【转载】JSON语法RFC4627

Network Working Group D. Crockford
Request for Comments: 4627 JSON.org
Category: Informational July 2006

The application/json Media Type for JavaScript Object Notation (JSON)

Status of This Memo

This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.

Copyright Notice

Copyright (C) The Internet Society (2006).

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.

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.

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

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RFC 4627 JSON July 2006

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].

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
        )

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

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RFC 4627 JSON July 2006

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.

  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

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.

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RFC 4627 JSON July 2006

     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 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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RFC 4627 JSON July 2006

     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

3. Encoding

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

4. 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.

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RFC 4627 JSON July 2006

5. Generators

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

6. 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

   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.

   Security considerations:

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

   A JSON text can be safely passed into JavaScript's eval() function
   (which compiles and executes a string) if all the characters not
   enclosed in strings are in the set of characters that form JSON
   tokens. This can be quickly determined in JavaScript with two
   regular expressions and calls to the test and replace methods.

   var my_JSON_object = !(/[^,:{}[]0-9.-+Eaeflnr-u \n\r\t]/.test(
   text.replace(/"(\.|[^"\])*"/g, ''))) &&
   eval('(' + text + ')');

   Interoperability considerations: n/a

   Published specification: RFC 4627

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RFC 4627 JSON July 2006

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

7. Security Considerations

   See Security Considerations in Section 6.

8. 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]

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RFC 4627 JSON July 2006

    }

}

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"
}
]

9. References

9.1. 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>.

[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. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 4234, October 2005.

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RFC 4627 JSON July 2006

[UNICODE] The Unicode Consortium, "The Unicode Standard Version 4.0",
2003, http://www.unicode.org/versions/Unicode4.1.0/.

Author's Address

Douglas Crockford
JSON.org
EMail: douglas@crockford.com

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RFC 4627 JSON July 2006

Full Copyright Statement

Copyright (C) The Internet Society (2006).

This document is subject to the rights, licenses and restrictions
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