The JSON Data Interchange Format
draft-ietf-json-rfc4627bis-01
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 7158.
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|
|---|---|---|---|
| Author | Douglas Crockford | ||
| Last updated | 2013-06-06 | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
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| Stream | WG state | WG Document | |
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draft-ietf-json-rfc4627bis-01
Operations Area Working Group D. Crockford
Internet-Draft JSON.org
Intended status: Standards Track June 06, 2013
Expires: December 08, 2013
The JSON Data Interchange Format
draft-ietf-json-rfc4627bis-01
Abstract
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.
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Task Force (IETF). Note that other groups may also distribute
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on December 08, 2013.
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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions Used in This Document . . . . . . . . . . . . 2
1.2. Changes from RFC 4627 . . . . . . . . . . . . . . . . . . 3
2. JSON Grammar . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Values . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2. Objects . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.3. Arrays . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.4. Numbers . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.5. Strings . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Parsers . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Generators . . . . . . . . . . . . . . . . . . . . . . . . . 7
5. Security Considerations . . . . . . . . . . . . . . . . . . . 7
6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 8
7. Normative References . . . . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
JSON is a text format for the serialization of structured data. It
was inspired by the object literals of JavaScript, as defined in the
ECMAScript Programming Language Standard, Fifth 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 characters.
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. JSON stands for JavaScript Object Notation.
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].
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The grammatical rules in this document are to be interpreted as
described in [RFC5234].
1.2. Changes from RFC 4627
This section lists all changes between this document and the text in
RFC 4627.
o Applied errata #607 from RFC 4627 to correctly align the artwork
for the definition of "object".
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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2.1. 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
2.2. 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. If a key is
duplicated, a parser MAY reject. If it does not reject, then it MUST
take only the last of the duplicated key pairs.
object = begin-object [ member *( value-separator member ) ]
end-object
member = string name-separator value
2.3. 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
2.4. Numbers
A number is represented in base 10 with no superfluous leading zeroes
or punctuation such as commas or spaces. It may have a preceding
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minus sign. It may have a "."-prefixed fractional part. It may have
an exponent, prefixed by "e" or "E" and optionally "+" or "-".
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
2.5. Strings
The representation of strings is similar to conventions used in the C
family of programming languages. A string is a sequence of code
units wrapped with quotation marks. All 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 Unicode 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".
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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 "\\".
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
The following four cases MUST all produce the same result:
"\u002F"
"\u002F"
"\/"
"/"
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". A generator SHOULD NOT emit unpaired surrogates. A
parser MAY reject JSON text containing unpaired surrogates.
3. 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.
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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.
4. Generators
A JSON generator produces JSON text. The resulting text MUST
strictly conform to the JSON grammar.
5. Security Considerations
With any data format, it is important to encode correctly. Care must
be taken when constructing JSON texts by concatenation. For example:
account = 4627;
comment = "\",\"account\":262"; // provided by attacker
json_text = "(\"account\":" + account + ",\"comment\":\"" + comment + "\"}";
The result will be
{"account":4627,"comment":"","account":262}
which some parsers MAY see as being the same as
{"comment":"","account":262}
This confusion allows an attacker to modify the account property or
any other property.
It is much wiser to use JSON generators, which are available in many
forms for most programming languages, to do the encoding, avoiding
the confusion hazard.
JSON is so similar to some programming languages that the native
parsing ability of the language processors can be used to parse JSON
texts. This should be avoided because the native parser will accept
code which is not JSON.
For example, JavaScript's eval() function is able parse JSON text,
but is can also parse programs. If an attacker can inject code into
the JSON text (as we saw above), then it can compromise the system.
JSON parsers should always be used instead.
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The web browser's script tag is an alias for the eval() function. It
should not be used to deliver JSON text to web browsers.
6. 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:
[
{
"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"
}
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]
7. Normative References
[ECMA] European Computer Manufacturers Association, "ECMAScript
Language Specification Fifth Edition ", December 2009,
<http://www.ecma-international.org/publications/files/
ecma-st/ECMA-262.pdf>.
[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 6.2
", 2012, <http://www.unicode.org/versions/Unicode6.2.0/>.
Author's Address
Douglas Crockford
JSON.org
Email: douglas@crockford.com
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