JSON Pointer
draft-ietf-appsawg-json-pointer-01

Abstract

JSON Pointer defines a string syntax for identifying a specific value within a JSON document.

Status of this Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on September 08, 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. 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. Syntax
• 4. Evaluation
• 5. JSON String Representation
• 6. URI Fragment Identifier Representation
• 7. Error Handling
• 8. IANA Considerations
• 9. Security Considerations
• 10. Acknowledgements
• 11. References
• Appendix A. Examples
• Authors' Addresses

1. Introduction

This specification defines JSON Pointer, a string syntax for identifying a specific value within a JavaScript Object Notation (JSON) [RFC4627] text document. This syntax is intended to be easily expressed in JSON string values and Uniform Resource Identifier (URI) [RFC3986] fragment identifiers.

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 [RFC2119].

This specification expresses normative syntax rules using Augmented Backus-Naur Form [RFC5234] (ABNF) notation.

3. Syntax

A JSON Pointer is a [Unicode] string containing a sequence of zero or more reference tokens, each prefixed by a '/' (%x2F) character.

If a reference token contains '/' (%x2F) or '^' (%x5E) characters, such characters MUST each be prefixed (escaped) with a '^' (%x5E) character.

ABNF syntax:

json-pointer = *( "/" reference-token )
reference-token = *( unescaped / escaped )
unescaped = %x00-2E / %x30-5B / %x5D-10FFFF
escaped = "^" ( "/" / "^" )
         

It is an error condition if a JSON Pointer value does not conform to this syntax.

4. Evaluation

Evaluation of a JSON Pointer begins with a reference to the root value of a JSON text document and completes with a reference to some value within the document. Each reference token in the JSON Pointer is sequentially evaluated.

Evaluation of each reference token begins by unescaping any escaped character sequence; this is performed by removing the '^' (escape) prefix. The reference token then modifies which value is referenced according to the following scheme:

• If the currently referenced value is a JSON object, the new referenced value is the object member with the name identified by the reference token. The member name is equal to the token if it has the same number of Unicode characters as token and their codepoints are positionwise equal. If a referenced member name is not unique in an object, the member that is referenced is undefined.
• If the currently referenced value is a JSON array, the reference token MUST contain characters that represent an unsigned base-10 integer value, and the new referenced value is the array element with the zero-based index identified by the token.

If a reference token is being evaluated against a JSON document, the implementation MAY evaluate each token against a concrete value, and terminate evaluation with an error condition if a evaluation fails to resolve a concrete value.

5. JSON String Representation

A JSON Pointer MAY be represented in a JSON string value. Per [RFC4627], section 2.5, all instances of quotation mark '"' (%x22), reverse solidus '\' (%x5C) and control (%x00-1F) characters MUST be escaped.

6. URI Fragment Identifier Representation

A JSON Pointer MAY be represented in a URI fragment identifier. The JSON pointer MUST be UTF-8 [RFC3629] encoded as octets; octets not in the URI "unreserved" set SHOULD be percent-encoded, per [RFC3986], section 2.5.

7. Error Handling

In the event of an error condition, evaluation of the JSON Pointer fails to complete.

8. IANA Considerations

This document has no IANA actions.

9. Security Considerations

A given JSON Pointer is not guaranteed to reference an actual JSON value. Implementations should be aware of this and take appropriate precautions.

10. Acknowledgements

The following individuals contributed ideas, feedback and wording, which contributed to the content of this specification:

• Mike Acar, Carsten Bormann, Tim Bray, Jacob Davies, Martin J. Dürst, Björn Höhrmann, James H. Manger, Mark Nottingham, Drew Perttula, Julian Reschke.

11. References

Appendix A. Examples

The following examples illustrate the use of JSON Pointers in URI fragments for a JSON text document located at http://example.com/example.json, with the following value:

{
    "foo": {
        "bar": [ "element0", "element1" ],
        "inner object": {
            "baz": "qux"
    }
}
                 

http://example.com/example.json#

Resolves to the object value at the root of the JSON text document.

http://example.com/example.json#/foo

Resolves to the object value of the "foo" member in the root object.

http://example.com/example.json#/foo/inner%20object

Resolves to the object value of the "inner object" member in the "foo" object value in the root object.

http://example.com/example.json#/foo/inner%20object/baz

Resolves to the string value "qux", which is the value of the "baz" member in the "inner object" member in the "foo" member in the root object.

http://example.com/example.json#/foo/bar/0

Resolves to the string value "element0", which is the first value in the "bar" array in the "foo" member in the root object.

Authors' Addresses