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Versions: (draft-snell-merge-patch) 00 01 02 03 04 05 06 07 RFC 7386

Applications Area Working Group                                 J. Snell
Internet-Draft
Intended status: Standards Track                       November 18, 2013
Expires: May 22, 2014


                            JSON Merge Patch
                 draft-ietf-appsawg-json-merge-patch-02

Abstract

   This specification defines the JSON merge patch format and processing
   rules.

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 May 22, 2014.

Copyright Notice

   Copyright (c) 2013 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.






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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Processing Merge Patch Documents  . . . . . . . . . . . . . .   3
   3.  Example . . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   6.  Normative References  . . . . . . . . . . . . . . . . . . . .   7
   Appendix A.  Example Test Cases . . . . . . . . . . . . . . . . .   7
   Appendix B.  Example JavaScript Implementation  . . . . . . . . .   8
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  10

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
   subset of 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:








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     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.

   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.  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.

   The following rules MUST be applied to determine what changes are to
   be made:

   1.  If the roots of either the merge patch or target resource
       documents are JSON Arrays, the target resource is replaced, in
       whole, by the merge patch document.  Any null member contained in
       the merge patch MUST be ignored and treated as if those members
       are undefined.

   2.  If, however, the roots of the merge patch or target resource
       documents are Objects, iterate through each member of merge patch
       object and determine the following:

       *  If an equivalent member in the target resource is currently
          undefined, and the given value in the merge patch is not null,
          the member is added to the target.



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       *  If the value given by the merge patch is null and the
          equivalent member is defined in the target resource, the
          existing member is removed.

       *  If the value given by the merge patch is either a non-null
          JSON primitive or Array, and the equivalent member is defined
          in the target, the existing value is replaced with the given
          value.  Any null member contained in a provided array MUST be
          ignored and treated as if the member was undefined, even
          within array or object members within the array.

       *  If the value given by the merge patch is a JSON object, and
          the equivalent member is defined in the target resource with a
          JSON primitive or Array value, that existing value is replaced
          in whole by the object provided.  Any null member in arrays or
          objects within the provided data MUST be ignored and treated
          as if the member was undefined.

       *  If the value given by the merge patch is a JSON object, and
          the equivalent member is currently defined in the target
          resource with an Object value, then recursively apply Rule #2
          to the two objects.

       *  Any member currently defined in the target resource that does
          not explicitly appear within the merge patch is to remain
          untouched and unmodified.

   Once the set of intended modifications is derived from the merge
   patch document, the recipient is free to determine the
   appropriateness of the modification based on it's own understanding
   of the target resource.  If the recipient is unable to apply any
   individual modification described by the merge patch document, it
   MUST NOT apply any of the changes and MUST stop processing the
   modification.

   If the merge patch document attempts to remove a member from the
   target resource that does not currently exist, the recipient SHOULD
   NOT consider the request to be in error.  The requested removal
   SHOULD be ignored as the final modified state of the target will
   still accurately reflect the merge documents original intent.

3.  Example

   For example, given the following example JSON document:







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   {
     "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" from the "author" object, and remove the word
   sample from the "tags" Array, would send the following request:

     PATCH /my/resource HTTP/1.1
     Host: example.org
     Content-Type: application/merge-patch+json; charset="UTF-8"

     {
       "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



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      Required parameters: None

      Optional parameters: "charset" : Specifies the character set
      encoding.  If not specified, a default of "UTF-8" is assumed.

      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 6 [RFC4627].

      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: James M
      Snell <jasnell@gmail.com>

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



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6.  Normative References

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

   [RFC4627]  Crockford, D., "The application/json Media Type for
              JavaScript Object Notation (JSON)", RFC 4627, July 2006.

   [RFC5789]  Dusseault, L. and J. Snell, "PATCH Method for HTTP", RFC
              5789, March 2010.

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"]

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

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



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

     {"a":"foo"}     {"b": [         {"a":"foo",
                       3,             "b": [3, {}]
                       null,         }
                       {"x":null}
                      ]
                     }

     [1,2]           [1,null,3]      [1,3]

     [1,2]           [1,null,2]      [1,2]

     {"a":"b"}       {"a": [         {"a": [
                       {"z":1,         {"z":1}
                        "b":null      ]
                       }             }
                      ]
                     }

     {"a":"foo"}     null            Invalid Patch

     {"a":"foo"}     "bar"           Invalid Patch

Appendix B.  Example JavaScript Implementation

   The following example implementation is provided as is, without
   warranty.  It is provided in the public domain.  Note that this
   example is provided strictly for illustrative purposes and has not
   been optimized for performance or reliability in any way.

   // Apply the patch to the original, return the
   // modified object... this will mutate the
   // passed in object in place as well...
   function apply(orig, patch) {
     if (patch == null)
       return orig;
     else if (patch instanceof Array)
       orig = purge_nulls(patch);
     else if (is_primitive(patch))
       orig = patch;
     else if (patch instanceof Object) {
       if (orig instanceof Array) {
         orig = purge_nulls(patch);
       } else {



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         for (m in patch) {
           if (orig.hasOwnProperty(m)) {
             if (patch[m] == null)
               delete orig[m];
             else {
               if (is_primitive(patch[m]))
                 orig[m] = patch[m];
               else {
                 if (orig[m] instanceof Array)
                   orig[m] = purge_nulls(patch[m]);
                 else
                   orig[m] = apply(orig[m],patch[m]);
               }
             }
           } else if (patch[m] != null)
             orig[m] = purge_nulls(patch[m]);
         }
       }
     }
     return orig;
   }

   function is_primitive(val) {
     var m = typeof val;
     return m == 'string'  ||
            m == 'number'  ||
            m == 'boolean';
   }

   function purge_nulls(obj) {
     var ret = obj;
     if (!is_primitive(obj)) {
       if (obj instanceof Array) {
         var ret = [];
         for (m in obj)
           if (obj[m] != null)
             ret.push(purge_nulls(obj[m]));
       } else if (obj instanceof Object) {
         var ret = {};
         for (m in obj) {
           if (obj[m])
             ret[m] = purge_nulls(obj[m]);
         }
       }
     }
     return ret;
   }




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   // Define the original object...
   var orig = {
     "a": "b",
     "c": {
       "d": [1,2,3],
       "e": {
         "f": 1
       }
     }
   }

   // Define the patch...
   var patch = {
     "c": {
       "d": [1,2],
       "e": {
         "f": null
       }
     }
   }

   // Apply the patch...
   var modified = apply(orig,patch);

Author's Address

   James M Snell

   Email: jasnell@gmail.com






















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