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Versions: 00 draft-handrews-relative-json-pointer

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.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on January 02, 2014.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   described in the Simplified 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  . . . . . . . . . . . . . . . . .   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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