AMF serialization & deserialization in JS

Status:

Cross-browser compatibility

Intro

AMF (Action Message Format) is a binary data serialization protocol. Simply put, it transforms objects in memory into a binary string, and can reverse this binary string into an object in memory. It can be used just like JSON, and this library has been build to provide a similar API to that exposed by the JSON functionality in JavaScript.

Purpose

The purpose of this library is to provide a consistent and symmetric implementation of the AMF specification in both PHP & JavaScript.

Why use AMF?

Well, it's up to you. JSON is perfectly suited to the web, however it does have some shortcomings which are addressed by AMF. For starters, JSON cannot handle complex object graphs with circular references; additionally, it cannot serialize dates & byte arrays - you would need to do some additional work to support these in JSON (convert date to unix timestamp, byte arrays to base64).

Should I stop using JSON?

Hells no. JSON is great; AMF can simply provide you with some additional functionality which could help you build your web app.

Getting Started

To begin using this library, you will need to install it via Composer:

bower install -S infomaniac-amf.js#latest

This will download the repository for you and make the library available for inclusion. For convenience, a file dist/amf.js has been compiled for you with all of its dependencies, uglified and browserified. The file is a mere 43kb.

<script src="bower_components/infomaniac-amf.js/dist/amf.js" type="text/javascript"></script>

Usage

Here is a simple example of encoding an object to AMF:

var data = {
	any: 'data',
	you: 'like!'
};

var encodedData = AMF.stringify(data);
console.log(encodedData);

This will produce a binary string which represents your given data.

If you were to inspect the HTTP traffic of a page that produces AMF data, using a tool such as Charles Proxy, you would see the following output:

To decode this string, simply do the following:

var data = {
	any: 'data',
	you: 'like!'
};

var encodedData = AMF.stringify(data);
console.log(AMF.parse(encodedData));

If you were to console.log this data, it would look identical to the input data given to the AMF.stringify function.

Object {any: "data", you: "like!"} 

Extra Features

Class-mapping

AMF allows you to encode an object and retain some metadata about it; for example, when serializing an instance of a class (not Object) the library will retain the class' fully qualified namespace name and use it to reconstruct an object of that type upon decoding.

Consider the following class:

var Person = function() {
	this.name = 'Bob';
	this._classMapping = 'Person';
};

If we encode an instance of this object, by default its class type will be ignored and when the data is decoded, the resulting value will be a plain PHP Object instance.

var Person = function() {
	this._classMapping = 'Person';
};

var data = new Person();
data.name = "Bob";

var encodedData = AMF.stringify(data);
console.log(AMF.parse(encodedData));

...will produce...

Object {name: "Bob"}

In order to retain the class type in AMF, you will need to add the following:

1. an additional flag to the AMF.stringify function call
2. define a _classMapping variable on the object(s) being encododed, and
3. register a "class alias" using AMF.registerClassAlias to associate the _classMapping value to its related class type

var Person = function() {
	this._classMapping = 'Person';
};

var data = new Person();
data.name = "Bob";

var encodedData = AMF.stringify(data, AMF.CLASS_MAPPING);
AMF.registerClassAlias('Person', Person);

console.log(AMF.parse(encodedData));

Now, when this data is decoded, the library will attempt to create a new instance of the Person class and set its public property name to "Bob".

Person {_classMapping: "Person", name: "Bob"} 

Data Encoding (Serialization)

The AMF spec allows for the serialization of several different data-types.

Here is a link to the latest specification: AMF3 Spec - January 2013

This library implements 10 of the 18 data-types described in the specification. The reason for the support of only a subset of these types can be seen in two lights: utility and limitation. Here is an exhaustive list of the data-types available:

Data-Type	Included	Reason for exclusion
Undefined	✔	-
Null	✔	-
False	✔	-
True	✔	-
Integer	✔	-
Double	✔	-
String	✔	-
XML Document	✗	Who needs XML?
Date	✔	-
Array	✔	-
Object	✔	-
XML	✗	Who needs XML?
ByteArray	✔	-
Vector	✗	Not high priority - also, possible browser incompat issue with JS
Vector	✗	Not high priority - also, possible browser incompat issue with JS
Vector	✗	Not high priority - also, possible browser incompat issue with JS
Vector	✗	Not high priority - also, possible browser incompat issue with JS
Dictionary	✗	PHP cannot use objects are array keys

License

This project is licensed under the MIT license.

Acknowledgements

While writing this library, I used several libraries to validate my progress, and to help me come unstuck. I would like to extend a special thanks to the following libraries and individuals:

• SabreAMF
• AmfPhp
• Charles Proxy's wonderful AMF implementation
• Arseny Vakhrushev (neoxic) for his patience, guidance, advice and help
• Robert Cesaric, Grant McMullin and Andre Venter for their insight and advice
• My esteemed colleagues at Zando