wson

A Stringifier and Parser for the WSON data-interchange format.

Usage

$ npm install wson

import wsonFactory from 'wson'
const WSON = wsonFactory()

const entry = {
  name: 'otto',
  size: 177.3,
  completed: ['forth', 'javascript', "c++", 'haskell'],
  active: true,
}

const s = WSON.stringify(entry)
console.log(s)
// '{active|completed:[forth|javascript|c++|haskell]|name:otto|size:#177.3}'

const newEntry = WSON.parse(s)
// equivalent to entry

There is a somewhat faster native C++ implementation of a WSON-parser and WSON-stringifyer: wson-addon. Since version 2.6.0 of the wson-module the optional dependency to wson-addon been removed. Now the native implementation can be attached manually by using the option addon:

import wsonFactory from 'wson'
import addon from 'wson-addon'
const WSON = wsonFactory({ addon })

Motivation (why yet another format?)

We demanded a format that:

• is deterministic (stringification does not depend on key insertion order or unjustified assumptions about the js-engine).
• is textual, so it can be used as a key itself.
• is terse, especially does grow linearly in length when stringified recursively (\-escaping grows exponentially).
• is reasonably human readable.
• can be parsed reasonably fast.
• can handle cyclic structures.
• is extensible.
• can parse strings that contain WSON mixed with other stuff.

Since we found shortcomings in all present formats, we decided to create WSON:

WSON

This is an informal description of the WSON-Syntax. There is also an EBNF-file in the doc-directory and a syntax-diagram created from it.

Escaping

There are 8 special characters: {, }, [, ], #, :, |, `. If they occur in strings the will be escaped using these counterparts:

original	escaped
{	`o
}	`c
[	`a
]	`e
#	`l
:	`i
|	`p
`	`q

The special characters have been chosen to be expectable rare in natural language texts to minimize the need for escaping. E.g. delimiter is | instead of ,.

Strings

Strings are stringified verbatim (without any quotes). If they have special characters in them, they got escaped. The empty string is stringified as #.

Examples:

javascript	WSON
"abc"	abc
"say: \"hello\""	say`i "hello"
""	#

Literals

Booleans, null, undefined are stringified by these patterns:

javascript	WSON
false	#f
true	#t
null	#n
undefined	#u

Numbers are stringified by # prepended to the number converted to a string.

Examples:

javascript	WSON
42	#42
42.1	#42.1

Date-objects are stringified by #d prepended to the valueOf-number (i.e. the milliseconds since midnight 01 January, 1970 UTC) converted to a string.

Examples:

javascript	WSON
new Date(1400000000000)	#d1400000000000

Arrays

Arrays are stringified by their stringified components concatenated by |, enclosed by [, ].

javascript	WSON
[]	[]
["foo"]	[foo]
[""]	[#]
["foo",true,42]	[foo|#t|#42]
["foo",["bar","baz"]]	[foo|[bar|baz]]

Objects

Objects are stringified by their stringified key-value pairs concatenated by |, enclosed by {, }. Key-value pairs are stringified this way:

• If the value is true: just the escaped key (This is meant to be handy for set-like objects.)
• Else: escaped key : stringified value

The pairs are sorted by key (sorting is done before escaping).

javascript	WSON
{}	{}
{a: "A", b: "B"}	{a:A|b:B}
{b: "A", a: "B"}	{a:A|b:B}
{a: true, b: true}	{a|b}
{a: {c: 42}, b: [3,4]}	{a:{c:#42}|b:[#3|#4]}
{a: "A", "": "B"}	{a:A|#:B}

Values

A value can be any of string, literal, array, and object. Note that array components and object values are values, but object keys are strings.

Backrefs

WSON is able to stringify and parse cyclic structures by means of backrefs. A backref is represented by | followed by a number, that says how many levels to go up. (0 resolves to the current array or objects, 1 resolves to the structure that contains the current structure and so on.)

javascript	WSON
x = {}; x.y = x	{y:|0}
x = {a:[]}; x.a.push(x)	{a:[|1]}

Custom Objects

WSON can be extended to stringify and parse custom objects by means of connectors.

A connector is used to stringify a custom object by:

• by: the objects's constructor. Only objects with exactly that constructor use this connector to stringify.
• split: a function of obj that returns an array of arguments args that can be used to recreate obj. This may be specified as member function __wsonsplit__, too.

A connector is used to create a custom object by:

• create: a function that takes an array of arguments args to create the object obj. This may be specified as static member function __wsoncreate__, too.

Alternatively these functions may be used to use 2-stage creation:

• precreate: a function that creates the (empty) object obj. This may be specified as static member function __wsonprecreate__, too.
• postcreate: a function that takes obj and args to populate obj. Should return obj, null, undefined or a new instance of by. This may be specified as member function __wsonpostcreate__, too.

If no create or postcreate are specified, a default create is implemented as new by(...args). NOTE: This behaviour has changed since v2.2.0 as the old mechanism (auto-implementing postcreate by calling the contructor as a function without new) is no longer available in modern typescript.

An extended WSON stringifier/parser is created by passing a connectors option to wson. connectors should be an object that maps cname keys to connector objects. If a value is given as a function Foo the connector is constructed as {by: Foo}.

The WSON representation of a custom object is:

[: cname (list of args, each prepended by |) ]

Examples:

Provide a __wsonsplit__ method (use default create):

import wsonFactory from 'wson'

class Point {
  constructor(x, y) {
    this.x = x 
    this.y = y 
  }
  __wsonsplit__() {
    return [this.x, this.y]
  }
}

const WSON = wsonFactory({connectors: {Point}})

const point1 = new Point(3, 4)

const s = WSON.stringify(point1);
console.log('s=', s); // [:Point|#3|#4]
const point2 = WSON.parse(s);

Or equivalently specify split non-invasievely:

import wsonFactory from 'wson';

class Point {
  constructor(x, y) {
    this.x = x 
    this.y = y 
  }
}

const WSON = wsonFactory({connectors: {
  Point: {
    by: Point,
    split: (point) => [point.x, point.y],
  }
}})

const point1 = new Point(3, 4)
const s = WSON.stringify(point1)
console.log('s=', s) // [Point:#3|#4]
const point2 = WSON.parse(s)

Specify split and postcreate (use default precreate):

import wsonFactory from 'wson';

class Point {
  constructor(x, y) {
    this.x = x 
    this.y = y 
  }
}

const WSON = wsonFactory({connectors: {
  Point: {
    by: Point,
    // reverse order of args for some strange reason
    split: (point) => [point.y, point.x],
    postcreate: (point, args) => { [point.y, point.x] = args; return point }
  }
}});

const point1 = new Point(3, 4)
const s = WSON.stringify(point1)
console.log('s=', s) // [Point:#4|#3]
const point2 = WSON.parse(s)

Alternately you could specify create (see Corner cases below):

const WSON = wsonFactory({connectors: {
  Point: {
    by: Point,
    split: (point) => [point.y, point.x],
    create: (args) => new Point(args[1], args[0]),
  }
}});

Corner cases:

You can use together backrefs and custom objects. For example this will work:

const pointCyc = new Point(5) // leave 'y' undefined for now
const points = [pointCyc, pointCyc]
pointCyc.y = points
const s = WSON.stringify(pointCyc)

provided that:

• You use 2-stage creation (don't use create).
• postcreate does return that very object which has been passed in (or null).

API

const WSON = wsonFactory(options)

Creates a new WSON processor. Recognized options are:

• addon (optional native module)
• useAddon (boolean, default: undefined):
  • false: An installed wson-addon is ignored.
  • true: The addon is forced. An exception is thrown if the addon is missing.
  • undefined: The addon is used when it is available.
• version (number, default: undefined): the WSON-version to create the processor for. This document describes version 1. If this is undefined, the last available version is used.
• connectors (optional): an object that maps cnames to connectors.

WSON.stringify(val, options)

Returns the WSON representation of val.

• options:
  • haverefCb (function(val)): a function that can create backrefs outside of val. It should return an integer >= 0 for a preexistent enclosing object, otherwise null. I.e. haverefCb and backrefCb are expected to be inverses.

WSON.parse(str, options)

Returns the value of the WSON string str. If str is ill-formed, a ParseError will be thrown.

• options:
  • backrefCb (function(refIdx)): a function that can resolve backrefs outside of the item that corresponds to str. refIdx=0 will refer to next enclosing object.

WSON.parsePartial(str, options)

Parse a string with embedded WSON strings by intercepting the WSON lexer/parser.

• str: The string to be parsed.
• options:
  • howNext: determines how the next chunk should be handled. This may be an array [nextRaw, skip] or just boolean nextRaw. skip is the number of characters to be skipped first (Say, they have been proceeded by other means). Then, if nextRaw is:
    • true, just the lexer is to be used. The next value passed to cb will be either:
      • One of the special characters {, }, [, ], #, :, |. This is signaled by isValue == false.
      • A non-empty string that results by unescaping until the next special character. This is signaled by isValue == true.
    • false, an attempt to parse is requested. The next value passed to cb will be either:
      • One of the special characters }, ], :, | that may not start a valid WSON string. This is signaled by isValue == false.
      • The value of the next WSON string. This is signaled by isValue == true. If this sub-string is ill-formed, a ParseError will be thrown. Any other value of howNext will cause parsePartial to stop immediately with a result of false.
  • cb (function(isValue, value, pos)): This callback reports the next chunk according to howNext. pos will be set to the next (yet unparsed) position in str. The return value of cb is used as howNext for next parsing step.
  • backrefCb (function(refIdx)): a function that can resolve backrefs outside of the item that corresponds to str. refIdx=0 will refer to next enclosing object.

If parseNext happens to parse the complete str, it will return true.

WSON.escape(str)

Returns str with the special characters replaced by their corresponding escape sequences.

WSON.unescape(str)

Returns str with encountered escape sequence replaced by their counterparts. If str contains invalid escape sequences, a ParseError will be thrown.

WSON.getTypeid(value)

Returns a numeric type-id of value. This function is exposed as it may be useful for extending WSON.

value	typeid
undefined	1
null	2
Boolean	4
Number (NaN, too)	8
Date	16
String	20
Array	24
other Object	32

WSON.connectorOfCname(cname)

Returns the normalized connector for cname (or null if none is found).

WSON.connectorOfValue(value)

Returns the normalized connector for value (or null if none is found).

wson.ParseError

This may be thrown by WSON.parse and WSON.parsePartial. It provides these fields:

• s: the original ill-formed string.
• pos: the position in s where passing has stumbled.
• cause: some textual description of what caused to reject the string s.