One document matched: draft-snell-merge-patch-04.txt
Differences from draft-snell-merge-patch-03.txt
Network Working Group J. Snell
Internet-Draft October 4, 2012
Intended status: Informational
Expires: April 7, 2013
The application/json-merge-patch Media Type
draft-snell-merge-patch-04
Abstract
This specification defines the application/json-merge-patch media
type and it's intended use with the HTTP PATCH method defined by RFC
5789.
Status of this Memo
This Internet-Draft is submitted to IETF 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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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 April 7, 2013.
Copyright Notice
Copyright (c) 2012 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
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described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. The "application/json-merge-patch" Media Type . . . . . . . . . 4
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
4. Security Considerations . . . . . . . . . . . . . . . . . . . . 7
5. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5.1. Normative References . . . . . . . . . . . . . . . . . . . 7
5.2. Informational References . . . . . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 8
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1. Introduction
The HTTP PATCH method [RFC5789] provides a mechanism for requesting
partial modifications of resources. The payload entity contained by
a PATCH request provides a description of the changes that are to be
made to a target resource. The general term used to describe such
payloads is a "Patch Document".
A partial modification request using PATCH can generally take one of
two forms. The Patch Document can either
o Provide an explicit description of the changes being requested --
as is done, for instance, with the JSON Patch format described in
[I-D.ietf-appsawg-json-patch] -- or,
o Provide a modified subset of the original resource and allow the
Server to determine the set of changes being requested.
Either approach is valid. However, when using the latter approach --
generally termed a "Merge Patch" within this specification -- it is
often difficult for a server to determine the client's exact intent
when using generic media types that do not have clearly defined PATCH
semantics. The JSON format [RFC4627] is one such example.
To best illustrate the problem -- albeit with an example that is
somewhat extreme -- consider an example where a user agent wishes to
modify the following JSON Patch Document currently existing on a
server:
[
{"op": "add", "path": "/title", "value":"Goodbye!"},
{"op": "remove", "path": "/link"}
]
Supposing the user agent wishes to remove the "remove" statement from
the document and change the "value" of the "title" from "Goodbye" to
"Hello World", if it sends the following request to the server
intending to perform a Merge Patch style modification:
PATCH /patches/1 HTTP/1.1
Host: example.org
Content-Type: application/json-patch
[{"op":"add", "path": "title", "value":"Hello world"}]
The server has no choice but to interpret the request as a normal
JSON Patch operation, resulting in an unintended modification of the
target resource.
What is needed in this case is a mechanism that will allow the user
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agent sending the PATCH request to explicitly signal that it is
requesting a Merge Patch style modification of the resource.
Using the "application/json-merge-patch" Media Type defined herein,
the user agent's original intent can be clearly and unambiguously
communicated to the server within the request:
PATCH /patches/1 HTTP/1.1
Host: example.org
Content-Type: application/json-merge-patch; charset="UTF-8"
[{"op":"add", "path": "title", "value":"Hello world"}]
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. The "application/json-merge-patch" Media Type
The "application/json-merge-patch" Media Type is used to identify
JSON documents that describe, by example, a set of changes that are
to be made to a target resource. When used within an HTTP PATCH
request, it is the responsibility of the server receiving and
processing the request to inspect the payload entity and determine
the specific set of operations that are to be performed to modify the
target resource. The actual set of modifications to be made will be
specific to the semantics and requirements of the target resource.
The "application/json-merge-patch" media type MAY contain a "charset"
parameter that is used to identify the character set encoding
utilized.
For example, given the following example JSON document:
{
"title": "Goodbye!",
"author" : {
"givenName" : "John",
"familyName" : "Doe"
},
"tags":["example","sample"],
"content": "This will be unchanged"
}
If the intent is to change the value of the "title" member to from
"Goodbye!" to the value "Hello!", add a new "phoneNumber" member,
remove the "familyName" member from the "author" object, and remove
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the word sample from the "tags" Array, the user-agent would send the
following request:
PATCH /my/resource HTTP/1.1
Host: example.org
Content-Type: application/json-merge-patch; charset="UTF-8"
{
"title": "Hello!",
"phoneNumber": "+01-123-456-7890",
"author": {
"familyName": null
}
"tags": ["example"]
}
Upon receiving the request, the server is responsible for inspecting
the payload and determining, based on it's own understanding of the
target resource media type and the underlying data model the target
resource represents, what specific operations will be applied to
modify the resource.
A server receiving this patch request MUST apply the following rules
to determine the specific set of change operations to be performed:
1. If the root of the JSON data provided in the payload is an Array,
the target resource is to be replaced, in whole, by the provided
data.
2. If the root of the JSON data provided in the payload is an
Object, for each distinct member specified in that object:
* If the member is currently undefined within the target
resource, the member and the given value is to be added to the
target.
* If the value is explicitly set to null and that member is
currently defined within the target resource, the existing
member is removed.
* If the value is either a non-null JSON primitive or an Array
and that member is currently defined within the target
resource, the existing value for that member is to be replaced
with that provided.
* If the value is a JSON object and that member is currently
defined for the target resource and the existing value is a
JSON primitive or Array, the existing value is to be replaced
in whole by the object provided.
* If the value is a JSON object and that member is currently
defined within the target resource and the existing value is
also a JSON object, then recursively apply Rule #2 to each
object.
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* Any member currently defined within the target resource that
does not explicitly appear within the patch is to remain
untouched and unmodified.
Applying these rules to the previous example, the set of specific
change operations the server would derive from the request would be:
o Change the existing value of the "title" member from "Goodbye!" to
"Hello!",
o Add the "phoneNumber" member with a value of "+01-123-456-7890",
o Remove the "familyName" member from the current object value
associated with the "author" member, and
o Change the existing value of the "tags" member from
["example","sample"] to ["example"].
The resulting JSON document would be similar to (note that the
specific ordering of members within JSON documents is insigificant):
{
"title": "Hello!",
"author" : {
"givenName" : "John"
},
"tags":["example"],
"content": "This will be unchanged",
"phoneNumber": "+01-123-456-7890"
}
Once the set of intended modifications is derived from the request,
the server is free to determine the appropriateness of the
modification based on it's own understanding of the target resource.
For instance, in the previous example, it is possible that the
"familyName" member might be required within the target resource and
cannot be removed. Note that in such cases, per [RFC5789], Section
2, the server is REQUIRED to reject the entire PATCH request using an
HTTP error response code appropriate to the error condition.
If the request attempts to remove a member from the target resource
that does not currently exist, the server SHOULD NOT consider the
request to be in error. The requested removal operation is simply be
ignored by the server as the final modified state of the target
resource will still accurately reflect the user-agent's original
intention.
3. IANA Considerations
This specification registers the following additional MIME Media
Types:
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Type name: application
Subtype name: json-merge-patch
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/
json-merge-patch" 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
4. Security Considerations
The "application/json-merge-patch" 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/json-merge-patch" Media Type.
5. References
5.1. 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.
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[RFC5789] Dusseault, L. and J. Snell, "PATCH Method for HTTP",
RFC 5789, March 2010.
5.2. Informational References
[I-D.ietf-appsawg-json-patch]
Bryan, P. and M. Nottingham, "JSON Patch",
draft-ietf-appsawg-json-patch-05 (work in progress),
September 2012.
Author's Address
James M Snell
Email: jasnell@gmail.com
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