| Internet-Draft | Relative JSON Pointers | December 2020 |
| Luff, et al. | Expires 11 June 2021 | [Page] |
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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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.¶
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].¶
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 '#'.¶
The ABNF syntax of a Relative JSON Pointer is:¶
relative-json-pointer = non-negative-integer [index-manipulation] <json-pointer>
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 <json-pointer> follows the production defined in RFC 6901, Section 3 [RFC6901] ("Syntax").¶
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 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 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:¶
The concerns surrounding JSON String representation of a Relative JSON Pointer are identical to those laid out in RFC 6901, Section 5 [RFC6901].¶
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"
"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"
¶
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.¶
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.¶
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 acceptable syntax does not imply that the other syntax is also acceptable.¶
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.¶
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.¶
This section to be removed before leaving Internet-Draft status.¶