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Versions: (RFC 4627) 00 01 02 03 04 05 06 07 08 09 10 RFC 7158

JSON Working Group                                          T. Bray, Ed.
Internet-Draft                                              Google, Inc.
Obsoletes: 4627 (if approved)                          November 06, 2013
Intended status: Standards Track
Expires: May 10, 2014


                    The JSON Data Interchange Format
                     draft-ietf-json-rfc4627bis-07

Abstract

   JavaScript Object Notation (JSON) is a lightweight, text-based,
   language-independent data interchange format.  It was derived from
   the ECMAScript Programming Language Standard.  JSON defines a small
   set of formatting rules for the portable representation of structured
   data.

   This document makes no changes to the definition of JSON; it repairs
   specification errors and offers experience-based interoperability
   guidance.

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 May 10, 2014.

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



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   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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Conventions Used in This Document . . . . . . . . . . . .   3
     1.2.  Specifications of JSON  . . . . . . . . . . . . . . . . .   3
     1.3.  Introduction to This Revision . . . . . . . . . . . . . .   4
   2.  JSON Grammar  . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Values  . . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Objects . . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   5.  Arrays  . . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   6.  Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . .   6
   7.  Strings . . . . . . . . . . . . . . . . . . . . . . . . . . .   7
   8.  String and Character Issues . . . . . . . . . . . . . . . . .   8
     8.1.  Encoding and Detection  . . . . . . . . . . . . . . . . .   8
     8.2.  Unicode Characters  . . . . . . . . . . . . . . . . . . .   8
     8.3.  String Comparison . . . . . . . . . . . . . . . . . . . .   9
   9.  Parsers . . . . . . . . . . . . . . . . . . . . . . . . . . .   9
   10. Generators  . . . . . . . . . . . . . . . . . . . . . . . . .   9
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   12. Security Considerations . . . . . . . . . . . . . . . . . . .  10
   13. Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .  10
   14. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  11
   15. References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     15.1.  Normative References . . . . . . . . . . . . . . . . . .  12
     15.2.  Informative References . . . . . . . . . . . . . . . . .  12
   Appendix A.  Changes from RFC 4627  . . . . . . . . . . . . . . .  13
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   JavaScript Object Notation (JSON) is a text format for the
   serialization of structured data.  It is derived from the object
   literals of JavaScript, as defined in the ECMAScript Programming
   Language Standard, Third Edition [ECMA-262].

   JSON can represent four primitive types (strings, numbers, booleans,
   and null) and two structured types (objects and arrays).

   A string is a sequence of zero or more Unicode characters [UNICODE].






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   An object is an unordered collection of zero or more name/value
   pairs, where a name is a string and a value is a string, number,
   boolean, null, object, or array.

   An array is an ordered sequence of zero or more values.

   The terms "object" and "array" come from the conventions of
   JavaScript.

   JSON's design goals were for it to be minimal, portable, textual, and
   a subset of JavaScript.

1.1.  Conventions Used in This Document

   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].

   The grammatical rules in this document are to be interpreted as
   described in [RFC5234].

1.2.  Specifications of JSON

   This document is an update of [RFC4627], which described JSON and
   registered the Media Type "application/json".

   A description of JSON in ECMAScript terms appears in version 5.1 of
   the ECMAScript specification [ECMA-262], section 15.12.  JSON is also
   described in [ECMA-404].  ECMAscript 5.1 enumerates the differences
   between JSON as described in that specification and in RFC4627.  The
   most significant is that ECMAScript 5.1 does not require a JSON Text
   to be an Array or an Object; thus, for example, the following would
   all be valid JSON texts in the ECMAScript context:

   o  "Hello world!"

   o  42

   o  true

   All of the specifications of JSON syntax agree on the syntactic
   elements of the language.









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1.3.  Introduction to This Revision

   In the years since the publication of RFC 4627, JSON has found very
   wide use.  This experience has revealed certain patterns which, while
   allowed by its specifications, have caused interoperability problems.

   Also, a small number of errata have been reported.

   This revision does not change any of the rules of the specification;
   all texts which were legal JSON remain so, and none which were not
   JSON become JSON.  The revision's goal is to fix the errata and
   highlight practices which can lead to interoperability problems.

2.  JSON Grammar

   A JSON text is a sequence of tokens.  The set of tokens includes six
   structural characters, strings, numbers, and three literal names.

   A JSON text is a serialized object or array.

   JSON-text = object / array


   These are the six structural characters:

      begin-array     = ws %x5B ws  ; [ left square bracket

      begin-object    = ws %x7B ws  ; { left curly bracket

      end-array       = ws %x5D ws  ; ] right square bracket

      end-object      = ws %x7D ws  ; } right curly bracket

      name-separator  = ws %x3A ws  ; : colon

      value-separator = ws %x2C ws  ; , comma


   Insignificant whitespace is allowed before or after any of the six
   structural characters.

   ws = *(
           %x20 /              ; Space
           %x09 /              ; Horizontal tab
           %x0A /              ; Line feed or New line
           %x0D )              ; Carriage return





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3.  Values

   A JSON value MUST be an object, array, number, or string, or one of
   the following three literal names:

   false null true


   The literal names MUST be lowercase.  No other literal names are
   allowed.

      value = false / null / true / object / array / number / string

      false = %x66.61.6c.73.65   ; false

      null  = %x6e.75.6c.6c      ; null

      true  = %x74.72.75.65      ; true


4.  Objects

   An object structure is represented as a pair of curly brackets
   surrounding zero or more name/value pairs (or members).  A name is a
   string.  A single colon comes after each name, separating the name
   from the value.  A single comma separates a value from a following
   name.  The names within an object SHOULD be unique.

      object = begin-object [ member *( value-separator member ) ]
               end-object

      member = string name-separator value


   An object whose names are all unique is interoperable in the sense
   that all software implementations which receive that object will
   agree on the name-value mappings.  When the names within an object
   are not unique, the behavior of software that receives such an object
   is unpredictable.  Many implementations report the last name/value
   pair only; other implementations report an error or fail to parse the
   object; other implementations report all of the name/value pairs,
   including duplicates.









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5.  Arrays

   An array structure is represented as square brackets surrounding zero
   or more values (or elements).  Elements are separated by commas.

   array = begin-array [ value *( value-separator value ) ] end-array


6.  Numbers

   The representation of numbers is similar to that used in most
   programming languages.  A number contains an integer component that
   may be prefixed with an optional minus sign, which may be followed by
   a fraction part and/or an exponent part.

   Octal and hex forms are not allowed.  Leading zeros are not allowed.

   A fraction part is a decimal point followed by one or more digits.

   An exponent part begins with the letter E in upper or lowercase,
   which may be followed by a plus or minus sign.  The E and optional
   sign are followed by one or more digits.

   Numeric values that cannot be represented in the grammar below (such
   as Infinity and NaN) are not permitted.

      number = [ minus ] int [ frac ] [ exp ]

      decimal-point = %x2E       ; .

      digit1-9 = %x31-39         ; 1-9

      e = %x65 / %x45            ; e E

      exp = e [ minus / plus ] 1*DIGIT

      frac = decimal-point 1*DIGIT

      int = zero / ( digit1-9 *DIGIT )

      minus = %x2D               ; -

      plus = %x2B                ; +

      zero = %x30                ; 0






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   This specification allows implementations to set limits on the range
   and precision of numbers accepted.  Since software which implements
   IEEE 754-2008 binary64 (double precision) numbers [IEEE754] is
   generally available and widely used, good interoperability can be
   achieved by implementations which expect no more precision or range
   than these provide, in the sense that implementations will
   approximate JSON numbers within the expected precision.  A JSON
   number such as 1E400 or 3.141592653589793238462643383279 may indicate
   potential interoperability problems since it suggests that the
   software which created it it expected greater magnitude or precision
   than is widely available.

   Note that when such software is used, numbers which are integers and
   are in the range [-(2**53)+1, (2**53)-1] are interoperable in the
   sense that implementations will agree exactly on their numeric
   values.

7.  Strings

   The representation of strings is similar to conventions used in the C
   family of programming languages.  A string begins and ends with
   quotation marks.  All Unicode characters may be placed within the
   quotation marks except for the characters that must be escaped:
   quotation mark, reverse solidus, and the control characters (U+0000
   through U+001F).

   Any character may be escaped.  If the character is in the Basic
   Multilingual Plane (U+0000 through U+FFFF), then it may be
   represented as a six-character sequence: a reverse solidus, followed
   by the lowercase letter u, followed by four hexadecimal digits that
   encode the character's code point.  The hexadecimal letters A though
   F can be upper or lowercase.  So, for example, a string containing
   only a single reverse solidus character may be represented as
   "\u005C".

   Alternatively, there are two-character sequence escape
   representations of some popular characters.  So, for example, a
   string containing only a single reverse solidus character may be
   represented more compactly as "\\".

   To escape an extended character that is not in the Basic Multilingual
   Plane, the character is represented as a twelve-character sequence,
   encoding the UTF-16 surrogate pair.  So, for example, a string
   containing only the G clef character (U+1D11E) may be represented as
   "\uD834\uDD1E".

      string = quotation-mark *char quotation-mark




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      char = unescaped /
          escape (
              %x22 /          ; "    quotation mark  U+0022
              %x5C /          ; \    reverse solidus U+005C
              %x2F /          ; /    solidus         U+002F
              %x62 /          ; b    backspace       U+0008
              %x66 /          ; f    form feed       U+000C
              %x6E /          ; n    line feed       U+000A
              %x72 /          ; r    carriage return U+000D
              %x74 /          ; t    tab             U+0009
              %x75 4HEXDIG )  ; uXXXX                U+XXXX

      escape = %x5C              ; \

      quotation-mark = %x22      ; "

      unescaped = %x20-21 / %x23-5B / %x5D-10FFFF


8.  String and Character Issues

8.1.  Encoding and Detection

   JSON text SHALL be encoded in Unicode.  The default encoding is
   UTF-8.

   Since the first two characters of a JSON text will always be ASCII
   characters [RFC0020], it is possible to determine whether an octet
   stream is UTF-8, UTF-16 (BE or LE), or UTF-32 (BE or LE) by looking
   at the pattern of nulls in the first four octets.

   00 00 00 xx  UTF-32BE
   00 xx 00 xx  UTF-16BE
   xx 00 00 00  UTF-32LE
   xx 00 xx 00  UTF-16LE
   xx xx xx xx  UTF-8


8.2.  Unicode Characters

   When all the strings represented in a JSON text are composed entirely
   of Unicode characters [UNICODE] (however escaped), then that JSON
   text is interoperable in the sense that all software implementations
   which parse it will agree on the contents of names and of string
   values in objects and arrays.

   However, the ABNF in this specification allows member names and
   string values to contain bit sequences which cannot encode Unicode



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   characters, for example "\uDEAD" (a single unpaired UTF-16
   surrogate).  Instances of this have been observed, for example when a
   library truncates a UTF-16 string without checking whether the
   truncation split a surrogate pair.  The behavior of software which
   receives JSON texts containing such values is unpredictable; for
   example, implementations might return different values for the length
   of a string value, or even suffer fatal runtime exceptions.

8.3.  String Comparison

   Software implementations are typically required to test names of
   object members for equality.  Implementations which transform the
   textual representation into sequences of Unicode code units, and then
   perform the comparison numerically, code unit by code unit, are
   interoperable in the sense that implementations will agree in all
   cases on equality or inequality of two strings.  For example,
   implementations which compare strings with escaped characters
   unconverted may incorrectly find that "a\b" and "a\u005Cb" are not
   equal.

9.  Parsers

   A JSON parser transforms a JSON text into another representation.  A
   JSON parser MUST accept all texts that conform to the JSON grammar.
   A JSON parser MAY accept non-JSON forms or extensions.

   An implementation may set limits on the size of texts that it
   accepts.  An implementation may set limits on the maximum depth of
   nesting.  An implementation may set limits on the range and precision
   of numbers.  An implementation may set limits on the length and
   character contents of strings.

10.  Generators

   A JSON generator produces JSON text.  The resulting text MUST
   strictly conform to the JSON grammar.

11.  IANA Considerations

   The MIME media type for JSON text is application/json.

   Type name:  application

   Subtype name:  json

   Required parameters:  n/a

   Optional parameters:  n/a



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   Encoding considerations:  8bit if UTF-8; binary if UTF-16 or UTF-32.
      JSON may be represented using UTF-8, UTF-16, or UTF-32.  When JSON
      is written in UTF-8, JSON is 8bit compatible.  When JSON is
      written in UTF-16 or UTF-32, the binary content-transfer-encoding
      must be used.

   Interoperability considerations:  Described in this document

   Published specification:  This document

   Applications that use this media type:  JSON has been used to
      exchange data between applications written in all of these
      programming languages: ActionScript, C, C#, Clojure, ColdFusion,
      Common Lisp, E, Erlang, Go, Java, JavaScript, Lua, Objective CAML,
      Perl, PHP, Python, Rebol, Ruby, Scala, and Scheme.

   Additional information:  Magic number(s): n/a
      File extension(s): .json
      Macintosh file type code(s): TEXT

   Person & email address to contact for further information:  IESG
      <iesg@ietf.org

   Intended usage:  COMMON

   Restrictions on usage:  none

   Author:  Douglas Crockford
      douglas@crockford.com

   Change controller:  IESG
      <iesg@ietf.org

12.  Security Considerations

   Generally there are security issues with scripting languages.  JSON
   is a subset of JavaScript, but excludes assignment and invocation.

   Since JSON's syntax is borrowed from JavaScript, it is possible to
   use that language's "eval()" function to parse JSON texts.  This
   generally constitutes an unacceptable security risk, since the text
   could contain executable code along with data declarations.  The same
   consideration applies in any other programming language in which JSON
   texts conform to that language's syntax.

13.  Examples

   This is a JSON object:



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   {
     "Image": {
         "Width":  800,
         "Height": 600,
         "Title":  "View from 15th Floor",
         "Thumbnail": {
             "Url":    "http://www.example.com/image/481989943",
             "Height": 125,
             "Width":  100
         },
     "Animated" : false,
         "IDs": [116, 943, 234, 38793]
       }
   }


   Its Image member is an object whose Thumbnail member is an object and
   whose IDs member is an array of numbers.

   This is a JSON array containing two objects:

   [
     {
        "precision": "zip",
        "Latitude":  37.7668,
        "Longitude": -122.3959,
        "Address":   "",
        "City":      "SAN FRANCISCO",
        "State":     "CA",
        "Zip":       "94107",
        "Country":   "US"
     },
     {
        "precision": "zip",
        "Latitude":  37.371991,
        "Longitude": -122.026020,
        "Address":   "",
        "City":      "SUNNYVALE",
        "State":     "CA",
        "Zip":       "94085",
        "Country":   "US"
     }
   ]


14.  Contributors





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   RFC 4627 was written by Douglas Crockford.  This document was
   constructed by making a relatively small number of changes to that
   document; thus the vast majority of the text here is his.

15.  References

15.1.  Normative References

   [IEEE754]  IEEE, "IEEE Standard for Floating-Point Arithmetic", 2008,
              <http://grouper.ieee.org/groups/754/>.

   [RFC0020]  Cerf, V., "ASCII format for network interchange", RFC 20,
              October 1969.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [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", 2003-,
              <http://www.unicode.org/versions/latest/>.

              Note that this reference is to the latest version of
              Unicode, rather than to a specific release.  It is not
              expected that future changes in the UNICODE specification
              will impact the syntax of JSON.

15.2.  Informative References

   [ECMA-262]
              European Computer Manufacturers Association, "ECMAScript
              Language Specification 5.1 Edition ", June 2011,
              <http://www.ecma-international.org/ecma-262/5.1/>.

   [ECMA-404]
              Ecma International, "The JSON Data Interchange Format ",
              October 2013, <http://www.ecma-international.org/
              publications/standards/Ecma-404.htm>.

   [RFC4627]  Crockford, D., "The application/json Media Type for
              JavaScript Object Notation (JSON)", RFC 4627, July 2006.









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Appendix A.  Changes from RFC 4627

   This section lists changes between this document and the text in RFC
   4627.

   o  Changed Working Group attribution to JSON Working Group.

   o  Changed title and abstract of document.

   o  Change the reference to [UNICODE] to be be non-version-specific.

   o  Added a "Specifications of JSON" section.

   o  Added an "Introduction to this Revision" section.

   o  Added language about duplicate object member names and
      interoperability.

   o  Applied erratum #607 from RFC 4627 to correctly align the artwork
      for the definition of "object".

   o  Changed "as sequences of digits" to "in the grammar below" in
      "Numbers" section.

   o  Added language about number interoperability as a function of
      IEEE754, and an IEEE754 reference.

   o  Added language about interoperability and Unicode characters, and
      about string comparisons.  To do this, turned the old "Encoding"
      section into a "String and Character Issues" section, with three
      subsections: The old "Encoding" material, and two new sections for
      "Unicode Characters" and "String Comparison".

   o  Changed guidance in "Parsers" section to point out that
      implementations may set limits on the range "and precision" of
      numbers.

   o  Updated and tidied the "IANA Considerations" section.

   o  Made a real "Security Considerations" section, and lifted the text
      out of the existing "IANA Considerations" section.

   o  Applied erratum #3607 from RFC 4627 by removing the security
      consideration that begins "A JSON text can be safely passed" and
      the JavaScript code that went with that consideration.

   o  Added a note to the "Security Considerations" section pointing out
      the risks of using the "eval()" function in JavaScript or any



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      other language in which JSON texts conform to that language's
      syntax.

   o  Changed "100" to 100 and added a boolean field, both in the first
      example.

   o  Added "Contributors" section crediting Douglas Crockford.

   o  Added a reference to RFC4627.

   o  Moved the ECMAScript reference from Normative to Informative,
      updated it to reference ECMAScript 5.1, and added reference to
      ECMA 404.

Author's Address

   Tim Bray (editor)
   Google, Inc.

   Email: tbray@textuality.com































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