JSON Working Group T. Bray, Ed.
Internet-Draft Google, Inc.
Obsoletes: 4627 (if approved) October 11, 2013
Intended status: Standards Track
Expires: April 14, 2014
The JSON Data Interchange Format
draft-ietf-json-rfc4627bis-06
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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Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
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. Specifications of JSON . . . . . . . . . . . . . . . . . 3
1.3. Introduction to This Revision . . . . . . . . . . . . . . 3
2. JSON Grammar . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Values . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Objects . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
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 . . . . . . . . . . . . . . . 12
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).
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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.
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, these constructs
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.
1.3. Introduction to This Revision
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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
3. Values
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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.
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
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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
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
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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".
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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. 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.
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However, the ABNF in this specification allows member names and
string values to contain bit sequences which cannot encode Unicode
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
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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.
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
.
[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, Version 4.0
", 2003, .
15.2. Informative References
[ECMA-262]
European Computer Manufacturers Association, "ECMAScript
Language Specification 5.1 Edition ", June 2011, .
[ECMA-404]
Ecma International, "The JSON Data Interchange Format ",
October 2013, .
[RFC4627] Crockford, D., "The application/json Media Type for
JavaScript Object Notation (JSON)", RFC 4627, July 2006.
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 of document.
o Change the reference to [UNICODE] to be be non-version-specific.
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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
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.
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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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