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Internet Engineering Task Force (IETF)                     P. Bryan, Ed.Request for Comments: 6901                                Salesforce.comCategory: Standards Track                                         K. ZypISSN: 2070-1721                                            SitePen (USA)                                                      M. Nottingham, Ed.                                                                  Akamai                                                              April 2013JavaScript Object Notation (JSON) PointerAbstract   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 inSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://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 toBCP 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 2013Table of Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .22.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . . .23.  Syntax  . . . . . . . . . . . . . . . . . . . . . . . . . . . .24.  Evaluation  . . . . . . . . . . . . . . . . . . . . . . . . . .35.  JSON String Representation  . . . . . . . . . . . . . . . . . .46.  URI Fragment Identifier Representation  . . . . . . . . . . . .57.  Error Handling  . . . . . . . . . . . . . . . . . . . . . . . .68.  Security Considerations . . . . . . . . . . . . . . . . . . . .69.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . .710. References  . . . . . . . . . . . . . . . . . . . . . . . . . .710.1.  Normative References . . . . . . . . . . . . . . . . . . .710.2.  Informative References . . . . . . . . . . . . . . . . . .71.  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 (seeSection 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.  SeeSection 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"      86.  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       87.  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 20139.  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.  References10.1.  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 2013Authors' 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.netBryan, et al.                Standards Track                    [Page 8]