W3C

Widgets 1.0: The widget Interface

Editor's Draft 4 November 2009

This Version:
http://www.w3.org/TR/2009/WD-widgets-apis-20091104/
Latest Version:
http://www.w3.org/TR/widgets-apis/
Previous Versions:
http://www.w3.org/TR/2009/WD-widgets-apis-20090423/
http://www.w3.org/TR/2009/WD-widgets-apis-20090205/
Editors:
Marcos Cáceres, Opera Software ASA
Robin Berjon, Vodafone
Arve Bersvendsen, Opera Software ASA

Abstract

This specification defines an application programming interface (APIs) for widgets that provides, amongst other things, functionality for accessing a widget's metadata and persistently storing data.

Status of this Document

This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at http://www.w3.org/TR/.

This document was produced by a group operating under the 5 February 2004 W3C Patent Policy. W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.

This is the 4 November 2009 Last Call Working Draft version of the "Widgets 1.0: The widget Interface" specification. The Last Call period ends on 15 September 2009. The requirements, which are listed in the specification, were addressed and specified through extensive research, and via consultation with W3C members and the public via the Working Group's mailing lists (WAF archive, WebApps archive). The purpose of this Last Call is to give external interested parties a final opportunity to publicly comment on how the API should work within widgets before the Working Group issues a call for implementations. The Working Group's goal is to make sure that vendor's requirements for an API for widgets have been effectively addressed and

This document is produced by the Web Applications WG, part of the Rich Web Clients Activity in the W3C Interaction Domain. It is expected that this document will progress along the W3C's Recommendation track. Publication as a Working Draft does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.

You can find the latest Editor's Draft of this document in the W3C's CVS repository, which is updated on a very regular basis. The public is encouraged to send comments to the Web Apps Working Group's public mailing list public-webapps@w3.org (archive). See W3C mailing list and archive usage guidelines. A detailed list of changes from the previous version is also available from the W3C's CVS server.

Interested parties should be aware that this document is not stable and should not be implemented. Interested parties who are not taking part in the discussions are likely to find the specification changing out from under them in incompatible ways. If you are interested in implementing this document before it eventually reaches the Candidate Recommendation stage, join the aforementioned mailing lists and take part in the discussions.

Table of Contents

1 Introduction

This section is non-normative.

This specification defines an application programming interface that enables baseline functionality for widgets, including the ability to:

1.1 The Widget Family of Specifications

This section is non-normative.

This specification is part of the Widgets 1.0 family of specifications, which together standardize widgets as a whole. The list of specifications that make up the Widgets 1.0 Family of Specifications can be found on the Working Group's wiki.

1.2 Design Goals and Requirements

This section is non-normative.

The design goals and requirements for this specification are documented in the Widgets 1.0 Requirements [Widgets-Reqs] document.

This document addresses some of the requirements relating to Application Programming Interfaces of the 30 April 2009 Working Draft of the Widgets 1.0: Requirements Document:

2 Definitions

The following definitions are used throughout this specification. Please note that other terms are given throughout this document and defined where they are used.

Author script

An script running within a widget instance (e.g., some ECMAScript).

Configuration document

A configuration document is a file called "config.xml" at the root of the widget package as specified in the [Widgets-Packaging] specification.

Feature

A runtime component (e.g. a device API, video decoder, etc.) that is made available by the user agent to the widget instance as a direct result of an author requesting its availability via a feature element in the widget's configuration document.

Getting

A DOM attribute is said to be getting when its value is being retrieved (e.g. by an author script).

Initialization

When a user agent first runs a widget package through the Steps for Processing a Widget Package, as specified in the [Widgets-Packaging] specification, prior to runtime.

 
 
Preference

A persistently stored name-value pair that is associated with the widget the first time the widget is initiated.

Setting

A DOM attribute is said to be setting when a new value is assigned to it (e.g. by an author script).

Start file

A start file designates a file from the widget package to be loaded by the user agent when it instantiates the widget, as specified in the [Widgets-Packaging] specification.

Supports

A user agent implements a mentioned specification or conformance clause.

Valid IRI

A string that matches the IRI token of the [RFC3987] specification.

Viewport

A CSS viewport. For a start file rendered on continuous media, as defined in the [CSS21] specification, a viewport is the area on which the Document of the start file is rendered by the user agent. The dimensions of a viewport excludes scrollbars, toolbars, and other user interface "chrome".

Widget Instance

A widget instance is a top-level browsing context whose origin is valid IRI. The concepts of a top-level browsing context and origin are defined in [HTML5].

3 Conformance

All examples and notes in this specification are non-normative, as are all sections explicitly marked non-normative. Everything else in this specification is normative.

The key words must, must not, should, recommended, may and optional in the normative parts of this specification are to be interpreted as described in [RFC2119].

The only conformance class defined by this specification is user agents. Conformance requirements phrased as algorithms or specific steps can be implemented in any manner, so long as the end result is equivalent to what would be archived when following the specification. (In particular, the algorithms defined in this specification are intended to be easy to follow, and not intended to be performant.)

4 User Agents

A user agent is a software implementation of this specificaiton that also supports the [Widgets-Packaging] specification.

Note: The user agent described in this specification does not denote a "widget user agent" at large. That is, a user agent that implements all the specifications, and dependencies, defined in the Widgets 1.0: Family of Specifications. The user agent described in this specification is only concerned with the behavior of programming interfaces. A user agent needs to impose implementation-specific limits on otherwise unconstrained inputs, e.g. to prevent denial of service attacks, to guard against running out of memory, or to work around platform-specific limitations.

Note: Implementers can partially check their level of conformance to this specification by successfully passing the test cases of the [A&E-Test-Suite]. Note, however, that passing all the tests in the test suite does not imply conformance to this specification; It only implies that the implementation conforms to aspects tested by the test suite.

5 The Widget Interface

The Widget interface primarily provides access to metadata derived from processing the widget's configuration document. The interface also allows authors to access persistently-stored preferences (via the preferences attribute).

This specification uses [WebIDL] to define the application programming interfaces.

A user agent must implement the Widget interface as a widget attribute in the global object context of the widget's start file.

A user agent whose start file implements HTML5's Window interface, must implement the Widget interface as the widget attribute of the window object in the following manner:

[Supplemental, NoInterfaceObject]
interface WindowWidget {
  readonly attribute Widget widget;
};

Window implements WindowWidget;

The Widget object provides the following attributes and methods:

interface Widget {
    readonly attribute DOMString     author;
    readonly attribute DOMString     authorEmail;
    readonly attribute DOMString     authorHref;
    readonly attribute DOMString     description;
    readonly attribute DOMString     id;
    readonly attribute DOMString     name;
    readonly attribute DOMString     shortName;
    readonly attribute Storage       preferences;
    readonly attribute DOMString     version;
    readonly attribute unsigned long height;
    readonly attribute unsigned long width;

    void openURL(in DOMString iri);
};

Note: A user agent can support the Storage interface on DOM attributes other than the preferences attribute (e.g., a user agent can to support the [WebStorage] specification's localStorage attribute of the window object in conjunction to preferences attribute

Note: for the sake of interoperability across widget user agents, and where it makes sense, authors should use the preferences attribute over other APIs that provide a Storage interface.

5.1 Metadata Attribute Values

During the [Widgets-Packaging] specification's steps for processing a widget package, the resulting data is stored by the user agent in the Table of Configuration Defaults that is defined in the [Widgets-Packaging] specification. Most of the attributes of the widget interface correspond to the metadata derived from processing a widget's configuration document.

Upon initialization of the widget object, a user agent must set the attributes identified in the left column of the configuration attributes table to the values that correspond to the Table of Configuration Defaults as defined in [Widgets-Packaging] (identified by the values in the right hand column).

Configuration Attributes Table
Attributes Values in Table of Configuration Defaults
author author name
authorEmail author email
authorHref author href
description widget description
id widget id
name widget name
version widget version
shortName widget short name

Upon getting any of the attributes in the configuration attributes table, a user agent must return the value the configuration attributes table.

5.1.1 Usage Example

This section is non-normative.



// Hypothetical example that emails a bug to an Author
function emailBug(bug){
    var subject  = widget.name   + " (" + widget.version + ")";
    var to       = widget.authorEmail;
    var emailURI =    "mailto:"   + to 
                    + "?subject=" + escape(subject) 
                    + "&body="    + escape(bug); 
  
  //use email client to send email
  widget.openURL(emailURI); 
}  


// Hypothetical example that generates an about box 
// using metadata from a widget's configuration document. 
function makeAboutBox(){
    var title    = "<h1>" + widget.name + "</h1>";
    var version  = "<h2>Version: " + widget.version + "</h2>";
    var id       = "<p><small>" + widget.id +"</small></p> <hr/>";
    var auth     = "<p>Created by: " + widget.author + "</p>"; 
    var homepage = "<p>My Site: "  +widget.authorHref + "</p>" 
    var desc     = "<h3>About this Widget</h3><p>"  
                  + widget.description + "</p>";
    var box      = "<div id='aboutBox'>" 
    + title + version + id + auth + desc +
    "</div>";
    document.getElementById("console").innerHTML = box; 
}

5.2 The width Attributes

Upon getting the width, a user agent must return the width of the widget instance’s viewport in [CSS21] pixels.

5.2.1 Usage Example

This section is non-normative.


function getHypotenuse(){
    var x   = widget.width;  
    var y   = widget.height;  
    var hyp = Math.sqrt(x*x + y*y);
    return hyp;
}

5.3 The height Attribute

Upon getting the height attribute, a user agent must return the height of the widget instance’s viewport in [CSS21] pixels.

5.3.1 Usage Example

This section is non-normative.


function getHypotenuse(){
    var x   = widget.width;  
    var y   = widget.height;  
    var hyp = Math.sqrt(x*x + y*y);
    return hyp;
}

5.4 The preferences attribute

The purpose of the preferences attribute is to allow authors to manipulate the storage area that is unique for the instance of a widget.

Upon invocation of the setItem() or removeItem() method by an author script on a read-only item, user agent must throw a NO_MODIFICATION_ALLOWED_ERR exception and must not fire a storage event (described in [WebStorage]). The NO_MODIFICATION_ALLOWED_ERR is defined in the [DOM3Core] specification.

Upon invocation of the preferences attribute's clear() method, a user agent must not remove read-only items and corresponding values from a storage area. A user agent, must, however, remove other items from the storage area in the manner described in the [WebStorage] specification.

Upon getting, via the key() and getItem() methods, a user agent must allow a read-only key to be read by author scripts.

When the preferences attribute is accessed, the user agent must run the following steps:

  1. If the Document's effective script origin is not the same origin as the Document's origin, then throw a SECURITY_ERR exception and abort these steps. The concept of effective script origin and same origin are defined in [HTML5].

  2. Check to see if the user agent has associated a storage area for the origin of the Document of the Window object on which the method was invoked. If a user agent has not previously associated a storage area with the instance of a widget, then the user agent must initialize the preferences attribute.

  3. Return the Storage object associated with that origin's storage area. Each Document object must have a separate object for its widget's preferences attribute.

5.4.1 Usage Example

This section is non-normative.


<!doctype html>
...
<fieldset id="prefs-form">
  <legend>Game Options</legend>
  <label>Volume:  <input type="range" min="0" max="100" name="volume"/> </label> 
  <label>Difficulty:  <input type="range" min="0" max="100" name="difficulty"/> </label>

  <input type="button" value="Save" onclick="savePrefs()"/>
  <input type="button" value="load" onclick="loadPrefs()"/>

</fieldset>
...

<script>
var form   = document.getElementById("prefs-form");
var fields = form.querySelectorAll("input[type='range']"); 
  
function loadPrefs () {
   for(i in fields){
      var field = fields[i];
      if (typeof widget.preferences[field.name] != "undefined") {
        field.value = widget.preferences[field.name]; 
      }
   }  
}

function savePrefs () {
  for(var i = 0; i < fields.length; i++){
      var field = fields[i];
      widget.preferences[field.name] = field.value;
  }
}
</script>

5.4.2 Initialization of the preferences Attribute

The steps to initialize the preferences attribute are given by the following algorithm:

  1. Establish the instance of a widget for this widget and create a storage area that is unique for the origin.

  2. If the widget preferences variable of the Table of Configuration Defaults contains any preferences, then for each preference held by widget preferences:

    1. Let pref-key be the name of the preference.

    2. If the pref-key already exists in the storage area, stop processing this preference: go back to step 2 in this algorithm, and process the next preference (if any).

    3. Let pref-value be the value of the preference.

    4. Directly write pref-key and pref-value to the storage area (i.e., don't use the Storage interface):

      1. If the user agent cannot write to the storage area (e.g., because it ran out of disk space, or the space quota was exceeded, etc.), terminate all processing of this widget. It is recommended that the use agent inform the end-user of the error.

      2. If this preference's associated readonly value is true, then flag this key as a protected key in the storage area.

  3. Implement the Storage interface on the storage area, and make the preferences attribute a pointer to that storage area.

5.5 The openURL() Method

The openURL() method provides authors with a means to defer the handling of IRIs, defined in [RFC3987], to an appropriate scheme handler for the given IRI scheme (if one is available). The openURL() method takes a valid IRI as an argument.

When invoked, a user agent should handle the provided iri with the appropriate handler for the given URI scheme. If there is no such scheme handler, or it is otherwise rejected by the user agent (e.g., because of security policy or user prompting), then the user agent must act as if the method had not been invoked.

If the iri is not a valid IRI, the user agent should inform the end-user that the request to handle the IRI method has failed.

The user agent should inform the end-user when a request to handle the IRI via the openURL() method has failed.

If a relative reference is used as an argument for openURL(), a user agent must act as if the openURL() method had not been invoked.

5.5.1 Usage Example

This section is non-normative.


//open email 
openURL("mailto:jsmith@example.org?subject=A%20Hello&body=hi"); 

//make a phone call 

openURL("tel:+1234567678");

//open a web page
openURL("http://example.org");

//send and sms
openURL("sms:+41796431851,+4116321035;?body=hello%20there");

//SSH 
openURL("ssh://user@host.example.com:2222");

6 Storage Areas

A storage area is a data-store that is unique for the widget instance, which a user agent uses to store key-value pairs that pertain to the preferences attribute. An author script interacts with the storage area via the [WebStorage] specification's Storage interface.

To facilitate the storage of preferences during the initialization of the preferences attribute, a user agent must have the ability to directly read and write to a storage area without invoking the methods of the [WebStorage] specification's Storage interface.

A user agent must preserve the values stored in a storage area when a widget is re-instantiated (i.e., if the widget is closed, the data is saved; when the device is rebooted and the widget is reopened, the save data is made available to the storage area).

A user agent may expire data from a storage area for security reasons, or when requested to do so by the end user, or if the user agent detects that it has limited storage space.

6.1 Read-only Items in the Storage Area

As an extension to the [WebStorage] specification, this specification allows certain key-value pairs (items) in a storage area to be read-only: a read-only item is an item in a storage area that cannot be modified or deleted by an author script. A read-only item always represents a preference that author explicitly flagged as "read-only" in the widget's configuration document (denoted by the preference having readonly attribute value set to true). Read-only items are created by the user agent when the preferences attribute is initialized.

Acknowledgements

Max Froumentin, Rune F. Halvorsen, Scott Wilson, Addison Phillips, Alexander Dreiling, Arun Ranganathan, Arthur Barstow, Bárbara Barbosa Neves, Brian Wilson, Bjoern Hoehrmann, Benoit Suzanne, Bert Bos, Boris Zbarsky, Bradford Lassey, Cameron McCormack, Cliff Schmidt, Claudio Venezia, Coach Wei, Corin Edwards, Dan Brickley, David Clarke, Dean Jackson, David Pollington, Doug Schepers, Ed Voas, Felix Sasaki, Francois Daoust, Gautam Chandna, Geir Pedersen, Gene Vayngrib, Gorm Haug Eriksen, Guido Grassel, Hari Kumar G, Ian Hickson, Jay Sweeney, Jere Käpyaho, Jim Ley, Jon Ferraiolo, Jose Manuel Cantera Fonseca, Josh Soref, Jouni Hakala, Joey Bacalhau, Kevin Lawver, Kai Hendry, Krzysztof Maczyński, Lachlan Hunt, Marc Silbey, Marcin Hanclik, Mark Baker, Mikko Pohja, Mohamed Zergaoui, Olli Immonen, Philipp Heltewig, Philip Taylor, Scott Wilson, Stephen Paul Weber.

Normative References

[CSS21]
Cascading Style Sheets Level 2 Revision 1 (CSS 2.1) Specification, B. Bos, I. Hickson, T. Çelik, H. Wium Lie. W3C Candidate Recommendation 23 April 2009.
[DOM3Core]
Document Object Model (DOM) Level 3 Core Specification, A. Le Hors, P. Le Hégaret, L. Wood, G. Nicol, J. Robie, M. Champion, S. Byrne, editors. World Wide Web Consortium, April 2004.
[RFC2119]
Key words for use in RFCs to Indicate Requirement Levels, RFC2119, S. Bradner. March 1997.
[RFC3987]
Internationalized Resource Identifiers (IRIs). RFC3987, M. Duerst, M. Suignard. January 2005.
[URI]
Uniform Resource Identifier (URI): Generic Syntax.RFC 3986, T. Berners-Lee, R. Fielding and L. Masinter. January 2005.
[Widgets-Packaging]
Widgets 1.0: Packaging and Configuration. M. Caceres, Ed. W3C Last Call Working Draft May 2009. (Work in progress)
[WebIDL]
Web IDL. Cameron McCormack. W3C Working Draft, 19 December 2008. (Work in progress).
[WebStorage]
Web Storage. I. Hickson. W3C Working Draft, 23 April 2009. (Work in progress).

Informative References

[Widgets-Landscape]
Widgets 1.0: The Widget Landscape (Q1 2008). M. Caceres. W3C Working Draft. 14 April 2008.
[Widgets-DigSig]
Widgets 1.0: Digital Signature
[A&E-Test-Suite]
Forthcoming.
[Widgets-Access]
Widgets 1.0: Access Requests Policy. Robin Berjon. W3C Working Draft 4 August 2009 (Work in progress).
[Widgets-Reqs]
Widgets 1.0 Requirements, M. Cáceres and M. Priestley. W3C Working Draft, 30 April 2009 (Work in progress).
[Widgets-Views]
Widgets 1.0: Media Query Extensions. A. Bersvendsen and M. Caceres. Unpublished editors' draft.
[Widgets-Updates]
Widgets 1.0: Updates. M. Cáceres. W3C Working Draft, 7 October 2008 (Work in progress).
[HTTP]
Hypertext Transfer Protocol -- HTTP/1.1, RFC 2616, R. Fielding, et al. June 1999.