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jss.js
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jss.js
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"use strict;"
/*
* Copyright (c) 2011, Ilya Bobyr <[email protected]>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* o Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
*
* o Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
/*
* This is modelled after the JSON interface, except that the output string,
* while been valid JSON, will also carry some type information that may be used
* to reconstruct the original user class instances in addition to the basic
* ECMA Script data types.
*
* Class information is written using names of the constructors. At the moment
* the stringify() will check the global object for any properties that point to
* Function objects that may be used as constructors and will use these property
* names to refer to the relevant constructors. If a relevant constructor can
* not be found an exceptions will be thrown. In the future it would make sense
* to add a registration functionality for the constructors to enable for a more
* elaborate use cases.
*
* parse() will look for constructors as properties of the global object using
* the recorded names.
*
* JSS stand for JavaScript Serialization.
*/
JSS = {};
/*
* stringify() will output a JSON representation of the value with some
* additional information added. The value will be wrapped into the following
* object:
* {
* "jss": 1,
* "v": value
* }
*
* "jss" key value is a version of JSS used to do serialization. "v" is the
* actual value.
*
* stringify() will invoke JSON.stringify on the value, so if there is a
* toJSON() method defined in the object prototype it will be used.
*
* If the value is an object who's prototype is not Number, String, Boolean,
* Object or Array stringify() will try to find the object constructor among the
* enumerable properties of the global object. If unsuccessful an exception
* will be thrown. If successful the name of the property will be used to
* encode the object type.
*
* stringify() may add type information to the objects been serialized. When
* serialization is done all the added properties are removed from the source
* object and/or its subobjects.
*
* It is OK for toJSON() to return anything different from the original value.
* stringify() will still use the constructor of the original object been
* serialized.
*
* In version 1 the type name will be written as a value of a key named "$t",
* unless the key is already present in the original object or the object
* returned by toJSON(). In this case stringify() will find largest <n> such
* that the property with name "$t<n>" is present on the object and will use
* name "$t<n+1>" to store the type name.
*
* If a plain object is been serialized and it already has a property named "$t"
* or "$t<n>" (n in {0, 1, ... }) stringify() will behave as if it would have a
* type name of null. This way parse() will not try to reconstruct this object
* as a user class instance. Otherwise plain object are not modified.
*
* space is an optional argument that has the same value as in JSON.stringify().
*/
JSS.stringify = function (value, space)
{
var modifiedObjs = [];
var allConstructors = JSS._getAllConstructors(JSS._global);
function removeAddedProps()
{
for (var i = 0; i < modifiedObjs.length; ++i)
{
var { obj: obj, key: key } = modifiedObjs[i];
delete obj[key];
}
modifiedObjs.length = 0;
};
function addTypeProperty(obj, typeName)
{
var key = JSS._getVacantTypeNameKey(obj);
modifiedObjs.push({ obj: obj, key: key });
obj[key] = typeName;
};
function wasAugmented(obj)
{
for (var i = 0; i < modifiedObjs.length; ++i)
if (modifiedObjs[i].obj === obj)
return true;
return false;
};
/*
* Returns a name of the global object property that holds a reference to a
* constructor that has the same prototype object attached to it as the obj
* prototype object.
* If the obj is a plain object returns Object.prototype.
* Otherwise returns undefined.
*/
function getTypeName(obj)
{
switch (typeof obj)
{
case "undefined":
return undefined;
case "object":
if (obj === null)
return undefined;
break;
case "boolean":
return undefined;
case "number":
return undefined;
case "string":
return undefined;
case "function":
return undefined;
default:
return undefined;
}
var prototype = Object.getPrototypeOf(obj);
if (prototype === Object.prototype)
return Object.prototype;
if (prototype === Array.prototype)
return undefined;
var name = allConstructors.getNameByPrototype(prototype);
if (name !== undefined)
return name;
throw new TypeError("JSS.stringify can not find a constructor"
+ " for an object: " + obj);
};
function replacer(key, value)
{
/* JSON.stringify() Str algorithm will provide the parent object as this. */
var parent = this;
var originalValue = parent[key];
/*
* There is a bug in Firefox < 5 that causes the replacer to be invoked
* twice in some cases. While this bug:
*
* https://bugzilla.mozilla.org/show_bug.cgi?id=636079
*
* says that it may happen only in case the value is modified I see double
* calls even for simple values that are not modified.
* But it works fine with XulRunner 5.
*/
if (!JSS._bug636079 || !wasAugmented(originalValue))
{
var typeName = getTypeName(originalValue);
if (typeName !== undefined)
{
/*
* As a special case getTypeName may return an Object.prototype instead
* of a string to indicated a plain object.
*/
if (typeName === Object.prototype)
{
if (JSS._hasTypeProperty(originalValue))
/*
* We need to be able to distinguish preexisting properties with
* the name we use to note types on objects from our added
* properties. In order to do so we always add our property even
* to plain objects if the already have a property with a name
* that may later confuse parse().
*/
addTypeProperty(value, null);
}
else
addTypeProperty(value, typeName);
}
}
return value;
};
var str = JSON.stringify({ jss: JSS._version, v : value },
replacer, space);
removeAddedProps();
return str;
};
/*
* Does an opposite to what stringify() do. Parses a string as if it would be a
* JSON encoded representation of some value wrapped into the following:
*
* {
* "jss": 1,
* "v": value
* }
*
* "jss" key value is a version of JSS used to do serialization. "v" is the
* actual value.
*
* parse() will invoke JSON.parse() on the text, so the parsing rules are the
* same. After parsing parse() will remove any additional information added by
* stringify() including the wrapping object with version and any other
* information.
*
* If stringify() serialized a user class instance parse() will try to
* reconstruct it. It will search through the global object enumerable
* properties for one that has the same name as was recorded during
* serialization under "$t" or "$t<n>". parse() will set the object prototype
* to be equal to the prototype associated with the constructor, though the
* constructor will not be invoked.
* If there is a property named "fromJSON" on the *constructor* (not the
* prototype) and the property value has type "function", parse() will invoke
* this function passing the reconstructed object (not connected to the
* prototype) as the only argument and will use the result of the call as the
* actual value.
*
* parse() will throw:
* - SyntaxErro() if the value is not property wrapped.
* - TypeError() if the version in the text is higher than the one that pasre()
* can deserialize.
* - TypeError() if the "fromJSON" is present on the constructor but is not a
* function.
* - TypeError() if an object (or a subobject) has a type name attached to it
* but parse() can not find a global object property with a matching name or
* does not have a prototype property.
*/
JSS.parse = function (text)
{
var allConstructors = JSS._getAllConstructors(JSS._global);
function reviver(name, val)
{
if (typeof val != "object")
return val;
var typePropName = JSS._getTypePropertyName(val);
if (typePropName === undefined)
return val;
var typeName = val[typePropName];
delete val[typePropName];
if (typeName === null)
/* An Object with type name like named properties. */
return val;
var e = allConstructors.getConstructorAndPrototypeByName(typeName);
if (e === undefined)
throw TypeError("JSON.parse can not find a constructor for type "
+ "'" + typeName + "'.");
var { constructor: constructor, prototype: prototype } = e;
var r = null;
if (constructor.hasOwnProperty("fromJSON"))
{
var fromJSON = constructor.fromJSON;
if (typeof fromJSON !== "function")
throw TypeError("JSS.parse found a 'fromJSON' property for type "
+ "'" + typeName + "' but it is not a function.");
r = fromJSON(val);
}
else
{
r = Object.create(prototype);
for (var n in val)
r[n] = val[n];
}
return r;
};
var obj = JSON.parse(text, reviver);
/*
* It seems unfortunate that the wrapper format and version check is done so
* late, but even if moved into the reviver the algorithm used by JSON.parse()
* will pass the wrapper to the reviver as the very last object.
* For this version it does not seem to pose a problem, but if may be an issue
* if reviver logic would have to depend on the archive version been
* deserialized.
*/
if (!(obj instanceof Object))
throw SyntaxError("JSS.parse expectes the value to be wrapped. "
+ "Got: " + text);
if (typeof obj["jss"] !== "number")
throw SyntaxError("JSS.parse expects a \"jss\" property with the version "
+ "number as the value in the wrapping object. Got: " + text);
if (obj.jss > JSS._version)
throw TypeError("JSS.parse can not read archives with format version "
+ obj.jss + " maximum supported version is " + JSS._version);
if (!obj.hasOwnProperty("v"))
throw SyntaxError("Jss.prase expects a \"v\" property wit the actual value"
+ " in the wrapping object. Got: " + text);
return obj.v;
}
/*
* === Implementation ===
*/
JSS._global = this;
JSS._version = 1;
JSS._typeNameKey = "$t";
JSS._typeNameKeyRe = /^\$t(\d*)$/;
/* Search for usage - there is a comment explaining what is this about. */
JSS._bug636079 = false;
JSS._AllConstructors = function()
{
this.all = {};
}
JSS._AllConstructors.prototype =
{
add: function (name, constructor, prototype)
{
this.all[name] = { constructor: constructor, prototype: prototype };
},
getNameByPrototype: function (prototype)
{
var all = this.all;
for (var name in all)
{
var e = all[name];
if (e.prototype === prototype)
return name;
}
return undefined;
},
getConstructorAndPrototypeByName: function (name)
{
var all = this.all;
if (name in all)
return all[name];
return undefined;
}
};
JSS._getAllConstructors = function(global)
{
var r = new JSS._AllConstructors();
for (var n in global)
{
var func = global[n];
if (typeof func != "function")
continue;
var prototype = func["prototype"];
if (prototype === undefined)
continue;
r.add(n, func, prototype);
}
return r;
}
JSS._hasTypeProperty = function (obj)
{
for (var n in obj)
if (JSS._typeNameKeyRe.test(n))
return true;
return false;
}
JSS._getVacantTypeNameKey = function (obj)
{
var maxN = JSS._getTypePropertyIndex(obj);
var key = JSS._typeNameKey;
if (maxN > -1)
return key + (maxN + 1);
if (maxN > -2)
return key + "0";
return key;
}
JSS._getTypePropertyName = function (obj)
{
var maxN = JSS._getTypePropertyIndex(obj);
var key = JSS._typeNameKey;
if (maxN > -1)
return key + maxN;
if (maxN > -2)
return key;
return undefined;
}
/*
* Search common to _getVacantTypeNameKey and _getTypePropertyName.
*/
JSS._getTypePropertyIndex = function (obj)
{
var maxN = -2;
var m;
for (var n in obj)
{
if (m = JSS._typeNameKeyRe.exec(n))
{
var n = m[1] === "" ? -1 : +m[1];
if (maxN < n)
maxN = n;
}
}
return maxN;
}
/* vim: set et sts=2 sw=2 tw=80 spell spl=en: */