JSON Pointer
draft-ietf-appsawg-json-pointer-02

Applications Area Working Group                            P. Bryan, Ed.
Internet-Draft                                                 ForgeRock
Intended status: Informational                                    K. Zyp
Expires: January 5, 2013                                   SitePen (USA)
                                                      M. Nottingham, Ed.
                                                               Rackspace
                                                            July 4, 2012

                              JSON Pointer
                   draft-ietf-appsawg-json-pointer-02

Abstract

   JSON Pointer defines a string syntax for identifying a specific value
   within a JSON 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 January 5, 2013.

Copyright Notice

   Copyright (c) 2012 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  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Syntax  . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   4.  Evaluation  . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   5.  JSON String Representation  . . . . . . . . . . . . . . . . . . 4
   6.  URI Fragment Identifier Representation  . . . . . . . . . . . . 5
   7.  Error Handling  . . . . . . . . . . . . . . . . . . . . . . . . 5
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   9.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 6
   11. Normative References  . . . . . . . . . . . . . . . . . . . . . 6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 7

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1.  Introduction

   This specification defines JSON Pointer, a string syntax for
   identifying a specific value within a JavaScript Object Notation
   (JSON) [RFC4627] document.  It is intended to be easily expressed in
   JSON string values and Uniform Resource Identifier (URI) [RFC3986]
   fragment identifiers.

2.  Conventions

   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 [RFC2119].

   This specification expresses normative syntax rules using Augmented
   Backus-Naur Form [RFC5234] (ABNF) notation.

3.  Syntax

   A JSON Pointer is a [Unicode] string containing a sequence of zero or
   more reference tokens, each prefixed by a '/' (%x2F) character.

   If a reference token contains '~' (%x7E) or '/' (%x2F) characters,
   they MUST be encoded as '~0' and '~1' respectively.

   ABNF syntax:

   json-pointer = *( "/" reference-token )
   reference-token = *( unescaped / escaped )
   unescaped = %x00-2E / %x30-7D / %x7F-10FFFF
   escaped = "~" ( "0" / "1" )

   It is an error condition if a JSON Pointer value does not conform to
   this syntax (see Section 7).

4.  Evaluation

   Evaluation of a JSON Pointer begins with a reference to the root
   value of a JSON text document and completes with a reference to some
   value within the document.  Each reference token in the JSON Pointer
   is sequentially evaluated.

   Evaluation of each reference token begins by decoding any escaped
   character sequence; this is performed by first transforming any
   occurrence of the sequence '~1' to '/', then transforming any

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   occurrence of the sequence '~0' to '~'.

   The reference token then modifies which value is referenced according
   to the following scheme:

      If the currently referenced value is a JSON object, the new
      referenced value is the object member with the name (after
      unescaping any backslash escape sequences that can occur in a JSON
      string) identified by the reference token.  The member name is
      equal to the token if it has the same number of Unicode characters
      as token and their code points are position-wise equal.  If a
      referenced member name is not unique in an object, the member that
      is referenced is undefined.

      If the currently referenced value is a JSON array, the reference
      token MUST contain characters that represent an unsigned base-10
      integer value (possibly with leading zeros), and the new
      referenced value is the array element with the zero-based index
      identified by the token.

   If a reference token is being evaluated against a JSON document, the
   implementation MAY evaluate each token against a concrete value, and
   terminate evaluation with an error condition if a evaluation fails to
   resolve a concrete value (see Section 7).

5.  JSON String Representation

   A JSON Pointer can be represented in a JSON string value.  Per
   [RFC4627], section 2.5, all instances of quotation mark '"' (%x22),
   reverse solidus '\' (%x5C) and control (%x00-1F) characters MUST be
   escaped.

   For example, given the JSON document

   {
      "foo": ["bar", "baz"],
      "": 0
      "a/b": 1,
      "c%d": 2,
      "e^f": 3,
      "g|h": 4,
      "i\\j": 5,
      "k\"l": 6,
      " ": 7,
      "m~n": 8
   }

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   Then the following JSON strings evaluate to the accompanying values:

    ""         // the whole document
    "/foo"       ["bar", "baz"]
    "/foo/0"    "bar"
    "/"          0
    "/a~1b"      1
    "/c%d"       2
    "/e^f"       3
    "/g|h"       4
    "/i\\j"      5
    "/k\"l"      6
    " "          7
    "m~0n"       8

6.  URI Fragment Identifier Representation

   A JSON Pointer can be represented in a URI fragment identifier. by
   encoding it into octets, using UTF-8 [RFC3629], percent-encoding
   those characters not allowed by the fragment rule in [RFC3986].

   Given the same example document as above, the following URI fragment
   identifiers evaluate to the accompanying values:

    #                  // the whole document
    #/foo            ["bar", "baz"]
    #/foo/0         "bar"
    #/               0
    #/a~1b           1
    #/c%25d          2
    #/e%5Ef          3
    #/g%7Ch          4
    #/i%5Cj          5
    #/k%22l          6
    #/%20            7
    #/m~0n           8

7.  Error Handling

   In the event of an error condition, evaluation of the JSON Pointer
   fails to complete.

   This includes, but is not limited to:

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   o  Invalid pointer syntax

   o  A pointer that references a non-existent value

   This specification does not define how errors are handled; an
   application of JSON Pointer SHOULD specify the impact and handling of
   each type of error.

   For example, some applications might stop pointer processing upon an
   error; others may attempt to recover from missing values by inserting
   default ones.

8.  IANA Considerations

   TBD

9.  Security Considerations

   A given JSON Pointer is not guaranteed to reference an actual JSON
   value.  Implementations should be aware of this and take appropriate
   precautions.

   Note that JSON pointers can contain the NUL (Unicode U+0000)
   character, which may not be representable in all programming
   languages.

10.  Acknowledgements

   The following individuals contributed ideas, feedback and wording to
   this specification:

      Mike Acar, Carsten Bormann, Tim Bray, Jacob Davies, Martin J.
      Duerst, Bjoern Hoehrmann, James H. Manger, Drew Perttula, Julian
      Reschke.

11.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
              10646", STD 63, RFC 3629, November 2003.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform

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              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, January 2005.

   [RFC4627]  Crockford, D., "The application/json Media Type for
              JavaScript Object Notation (JSON)", RFC 4627, July 2006.

   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

   [Unicode]  The Unicode Consortium, "The Unicode Standard, Version
              6.0", October 2011,
              <http://www.unicode.org/versions/Unicode6.0.0/>.

Authors' Addresses

   Paul C. Bryan (editor)
   ForgeRock

   Phone: +1 604 783 1481
   Email: pbryan@anode.ca

   Kris Zyp
   SitePen (USA)

   Phone: +1 650 968 8787
   Email: kris@sitepen.com

   Mark Nottingham (editor)
   Rackspace

   Email: mnot@mnot.net

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