Applications Area Working Group P. Bryan, Ed.
Internet-Draft Salesforce.com
Intended status: Informational K. Zyp
Expires: April 25, 2013 SitePen (USA)
M. Nottingham, Ed.
October 22, 2012
JSON Pointer
draft-ietf-appsawg-json-pointer-05
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 April 25, 2013.
Copyright Notice
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document authors. All rights reserved.
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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 . . . . . . . . . . . . . . . . . . . . . . . . 6
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
9. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
11.1. Normative References . . . . . . . . . . . . . . . . . . . 7
11.2. Informative References . . . . . . . . . . . . . . . . . . 7
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 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 containing a sequence of zero or
more reference tokens, each prefixed by a '/' (%x2F) character.
Since the characters '~' (%x7E) and '/' (%x2F) have a special meaning
in JSON Pointer, they need to be encoded as '~0' and '~1'
respectively, when appearing in a reference token.
Its ABNF syntax is:
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 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
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occurrence of the sequence '~1' to '/', then transforming any
occurrence of the sequence '~0' to '~'.
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 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, and evaluation fails (see below).
o If the currently referenced value is a JSON array, the reference
token MUST contain either:
* characters that represent an unsigned base-10 integer value
(possibly with leading zeros), making the new referenced value
is 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.
If a reference token is being evaluated against a JSON document,
implementations will evaluate each token against the document's
contents, and terminate evaluation with an error condition if it
fails to resolve a concrete value for any of the JSON pointer's
reference tokens. See Section 7 for details.
Note that the use of the "-" character to index an array will always
result in such an error; applications of JSON Pointer thus need to
specify how it is to be handled, if it is to be useful.
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
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{
"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:
"" // 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 nominate 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:
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# // 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:
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. 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.
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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
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.
[Unicode] The Unicode Consortium, "The Unicode Standard, Version
6.0", October 2011,
<http://www.unicode.org/versions/Unicode6.0.0/>.
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
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Kris Zyp
SitePen (USA)
Phone: +1 650 968 8787
Email: kris@sitepen.com
Mark Nottingham (editor)
Email: mnot@mnot.net
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