[Docs] [txt|pdf|xml] [Tracker] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 RFC 5789

Individual Submission                                       L. Dusseault
Internet-Draft                                                      OSAF
Expires: April 29, 2008                                         J. Snell
                                                        October 27, 2007


                         PATCH Method for HTTP
                     draft-dusseault-http-patch-10

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   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."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on April 29, 2008.

Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   Several applications extending HTTP require a feature to do partial
   resource modification.  Existing HTTP functionality only allows a
   complete replacement of a document.  This proposal adds a new HTTP
   method, PATCH, to modify an existing HTTP resource.







Dusseault & Snell        Expires April 29, 2008                 [Page 1]

Internet-Draft                 HTTP PATCH                   October 2007


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  The PATCH Method . . . . . . . . . . . . . . . . . . . . . . .  3
     2.1.  A simple PATCH example . . . . . . . . . . . . . . . . . .  5
     2.2.  Error handling . . . . . . . . . . . . . . . . . . . . . .  5
   3.  Advertising Support in OPTIONS . . . . . . . . . . . . . . . .  6
     3.1.  The Accept-Patch Header  . . . . . . . . . . . . . . . . .  7
     3.2.  An example OPTIONS request and response  . . . . . . . . .  7
   4.  209 Content Returned . . . . . . . . . . . . . . . . . . . . .  7
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  7
     5.1.  The 'Accept-Patch' Response Header . . . . . . . . . . . .  8
     5.2.  HTTP Status codes  . . . . . . . . . . . . . . . . . . . .  8
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     7.1.  Normative References . . . . . . . . . . . . . . . . . . .  9
     7.2.  Informative References . . . . . . . . . . . . . . . . . .  9
   Appendix A.  Acknowledgements  . . . . . . . . . . . . . . . . . .  9
   Appendix B.  Changes . . . . . . . . . . . . . . . . . . . . . . .  9
     B.1.  Changes from -00 . . . . . . . . . . . . . . . . . . . . .  9
     B.2.  Changes from -01 . . . . . . . . . . . . . . . . . . . . .  9
     B.3.  Changes from -02 . . . . . . . . . . . . . . . . . . . . . 10
     B.4.  Changes from -03 . . . . . . . . . . . . . . . . . . . . . 10
     B.5.  Changes from -04 . . . . . . . . . . . . . . . . . . . . . 10
     B.6.  Changes from -05 . . . . . . . . . . . . . . . . . . . . . 10
     B.7.  Changes from -06 . . . . . . . . . . . . . . . . . . . . . 11
     B.8.  Changes from -07 . . . . . . . . . . . . . . . . . . . . . 11
     B.9.  Changes from -08 . . . . . . . . . . . . . . . . . . . . . 12
     B.10. Changes from -09 . . . . . . . . . . . . . . . . . . . . . 12
   Appendix C.  Notes to RFC Editor . . . . . . . . . . . . . . . . . 12
   Appendix D.  Editorial Notes . . . . . . . . . . . . . . . . . . . 12
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
   Intellectual Property and Copyright Statements . . . . . . . . . . 14


















Dusseault & Snell        Expires April 29, 2008                 [Page 2]

Internet-Draft                 HTTP PATCH                   October 2007


1.  Introduction

   This specification defines the new HTTP 1.1 [RFC2616] method PATCH
   that is used to apply partial modifications to a HTTP resource.

   A new method is necessary to improve interoperability and prevent
   errors.  The PUT method is already defined to overwrite a resource
   with a complete new body, and can not be reused to do partial
   changes.  Otherwise, proxies and caches and even clients and servers
   may get confused as to the result of the operation.

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


2.  The PATCH Method

   The PATCH method requests that a set of changes described in the
   request entity be applied to the resource identified by the Request-
   URI.  The set of changes is represented in a format called a "patch
   document" identified by a media type.  PATCH is neither safe or
   idempotent as defined by [RFC2616] Section 9.1.

   The difference between the PUT and PATCH requests is reflected in the
   way the server processes the enclosed entity to modify the resource
   identified by the Request-URI.  In a PUT request, the enclosed entity
   is considered to be a modified version of the resource stored on the
   origin server and the client is requesting that stored version be
   replaced.  With PATCH, however, the enclosed entity contains a set of
   instructions describing how a resource currently residing on the
   origin server should be modified to produce a new version.  The
   changes described by the entity MAY result in the creation of one or
   more new resources on the server, however it is not intended that the
   body of the PATCH request be used as the content of such resources.

   The server MUST always apply the entire set of changes atomically and
   never provide (e.g. in response to a GET during this operation) a
   partially-modified representation.  If the entire patch document
   cannot be successfully applied then the server MUST fail the entire
   request, applying none of the changes.  The determination of what
   constitutes a successful PATCH can vary depending on the patch
   document and the type of resource being modified.  The actual method
   for determining how to apply the patch document to the resource is
   defined entirely by the origin server.  See Error Handling in section
   2.2 for details on status codes and possible error conditions.

   If the request passes through a cache and the Request-URI identifies



Dusseault & Snell        Expires April 29, 2008                 [Page 3]

Internet-Draft                 HTTP PATCH                   October 2007


   one or more currently cached entities, those entries SHOULD be
   treated as stale.  Responses to this method are not cacheable, unless
   the response includes appropriate Cache-Control or Expires header
   fields or the response uses the 209 Content Returned status code as
   defined in Section 4.  The 303 (See Other) response can be used to
   direct the user agent to retrieve a cacheable resource.

   Collisions from multiple requests are more dangerous than PUT
   collisions, because a patch document that is not operating from a
   known base point may corrupt the resource.  Clients wishing to apply
   a patch document to a known entity can first acquire the strong ETag
   of the resource to be modified, and use that Etag in the If-Match
   header on the PATCH request to verify that the resource is still
   unchanged.  If a strong ETag is not available for a given resource,
   the client can use If-Unmodified-Since as a less-reliable safeguard.

   It is RECOMMENDED that Servers provide strong ETags for all resources
   for which PATCH is supported.

   If a PATCH request contains any entity-headers the server does not
   understand, the server MUST return a 501 (Not Implemented) response.
   A server that understands a particular entity-header can choose to
   ignore it; however, doing so can produce results that are unexpected
   or unintended by the client.  All entity-headers contained in the
   request apply only to the contained patch document and MUST NOT be
   applied to the resource being modified.

   If the Request-URI identifies a resource with multiple alternate
   representations, the server can choose to respond in a variety of
   ways.  For instance, the server can decide which representation to
   alter and might even be able to change them all consistently
   depending on the patch format.  A particular patch document might be
   able to identify specific representations to modify or might be
   capable of describing changes to multiple representations.  If the
   server cannot choose a representation, it can reject the request with
   an error or the server can choose to redirect the request (e.g. using
   301 Moved Permanently or 302 Found), in which case the user agent
   makes its own decision regarding whether or not to proceed with the
   request.

   Clients are advised to take caution when sending multiple PATCH
   requests, or sequences of requests that include PATCH, over a
   pipelined connection as there are no guarantees that pipelined
   requests will be processed by the server in the same order in which
   the client sends them.  Such sequences of requests can be made safer
   by using conditional request mechanisms such as If-Match.  See
   [RFC2616] Section 8.1.2.2 for additional details regarding pipelining
   and non-idempotent requests.



Dusseault & Snell        Expires April 29, 2008                 [Page 4]

Internet-Draft                 HTTP PATCH                   October 2007


   There is no guarantee that a resource can be modified with PATCH.
   Further, it is expected that different patch document formats will be
   appropriate for different types of resources and that no single
   format will be appropriate for all types of resources.  Therefore,
   there is no single default patch document format that implementations
   are required to support.  Servers MUST ensure that a received patch
   document is appropriate for the type of resource identified by the
   Request-URI.

2.1.  A simple PATCH example

       PATCH /file.txt HTTP/1.1
       Host: www.example.com
       Content-type: application/example
       If-Match: "e0023aa4e"
       Content-Length: 100

       [description of changes]

   This example illustrates use of a hypothetical patch document on an
   existing resource.

   Successful PATCH response to existing text file

       HTTP/1.1 204 No Content
       ETag: "e0023aa4f"
       Content-MD5: Q2hlY2sgSW50ZWdyaXR5IQ==

2.2.  Error handling

   There are several known conditions under which a PATCH request can
   fail.

   Malformed patch document:  Can be specified using a 400 Bad Request
      when the server finds that the patch document provided by the
      client was improperly formatted.  The definition of badly
      formatted depends on the patch document chosen, but generally if
      the server finds it cannot handle the patch due to the
      serialization of the patch document, this response ought to be
      appropriate.
   Unsupported patch document:  Specified using a 415 Unsupported Media
      Type when the client uses a patch document format that the server
      does not support for the resource identified by the Request-URI.
      Such a response SHOULD include an Accept-Patch response header as
      described in Section 3.1 to notify the client what patch document
      formats are supported.





Dusseault & Snell        Expires April 29, 2008                 [Page 5]

Internet-Draft                 HTTP PATCH                   October 2007


   Unprocessable request:  Can be specified with a 422 Unprocessable
      Entity [RFC4918] when the server understands the patch document
      and the syntax of the patch document appears valid, but the server
      is incapable of processing the request.  There are a number of
      situations that could lead to such a result, for example:
      *  The client attempted to apply a patch document to an empty
         resource, but the patch document chosen cannot be applied to an
         empty resource.
      *  The client attempted to apply a structural modification and the
         structures assumed to exist did not exist (e.g. a patch which
         specifies changing element 'foo' to element 'bar' but element
         'foo' doesn't exist).
      *  The client attempted to modify a resource in a way that would
         cause the resource to become invalid.  For instance, a
         modification to a well-formed XML document that would cause it
         to no longer be well-formed.
      *  The client attempted to modify a resource that has multiple
         representations but the server was unable to choose which
         representation to modify.
   Conflicting modification:  Specified with a 412 Precondition Failed
      when a client uses either the If-Match or If-Unmodified-Since
      request headers and attempts to apply a patch document to a
      resource whose state has changed since the patch was created.  If
      the server detects a possible conflicting modification and neither
      the If-Match or If-Unmodified-Since request headers are used, the
      server can return a 409 Conflict response.
   Concurrent modification:  When a server receives multiple concurrent
      requests to modify a resource, those requests SHOULD be queued and
      processed in the order in which they are received.  If a server is
      incapable of queuing concurrent requests, all subsequent requests
      SHOULD be rejected until the first modification request is
      complete.

   Other HTTP status codes can also be used under the appropriate
   circumstances.

   The entity body of error responses SHOULD contain enough information
   to communicate the nature of the error to the client.  The content-
   type of the response entity can vary across implementations.


3.  Advertising Support in OPTIONS

   A server can advertise its support for the PATCH method by adding it
   to the listing of allowed methods in the "Allow" OPTIONS response
   header defined in HTTP/1.1.





Dusseault & Snell        Expires April 29, 2008                 [Page 6]

Internet-Draft                 HTTP PATCH                   October 2007


3.1.  The Accept-Patch Header

   Clients also need to know whether the server supports specific patch
   document formats, so this specification introduces a new response
   header "Accept-Patch" used to specify the patch document formats
   accepted by the server.  "Accept-Patch" MUST appear in the OPTIONS
   response for any resource that supports the use of the PATCH method.
   The presence of the "Accept-Patch" header in response to any method
   is an implicit indication that PATCH is allowed on the resource
   identified by the Request-URI.

   Accept-Patch = "Accept-Patch" ":" #( media-range )

   The Accept-Patch header specifies a listing of media ranges as
   defined by [RFC2616], Section 14.1.  Note that, unlike the HTTP
   Accept request header, the Accept-Patch header does not use quality
   factors.

3.2.  An example OPTIONS request and response


       [request]

       OPTIONS /example/buddies.xml HTTP/1.1
       Host: www.example.com

       [response]

       HTTP/1.1 200 OK
       Allow: GET, PUT, POST, OPTIONS, HEAD, DELETE, PATCH
       Accept-Patch: application/example, text/example


   The examples show a server that supports PATCH generally using two
   hypothetical patch documents.


4.  209 Content Returned

   The 209 "Content Returned" status code can be used to indicate that a
   response is equivalent to what would have been returned with a 200
   status code response to a GET sent to the URI immediately following
   the successful completion of the request.


5.  IANA Considerations





Dusseault & Snell        Expires April 29, 2008                 [Page 7]

Internet-Draft                 HTTP PATCH                   October 2007


5.1.  The 'Accept-Patch' Response Header

   The 'Accept-Patch' response header should be added to the permanent
   registry (see [RFC3864]).


       Header field name: Accept-Patch

       Applicable Protocol: HTTP

       Status: standard

       Author/Change controller: IETF

       Specification document: this specification

5.2.  HTTP Status codes

   This specification defines the 209 Content Returned status code
   (Section 3) to be updated in the registry at
   <http://www.iana.org/assignments/http-status-codes>.


6.  Security Considerations

   The security considerations for PATCH are nearly identical to the
   security considerations for PUT.  In addition, one might be concerned
   that a document that is patched might be more likely to be corrupted,
   but that concern can be addressed through the use of mechanisms such
   as conditional requests using ETags and the If-Match request header.

   Sometimes an HTTP intermediary might try to detect viruses being sent
   via HTTP by checking the body of the PUT/POST request or GET
   response.  The PATCH method complicates such watch-keeping because
   neither the source document nor the patch document might be a virus,
   yet the result could be.  This security consideration is not
   materially different from those already introduced by byte-range
   downloads, downloading patch documents, uploading zipped (compressed)
   files and so on.

   Individual patch documents will have their own specific security
   considerations that will likely vary depending on the types of
   resources being patched.  The considerations for patched binary
   resources, for instance, will be different than those for patched XML
   documents.


7.  References



Dusseault & Snell        Expires April 29, 2008                 [Page 8]

Internet-Draft                 HTTP PATCH                   October 2007


7.1.  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.

   [RFC3864]  Klyne, G., Nottingham, M., and J. Mogul, "Registration
              Procedures for Message Header Fields", BCP 90, RFC 3864,
              September 2004.

7.2.  Informative References

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


Appendix A.  Acknowledgements

   PATCH is not a new concept, it first appeared in HTTP in drafts of
   version 1.1 written by Roy Fielding and Henrik Frystyk.

   Thanks to Adam Roach, Chris Sharp, Julian Reschke, Geoff Clemm, Scott
   Lawrence, Jeffrey Mogul, Roy Fielding, Greg Stein, Jim Luther, Alex
   Rousskov, Jamie Lokier, Joe Hildebrand, Mark Nottingham and Michael
   Balloni for review and advice on this document.


Appendix B.  Changes

B.1.  Changes from -00

   OPTIONS support: removed "Patch" header definition and used Allow and
   new "Accept-Patch" headers instead.

   Supported delta encodings: removed vcdiff and diffe as these do not
   have defined MIME types and did not seem to be strongly desired.

   PATCH method definition: Clarified cache behavior.

B.2.  Changes from -01

   Removed references to XCAP - not yet a RFC.

   Fixed use of MIME types (this "fix" now obsolete)




Dusseault & Snell        Expires April 29, 2008                 [Page 9]

Internet-Draft                 HTTP PATCH                   October 2007


   Explained how to use MOVE or COPY in conjunction with PATCH, to
   create a new resource based on an existing resource in a different
   location.

B.3.  Changes from -02

   Clarified that MOVE and COPY are really independent of PATCH.

   Clarified when an ETag must change, and when Last-Modified must be
   used.

   Clarified what server should do if both Content-Type and IM headers
   appear in PATCH request.

   Filled in missing reference to DeltaV and ACL RFCs.

   Stopped using 501 Unsupported for unsupported delta encodings.

   Clarified what a static resource is.

   Refixed use of MIME types for patch formats.

   Limited the scope of some restrictions to apply only to usage of
   required diff format.

B.4.  Changes from -03

   Various typographical, terminology consistency, and other minor
   clarifications or fixes.

B.5.  Changes from -04

   Moved paragraphs on ACL and RFC3229 interoperability to new section.

   Added security considerations.

   Added IANA considerations, registration of new namespace, and
   discontinued use of "DAV:" namespace for new elements.

   Added example of error response.

B.6.  Changes from -05

   Due to various concerns it didn't seem likely the application/gdiff
   registration could go through so switching to vcdiff as required diff
   format, and to RFC3229's approach to specifying diff formats,
   including use of the IM header.




Dusseault & Snell        Expires April 29, 2008                [Page 10]

Internet-Draft                 HTTP PATCH                   October 2007


   Clarified what header server MUST use to return MD5 hash.

   Reverted to using 501 Unsupported for unsupported delta encodings.

B.7.  Changes from -06

   The reliance on RFC 3229 defined patch documents has been factored
   out in favor of delta encodings identified by MIME media type.

   The required use of DeltaV-based error reporting has been removed in
   favor of using basic HTTP status codes to report error conditions.

   The Accept-Patch response header has been redefined as a listing of
   media-ranges, similar to the Accept request header.

   Added James Snell as a co-author.

B.8.  Changes from -07

   Terminology change from "delta encoding" to "patch document"

   Added clarification on the safety and idempotency of PATCH

   Updated the caching rules of PATCH responses

   200 responses MUST include a representation of the modified resource.
   204 responses are used to indicate successful response without
   returning a representation.

   Suggest using 422 Unprocessable Entity to indicate that a properly
   formatted patch document cannot be processed

   Clarify the use of 412 and 409 to indicate concurrent and conflicting
   resource modifications.

   Added registration for the Accept-Patch header.

   Relaxed the requirements for the use of If-Match and If-Unmodified-
   Since.

   Add language that clarifies the difference between PUT and PATCH.

   Add language that clarifies the issues with PATCH and Content
   Negotiation.

   Use of Accept-Patch on any response implies that PATCH is supported.

   Add language advising caution when pipelining PATCH requests.



Dusseault & Snell        Expires April 29, 2008                [Page 11]

Internet-Draft                 HTTP PATCH                   October 2007


B.9.  Changes from -08

   Addition of the 209 Content Returned status code

   Addition of the Prefer header field mechanism

   Removed the paragraph discussing the use of 200+Content-Location.
   This is replaced by the 209 Content Returned status code.

B.10.  Changes from -09

   Move the prefer header to a separate document

   Restructure the document sections.


Appendix C.  Notes to RFC Editor

   The RFC Editor should remove this section and the Changes section.


Appendix D.  Editorial Notes

   There are several outstanding issues with the Prefer section:

   o  Should the Prefer section be separated out into a separate I-D?
   o  We need to determine how new preference codes are created/
      registered
   o  Are warn-codes ok or do we need a new response header?


Authors' Addresses

   Lisa Dusseault
   Open Source Application Foundation
   2064 Edgewood Dr.
   Palo Alto, CA  94303
   US

   Email: lisa@osafoundation.org











Dusseault & Snell        Expires April 29, 2008                [Page 12]

Internet-Draft                 HTTP PATCH                   October 2007


   James M Snell


   Phone:
   Email: jasnell@gmail.com
   URI:   http://www.snellspace.com













































Dusseault & Snell        Expires April 29, 2008                [Page 13]

Internet-Draft                 HTTP PATCH                   October 2007


Full Copyright Statement

   Copyright (C) The IETF Trust (2007).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
   THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
   OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


Intellectual Property

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at
   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at
   ietf-ipr@ietf.org.


Acknowledgment

   Funding for the RFC Editor function is provided by the IETF
   Administrative Support Activity (IASA).





Dusseault & Snell        Expires April 29, 2008                [Page 14]


Html markup produced by rfcmarkup 1.109, available from https://tools.ietf.org/tools/rfcmarkup/