Network Working Group J.M. Snell
Internet-Draft March 2012
Intended status: Informational
Expires: August 31, 2012
The application/merge-patch Media Type
draft-snell-merge-patch-01
Abstract
This specification defines the application/merge-patch media type and
it's intended use with the HTTP PATCH method defined by RFC 5789; as
well as the "application/json+merge-patch" variation that defines the
"Merge Patch" semantics for JSON documents.
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
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 August 31, 2012.
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 carefully, as they describe your rights
and restrictions with respect to this document.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. The "application/merge-patch" Media Type . . . . . . . . . . . 3
2.1. The "type" Parameter . . . . . . . . . . . . . . . . . . . 4
2.2. The "charset" Parameter . . . . . . . . . . . . . . . . . 4
2.3. Type-Specific Variations . . . . . . . . . . . . . . . . . 4
3. The "application/json+merge-patch" Type Specific Variation . . 5
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
Snell Expires August 31, 2012 [Page 1]
Internet-Draft application/merge-patch March 2012
4.1. application/merge-patch . . . . . . . . . . . . . . . . . 7
4.2. application/json+merge-patch . . . . . . . . . . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
6.1. Normative References . . . . . . . . . . . . . . . . . . . 8
6.2. Informational References . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 9
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 the 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 version of the original resource and allow the
Server to determine to specific set of changes being requested.
Either approach is equally valid. However, it is important to note
that when using PATCH with the second approach -- generally called a
"Merge Patch" -- it is often difficult for a server to determine the
clients exact intent when generic media types that do not have
clearly defined PATCH semantics defined are used.
To best illustrate the problem -- albeit with an example that is
somewhat extreme -- consider an example where we have the following
JSON Patch Document currently existing on a server that we wish to
modify:
[
{"add":"title","value":"Goodbye!"},
{"remove":"link"}
]
If we send 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
[{"add":"title","value":"Hello world"}]
The server has no choice but to interpret this request as a normal
JSON Patch operation, resulting in an unintended modification of the
target resource.
Snell Expires August 31, 2012 [Page 2]
Internet-Draft application/merge-patch March 2012
What is needed in this case is a mechanism that will allow the user
agent sending the PATCH request to explicitly signal that it is
requesting a Merge Patch style modification of the resource.
Using the "application/merge-patch" Media Type defined herein, the
user agents 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/merge-patch;
type="application/json+patch"; charset="UTF-8"
[{"add":"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/merge-patch" Media Type
The "application/merge-patch" Media Type is used to identify document
resources 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
media type of the target resource.
For example, given the following example JSON document:
{
"title": "Goodbye!",
"author" : {
"givenName" : "James",
"familyName" : "Snell"
},
"tags":["example","sample"]
}
If my intent is to change only the value of the "title" property from
it's current value "Goodbye!" to the new value "Hello!", I would
send the following request:
PATCH /my/resource HTTP/1.1
Host: example.org
Content-Type: application/merge-patch;
type="application/json"; charset="UTF-8""
{
"title": "Hello!"
Snell Expires August 31, 2012 [Page 3]
Internet-Draft application/merge-patch March 2012
}
Upon receiving the request, the server is responsible for inspecting
the payload and will determine, 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.
The "application/merge-patch" media type intentionally makes the
receiving party responsible for determining how the target resource
is to be modified.
2.1. The "type" Parameter
By itself, the "application/merge-patch" media type does not define a
specific serialization format and MAY contain data of any type.
Unless using a type-specific variation (Section 2.3) of the
"application/merge-patch" media type, such as "application/json
+merge-patch" (Section 3), the "application/merge-patch" MUST specify
a type parameter whose value is the actual MIME Media Type of the
payload.
For example, if using the "application/merge-patch" media type to
request modifications in an XML document, the "type" parameter would
specify the appropriate XML media type:
PATCH /my/resource HTTP/1.1
Host: example.org
Content-Type: application/merge-patch;
type="application/xml"; charset="UTF-8"
foo
2.2. The "charset" Parameter
When the "application/merge-patch" resource contains character-based
data (e.g. plain text, XML, JSON, and so forth), the "charset"
parameter SHOULD be used to identify the character set encoding
utilized.
2.3. Type-Specific Variations
This document recommends the use of a naming convention (a suffix of
"+merge-patch") for identifying Media Type specific variations of
"application/merge-patch".
Media Type specific variations of "application/merge-patch" define
the specific details of how a server SHOULD derive the set of actual
change operations being requested in a PATCH operation relative to
one or more specific media types. The variation also defines the
specific payload type required for the request.
Snell Expires August 31, 2012 [Page 4]
Internet-Draft application/merge-patch March 2012
When a Media Type specific variation is used, such as "application/
json+merge-patch", the "type" parameter MAY be specified to provide
additional specific type information.
In the following example, the request clearly indicates that the
"application/json+merge-patch" Type Specific Variation is utilized
with the "type" attribute providing additional contextual information
about what specific variation of the JSON Document format is
contained in the request.
PATCH /my/resource HTTP/1.1
Host: example.org
Content-Type: application/json+merge-patch;
type="application/stream+json"; charset="UTF-8"
{
"verb": "POST"
}
3. The "application/json+merge-patch" Type Specific Variation
The "application/json+merge-patch" Media Type is a Type Specific
Variation of the "application/merge-patch" Media Type that uses a
JSON data structure to describe the changes to be made to a target
resource.
For example, given the following example JSON document:
{
"title": "Goodbye!",
"author" : {
"givenName" : "James",
"familyName" : "Snell"
},
"tags":["example","sample"]
}
If the intent is to change the value of the "title" property to from
"Goodbye!" to the value "Hello!", add a new "phoneNumber" property,
remove the "familyName" property from the "author" object, and remove
the word sample from the "tags" Array, the user-agent would send the
following request:
Snell Expires August 31, 2012 [Page 5]
Internet-Draft application/merge-patch March 2012
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"]
}
Note that while the payload of "application/json+merge-patch"
resources MUST be any valid subtype of the "application/json" media
type, the target resource to which a PATCH request using "application
/json+merge-patch" is sent can be of any arbitrary media type. It is
the server's responsibility to determine how to apply the specific
semantics of the Merge Patch operation to the target resource.
A server receiving this patch request MUST determine the specific set
of change operations to be performed by analyzing the JSON data
contained in the payload of the request relative to the target
resource and applying the following rules:
1. If the root of the JSON data provided in the payload is a JSON
Array, the target resource is to be replaced, in whole, by the
provided JSON data.
2. If the root of the JSON data provided in the payload is a JSON
Object, for each distinct property specified in that object:
* If the property is currently not specified for the target
resource, the property and the given value is to be added to
the target.
* If the value is explicitly set to null and that property is
currently specified for the target resource, the existing
value is removed.
* If the value is either a non-null JSON primitive or an Array
and that property is currently specified for the target
resource, the existing value is to be replaced with that
provided.
* If the value is a JSON object and that property is currently
specified 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 property is currently
specified for the target resource and the existing value is
also a JSON object, then recursively apply Rule #2 to each
object.
Applying these rules to the previous example, the set of specific
change operations the server would derive from the request would be:
Snell Expires August 31, 2012 [Page 6]
Internet-Draft application/merge-patch March 2012
o Change the existing value of the "title" property from "Goodbye!"
to "Hello!",
o Add the "phoneNumber" property with a value of "+01-123-456-7890",
o Remove the "familyName" property from the current object value
associated with the "author" property, and
o Change the existing value of the "tags" property from
["example","sample"] to ["example"].
Note that 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" property could 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 PATCH request using
an HTTP error response code appropriate to the error condition.
If the request attempts to remove a property from the target resource
that does not currently exist, the server SHOULD NOT consider the
request to be in error. The requested removal operation SHOULD
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.
4. IANA Considerations
This specification registers the following additional MIME Media
Types:
4.1. application/merge-patch
Type name: application
Subtype name: merge-patch
Required parameters: "type" : A MIME Media Type
Optional parameters: "charset" : Specifies the character set
encoding type when the "application/merge-patch" resource contains
character-based content.
Encoding considerations: The specific encoding considerations will
vary dependent on the specific MIME Media Type specified by the
"type" parameter.
Security considerations: As defined in this specification.
Interoperability considerations: There are no known
interoperability issues.
Published specification: This specification.
Applications that use this media type: This media type is intended
primarily for use with the HTTP PATCH method.
Additional information:
Magic number(s): N/A
File extension(s): N/A
Macintosh file type code(s): "BINARY"
Person & email address to contact for further information: James M
Snell
Snell Expires August 31, 2012 [Page 7]
Internet-Draft application/merge-patch March 2012
Intended usage: COMMON
Restrictions on usage: None.
Author: James M Snell
Change controller: IETF
4.2. application/json+merge-patch
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.
Interoperability considerations: There are no known
interoperability issues.
Published specification: This specification.
Applications that use this media type: This media type is intended
primarily for use with the HTTP PATCH method.
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
Intended usage: COMMON
Restrictions on usage: None.
Author: James M Snell
Change controller: IETF
5. Security Considerations
The "application/merge-patch" Media Type and all Type-Specific
Variations are intended for use as a mechanism to allow user-agents
requesting partial modification of a target resource to indicate an
intention for the server to determine the specific set of change
operations that are to be applied to the target resource. As such,
it is the servers responsibility to determine the appropriateness of
any given change as well as the user-agents authorization to request
such changes.
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" Media Type (and all Type-Specific
Variations).
6. References
6.1. Normative References
Snell Expires August 31, 2012 [Page 8]
Internet-Draft application/merge-patch March 2012
[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.
6.2. Informational References
[I-D.ietf-appsawg-json-patch]
Bryan, P., "JSON Patch", Internet-Draft draft-ietf-
appsawg-json-patch-01, March 2012.
Author's Address
James M Snell
Email: jasnell@gmail.com
Snell Expires August 31, 2012 [Page 9]