draft-bhutton-relative-json-pointer-00

draft-bhutton-relative-json-pointer-00
Internet Engineering Task Force G. Luff
Internet-Draft
Intended status: Informational H. Andrews, Ed.
Expires: June 11, 2021
B. Hutton, Ed.
December 8, 2020
Relative JSON Pointers
draft-bhutton-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.

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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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.

Table of Contents
. Introduction . . . . . . . . . . . . . . . . . . . . . . . .
. Conventions and Terminology . . . . . . . . . . . . . . . . .
. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . .
. Evaluation . . . . . . . . . . . . . . . . . . . . . . . . .
. JSON String Representation . . . . . . . . . . . . . . . . .
5.1
. Examples . . . . . . . . . . . . . . . . . . . . . . . .
. Non-use in URI Fragment Identifiers . . . . . . . . . . . . .
. Error Handling . . . . . . . . . . . . . . . . . . . . . . .
. Relationship to JSON Pointer . . . . . . . . . . . . . . . .
. Acknowledgements . . . . . . . . . . . . . . . . . . . . . .
10
. Security Considerations . . . . . . . . . . . . . . . . . . .
11
. References . . . . . . . . . . . . . . . . . . . . . . . . .
11.1
. Normative References . . . . . . . . . . . . . . . . . .
11.2
. Informative References . . . . . . . . . . . . . . . . .
Appendix A
. ChangeLog . . . . . . . . . . . . . . . . . . . . .
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . .
. Introduction
JSON Pointer (
RFC 6901
RFC6901
]) is a syntax for specifying
locations in a JSON document, starting from the document root. This
document defines a related syntax allowing identification of relative
locations from within the document.
. 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
].
. Syntax
A Relative JSON Pointer is a Unicode string in UTF-8 encoding (see
RFC 8259, Section 8
RFC8259
]), comprising a non-negative 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 unambiguous, because a JSON Pointer must be either zero-
length or start with a '/' (%x2F). Similarly, a JSON Pointer will
never be ambiguous with the '#'.
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The ABNF syntax of a Relative JSON Pointer is:

relative-json-pointer = non-negative-integer [index-manipulation]
relative-json-pointer =/ non-negative-integer "#"
index-manipulation = ("+" / "-") non-negative-integer
non-negative-integer = %x30 / %x31-39 *( %x30-39 )
; "0", or digits without a leading "0"

where follows the production defined in
RFC 6901,
Section 3
RFC6901
] ("Syntax").
. 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 non-negative-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 next character is a plus ("+") or minus ("-"), followed by
another continuous sequence of decimal digits, the following steps
are taken using the decimal numeric value of that plus or minus sign
and decimal sequence:

If the current referenced value is not an item of an array, then
evaluation fails (see below).

If the referenced value is an item of an array, then the new
referenced value is the item of the array indexed by adding the
decimal value (which may be negative), to the index of the current
referenced value.
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If the remainder of the Relative JSON Pointer is a JSON Pointer, then
evaluation proceeds as per
RFC 6901, Section 5
RFC6901
] 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.
. JSON String Representation
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
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Starting from the value "baz" (inside "foo"), the following JSON
strings evaluate to the accompanying values:

"0" "baz"
"1/0" "bar"
"0-1" "bar"
"2/highly/nested/objects" true
"0#" 1
"0-1#" 0
"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"
. 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.
. 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.
. Relationship to JSON Pointer
Relative JSON Pointers are intended as a companion to JSON Pointers.
Applications MUST specify the use of each syntax separately.
Defining either JSON Pointer or Relative JSON Pointer as an
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acceptable syntax does not imply that the other syntax is also
acceptable.
. Acknowledgements
The language and structure of this specification are based heavily on
RFC6901
], sometimes quoting it outright.

This draft remains primarily as written and published by Geraint
Luff, with only minor subsequent alterations under new editorship.
10
. 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.
11
. References
11.1
. Normative References
RFC2119
] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels",
BCP 14
RFC 2119
DOI 10.17487/RFC2119, March 1997,
>.

RFC6901
] Bryan, P., Ed., Zyp, K., and M. Nottingham, Ed.,
"JavaScript Object Notation (JSON) Pointer",
RFC 6901
DOI 10.17487/RFC6901, April 2013,
>.
11.2
. Informative References
RFC8259
] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", STD 90,
RFC 8259
DOI 10.17487/RFC8259, December 2017,
>.
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Appendix A
. ChangeLog
[[CREF1: This section to be removed before leaving Internet-Draft
status.]]
draft-bhutton-relative-json-pointer-00
* Add array forward and backward index manipulation
draft-handrews-relative-json-pointer-02
* Update to the latest JSON RFC
draft-handrews-relative-json-pointer-01
* The initial number is "non-negative", not "positive"
draft-handrews-relative-json-pointer-00
* Revived draft with identical wording and structure.

* Clarified how to use alongside JSON Pointer.
draft-luff-relative-json-pointer-00
* Initial draft.

Authors' Addresses

Geraint Luff
Cambridge
UK

EMail: luffgd@gmail.com

Henry Andrews (editor)

EMail: andrews_henry@yahoo.com

Ben Hutton (editor)

EMail: ben@jsonschema.dev
URI:
Luff, et al. Expires June 11, 2021 [Page 7]
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