A JSON Media Type for Describing Partial Modifications to JSON Documents
draft-pbryan-json-patch-00

Abstract

JSON (JavaScript Object Notation) Patch defines the media type "application/patch+json", a JSON-based document structure for specifying partial modifications to apply to a JSON document.

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 working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/.

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This Internet-Draft will expire on October 22, 2011.

Copyright Notice

Copyright (c) 2011 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.

Table of Contents

• 1. Introduction
• 2. Conventions
• 3. Patch Object Structure
• 3.1. patches
• 3.2. op
• 3.3. path
• 3.4. element
• 3.5. value
• 4. Patch Operations
• 4.1. add
• 4.2. remove
• 5. Error Handling
• 6. Acknowledgements
• 7. IANA Considerations
• 8. Security Considerations
• 9. References
• 9.1. Normative References
• 9.2. Informative References
• Appendix A. Examples
• Appendix A.1. Adding an Object Property
• Appendix A.2. Adding an Array Element
• Appendix A.3. Removing an Object Property
• Appendix A.4. Removing an Array Element
• Appendix A.5. Replacing a Value
• Appendix B. Changelog
• Appendix C. Open Issues
• Author's Address

1. Introduction

JavaScript Object Notation (JSON) [RFC4627] has become a popular format for the storage and transmission of structured data between systems. As a result, numerous web service APIs support the JSON media type. The HTTP PATCH [RFC5789] specification extends HTTP with a new method to perform partial modifications to resources.

This Internet-Draft proposes the JSON-Patch media type "application/patch+json", a JSON-based document structure for specifying partial modifications to apply to a JSON document.

2. Conventions

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119].

3. Patch Object Structure

A JSON-Patch document is a JSON document that contains an object which specifies the set of operations to apply to a target JSON document.

An example JSON-Patch document:

{
  "patches": [
    { "op": "remove", "path": "$.a.b.c" },
    { "op": "add", "path": "$.a.b", "element": "c", "value": "foo" }
  ]
}
             

3.1. patches

An array of objects; each object specifies a single patch operation to be applied to the target JSON document. Patch operations MUST be applied sequentially in the order they appear in the array. After the first patch has been applied, the resulting JSON document becomes the target for the next patch operation. This process repeats until all patches have been applied.

3.2. op

MUST be a string value. Specifies the patch operation to be applied. Defined patch operations are "add" and "remove".

3.3. path

MUST be a string value. Contains a concrete [JSONPath] expression (i.e. MUST contain only the root $, object property . [] and array subscript [] operators). It is an error condition if a path resolves to anything but a single node within the target JSON document.

3.4. element

MUST be a string or integer value. Specifies the child node to add into the node specified by the path. If string, specifies an object property to insert; if integer, specifies an array index to insert at. It is an error condition if the specified node type is incompatible with the "element" value (i.e. object with integer element, array with string element).

3.5. value

The value to insert into the specified node.

4. Patch Operations

The patch operations are "add" and "remove".

4.1. add

Adds a new property into an object or element into an array.

If adding a property into an object, the "element" specifies the property to be added. It is an error condition if the property already exists in the object.

If adding into an array, the "element" specifies the index where the value should be inserted. Any elements at or above the specified index are shifted one position to the right (i.e. indexes are incremented). It is an error condition if an addition would result in sparse allocation of array element(s).

4.2. remove

Removes the node specified by the path. It is an error condition if the node to be removed does not exist.

If removing an element from an array, any elements above the specified index are shifted one position to the left (i.e. indexes are decremented).

5. Error Handling

In the event of an error condition, whether patch processing ceases, and/or how error conditions are communicated and handled are left to the implementation to specify.

Enforcing safety and/or idempotency of a JSON patch document is specified and handled by the implementation, based-on any mechanisms in other related specifications, such as HTTP [RFC2616] and HTTP PATCH [RFC5789].

6. Acknowledgements

The structure of a JSON patch document was informed by the XML Patch document [RFC5261] specification.

7. IANA Considerations

The proposed MIME media type for the JSON patch document is "application/patch+json".

Type name: application

Subtype name: patch+json

Required parameters: none

Optional parameters: none

8. Security Considerations

This specification is based-on the JSON format, therefore has the same security considerations as [RFC4627].

This specification uses [JSONPath] expressions to resolve the nodes to be modified. Such expressions should not be evaluated directly by the implementation language interpreter due to the potential for injection of malicious code.

9. References

9.1. Normative References

9.2. Informative References

Appendix A. Examples

Appendix A.1. Adding an Object Property

An example target JSON document:

{
  "foo": "bar"
}
                 

A JSON patch document:

{
  "patches": [
    { "op": "add", "path": "$", "element": "baz", "value": "qux" }
  ]
}
                 

The resulting JSON document:

{
  "baz": "qux",
  "foo": "bar"
}
                 

Appendix A.2. Adding an Array Element

An example target JSON document:

{
  "foo": ["bar", "baz"]
}
                 

A JSON patch document:

{
  "patches": [
    { "op": "add", "path": "$.foo", "element": 1, "value": "qux" }
  ]
}
                 

The resulting JSON document:

{
  "foo": [ "bar", "qux", "baz" ]
}
                 

Appendix A.3. Removing an Object Property

An example target JSON document:

{
  "baz": "qux",
  "foo": "bar"
}
                 

A JSON patch document:

{
  "patches": [
    { "op": "remove", "path": "$.baz" }
  ]
}
                 

The resulting JSON document:

{
  "foo": "bar"
}
                 

Appendix A.4. Removing an Array Element

An example target JSON document:

{
  "foo": [ "bar", "qux", "baz" ]
}
                 

A JSON patch document:

{
  "patches": [
    { "op": "remove", "path": "$.foo[1]" }
  ]
}
                 

The resulting JSON document:

{
  "foo": ["bar", "baz"]
}
                 

Appendix A.5. Replacing a Value

Replacing a value is performed by removing a value and inserting it.

An example target JSON document:

{
  "baz": "qux",
  "foo": "bar"
}
                 

A JSON patch document:

{
  "patches": [
    { "op": "remove", "path": "$.baz" },
    { "op": "add", "path": "$", "element": "baz": "value": "boo" }
  ]
}
                 

The resulting JSON document:

{
  "baz": "boo",
  "foo": "bar"
}
                 

Appendix B. Changelog

Draft 00

• Initial draft.

Appendix C. Open Issues

1. [JSONPath] is an informal, de facto standard. Work is now in progress to get it published an Internet-Draft (with some likely changes).
2. Should define an accompanying JSON-Schema specification for the JSON-Patch document structure.

Author's Address