Internet Engineering Task Force G. Luff, Ed.
Internet-Draft
Intended status: Informational July 01, 2013
Expires: January 02, 2014
Relative JSON Pointers
draft-luff-relative-json-pointer-00
Abstract
JSON Pointer is a syntax for specifying locations in a JSON document,
starting from the document root. This document defines an extension
to the JSON Pointer syntax, allowing relative locations from within
the document.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Terminology . . . . . . . . . . . . . . . . . 2
3. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
4. Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . 3
5. JSON String Representation . . . . . . . . . . . . . . . . . 3
5.1. Examples . . . . . . . . . . . . . . . . . . . . . . . . 4
6. Non-use in URI Fragment Identifiers . . . . . . . . . . . . . 4
7. Error Handling . . . . . . . . . . . . . . . . . . . . . . . 5
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
9. Security Considerations . . . . . . . . . . . . . . . . . . . 5
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
10.1. Normative References . . . . . . . . . . . . . . . . . . 5
10.2. Informative References . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
JSON Pointer (RFC 6901 [RFC6901]) is a syntax for specifying
locations in a JSON document, starting from the document root. This
document defines an extension to the JSON Pointer syntax, allowing
relative locations from within the document.
2. Conventions and Terminology
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. Syntax
A Relative JSON Pointer is a Unicode string (see RFC 4627, Section 3
[RFC4627]), comprising a positive integer, followed by either a '#'
(%x23) character or a JSON Pointer (RFC 6901 [RFC6901]).
The separation between the integer prefix and the JSON Pointer will
always be unambigious, because a JSON Pointer must be either zero-
length or start with a '/' (%x2F). Similarly, a JSON Pointer will
never be ambiguous with the '#'.
The ABNF syntax of a Relative JSON Pointer is:
relative-json-pointer = positive-integer <json-pointer>
relative-json-pointer =/ positive-integer "#"
positive-integer = %x30 / %x31-39 *( %x30-39 )
; "0", or digits without a leading "0"
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where <json-pointer> follows the production defined in RFC 6901,
Section 3 [RFC6901] ("Syntax").
Figure 1
4. Evaluation
Evaluation of a Relative JSON Pointer begins with a reference to a
value within a JSON document, and completes with either a value
within that document, a string corresponding to an object member, or
integer value representing an array index.
Evaluation begins by processing the positive-integer prefix. This
can be found by taking the longest continuous sequence of decimal
digits available, starting from the beginning of the string, taking
the decimal numerical value. If this value is more than zero, then
the following steps are repeated that number of times:
If the current referenced value is the root of the document, then
evaluation fails (see below).
If the referenced value is an item within an array, then the new
referenced value is that array.
If the referenced value is an object member within an object, then
the new referenced value is that object.
If the remainder of the Relative JSON Pointer is a JSON Pointer, then
evaluation proceeds as per RFC 6901, Section 4 [RFC6901]
("Evaluation"), with the modification that the initial reference
being used is the reference currently being held (which may not be
root of the document).
Otherwise (when the remainder of the Relative JSON Pointer is the
character '#'), the final result is determined as follows:
If the current referenced value is the root of the document, then
evaluation fails (see below).
If the referenced value is an item within an array, then the final
evaluation result is the value's index position within the array.
If the referenced value is an object member within an object, then
the new referenced value is the corresponding member name.
5. JSON String Representation
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The concerns surrounding JSON String representation of a Relative
JSON Pointer are identical to those laid out in RFC 6901, Section 5
[RFC6901].
5.1. Examples
For example, given the JSON document:
{
"foo": ["bar", "baz"],
"highly": {
"nested": {
"objects": true
}
}
}
Starting from the value "baz" (inside "foo"), the following JSON
strings evaluate to the accompanying values:
"0" "baz"
"1/0" "bar"
"2/highly/nested/objects" true
"0#" 1
"1#" "foo"
Starting from the value {"objects":true} (corresponding to the member
key "nested"), the following JSON strings evaluate to the
accompanying values:
"0/objects" true
"1/nested/objects" true
"2/foo/0" "bar"
"0#" "nested"
"1#" "highly"
6. Non-use in URI Fragment Identifiers
Unlike a JSON Pointer, a Relative JSON Pointer can not be used in a
URI fragment identifier. Such fragments specify exact positions
within a document, and therefore Relative JSON Pointers are not
suitable.
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7. Error Handling
In the event of an error condition, evaluation of the JSON Pointer
fails to complete.
Evaluation may fail due to invalid syntax, or referencing a non-
existent value. This specification does not define how errors are
handled. An application of JSON Relative Pointer SHOULD specify the
impact and handling of each type of error.
8. Acknowledgements
The language and structure of this specification are based heavily on
RFC6901, sometimes quoting it outright.
9. Security Considerations
Evaluation of a given Relative JSON Pointer is not guaranteed to
reference an actual JSON value. Applications using Relative JSON
Pointer should anticipate this situation by defining how a pointer
that does not resolve ought to be handled.
As part of processing, a composite data structure may be assembled
from multiple JSON documents (in part or in full). In such cases,
applications SHOULD ensure that a Relative JSON Pointer does not
evaluate to a value outside the document for which is was written.
Note that JSON pointers can contain the NUL (Unicode U+0000)
character. Care is needed not to misinterpret this character in
programming languages that use NUL to mark the end of a string.
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC6901] Bryan, P., Zyp, K., and M. Nottingham, "JavaScript Object
Notation (JSON) Pointer", RFC 6901, April 2013.
10.2. Informative References
[RFC4627] Crockford, D., "The application/json Media Type for
JavaScript Object Notation (JSON)", RFC 4627, July 2006.
Author's Address
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Geraint Luff (editor)
Cambridge
UK
Email: luffgd@gmail.com
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