Internet DRAFT - draft-hha-relative-json-pointer

draft-hha-relative-json-pointer







Internet Engineering Task Force                                  G. Luff
Internet-Draft                                                          
Intended status: Informational                           H. Andrews, Ed.
Expires: 21 December 2023                                               
                                                          B. Hutton, Ed.
                                                            19 June 2023


                         Relative JSON Pointers
                   draft-hha-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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   This Internet-Draft will expire on 21 December 2023.

Copyright Notice

   Copyright (c) 2023 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
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   Please review these documents carefully, as they describe your rights
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   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.



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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  . . . . . . . . . . . . . . . . .   4
     5.1.  Examples  . . . . . . . . . . . . . . . . . . . . . . . .   4
   6.  Non-use in URI Fragment Identifiers . . . . . . . . . . . . .   5
   7.  Error Handling  . . . . . . . . . . . . . . . . . . . . . . .   5
   8.  Relationship to JSON Pointer  . . . . . . . . . . . . . . . .   5
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   10. Security Considerations . . . . . . . . . . . . . . . . . . .   6
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     12.1.  Normative References . . . . . . . . . . . . . . . . . .   6
     12.2.  Informative References . . . . . . . . . . . . . . . . .   6
   Appendix A.  ChangeLog  . . . . . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

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 a related syntax allowing identification of 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 in UTF-8 encoding (see
   RFC 8259, Section 8 [RFC8259]), comprising a non-negative integer, an
   optional index adjustment consisting of '+' (%x2B) or '-' (%x2D)
   followed by a positive integer, followed by either a '#' (%x23)
   character or a JSON Pointer (RFC 6901 [RFC6901]).

   The separation between the integer prefix (with optional adjustment)
   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:




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     relative-json-pointer = origin-specification ( "#" / json-pointer )
                           ; json-pointer from RFC 6901

     origin-specification  = non-negative-integer [ index-manipulation ]
     index-manipulation    = ( "+" / "-" ) positive-integer
     non-negative-integer  = "0" / positive-integer
     positive-integer      = %x31-39 *DIGIT
                           ; digits without a leading zero

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 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 the value is zero, the
   following steps are skipped.  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.

5.  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", "biz"],
                                   "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#"                      2
                              "1#"                        "foo"




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   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.

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.  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
   acceptable syntax does not imply that the other syntax is also
   acceptable.

9.  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.








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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.  IANA Considerations

   This document has no IANA actions.

12.  References

12.1.  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,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC6901]  Bryan, P., Ed., Zyp, K., and M. Nottingham, Ed.,
              "JavaScript Object Notation (JSON) Pointer", RFC 6901,
              DOI 10.17487/RFC6901, April 2013,
              <https://www.rfc-editor.org/info/rfc6901>.

12.2.  Informative References

   [RFC8259]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", STD 90, RFC 8259,
              DOI 10.17487/RFC8259, December 2017,
              <https://www.rfc-editor.org/info/rfc8259>.

Appendix A.  ChangeLog


   // This section to be removed before leaving Internet-Draft status.

   draft-hha-relative-json-pointer-00
      *  Fix ABNF omission for using # with index manipulation



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      *  Clarify handling of leading "0"

   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
   United Kingdom
   Email: luffgd@gmail.com


   Henry H. Andrews (editor)
   Email: andrews_henry@yahoo.com


   Ben Hutton (editor)
   Email: ben@jsonschema.dev
   URI:   https://jsonschema.dev

















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