Talk:Canonical JSON

JSON specification

Thanks for the effort, but there are several flaws in this specification: There are instances of JSON that cannot be encoded as "canonical JSON" and vice versa. Here is a copy of the JSON specification (RFC 4627), section 2 and 3. Any canonical JSON should refine this. -- User:JakobVoss

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
  )

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

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

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

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

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".

   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

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

Alternative Canonical JSON

Changes to RFC4627

Whitespace outside of strings is not allowed.

  begin-array     = %x5B  ; [ left square bracket

  begin-object    = %x7B  ; { left curly bracket

  end-array       = %x5D  ; ] right square bracket

  end-object      = %x7D  ; } right curly bracket

  name-separator  = %x3A  ; : colon

  value-separator = %x2C  ; , comma

Objects

The members production in object must consist of keys in lexicographically sorted order. If keys are repeated, the will be in lexicographically sorted order of their canonical values.

is "lexicographically sorted" properly defined?

Numbers

• Trailing zeroes are eliminated
• Exponent and decimal point are shifted until the number starts with '0.X' where X is is not zero
• There is always an exponent and it is always the small 'e' unless the exponent is zero, then it is removed
• Leading or trailing zeros of the exponent are removed
• Zero or minus zero is encoded as '0'

Maybe there is a better/easier way but you can normalize all numbers

Strings

All Unicode characters are placed within the quotation and MUST be normalized to unicode Normalization Form C (UAX #15). Only the following characters are escaped: quotation mark, reverse solidus, and the control characters (U+0000 through U+001F).

Encoding

Canonical JSON text MUST be encoded in Unicode UTF-8.