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rfc:rfc7396

Internet Engineering Task Force (IETF) P. Hoffman Request for Comments: 7396 VPN Consortium Obsoletes: 7386 J. Snell Category: Standards Track October 2014 ISSN: 2070-1721

                          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/rfc7396.

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.

Hoffman & Snell Standards Track [Page 1] RFC 7396 JSON Merge Patch October 2014

Table of Contents

 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"
   }
 }

Hoffman & Snell Standards Track [Page 2] RFC 7396 JSON Merge Patch October 2014

 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.

Hoffman & Snell Standards Track [Page 3] RFC 7396 JSON Merge Patch October 2014

 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"
 }

Hoffman & Snell Standards Track [Page 4] RFC 7396 JSON Merge Patch October 2014

 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].

Hoffman & Snell Standards Track [Page 5] RFC 7396 JSON Merge Patch October 2014

    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.

Hoffman & Snell Standards Track [Page 6] RFC 7396 JSON Merge Patch October 2014

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>.

Hoffman & Snell Standards Track [Page 7] RFC 7396 JSON Merge Patch October 2014

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}}}

Hoffman & Snell Standards Track [Page 8] RFC 7396 JSON Merge Patch October 2014

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

Hoffman & Snell Standards Track [Page 9]

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