Internet Engineering Task Force (IETF) P. Hoffman

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.

Hoffman & Snell Standards Track [Page 1]

RFC 7386 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 7386 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 7386 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 7386 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 7386 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 <[email protected]>

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 7386 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 7386 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 7386 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: [email protected]

James M. Snell

EMail: [email protected]

Hoffman & Snell Standards Track [Page 9]