Applications Area Working Group P. Bryan, Ed. Internet-Draft Salesforce.com Intended status: Standards Track K. Zyp Expires: July 26, 2013 SitePen (USA) M. Nottingham, Ed. Akamai January 22, 2013 JavaScript Object Notation (JSON) Pointer draft-ietf-appsawg-json-pointer-09 Abstract JSON Pointer defines a string syntax for identifying a specific value within a JavaScript Object Notation (JSON) document. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on July 26, 2013. 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. Expires July 26, 2013 [Page 1] Internet-Draft JSON Pointer January 2013 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 4. Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . 3 5. JSON String Representation . . . . . . . . . . . . . . . . . . 5 6. URI Fragment Identifier Representation . . . . . . . . . . . . 6 7. Error Handling . . . . . . . . . . . . . . . . . . . . . . . . 7 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7 9. Security Considerations . . . . . . . . . . . . . . . . . . . . 7 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8 11.1. Normative References . . . . . . . . . . . . . . . . . . . 8 11.2. Informative References . . . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8 Bryan, et al. Expires July 26, 2013 [Page 2] Internet-Draft JSON Pointer January 2013 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 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. 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 Bryan, et al. Expires July 26, 2013 [Page 3] Internet-Draft JSON Pointer January 2013 value of a JSON 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 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 position-wise 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). 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 (non-existant) 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. Bryan, et al. Expires July 26, 2013 [Page 4] Internet-Draft JSON Pointer January 2013 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 non-existent array element. Applications of JSON Pointer thus need to specify how it is to be handled, if it is to be useful. Any error condition that does not have a specific action defined for it 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. 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 } Then the following JSON strings evaluate to the accompanying values: Bryan, et al. Expires July 26, 2013 [Page 5] Internet-Draft JSON Pointer January 2013 "" // 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]. Note that a given media type needs to specify JSON Pointer as its fragment identifier syntax explicitly (usually, in its registration [RFC4288]); i.e., 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. 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 Bryan, et al. Expires July 26, 2013 [Page 6] Internet-Draft JSON Pointer January 2013 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: 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 This document has no impact upon IANA. 9. Security Considerations A given JSON Pointer is not guaranteed to reference an actual JSON value. Therefore, applications using JSON Pointer should anticipate this 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. 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. References Bryan, et al. Expires July 26, 2013 [Page 7] Internet-Draft JSON Pointer January 2013 11.1. 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. 11.2. Informative References [RFC4288] Freed, N. and J. Klensin, "Media Type Specifications and Registration Procedures", BCP 13, RFC 4288, December 2005. 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. Expires July 26, 2013 [Page 8]