Applications Area Working Group P. Hoffman
Internet-Draft VPN Consortium
Intended status: Standards Track J. Snell
Expires: January 1, 2015
June 30, 2014
JSON Merge Patch
draft-ietf-appsawg-json-merge-patch-03
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 subset of target resource's content.
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
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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 January 1, 2015.
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.
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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. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
7. Normative References . . . . . . . . . . . . . . . . . . . . 7
Appendix A. Example Test Cases . . . . . . . . . . . . . . . . . 7
Appendix B. Example JavaScript Implementation . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 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.
A JSON merge patch document can only be a JSON array or a JSON
object.
For example, given the following original JSON document:
{
"a": "b",
"c": {
"d": "e",
"f": "g"
}
}
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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.
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. Only one of the two rules will be applied.
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.
2. If the roots of both the merge patch and the target resource
documents are Objects, iterate through each member of merge patch
object and determine the following:
A. If an equivalent member in the target resource is currently
undefined, and the given value in the merge patch is not
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null, the member/value pair is added to the target. If an
equivalent member in the target resource is currently
undefined, and the given value in the merge patch is null, no
action is taken.
B. If an equivalent member in the target resource is any type,
and the given value in the merge patch is null, the existing
member is removed.
C. If an equivalent member in the target resource is any type,
and the given value in the merge patch is any type other than
an Object or null, the existing value is replaced with the
given value.
D. If an equivalent member in the target resource is any type
other than an Object, and the given value in the merge patch
is an Object, the existing value is replaced with the given
value.
E. If an equivalent member in the target resource is an Object,
and the given value in the merge patch is an Object, then
recursively apply Rule #2 to the two objects.
F. Any member currently defined in the target resource that does
not explicitly appear within the merge patch remains
untouched and unmodified.
It is not an error for the merge patch document to attempt to remove
a member from the target resource that does not currently exist.
This is because the final modified state of the target will still
accurately reflect the merge documents original intent.
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. For example, if a patch would remove a member of an
object that is semantically required by a processor, the processor
MUST not apply any of the patches.
3. Example
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For 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" 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:
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[[ NOTE: There were a few notes that the charset media type parameter
is unacceptable for a +json media type. ]]
Type name: application
Subtype name: merge-patch+json
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 [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: 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
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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.
6. Acknowledgements
Many people contributed significant ideas to this document. These
people include, but are not limited to, James Manger, Matt Miller,
Carsten Bormann, and Bjoern Hoehrmann. [[ NOTE: If you contributed
and we missed your name, please let us know. ]]
7. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5789] Dusseault, L. and J. Snell, "PATCH Method for HTTP", RFC
5789, March 2010.
[RFC7159] Bray, T., "The JavaScript Object Notation (JSON) Data
Interchange Format", RFC 7159, March 2014.
Appendix A. Example Test Cases
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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}
{"a":"foo"} null Invalid Patch
{"a":"foo"} "bar" Invalid Patch
Appendix B. Example JavaScript Implementation
[[ NOTE: This example refers to a previous version of this draft. It
needs to be updated to reflect the current draft. ]]
The following example implementation is provided as is, without
warranty. It is provided in the public domain. Note that this
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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 {
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;
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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;
}
// 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);
Authors' Addresses
Paul Hoffman
VPN Consortium
Email: paul.hoffman@vpnc.org
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James M Snell
Email: jasnell@gmail.com
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