| Network Working Group | J.M. Snell |
| Internet-Draft | October 2012 |
| Intended status: Informational | |
| Expires: April 02, 2013 |
The application/json-merge-patch Media Type
draft-snell-merge-patch-04
This specification defines the application/json-merge-patch media type and it's intended use with the HTTP PATCH method defined by RFC 5789.
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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
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 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].
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 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:
Applying these rules to the previous example, the set of specific change operations the server would derive from the request would be:
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.
This specification registers the following additional MIME Media Types:
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.
| [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. |
| [RFC4627] | Crockford, D., "The application/json Media Type for JavaScript Object Notation (JSON)", RFC 4627, July 2006. |
| [I-D.ietf-appsawg-json-patch] | Bryan, P and M Nottingham, "JSON Patch", Internet-Draft draft-ietf-appsawg-json-patch-05, September 2012. |