] Microsoft Developer Network, "PROPPATCH Method", June 2006, . [MSDN.aa563501] Microsoft Developer Network, "Brief Header", June 2006, . [MSDN.aa563950] Microsoft Developer Network, "Depth Header", June 2006, . [MSDN.aa580336] Microsoft Developer Network, "PROPFIND Method", June 2006, . [RFC6638] Daboo, C. and B. Desruisseaux, "Scheduling Extensions to CalDAV", RFC 6638, June 2012. [RFC6982] Sheffer, Y. and A. Farrel, "Improving Awareness of Running Code: The Implementation Status Section", RFC 6982, July 2013. Murchison Expires July 16, 2015 [Page 29] Internet-Draft Prefer in WebDAV January 2015 9.3. URIs [1] http://www.cyrusimap.org/ [2] http://www.cmu.edu/computing/ [3] http://calendarserver.org/ [4] http://www.apache.org/licenses/LICENSE-2.0.html [5] http://www.bedework.org/ [6] http://www.jasig.org/licensing [7] http://www.davical.org/ [8] http://www.gnu.org/philosophy/open-source-misses-the-point.html [9] http://www.gnu.org/licenses/gpl.html [10] http://www.acal.me/ [11] http://www.gnu.org/licenses/gpl.html [12] http://calendarserver.org/wiki/CalDAVTester [13] http://www.apache.org/licenses/LICENSE-2.0.html Appendix A. The Brief and Extended Depth Request Header Fields This document is based heavily on the Brief [MSDN.aa563501] and extended Depth [MSDN.aa563950] request header fields. The behaviors described in Section 2.1 and Section 2.3 are identical to those provided by the Brief header field when used with the PROPFIND [MSDN.aa580336] and PROPPATCH [MSDN.aa493854] methods respectively. The behavior described in Section 4 is identical to that provided by the "1,noroot" [MSDN.aa563950] and "infinity,noroot" [MSDN.aa563950] Depth header field values. Client and server implementations that already support the Brief header field can add support for the "return=minimal" preference with nominal effort. If a server supporting the Prefer header field receives both the Brief and Prefer header fields in a request, it MUST ignore the Brief header field and only use the Prefer header field preferences. Murchison Expires July 16, 2015 [Page 30] Internet-Draft Prefer in WebDAV January 2015 Appendix B. Change Log (To be removed by RFC Editor before publication) B.1. Since -07 o No substantive changes. Refreshed due to pending expiration. B.2. Since -06 o Updated HTTPbis and Prefer references to published RFCs. B.3. Since -05 o Allow a minimal PROPFIND/REPORT response to contain a DAV:status element rather than an empty DAV:propstat element. o Allow 204 (No Content) as a minimal PROPATCH success response. o Added justification for why a minimal MKCOL/MKCALENDAR success response must have an empty body. o Added text and an example of how "return=representation" can be employed with a conditional state-changing request and a 412 (Precondition Failed) response. o Added a note to the POST+GET example bringing attention to the lack of a validator header field in the POST response. o Reduced the number of inline references. o Limited most examples to vanilla WebDAV. o Reduced number of items in TOC. o Removed the recommendation that the legacy Brief header functionality should be implemented. o Added note about how a server should handle a request that contains both Brief and Prefer. o Other editorial tweaks from Julian Reschke. B.4. Since -04 o Added note stating where to send comments. Murchison Expires July 16, 2015 [Page 31] Internet-Draft Prefer in WebDAV January 2015 B.5. Since -03 o Limited "Updates" to just RFC 4918. o Consensus from CalConnect membership that a "depth-root" option is unnecessary at this point. o Consensus from CalConnect membership to remove Vary header field from PROPFIND and REPORT responses since these responses don't appear to be cached. o Updated "Implementation Status" section boilerplate to RFC 6982. o Added aCal to "Implementation Status" section. o Added note that servers SHOULD respond with Preference-Applied when return=minimal is used with PROPFIND or REPORT. B.6. Since -02 o Reintroduced "Updates" to header. o Added text noting that "return=representation" provides a level of atomicity to the operation. o Added "Implementation Status" section. o Tweaked/corrected some examples.. o Updated HTTPbis references. B.7. Since -01 o Removed "Updates" from header. o Fixed some missing/incorrect references. o Reintroduced Cache-Control:no-cache to MKCOL responses. B.8. Since -00 o Updated to comply with draft-snell-httpprefer-18. o Reordered "Minimal REPORT Response" and "Minimal PROPPATCH Response" sections. o Added some explanatory text to examples. Murchison Expires July 16, 2015 [Page 32] Internet-Draft Prefer in WebDAV January 2015 B.9. Since CalConnect XXIV o Updated references. o Stated that "depth-noroot" can be used in conjuction with "return=minimal". o Added text mentioning that "depth-noroot" is based on the MSDN "1,noroot" and "infinity,noroot" Depth header values. o The server behavior required when "return=minimal" would result in zero DAV:propstat elements has been changed from: /container/ HTTP/1.1 200 OK to the slightly more verbose: /container/ HTTP/1.1 200 OK Author's Address Murchison Expires July 16, 2015 [Page 33] Internet-Draft Prefer in WebDAV January 2015 Kenneth Murchison Carnegie Mellon University 5000 Forbes Avenue Pittsburgh, PA 15213 US Phone: +1 412 268 1982 Email: murch@andrew.cmu.edu Murchison Expires July 16, 2015 [Page 34]