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IETF RFC 6901



Last modified on Wednesday, April 3rd, 2013

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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/RFC 6901.

 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 top


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 [RFC 4627]. JSON Pointer is intended to be easily expressed in JSON string values as well as Uniform Resource Identifier (URI) [RFC 3986] 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 [RFC 2119]. This specification expresses normative syntax rules using Augmented Backus-Naur Form (ABNF) [RFC 5234] notation. 3. Syntax A JSON Pointer is a Unicode string (see [RFC 4627], 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 top

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 top

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 [RFC 4627], 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 top

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 [RFC 3629], while percent-encoding those characters not allowed by the fragment rule in [RFC 3986]. Note that a given media type needs to specify JSON Pointer as its fragment identifier syntax explicitly (usually, in its registration [RFC 6838]). 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 top

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 top

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 [RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC 3629] Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD 63, RFC 3629, November 2003. [RFC 3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, January 2005. [RFC 4627] Crockford, D., "The application/json Media Type for JavaScript Object Notation (JSON)", RFC 4627, July 2006. [RFC 5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, January 2008. 10.2. Informative References [RFC 6838] 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 top

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 top

RFC TOTAL SIZE: 13037 bytes PUBLICATION DATE: Wednesday, April 3rd, 2013 LEGAL RIGHTS: The IETF Trust (see BCP 78)


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