Internet Engineering Task Force (IETF)                        P. Hoffman
Request for Comments: 7386                                VPN Consortium
Category: Standards Track                                       J. Snell
ISSN: 2070-1721                                             October 2014

JSON Merge Patch

Abstract

   This specification defines the JSON merge patch format and processing
   rules.  The merge patch format is primarily intended for use with the
   HTTP PATCH method as a means of describing a set of modifications to
   a target resource's content.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7386.

Copyright Notice

   Copyright (c) 2014 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
   (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.

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Processing Merge Patch Documents  . . . . . . . . . . . . . .   3
   3.  Example . . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Appendix A.  Example Test Cases . . . . . . . . . . . . . . . . .   8
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1. Introduction

   This specification defines the JSON merge patch document format,
   processing rules, and associated MIME media type identifier.  The
   merge patch format is primarily intended for use with the HTTP PATCH
   method [RFC5789] as a means of describing a set of modifications to a
   target resource's content.

   A JSON merge patch document describes changes to be made to a target
   JSON document using a syntax that closely mimics the document being
   modified.  Recipients of a merge patch document determine the exact
   set of changes being requested by comparing the content of the
   provided patch against the current content of the target document.
   If the provided merge patch contains members that do not appear
   within the target, those members are added.  If the target does
   contain the member, the value is replaced.  Null values in the merge
   patch are given special meaning to indicate the removal of existing
   values in the target.

   For example, given the following original JSON document:

       {
         "a": "b",
         "c": {
       "d": "e",
       "f": "g"
         }
       }

   Changing the value of "a" and removing "f" can be achieved by
   sending:

       PATCH /target HTTP/1.1
       Host: example.org
       Content-Type: application/merge-patch+json

       {
         "a":"z",
         "c": {
       "f": null
         }
       }

   When applied to the target resource, the value of the "a" member is
   replaced with "z" and "f" is removed, leaving the remaining content
   untouched.

   This design means that merge patch documents are suitable for
   describing modifications to JSON documents that primarily use objects
   for their structure and do not make use of explicit null values.  The
   merge patch format is not appropriate for all JSON syntaxes.

2. Processing Merge Patch Documents

   JSON merge patch documents describe, by example, a set of changes
   that are to be made to a target resource.  Recipients of merge patch
   documents are responsible for comparing the merge patch with the
   current content of the target resource to determine the specific set
   of change operations to be applied to the target.

   To apply the merge patch document to a target resource, the system
   realizes the effect of the following function, described in
   pseudocode.  For this description, the function is called MergePatch,
   and it takes two arguments: the target resource document and the
   merge patch document.  The Target argument can be any JSON value or
   undefined.  The Patch argument can be any JSON value.

     define MergePatch(Target, Patch):
       if Patch is an Object:
         if Target is not an Object:
       Target = {} # Ignore the contents and set it to an empty Object
         for each Name/Value pair in Patch:
       if Value is null:
         if Name exists in Target:
           remove the Name/Value pair from Target
       else:
         Target[Name] = MergePatch(Target[Name], Value)
         return Target
       else:
         return Patch

   There are a few things to note about the function.  If the patch is
   anything other than an object, the result will always be to replace
   the entire target with the entire patch.  Also, it is not possible to
   patch part of a target that is not an object, such as to replace just
   some of the values in an array.

   The MergePatch operation is defined to operate at the level of data
   items, not at the level of textual representation.  There is no
   expectation that the MergePatch operation will preserve features at
   the textual-representation level such as white space, member
   ordering, number precision beyond what is available in the target's
   implementation, and so forth.  In addition, even if the target
   implementation allows multiple name/value pairs with the same name,
   the result of the MergePatch operation on such objects is not
   defined.

3. Example

   Given the following example JSON document:

       {
         "title": "Goodbye!",
         "author" : {
       "givenName" : "John",
       "familyName" : "Doe"
         },
         "tags":[ "example", "sample" ],
         "content": "This will be unchanged"
       }

   A user agent wishing to change the value of the "title" member from
   "Goodbye!" to the value "Hello!", add a new "phoneNumber" member,
   remove the "familyName" member from the "author" object, and replace
   the "tags" array so that it doesn't include the word "sample" would
   send the following request:

       PATCH /my/resource HTTP/1.1
       Host: example.org
       Content-Type: application/merge-patch+json

       {
         "title": "Hello!",
         "phoneNumber": "+01-123-456-7890",
         "author": {
       "familyName": null
         },
         "tags": [ "example" ]
       }

   The resulting JSON document would be:

       {
         "title": "Hello!",
         "author" : {
       "givenName" : "John"
         },
         "tags": [ "example" ],
         "content": "This will be unchanged",
         "phoneNumber": "+01-123-456-7890"
       }

4. IANA Considerations

   This specification registers the following additional MIME media
   types:

      Type name: application

      Subtype name: merge-patch+json

      Required parameters: None

      Optional parameters: None

      Encoding considerations: Resources that use the "application/
      merge-patch+json" media type are required to conform to the
      "application/json" media type and are therefore subject to the
      same encoding considerations specified in Section 8 of [RFC7159].

      Security considerations: As defined in this specification

      Published specification: This specification.

      Applications that use this media type: None currently known.

      Additional information:

         Magic number(s): N/A

         File extension(s): N/A

         Macintosh file type code(s): TEXT

      Person & email address to contact for further information: IESG

      Intended usage: COMMON

      Restrictions on usage: None

      Author: James M. Snell <jasnell@gmail.com>

      Change controller: IESG

5. Security Considerations

   The "application/merge-patch+json" media type allows user agents to
   indicate their intention for the server to determine the specific set
   of change operations to be applied to a target resource.  As such, it
   is the server's responsibility to determine the appropriateness of
   any given change as well as the user agent's authorization to request
   such changes.  How such determinations are made is considered out of
   the scope of this specification.

   All of the security considerations discussed in Section 5 of
   [RFC5789] apply to all uses of the HTTP PATCH method with the
   "application/merge-patch+json" media type.

6. References

6.1. Normative References

   [RFC7159]  Bray, T., "The JavaScript Object Notation (JSON) Data
              Interchange Format", RFC 7159, March 2014,
              <http://www.rfc-editor.org/info/rfc7159>.

6.2. Informative References

   [RFC5789]  Dusseault, L. and J. Snell, "PATCH Method for HTTP", RFC
              5789, March 2010,
              <http://www.rfc-editor.org/info/rfc5789>.

Appendix A. Example Test Cases

   ORIGINAL        PATCH            RESULT
   ------------------------------------------
   {"a":"b"}       {"a":"c"}       {"a":"c"}

   {"a":"b"}       {"b":"c"}       {"a":"b",
                                    "b":"c"}

   {"a":"b"}       {"a":null}      {}

   {"a":"b",       {"a":null}      {"b":"c"}
    "b":"c"}

   {"a":["b"]}     {"a":"c"}       {"a":"c"}

   {"a":"c"}       {"a":["b"]}     {"a":["b"]}

   {"a": {         {"a": {         {"a": {
     "b": "c"}       "b": "d",       "b": "d"
   }                 "c": null}      }
                   }               }

   {"a": [         {"a": [1]}      {"a": [1]}
     {"b":"c"}
    ]
   }

   ["a","b"]       ["c","d"]       ["c","d"]

   {"a":"b"}       ["c"]           ["c"]

   {"a":"foo"}     null            null

   {"a":"foo"}     "bar"           "bar"

   {"e":null}      {"a":1}         {"e":null,
                                    "a":1}

   [1,2]           {"a":"b",       {"a":"b"}
                    "c":null}

   {}              {"a":            {"a":
                    {"bb":           {"bb":
                     {"ccc":          {}}}
                      null}}}

Acknowledgments

   Many people contributed significant ideas to this document.  These
   people include, but are not limited to, James Manger, Matt Miller,
   Carsten Bormann, Bjoern Hoehrmann, Pete Resnick, and Richard Barnes.

Authors' Addresses

   Paul Hoffman
   VPN Consortium

   EMail: paul.hoffman@vpnc.org

   James M. Snell

   EMail: jasnell@gmail.com