JSON Working Group T. Bray, Ed.
Internet-Draft Google, Inc.
Obsoletes: 4627 (if approved) October 08, 2013
Intended status: Standards Track
Expires: April 11, 2014
The JSON Data Interchange Format
draft-ietf-json-rfc4627bis-05
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
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 April 11, 2014.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
Bray Expires April 11, 2014 [Page 1]
Internet-Draft JSON bis October 2013
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.
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
1.4. Changes from RFC 4627 . . . . . . . . . . . . . . . . . . 4
2. JSON Grammar . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Values . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Objects . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
6. Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
7. Strings . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
8. String and Character Issues . . . . . . . . . . . . . . . . . 9
8.1. Encoding and Detection . . . . . . . . . . . . . . . . . 9
8.2. Unicode Characters . . . . . . . . . . . . . . . . . . . 9
8.3. String Comparison . . . . . . . . . . . . . . . . . . . . 10
9. Parsers . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
10. Generators . . . . . . . . . . . . . . . . . . . . . . . . . 10
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
12. Security Considerations . . . . . . . . . . . . . . . . . . . 12
13. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 12
14. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 13
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
15.1. Normative References . . . . . . . . . . . . . . . . . . 13
15.2. Informative References . . . . . . . . . . . . . . . . . 14
Appendix A. Changes in -04 . . . . . . . . . . . . . . . . . . . 14
Appendix B. Changes in -05 . . . . . . . . . . . . . . . . . . . 14
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 15
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].
Bray Expires April 11, 2014 [Page 2]
Internet-Draft JSON bis October 2013
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.
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. Specifications of JSON
A description of JSON in ECMAScript terms first appeared in version
5.1 of the ECMAScript specification [ECMA-262], section 15.12. It
includes a description of 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, "Hello world!", "42", and "true" would all
be valid JSON texts in the ECMAScript 5.1 context.
JSON is also described in [ECMA-404].
None of the specifications of JSON syntax disagree on the syntax of
the language.
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.
Bray Expires April 11, 2014 [Page 3]
Internet-Draft JSON bis October 2013
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.
1.4. 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 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 Removed the language "Interoperability considerations: n/a" from
the "IANA Considerations" section.
o Made a real "Security Considerations" section, and lifted the text
out of the existing "IANA Considerations" section.
Bray Expires April 11, 2014 [Page 4]
Internet-Draft JSON bis October 2013
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 Added "Contributors" section crediting Douglas Crockford.
o Moved the ECMAScript reference from Normative to Informative,
updated it to reference ECMAScript 5.1, and added reference to
ECMA 404.
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.
Bray Expires April 11, 2014 [Page 5]
Internet-Draft JSON bis October 2013
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
Bray Expires April 11, 2014 [Page 6]
Internet-Draft JSON bis October 2013
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 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
Bray Expires April 11, 2014 [Page 7]
Internet-Draft JSON bis October 2013
This specification allows implementations to set limits on the range
and precision of numbers accepted. Since software which implements
IEEE 754-2008 [IEEE754] is generally available and widely used, good
interoperability can be achieved by implementations which expect no
more precision or range than provided by an IEEE 754 binary64 (double
precision) number, in the sense that implementations will approximate
JSON numbers within the expected precision. A JSON number which is
outside those bounds, 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".
Bray Expires April 11, 2014 [Page 8]
Internet-Draft JSON bis October 2013
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.
Bray Expires April 11, 2014 [Page 9]
Internet-Draft JSON bis October 2013
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
Bray Expires April 11, 2014 [Page 10]
Internet-Draft JSON bis October 2013
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
Bray Expires April 11, 2014 [Page 11]
Internet-Draft JSON bis October 2013
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 languages in which
JSON texts conform to that language's syntax.
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:
Bray Expires April 11, 2014 [Page 12]
Internet-Draft JSON bis October 2013
[
{
"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 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,
.
[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.
[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, .
Bray Expires April 11, 2014 [Page 13]
Internet-Draft JSON bis October 2013
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, .
Appendix A. Changes in -04
o Reworded Section 8.2 to talk about strings that are represented in
the JSON text, rather than the actual text itself. Also fine-
tuned the "will agree on" clause in the interoperability
description.
o Changed "20008" to "2008".
o Reworded numeric-interoperability language following on WG
discussion, notably referring to availability of software that
does IEEE754 and "approximate JSON numbers within the expected
precision". Also took out duplicate language about NaN and Inf.
o Changed "as sequences of digits" to "in the grammar below" in
"Numbers" section.
Appendix B. Changes in -05
o Removed the numbers-interop text about "frac" and "exp" parts.
o Added the obsoletes 4627 attribute.
o Moved the EcmaScript ref from normative to informative, and
redirected to point at 5.1.
o Changed numbers language to say that implementations can impose
limits on range *and precision*.
o Changed section title from "Character Model" to "String and
Character Issues".
o Added "Specifications of JSON" section, and included a reference
to ECMA-404.
o Removed the consensus-call link from the list of changes.
Bray Expires April 11, 2014 [Page 14]
Internet-Draft JSON bis October 2013
o Added a paragraph about not using eval() in JavaScript or other
languaegs where JSON syntax matches that language's syntax.
o Reorganized the list of changes so they're ordered like the spec,
and cleaned up language a bit.
Author's Address
Tim Bray (editor)
Google, Inc.
Email: tbray@textuality.com
Bray Expires April 11, 2014 [Page 15]