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rfc:rfc6901

Internet Engineering Task Force (IETF) P. Bryan, Ed. Request for Comments: 6901 Salesforce.com Category: Standards Track K. Zyp ISSN: 2070-1721 SitePen (USA)

                                                    M. Nottingham, Ed.
                                                                Akamai
                                                            April 2013
             JavaScript Object Notation (JSON) Pointer

Abstract

 JSON Pointer defines a string syntax for identifying a specific value
 within a JavaScript Object Notation (JSON) document.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc6901.

Copyright Notice

 Copyright (c) 2013 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
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Bryan, et al. Standards Track [Page 1] RFC 6901 JSON Pointer April 2013

Table of Contents

 1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 2
 2.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . 2
 3.  Syntax  . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
 4.  Evaluation  . . . . . . . . . . . . . . . . . . . . . . . . . . 3
 5.  JSON String Representation  . . . . . . . . . . . . . . . . . . 4
 6.  URI Fragment Identifier Representation  . . . . . . . . . . . . 5
 7.  Error Handling  . . . . . . . . . . . . . . . . . . . . . . . . 6
 8.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
 9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 7
 10. References  . . . . . . . . . . . . . . . . . . . . . . . . . . 7
   10.1.  Normative References . . . . . . . . . . . . . . . . . . . 7
   10.2.  Informative References . . . . . . . . . . . . . . . . . . 7

1. Introduction

 This specification defines JSON Pointer, a string syntax for
 identifying a specific value within a JavaScript Object Notation
 (JSON) document [RFC4627].  JSON Pointer is intended to be easily
 expressed in JSON string values as well as 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 (ABNF) [RFC5234] notation.

3. Syntax

 A JSON Pointer is a Unicode string (see [RFC4627], Section 3)
 containing a sequence of zero or more reference tokens, each prefixed
 by a '/' (%x2F) character.
 Because the characters '~' (%x7E) and '/' (%x2F) have special
 meanings in JSON Pointer, '~' needs to be encoded as '~0' and '/'
 needs to be encoded as '~1' when these characters appear in a
 reference token.

Bryan, et al. Standards Track [Page 2] RFC 6901 JSON Pointer April 2013

 The ABNF syntax of a JSON Pointer is:
    json-pointer    = *( "/" reference-token )
    reference-token = *( unescaped / escaped )
    unescaped       = %x00-2E / %x30-7D / %x7F-10FFFF
       ; %x2F ('/') and %x7E ('~') are excluded from 'unescaped'
    escaped         = "~" ( "0" / "1" )
      ; representing '~' and '/', respectively
 It is an error condition if a JSON Pointer value does not conform to
 this syntax (see Section 7).
 Note that JSON Pointers are specified in characters, not as bytes.

4. Evaluation

 Evaluation of a JSON Pointer begins with a reference to the root
 value of a JSON document and completes with a reference to some value
 within the document.  Each reference token in the JSON Pointer is
 evaluated sequentially.
 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 '/', and then transforming any
 occurrence of the sequence '~0' to '~'.  By performing the
 substitutions in this order, an implementation avoids the error of
 turning '~01' first into '~1' and then into '/', which would be
 incorrect (the string '~01' correctly becomes '~1' after
 transformation).
 The reference token then modifies which value is referenced according
 to the following scheme:
 o  If the currently referenced value is a JSON object, the new
    referenced value is the object member with the name identified by
    the reference token.  The member name is equal to the token if it
    has the same number of Unicode characters as the token and their
    code points are byte-by-byte equal.  No Unicode character
    normalization is performed.  If a referenced member name is not
    unique in an object, the member that is referenced is undefined,
    and evaluation fails (see below).

Bryan, et al. Standards Track [Page 3] RFC 6901 JSON Pointer April 2013

 o  If the currently referenced value is a JSON array, the reference
    token MUST contain either:
  • characters comprised of digits (see ABNF below; note that

leading zeros are not allowed) that represent an unsigned

       base-10 integer value, making the new referenced value the
       array element with the zero-based index identified by the
       token, or
  • exactly the single character "-", making the new referenced

value the (nonexistent) member after the last array element.

 The ABNF syntax for array indices is:
 array-index = %x30 / ( %x31-39 *(%x30-39) )
               ; "0", or digits without a leading "0"
 Implementations will evaluate each reference token against the
 document's contents and will raise an error condition if it fails to
 resolve a concrete value for any of the JSON pointer's reference
 tokens.  For example, if an array is referenced with a non-numeric
 token, an error condition will be raised.  See Section 7 for details.
 Note that the use of the "-" character to index an array will always
 result in such an error condition because by definition it refers to
 a nonexistent array element.  Thus, applications of JSON Pointer need
 to specify how that character is to be handled, if it is to be
 useful.
 Any error condition for which a specific action is not defined by the
 JSON Pointer application results in termination of evaluation.

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.
 Note that before processing a JSON string as a JSON Pointer,
 backslash escape sequences must be unescaped.

Bryan, et al. Standards Track [Page 4] RFC 6901 JSON Pointer April 2013

 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
 }
 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], while percent-encoding
 those characters not allowed by the fragment rule in [RFC3986].
 Note that a given media type needs to specify JSON Pointer as its
 fragment identifier syntax explicitly (usually, in its registration
 [RFC6838]).  That is, just because a document is JSON does not imply
 that JSON Pointer can be used as its fragment identifier syntax.  In
 particular, the fragment identifier syntax for application/json is
 not JSON Pointer.

Bryan, et al. Standards Track [Page 5] RFC 6901 JSON Pointer April 2013

 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.
 Error conditions include, but are not limited to:
 o  Invalid pointer syntax
 o  A pointer that references a nonexistent 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, while others may attempt to recover from missing values by
 inserting default ones.

8. Security Considerations

 A given JSON Pointer is not guaranteed to reference an actual JSON
 value.  Therefore, applications using JSON Pointer should anticipate
 this situation by defining how a pointer that does not resolve ought
 to be handled.
 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.

Bryan, et al. Standards Track [Page 6] RFC 6901 JSON Pointer April 2013

9. 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, and
    Julian Reschke.

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.
 [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
            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.

10.2. Informative References

 [RFC6838]  Freed, N., Klensin, J., and T. Hansen, "Media Type
            Specifications and Registration Procedures", BCP 13,
            RFC 6838, January 2013.

Bryan, et al. Standards Track [Page 7] RFC 6901 JSON Pointer April 2013

Authors' Addresses

 Paul C. Bryan (editor)
 Salesforce.com
 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)
 Akamai
 EMail: mnot@mnot.net

Bryan, et al. Standards Track [Page 8]

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