JSON Working Group T. Bray, Ed.
Internet-Draft Google, Inc.
Intended status: Standards Track September 18, 2013
Expires: March 22, 2014
The JSON Data Interchange Format
draft-ietf-json-rfc4627bis-03
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.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on March 22, 2014.
Copyright Notice
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions Used in This Document . . . . . . . . . . . . 3
1.2. Introduction to This Revision . . . . . . . . . . . . . . 3
1.3. Changes from RFC 4627 . . . . . . . . . . . . . . . . . . 3
2. JSON Grammar . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Values . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Objects . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
6. Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
7. Strings . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
8. Character Model . . . . . . . . . . . . . . . . . . . . . . . 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 . . . . . . . . . . . . . . . . . . . 11
13. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 11
14. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 12
15. Normative References . . . . . . . . . . . . . . . . . . . . 12
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 13
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].
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].
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.
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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 [RFC4234].
1.2. 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 the RFC, 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.
1.3. Changes from RFC 4627
This section lists all changes between this document and the text in
RFC 4627.
o Changed Working Group attribution to JSON Working Group.
o Changed title of doc per consensus call at http://www.ietf.org/
mail-archive/web/json/current/msg00736.html
o Applied erratum #607 from RFC 4627 to correctly align the artwork
for the definition of "object".
o Change the reference to [UNICODE] to be be non-version-specific.
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 Tim Bray as editor.
o Added an "Introduction to this Revision" section.
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o Added language about duplicate object member names and
interoperability.
o Added language about intereoperability as a function of number
ranges and IEEE754. Also added IEEE754 reference.
o Added language about interoperability and Unicode characters, and
about string comparisons. To do this, turned the old "Encoding"
section into a "Character Model" section, with three subsections:
The old "Encoding" material, and two new sections for "Unicode
Characters" and "String Comparison".
o Made a real XML-level "Security Considerations" section, and
lifted the text out of the existing "IANA Considerations" section.
o Removed the language "Interoperability considerations: n/a" from
the "IANA Considerations section.
o Added "Contributors" section crediting Douglas Crockford.
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.
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ws = *(
%x20 / ; Space
%x09 / ; Horizontal tab
%x0A / ; Line feed or New line
%x0D ; Carriage return
)
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
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object; other implementations report all of the name/value pairs,
including duplicates.
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 as sequences of digits
(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
of numbers accepted. While absolute interoperability cannot be
guaranteed, wide interoperability can be achieved by limiting numbers
in JSON texts to those within the precision and magnitude expressible
in an IEEE 754:20008 binary64 (double precision) number [IEEE754].
Numeric values that cannot be represented in the grammar above (such
as Infinity and NaN) are not permitted. Attempting to represent
numbers that cannot be exactly encoded as an IEEE 754:2008 binary64
number, such as 1E400, 9007199254740993, or
3.141592653589793238462643383279, may cause interoperability
problems.
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".
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string = quotation-mark *char quotation-mark
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. Character Model
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
A JSON text which is composed entirely of Unicode characters
[UNICODE] (however encoded) is interoperable in the sense that all
software implementations which parse it will agree on the contents of
names and values of object members. However, the ABNF in this
specification allows member names and string values to contain bit
sequences which cannot encode Unicode characters, for example
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"\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 a fatal runtime exception.
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 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
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The MIME media type for JSON text is application/json.
Type name: application
Subtype name: json
Required parameters: n/a
Optional parameters: n/a
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.
Published specification: RFC 4627
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#,
ColdFusion, Common Lisp, E, Erlang, Java, JavaScript, Lua,
Objective CAML, Perl, PHP, Python, Rebol, Ruby, 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:
Douglas Crockford
douglas@crockford.com
Intended usage: COMMON
Restrictions on usage: none
Author:
Douglas Crockford
douglas@crockford.com
Change controller:
Douglas Crockford
douglas@crockford.com
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12. Security Considerations
Generally there are security issues with scripting languages. JSON
is a subset of JavaScript, but excludes assignment and invocation.
13. Examples
This is a JSON object:
{
"Image": {
"Width": 800,
"Height": 600,
"Title": "View from 15th Floor",
"Thumbnail": {
"Url": "http://www.example.com/image/481989943",
"Height": 125,
"Width": "100"
},
"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:
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[
{
"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
RFC 4627 was written by Douglas Crockford. This document was
constructed by making a relatively small number of additions to and
subtractions from that document; thus the vast majority of the text
here is his.
15. Normative References
[ECMA] European Computer Manufacturers Association, "ECMAScript
Language Specification 3rd Edition ", December 1999,
<http://www.ecma-international.org/publications/files/
ecma-st/ECMA-262.pdf>.
[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.
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[RFC4234] Crocker, D., Ed. and P. Overell, "Augmented BNF for
Syntax Specifications: ABNF", RFC 4234, October 2005.
[UNICODE] The Unicode Consortium, "The Unicode Standard, Version 4.0
", 2003, <http://www.unicode.org/versions/latest/>.
Author's Address
Tim Bray (editor)
Google, Inc.
Email: tbray@textuality.com
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