discovery-api/Overview.src.html
author Rich Tibbett <richt@opera.com>
Mon, 12 Aug 2013 18:16:00 +1000
changeset 441 b4b2569b4e9b
parent 440 fcbaadc4fd54
child 447 5e36d90b8960
permissions -rw-r--r--
Fix [DAP-ISSUE-136]: Issues related to garbage collection
     1 <!DOCTYPE html>
     2 <!--
     3 
     4   THIS IS THE WORKING VERSION OF THE CURRENT SPECIFICATION!
     5 
     6   This specification is built using ReSpec.js <http://dev.w3.org/2009/dap/ReSpec.js/documentation.html>
     7 
     8   From time to time it's necessary to HTML5 Tidy this document using the tool @ <http://w3c.github.com/tidy-html5/>.
     9 
    10   The command used to format this document (Overview.src.html) is as follows (replacing all = signs with - signs!):
    11 
    12   @> tidy ==new-blocklevel-tags section ==char-encoding utf8 ==tidy-mark no ==indent yes ==indent-spaces 2 ==indent-attributes yes ==wrap 120 ==fix-bad-comments yes -m Overview.src.html
    13 
    14   To publish a new compiled version (Overview.html), we need to open this file (Overview.src.html) in any web browser.
    15   Once it has loaded we press 'Ctrl + Shift + S' (or 'Cmd' + 'Shift' + 'S' on Mac) and then select
    16   'Save as HTML (Source)' from the resulting menu.
    17 
    18   We then replace Overview.html with the produced HTML source of this process.
    19 
    20   Next we run HTML5 Tidy over our new Overview.html file with the following command (replacing all = signs with - signs!):
    21 
    22   @> tidy ==new-blocklevel-tags section ==char-encoding utf8 ==tidy-mark no ==indent yes ==indent-spaces 2 ==indent-attributes yes ==wrap 120 ==hide-comments yes -m Overview.html
    23 
    24   Now the specification is ready to be published :)
    25 
    26 -->
    27 <html>
    28   <head>
    29     <title>
    30       Network Service Discovery
    31     </title>
    32     <meta http-equiv='Content-Type'
    33           content='text/html; charset=utf-8'>
    34     <script type="text/javascript"
    35           class='remove'>
    36 var respecConfig = {
    37           specStatus:   "ED",
    38           //publishDate:  "2013-03-29",
    39           shortName:    "discovery-api",
    40           edDraftURI:   "http://dvcs.w3.org/hg/dap/raw-file/tip/discovery-api/Overview.html",
    41           previousMaturity: "FPWD",
    42           previousPublishDate: "2012-10-04",
    43           editors: [
    44             {
    45               name:       "Rich Tibbett",
    46               //url:        "http://richt.me/",
    47               company:    "Opera Software ASA",
    48               companyURL: "http://opera.com/"
    49             }
    50           ],
    51 
    52           wg:           "Device APIs Working Group",
    53           wgURI:        "http://www.w3.org/2009/dap/",
    54           wgPublicList: "public-device-apis",
    55           wgPatentURI:  "http://www.w3.org/2004/01/pp-impl/43696/status",
    56 
    57     //          extraCSS:     ["http://dvcs.w3.org/hg/dap/raw-file/tip/discovery-api/css/respec.nsd.css"],
    58     //          inlineCSS:    true,
    59           noIDLIn:      true
    60 
    61       };
    62     </script>
    63     <script src='http://www.w3.org/Tools/respec/respec-w3c-common'
    64           type="text/javascript"
    65           class='remove'
    66           async="">
    67 </script>
    68     <style>
    69 /* Custom ReSpec CSS (by Rich Tibbett) */
    70 
    71      /* Add better spacing to sections */
    72      section, .section { margin-bottom: 2em; }
    73 
    74      /* Add addition spacing to <ol> and <ul> for rule definition */
    75      ol.rule li, ul.rule li { padding:0.6em; }
    76 
    77      pre.widl { border: solid thin; background: #EEEEEE; color: black; padding: 0.5em 1em; position: relative; }
    78      pre.widl :link, pre.widl :visited { color: #000; background: transparent; }
    79      pre.widl:before { content: "IDL"; font: bold small sans-serif; padding: 0.5em; background: white; position: absolute; top: 0; margin: -1px 0 0 -4em; width: 1.5em; border: thin solid; border-radius: 0 0 0 0.5em }
    80 
    81      div.example { border: solid thin black; background: #FFFFF0; color: black; padding: 0.5em 1em; position: relative; margin: 1em 0 1em 4.6em; width: auto; }
    82      div.example:before { content: "EXAMPLE"; font: bold small sans-serif; padding: 0.5em; background: white; color: black; position: absolute; top: 0; margin: -1px 0 0 -7.6em; width: 5em; border: thin solid black; border-radius: 0 0 0 0.5em }
    83 
    84      dl.domintro { color: green; margin: 2em 0 2em 2em; padding: 0.5em 1em; border: none; background: #DDFFDD; }
    85      hr + dl.domintro, div.impl + dl.domintro { margin-top: 2.5em; margin-bottom: 1.5em; }
    86      dl.domintro dt, dl.domintro dt * { color: black; text-decoration: none; }
    87      dl.domintro dd { margin: 0.5em 0 1em 2em; padding: 0; }
    88      dl.domintro dd p { margin: 0.5em 0; }
    89      dl.domintro code {font-size: inherit; font-style: italic; }
    90      dl.domintro:before { display: table; margin: -1em -0.5em 0.5em auto; width: auto; content: 'This box is non-normative. Implementation requirements are given below this box.'; color: red; border: solid 2px; background: white; padding: 0 0.25em; font-size:0.8em; }
    91 
    92      table { border-collapse:collapse; border-style:hidden hidden none hidden }
    93      table thead { border-bottom:solid }
    94      table tbody th:first-child { border-left:solid }
    95      table td, table th { border-left:solid; border-right:solid; border-bottom:solid thin; vertical-align:top; padding:0.2em }
    96     </style>
    97     <script type="text/javascript"
    98           class="remove">
    99 // RESPEC DEFINITIONS STYLE OVERLOAD
   100         window.addEventListener('load', function() {
   101           var overrideStyleEl = document.createElement('style');
   102           overrideStyleEl.textContent += "\n  a.externalDFN { color: #00C; border-bottom: 1px dashed #00C; }";
   103           overrideStyleEl.textContent += "\n  a.internalDFN { color: #00C; text-decoration: solid; }";
   104           document.querySelector('body').appendChild(overrideStyleEl);
   105         }, false);
   106     </script>
   107   </head>
   108   <body>
   109     <section id='abstract'>
   110       <p>
   111         This specification defines a mechanism for an HTML document to discover and subsequently communicate with
   112         <abbr title="Hypertext Transfer Protocol">HTTP</abbr>-based services advertised via common discovery protocols
   113         within the current network.
   114       </p>
   115     </section>
   116     <section id='sotd'>
   117       <p>
   118         This document represents the early consensus of the group on the scope and features of the proposed API.
   119       </p>
   120     </section>
   121     <section class="informative">
   122       <h3>
   123         Introduction
   124       </h3>
   125       <p>
   126         To enable Web pages to connect and communicate with Local-networked Services provided over HTTP, this
   127         specification introduces the <a href="#navigatornetworkservice"><code>NavigatorNetworkService</code></a>
   128         interface.
   129       </p>
   130       <p>
   131         Using this <abbr title="Application Programming Interface">API</abbr> consists of requesting a well-known
   132         service type, known by developers and advertised by Local-networked Devices. User authorization, where the user
   133         connects the web page to discovered services, is expected before the web page is able to interact with any
   134         Local-networked Services.
   135       </p>
   136       <p>
   137         A web page creates a request to obtain connectivity to services running in the network by specifying a
   138         well-known discovery service type that it wishes to interact with.
   139       </p>
   140       <p>
   141         The user agent, having captured all advertised services on the network from the <a>service discovery
   142         mechanisms</a> included in this recommendation, attempts to match the requested service type to a discovered
   143         service according to the processing described herein.
   144       </p>
   145       <p>
   146         If a service connectivity request is successful then the Web page is provided with a promise-based success
   147         callback with the all necessary information to communicate with the authorized Local-networked Service. If the
   148         request fails then the Web page will receive a promise-based error callback containing an error code describing
   149         the cause of Local-networked Service connectivity failure.
   150       </p>
   151       <p>
   152         Once connected to a Local-networked Service the Web page can send requests and receive responses to the
   153         Local-networked Service via the messaging format and appropriate channel inferred from the service type
   154         authorized via the provided API. The Web page, once connected, can also receive service-pushed events, in the
   155         messaging format supported by the Local-networked Device, if such event subscription functionality is provided
   156         by the connected Local-networked Service.
   157       </p>
   158       <p>
   159         Services available within the local network can connect and disconnect at different times during the execution
   160         of a web page. The user agent can inform a web page when the state of networked services matching any of the
   161         requested valid service types change. Web pages can use this information to enable in-page experiences for
   162         communicating the state of networked services with the ability to change the particular service or set of
   163         services the page is connected to (by re-invoking the <a href=
   164         "#dom-navigator-getnetworkservices"><code>getNetworkServices()</code></a> method defined herein).
   165       </p>
   166       <div class="example">
   167         <p>
   168           Example of requesting a DNS-SD advertised service:
   169         </p>
   170         <hr>
   171         <pre class="highlight">
   172 function showServices( services ) {
   173   // Show a list of all the services provided to the web page
   174   for(var i = 0, l = services.length; i &lt; l; i++) console.log( services[i].name );
   175 }
   176 
   177 navigator.getNetworkServices('zeroconf:_boxee-jsonrpc._tcp').then(showServices);
   178 </pre>
   179       </div>
   180       <div class="example">
   181         <p>
   182           Example of requesting a UPnP advertised service, also handling error conditions:
   183         </p>
   184         <hr>
   185         <pre class="highlight">
   186 function showServices( services ) {
   187   // Show a list of all the services provided to the web page
   188   for(var i = 0, l = services.length; i &lt; l; i++) console.log( services[i].name );
   189 }
   190 
   191 function error( e ) {
   192   console.log( "Error occurred: " + e.code );
   193 }
   194 
   195 navigator.getNetworkServices('upnp:urn:schemas-upnp-org:service:ContentDirectory:1').then(showServices, error);
   196 </pre>
   197       </div>
   198       <div class="example">
   199         <p>
   200           Example of requesting either a DNS-SD or UPnP advertised service:
   201         </p>
   202         <hr>
   203         <pre class="highlight">
   204 function showServices( services ) {
   205   // Show a list of all the services provided to the web page (+ service type)
   206   for(var i = 0, l = services.length; i &lt; l; i++)
   207      console.log( services[i].name + '(' + services[i].type + ')' );
   208 }
   209 
   210 navigator.getNetworkServices([
   211   'zeroconf:_boxee-jsonrpc._tcp',
   212   'upnp:urn:schemas-upnp-org:service:ContentDirectory:1'
   213 ]).then(showServices);
   214 </pre>
   215       </div>
   216       <p>
   217         For more detailed examples, including examples of communicating with obtained networked services, see the
   218         <a href="#examples">Examples</a> section.
   219       </p>
   220     </section>
   221     <section id='conformance'>
   222       <p>
   223         Requirements phrased in the imperative as part of algorithms (such as "strip any leading space characters" or
   224         "return false and abort these steps") are to be interpreted with the meaning of the key word ("must", "should",
   225         "may", etc) used in introducing the algorithm.
   226       </p>
   227       <p>
   228         Some conformance requirements are phrased as requirements on attributes, methods or objects. Such requirements
   229         are to be interpreted as requirements on user agents.
   230       </p>
   231       <p>
   232         Conformance requirements phrased as algorithms or specific steps MAY be implemented in any manner, so long as
   233         the end result is equivalent. (In particular, the algorithms defined in this specification are intended to be
   234         easy to follow, and not intended to be performant.)
   235       </p>
   236       <p>
   237         The only conformance class defined by this specification is a <dfn>user agent</dfn>.
   238       </p>
   239       <p>
   240         User agents MAY impose implementation-specific limits on otherwise unconstrained inputs, e.g. to prevent denial
   241         of service attacks, to guard against running out of memory, or to work around platform-specific limitations.
   242       </p>
   243       <p>
   244         When support for a feature is disabled (e.g. as an emergency measure to mitigate a security problem, or to aid
   245         in development, or for performance reasons), user agents MUST act as if they had no support for the feature
   246         whatsoever, and as if the feature was not mentioned in this specification. For example, if a particular feature
   247         is accessed via an attribute in a Web IDL interface, the attribute itself would be omitted from the objects
   248         that implement that interface - leaving the attribute on the object but making it return null or throw an
   249         exception is insufficient.
   250       </p>
   251       <section>
   252         <h3>
   253           Dependencies
   254         </h3>This specification relies on several other underlying specifications.
   255         <dl>
   256           <dt>
   257             HTML
   258           </dt>
   259           <dd>
   260             Many fundamental concepts from HTML are used by this specification. [[!HTML5]]
   261           </dd>
   262           <dt>
   263             WebIDL
   264           </dt>
   265           <dd>
   266             The IDL blocks in this specification use the semantics of the WebIDL specification. [[!WEBIDL]]
   267           </dd>
   268         </dl>
   269       </section>
   270     </section>
   271     <section>
   272       <h3>
   273         Terminology
   274       </h3>
   275       <p>
   276         The construction "a <code>Foo</code> object", where <code>Foo</code> is actually an interface, is sometimes
   277         used instead of the more accurate "an object implementing the interface <code>Foo</code>".
   278       </p>
   279       <p>
   280         The term DOM is used to refer to the API set made available to scripts in Web applications, and does not
   281         necessarily imply the existence of an actual <code>Document</code> object or of any other <code>Node</code>
   282         objects as defined in the DOM Core specifications. [[!DOM4]]
   283       </p>
   284       <p>
   285         An IDL attribute is said to be <em>getting</em> when its value is being retrieved (e.g. by author script), and
   286         is said to be <em>setting</em> when a new value is assigned to it.
   287       </p>
   288       <p>
   289         A <dfn>valid service type</dfn> is any of the following:
   290       </p>
   291       <ul>
   292         <li>a string that begins with <code>upnp:</code> or <code>zeroconf:</code> followed by one or more characters
   293         in the ranges U+0021, U+0023 to U+0027, U+002A to U+002B, U+002D to U+002E, U+0030 to U+0039, U+0041 to U+005A,
   294         U+005E to U+007E.
   295         </li>
   296         <li>a string that begins with <code>dial:</code> followed by an integer version.
   297         </li>
   298       </ul>
   299       <p>
   300         A <a>valid service type</a> provided in the <code>type</code> attribute of the <a href=
   301         "#dom-navigator-getnetworkservices"><code>getNetworkServices()</code></a> method will be matched against the
   302         services currently contained in the <a>list of available service records</a> according to the algorithms
   303         defined in this specification.
   304       </p>
   305       <p>
   306         A <dfn>user-agent generated callback url</dfn> is a Local-network accessible URL endpoint that a <a>user
   307         agent</a> generates and maintains for receiving HTTP NOTIFY requests from UPnP Event sources. It is only
   308         required when the user agent implements UPnP Service Discovery as defined in this specification.
   309       </p>
   310       <p>
   311         In this specification we use the following terms to describe the processes required for Local-networked
   312         Services management:
   313       </p>
   314       <ul>
   315         <li>A <dfn>new service</dfn> is a Local-networked Service that has not previously been discovered or registered
   316         in the <a>list of available service records</a>.
   317         </li>
   318         <li>An <dfn>existing service</dfn> is a Local-networked Service that has previously been discovered and is
   319         registered in the <a>list of available service records</a>.
   320         </li>
   321         <li>A <dfn>current service</dfn> is a Local-networked Service, represented by a <a href=
   322         "#networkservice"><code>NetworkService</code></a> object, that is currently being shared with a web page via a
   323         <a href="#networkservices"><code>NetworkServices</code></a> object registered in the <a>list of active service
   324         managers</a>.
   325         </li>
   326       </ul>
   327     </section>
   328     <section>
   329       <h2>
   330         Security and privacy considerations
   331       </h2>
   332       <p>
   333         The API defined in this specification can be used to find and connect to devices and services within a user's
   334         current network. This discloses information related to a user's network: devices available on their network and
   335         the publicly-accessible services ("networked services") currently running and available on those devices. The
   336         distribution of this information could potentially compromise the user's privacy. A conforming implementation
   337         of this specification MUST provide a mechanism that protects the user's privacy. This mechanism MUST ensure
   338         that no networked service information is retrievable without the user's express permission.
   339       </p>
   340       <section>
   341         <h3>
   342           Privacy considerations for API implementations
   343         </h3>
   344         <p>
   345           A <a>user agent</a> MUST NOT provide networked service information to web sites without the express
   346           permission of the user. A user agent MUST acquire permission through a user interface, unless they have
   347           prearranged trust relationships with users, as described below. The user interface MUST include the document
   348           base URL. Those permissions that are acquired through the user interface and that are preserved beyond the
   349           current browsing session (i.e. beyond the time when the browsing context is navigated to another URL) MUST be
   350           revocable and a user agent MUST respect revoked permissions.
   351         </p>
   352         <p>
   353           Obtaining the user's express permission to access one API method does not imply the user has granted
   354           permission for the same web site to access any other methods that may be provided by this API, or to access
   355           the same method with a different set of arguments, as part of the same permission context. If a user has
   356           expressed permission for an implementation to, e.g. find a set of existing networked services, the
   357           implementation MUST seek the user's express permission if and when any subsequent functions are called on
   358           this API.
   359         </p>
   360         <p>
   361           A user agent MAY have prearranged trust relationships that do not require such user interfaces. For example,
   362           while a web browser will present a user interface when a web site performs a networked service lookup, a
   363           different runtime may have a prearranged, delegated security relationship with the user and, as such, a
   364           suitable alternative security and privacy mechanism with which to authorise the retrieval of networked
   365           service information.
   366         </p>
   367       </section>
   368       <section class="informative">
   369         <h3>
   370           Additional API implementation considerations
   371         </h3>
   372         <p>
   373           Further to the requirements listed in the previous section, implementors of the Network Service Discovery API
   374           are also advised to consider the following aspects that can negatively affect the privacy of their users: in
   375           certain cases, users can inadvertently grant permission to the user agent to disclose networked services to
   376           Web sites. In other cases, the content hosted at a certain URL changes in such a way that previously granted
   377           networked service permissions no longer apply as far as the user is concerned. Or the users might simply
   378           change their minds.
   379         </p>
   380         <p>
   381           Predicting or preventing these situations is inherently difficult. Mitigation and in-depth defensive measures
   382           are an implementation responsibility and not prescribed by this specification. However, in designing these
   383           measures, implementers are advised to enable user awareness of networked service sharing, and to provide easy
   384           access to interfaces that enable revocation of permissions that web applications have for accessing networked
   385           services via this API.
   386         </p>
   387       </section>
   388     </section>
   389     <section>
   390       <h2>
   391         Requesting networked services
   392       </h2>
   393       <pre class="widl">
   394 [Supplemental, NoInterfaceObject]
   395 interface <dfn id="navigatornetworkservice">NavigatorNetworkService</dfn> {
   396   <a class="externalDFN"
   397      href="http://dom.spec.whatwg.org/#promise">Promise</a> <a href=
   398      "#dom-navigator-getnetworkservices">getNetworkServices</a>( in any type );
   399 };
   400 <a class="externalDFN"
   401      href=
   402      "http://www.whatwg.org/specs/web-apps/current-work/complete/timers.html#navigator">Navigator</a> implements <a href=
   403      "#navigatornetworkservice">NavigatorNetworkService</a>;
   404 
   405 [NoInterfaceObject]
   406 interface <dfn id="navigatornetworkserviceerror">NavigatorNetworkServiceError</dfn> {
   407   const unsigned short <a href="#dom-navigatornetworkserviceerror-permission_denied">PERMISSION_DENIED_ERR</a> = 1;
   408   const unsigned short <a href="#dom-navigatornetworkserviceerror-unknown_type_prefix">UNKNOWN_TYPE_PREFIX_ERR</a> = 2;
   409   readonly attribute unsigned short <a href="#dom-navigatornetworkserviceerror-code">code</a>;
   410 };
   411 </pre>
   412       <section>
   413         <h2>
   414           Methods
   415         </h2>
   416         <dl class="domintro">
   417           <dt>
   418             <var title="">promise</var> = <var title="">window</var> . <code title="dom-navigator"><a href=
   419             "http://www.whatwg.org/specs/web-apps/current-work/complete/timers.html#navigator">navigator</a></code> .
   420             <code title="dom-navigator-getNetworkServices"><a href=
   421             "#dom-navigator-getnetworkservices">getNetworkServices</a></code> ( <var title="">type</var> )
   422           </dt>
   423           <dd>
   424             <p>
   425               Immediately returns a new <a href="http://dom.spec.whatwg.org/#promise"
   426                  class="externalDFN">Promise</a> object and then the user is prompted to select discovered network
   427                  services that have advertised support for the requested service type(s).
   428             </p>
   429             <p>
   430               The <var title="">type</var> argument contains one or more <a>valid service type</a> tokens that the web
   431               page would like to interact with.
   432             </p>
   433             <p>
   434               If the user accepts, the <var title="">promise</var> object is <a class="externalDFN"
   435                  href="http://dom.spec.whatwg.org/#concept-resolver-resolve">resolved</a>, with a <a href=
   436                  "#networkservices"><code>NetworkServices</code></a> object as its argument.
   437             </p>
   438             <p>
   439               If the user declines, or an error occurs, the <var title="">promise</var> object is <a class=
   440               "externalDFN"
   441                  href="http://dom.spec.whatwg.org/#concept-resolver-reject">rejected</a>.
   442             </p>
   443           </dd>
   444         </dl>
   445         <div>
   446           <p>
   447             When the <dfn id="dom-navigator-getnetworkservices"
   448                title="dom-navigator-getnetworkservices"><code>getNetworkServices(type)</code></dfn> method is called,
   449                the <a>user agent</a> MUST run the following steps:
   450           </p>
   451           <ol class="rule">
   452             <li>Let <var>Network Service Promise</var> be a new <a href="http://dom.spec.whatwg.org/#promise"
   453                   class="externalDFN"><code>Promise</code></a> object.
   454             </li>
   455             <li>Let <var>Network Service Promise's Resolver</var> be the default <a href=
   456             "http://dom.spec.whatwg.org/#concept-resolver"
   457                   class="externalDFN">resolver</a> of <var>Network Service Promise</var>.
   458             </li>
   459             <li>Return <var>Network Service Promise</var>, and run the remaining steps asynchronously.
   460             </li>
   461             <li>Let <var>requested control types</var> be initially set to an empty array.
   462             </li>
   463             <li>If <var>type</var> is an array consisting of one or more <a>valid service type</a> tokens, then let
   464             <var>requested control types</var> by the value of <var>type</var>, removing any non-<a>valid service
   465             type</a> tokens from the resulting array.
   466             </li>
   467             <li>If <var>type</var> is a string consisting of one <a>valid service type</a> token, then let
   468             <var>requested control types</var> be an array containing one item with a value of <var>type</var>.
   469             </li>
   470             <li>If <var>requested control types</var> is an array that contains at least one or more <a title=
   471             "valid service type">valid service type</a> tokens then continue to the step labeled <em>process</em>
   472             below. Otherwise, reject <var>Network Service Promise</var> by running the <a href=
   473             "http://dom.spec.whatwg.org/#concept-resolver-reject"
   474                   class="externalDFN">resolver reject algorithm</a> against the <var>Network Service Promise's
   475                   Resolver</var>, passing in a new <a href=
   476                   "#navigatornetworkserviceerror"><code>NavigatorNetworkServiceError</code></a> object whose <a href=
   477                   "#dom-navigatornetworkserviceerror-code"><code>code</code></a> attribute has the numeric value 2
   478                   (<a href=
   479                   "#dom-navigatornetworkserviceerror-unknown_type_prefix"><code>UNKNOWN_TYPE_PREFIX_ERR</code></a>) as
   480                   its argument, abort any remaining steps and return.
   481             </li>
   482             <li>
   483               <em>Process</em>: Let <var>services found</var> be an empty array.
   484             </li>
   485             <li>For each <var>available service</var> in the <a>list of available service records</a> run the following
   486             steps:
   487               <ol class="rule">
   488                 <li>For each <var>requested control type</var> in <var>requested control types</var>: If <var>available
   489                 service</var>'s <code>type</code> attribute equals the <var>requested control type</var> then let <var>
   490                   matched service</var> equal the value of <var>available service</var> and continue at the step
   491                   labeled <var>attach</var> below.
   492                 </li>
   493                 <li>Continue at the next <var>available service</var>.
   494                 </li>
   495                 <li>
   496                   <em>Attach</em>: If <var>matched service</var> is not empty then run the following steps:
   497                   <ol class="rule">
   498                     <li>Let <var>new service object</var> be a new <a href=
   499                     "#networkservice"><code>NetworkService</code></a> object, mapping the parameters of <var>matched
   500                     service</var> to this new object where possible.
   501                     </li>
   502                     <li>Append <var>new service object</var> to the <var>services found</var> array.
   503                     </li>
   504                   </ol>
   505                 </li>
   506               </ol>
   507             </li>
   508             <li>Optionally, e.g. based on a previously-established user preference, for security reasons, or due to
   509             platform limitations, the <a>user agent</a> MAY reject <var>Network Service Promise</var> by running the
   510             <a href="http://dom.spec.whatwg.org/#concept-resolver-reject"
   511                   class="externalDFN">resolver reject algorithm</a> against the <var>Network Service Promise's
   512                   Resolver</var>, passing in a new <a href=
   513                   "#navigatornetworkserviceerror"><code>NavigatorNetworkServiceError</code></a> object whose <a href=
   514                   "#dom-navigatornetworkserviceerror-code"><code>code</code></a> attribute has the numeric value 1
   515                   (<a href=
   516                   "#dom-navigatornetworkserviceerror-permission_denied"><code>PERMISSION_DENIED_ERR</code></a>) as its
   517                   argument, abort any remaining steps and return.
   518             </li>
   519             <li>The user agent MUST NOT provide the entry script's origin with a <a href=
   520             "#networkservices"><code>NetworkServices</code></a> object without prior permission given by the user.
   521               <p>
   522                 If <var>services found</var> is not an empty array then the <a>user agent</a> MAY choose to prompt the
   523                 user in a user-agent-specific manner for permission to provide the <a href=
   524                 "http://www.whatwg.org/specs/web-apps/current-work/complete/browsers.html#entry-script"
   525                    class="externalDFN">entry script</a>'s <a href=
   526                    "http://www.whatwg.org/specs/web-apps/current-work/complete/origin-0.html#origin"
   527                    class="externalDFN">origin</a> with a <a href="#networkservices"><code>NetworkServices</code></a>
   528                    object representing the <a>user-authorized</a> subset of <var>services found</var>.
   529               </p>
   530               <p>
   531                 Alternatively, the user agent MAY wish to skip this user opt-in step and choose to fulfill <var>Network
   532                 Service Promise</var> immediately based on a previously-established user preference, for security
   533                 reasons, or due to platform limitations. In such an implementation, if <var>Network Service
   534                 Promise</var> is to be fulfilled as a result of a previously-established user preference then the
   535                 <a>user agent</a> MUST continue at the next step of this algorithm.
   536               </p>
   537               <p>
   538                 If permission has been granted by the user to access one or more networked services then the <a>user
   539                 agent</a> SHOULD include an "ongoing local-network communication" indicator.
   540               </p>
   541               <p>
   542                 If permission has been denied by the user, <a>user agent</a> or platform, then the <a>user agent</a>
   543                 MUST reject <var>Network Service Promise</var> by running the <a href=
   544                 "http://dom.spec.whatwg.org/#concept-resolver-reject"
   545                    class="externalDFN">resolver reject algorithm</a> against the <var>Network Service Promise's
   546                    Resolver</var>, passing in a new <a href=
   547                    "#navigatornetworkserviceerror"><code>NavigatorNetworkServiceError</code></a> object whose <a href=
   548                    "#dom-navigatornetworkserviceerror-code"><code>code</code></a> attribute has the numeric value 1
   549                    (<a href=
   550                    "#dom-navigatornetworkserviceerror-permission_denied"><code>PERMISSION_DENIED_ERR</code></a>) as its
   551                    argument, abort any remaining steps and return.
   552               </p>
   553               <p>
   554                 If the user never responds or no previously-established user preference has been met, this algorithm
   555                 stalls on this step.
   556               </p>
   557             </li>
   558             <li>Let <var>services</var> be an empty array.
   559             </li>
   560             <li>If <var>services found</var> is not an empty array then set <var>services</var> to be an array of one
   561             or more <a href="#networkservice"><code>NetworkService</code></a> objects for which the user granted
   562             permission above - known as the current objects <dfn>user-authorized</dfn> services.
   563             </li>
   564             <li>Remove all previously whitelisted urls from the <a>entry script origin's URL whitelist</a> granted in
   565             the current <a href="http://www.whatwg.org/specs/web-apps/current-work/complete/browsers.html#entry-script"
   566                   class="externalDFN">entry script</a>'s <a href=
   567                   "http://www.whatwg.org/specs/web-apps/current-work/complete/origin-0.html#origin"
   568                   class="externalDFN">origin</a>.
   569             </li>
   570             <li>For each Object <var>service</var> in <var>services</var>, if any, run the following sub-steps:
   571               <ol class="rule">
   572                 <li>Add the <var>service</var>'s <code>url</code> parameter to the <a>entry script origin's
   573                   <abbr title="Uniform Resource Locator">URL</abbr> whitelist</a>.
   574                 </li>
   575                 <li>If <var>service</var>'s <code>type</code> parameter begins with the DOMString "<code>upnp:</code>"
   576                 and the <var>service</var>'s <code>eventsUrl</code> parameter is not empty then <a>setup a UPnP Events
   577                 Subscription</a> for <var>service</var>.
   578                 </li>
   579               </ol>
   580             </li>
   581             <li>Let <var>services manager</var> be a new <a href="#networkservices"><code>NetworkServices</code></a>
   582             object.
   583             </li>
   584             <li>Store <var>requested control types</var> against <var>services manager</var> as an internal variable.
   585             </li>
   586             <li>Set <var>services manager</var>'s <a href=
   587             "#dom-networkservices-servicesavailable"><code>servicesAvailable</code></a> attribute to the number of
   588             items currently found in the <a>list of available service records</a> whose <code>type</code> property
   589             matches any of the tokens requested in <var>requested control types</var>.
   590             </li>
   591             <li>Add <var>services</var>, if any, to the <var>services manager</var> object as its collection of
   592             <a>indexed properties</a>. If <var>services</var> is an empty array then the <var>services manager</var>
   593             does not have any <var>indexed properties</var>.
   594             </li>
   595             <li>Set <var>services manager</var>'s <a href="#dom-networkservices-length"><code>length</code></a>
   596             attribute to the number of items in <var>services</var>.
   597             </li>
   598             <li>Add <var>services manager</var> to the <a>list of active service managers</a>.
   599             </li>
   600             <li>The <a>user agent</a> MUST fulfill <var>Network Service Promise</var> by running the <a href=
   601             "http://dom.spec.whatwg.org/#concept-resolver-fulfill"
   602                   class="externalDFN">resolver fulfill algorithm</a> against the <var>Network Service Promise's
   603                   Resolver</var>, passing in <var>services manager</var> as its argument.
   604             </li>
   605           </ol>
   606           <p>
   607             The <a href="http://www.whatwg.org/specs/web-apps/current-work/complete/webappapis.html#task-source"
   608                class="externalDFN">task source</a> for these <a href=
   609                "http://www.whatwg.org/specs/web-apps/current-work/complete/webappapis.html#concept-task"
   610                class="externalDFN">tasks</a> is the <a href=
   611                "http://www.whatwg.org/specs/web-apps/current-work/complete/webappapis.html#user-interaction-task-source"
   612                class="externalDFN">user interaction task source</a>.
   613           </p>
   614           <p>
   615             When a <a href="#networkservice"><code>NetworkService</code></a> object is provided to a Web page, the
   616             <a>user agent</a> MUST add its <a href="#dom-networkservice-url"><code>url</code></a> to the <dfn>entry
   617             script origin's URL whitelist</dfn>. This list enables the Web page to override and initiate cross-site
   618             resource requests towards these URLs, and any sub-resources of these URLs, within the current <a href=
   619             "http://www.whatwg.org/specs/web-apps/current-work/complete/browsers.html#entry-script"
   620                class="externalDFN">entry script</a>'s <a href=
   621                "http://www.whatwg.org/specs/web-apps/current-work/complete/origin-0.html#origin"
   622                class="externalDFN">origin</a> via various existing mechanisms (e.g. Web Sockets, Server-Sent Events,
   623                Web Messaging, XMLHttpRequest).
   624           </p>
   625           <p>
   626             If the user navigates away from the <a href=
   627             "http://www.whatwg.org/specs/web-apps/current-work/complete/browsers.html#entry-script"
   628                class="externalDFN">entry script</a>'s <a href=
   629                "http://www.whatwg.org/specs/web-apps/current-work/complete/origin-0.html#origin"
   630                class="externalDFN">origin</a> or permission to access a given networked service is revoked at any time
   631                by the platform or user then the <a>user agent</a> <em class="ct">MUST</em> remove its previously
   632                whitelisted urls from the <a>entry script origin's URL whitelist</a>.
   633           </p>
   634           <p>
   635             There is no implied persistence to networked service sharing provided to a web page. It MUST NOT be
   636             possible to access a previously white-listed networked service without user authorization in all of the
   637             following cases:
   638           </p>
   639           <ul>
   640             <li>If the current script is reloaded at any point in the same or different window.
   641             </li>
   642             <li>if the current script reinvokes the <a href=
   643             "#dom-navigator-getnetworkservices"><code>getNetworkServices()</code></a> method at any point in its
   644             execution.
   645             </li>
   646             <li>If the user navigates forward or back in their history to reload the current page.
   647             </li>
   648             <li>If a script is running in a different origin.
   649             </li>
   650           </ul>
   651         </div>
   652       </section>
   653       <section>
   654         <h3>
   655           Error Handling
   656         </h3>
   657         <dl class="domintro">
   658           <dt>
   659             <var title="">error</var> . <code title="dom-NavigatorNetworkServiceError-code"><a href=
   660             "#dom-navigatornetworkserviceerror-code">code</a></code>
   661           </dt>
   662           <dd>
   663             <p>
   664               Returns the current error's error code. At the current time, this will be <code>1</code> or
   665               <code>2</code>, for which the corresponding error constants <a href=
   666               "#dom-navigatornetworkserviceerror-permission_denied"><code>PERMISSION_DENIED_ERR</code></a> and <a href=
   667               "#dom-navigatornetworkserviceerror-unknown_type_prefix"><code>UNKNOWN_TYPE_PREFIX_ERR</code></a> are
   668               defined.
   669             </p>
   670           </dd>
   671         </dl>
   672         <p>
   673           The <dfn id="dom-navigatornetworkserviceerror-code"
   674              title="dom-navigatornetworkserviceerror-code"><code>code</code></dfn> attribute of a <a href=
   675              "#navigatornetworkserviceerror"><code>NavigatorNetworkServiceError</code></a> object <em class=
   676              "ct">MUST</em> return the code for the error, which will be one of the following:
   677         </p>
   678         <dl>
   679           <dt>
   680             <dfn id="dom-navigatornetworkserviceerror-permission_denied"
   681                 title="dom-navigatornetworkserviceerror-permission_denied"><code>PERMISSION_DENIED_ERR</code></dfn>
   682                 (numeric value 1)
   683           </dt>
   684           <dd>
   685             The user or user agent denied the page permission to access any services.
   686           </dd>
   687           <dt>
   688             <dfn id="dom-navigatornetworkserviceerror-unknown_type_prefix"
   689                 title="dom-navigatornetworkserviceerror-unknown_type_prefix"><code>UNKNOWN_TYPE_PREFIX_ERR</code></dfn>
   690                 (numeric value 2)
   691           </dt>
   692           <dd>
   693             No <a>valid service type</a> tokens were provided in the method invocation.
   694           </dd>
   695         </dl>
   696       </section>
   697     </section>
   698     <section>
   699       <h2>
   700         Obtaining networked services
   701       </h2>
   702       <p>
   703         The <a href="#networkservices"><code>NetworkServices</code></a> interface represents a collection of zero or
   704         more <dfn>indexed properties</dfn> that are each a <a>user-authorized</a> <a href=
   705         "#networkservice"><code>NetworkService</code></a> object.
   706       </p>
   707       <p>
   708         A <a href="#networkservices"><code>NetworkServices</code></a> object is the <a href=
   709         "http://dom.spec.whatwg.org/#concept-promise-result"
   710            class="externalDFN">promise result</a> from a call to <a href=
   711            "#dom-navigator-getnetworkservices"><code>getNetworkServices()</code></a>.
   712       </p>
   713       <pre class="widl">
   714 [NoInterfaceObject]
   715 interface <dfn id="networkservices">NetworkServices</dfn> {
   716   readonly attribute unsigned long    <a href="#dom-networkservices-length">length</a>;
   717   getter <a href="#networkservice">NetworkService</a> (unsigned long index);
   718   <a href="#networkservice">NetworkService</a>? <a href=
   719 "#dom-networkservices-getservicebyid">getServiceById</a>(DOMString id);
   720 
   721   readonly attribute unsigned long    <a href="#dom-networkservices-servicesavailable">servicesAvailable</a>;
   722 
   723   // event handler attributes
   724            attribute <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/webappapis.html#eventhandler"
   725      class="externalDFN">EventHandler</a>     <a href="#dom-networkservices-onserviceavailable">onserviceavailable</a>;
   726            attribute <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/webappapis.html#eventhandler"
   727      class="externalDFN">EventHandler</a>     <a href=
   728      "#dom-networkservices-onserviceunavailable">onserviceunavailable</a>;
   729 
   730 };
   731 
   732 <a href="#networkservices">NetworkServices</a> implements <a href=
   733 "http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#interface-eventtarget"
   734      class="externalDFN">EventTarget</a>;
   735 </pre>
   736       <section>
   737         <h2>
   738           Attributes
   739         </h2>
   740         <dl class="domintro">
   741           <dt>
   742             <code title="dom-networkservices-length"><a href="#dom-networkservices-length">length</a></code>
   743           </dt>
   744           <dd>
   745             <p>
   746               Returns the current number of <a>indexed properties</a> in the current object's collection.
   747             </p>
   748           </dd>
   749           <dt>
   750             <code title="dom-networkservices-servicesavailable"><a href=
   751             "#dom-networkservices-servicesavailable">servicesAvailable</a></code>
   752           </dt>
   753           <dd>
   754             <p>
   755               Returns the current number of items matching one of the app-requested <a>valid service type</a> tokens in
   756               the <a>list of available service records</a>.
   757             </p>
   758           </dd>
   759         </dl>
   760         <div>
   761           <p>
   762             The <dfn id="dom-networkservices-length"><code>length</code></dfn> attribute MUST return the number of
   763             <a href="#networkservice"><code>NetworkService</code></a> objects represented by the collection.
   764           </p>
   765           <p>
   766             The <dfn id="dom-networkservices-servicesavailable"><code>servicesAvailable</code></dfn> attribute MUST
   767             return the number of services in the <a>list of available service records</a> whose <code>type</code>
   768             attribute matches any of the <a>valid service type</a> tokens that were initially used to create the
   769             current <a href="#networkservices"><code>NetworkServices</code></a> object.
   770           </p>
   771         </div>
   772       </section>
   773       <section>
   774         <h2>
   775           Methods
   776         </h2>
   777         <dl class="domintro">
   778           <dt>
   779             <code title="networkservices-getter"><a href="#networkservices">services</a></code> [ <var title=
   780             "">index</var> ]
   781           </dt>
   782           <dd>
   783             <p>
   784               Returns the specified <a href="#networkservice"><code>NetworkService</code></a> object.
   785             </p>
   786           </dd>
   787           <dt>
   788             <code title="networkservices-getter"><a href="#networkservices">services</a></code> . <code title=
   789             "dom-networkservices-getservicebyid"><a href=
   790             "#dom-networkservices-getservicebyid">getServiceById</a></code> ( <var title="">id</var> )
   791           </dt>
   792           <dd>
   793             <p>
   794               Returns the <a href="#networkservice"><code>NetworkService</code></a> object with the given identifier,
   795               or null if no service has that identifier.
   796             </p>
   797           </dd>
   798         </dl>
   799         <p>
   800           A <a href="#networkservices"><code>NetworkServices</code></a> object represents the current collection of
   801           zero or more <a href="#networkservice"><code>NetworkService</code></a> objects - its <a>indexed
   802           properties</a>. The <a>indexed properties</a> of a <a href=
   803           "#networkservices"><code>NetworkServices</code></a> object are <span>immutable</span> meaning that <a>indexed
   804           properties</a> cannot be added and <a>indexed properties</a> cannot be removed for the lifetime of a <a href=
   805           "#networkservices"><code>NetworkServices</code></a> object.
   806         </p>
   807         <p>
   808           The <a href=
   809           "http://www.whatwg.org/specs/web-apps/current-work/multipage/infrastructure.html#supported-property-indices"
   810              class="externalDFN">supported property indices</a> of <a href=
   811              "#networkservices"><code>NetworkServices</code></a> objects at any instant are the numbers from zero to
   812              the number of the <a href="#networkservice"><code>NetworkService</code></a> objects in the collection
   813              minus one.
   814         </p>
   815         <p class="note">
   816           Each service in a <a href="#networkservices"><code>NetworkServices</code></a> object thus has an index; the
   817           first has the index 0, and each subsequent service is numbered one higher than the previous one.
   818         </p>
   819         <p>
   820           To <a href=
   821           "http://www.whatwg.org/specs/web-apps/current-work/multipage/infrastructure.html#determine-the-value-of-an-indexed-property"
   822              class="externalDFN">determine the value of an indexed property</a> for a given index <var>index</var> in a
   823              <a href="#networkservices"><code>NetworkServices</code></a> object the user agent MUST return the <a href=
   824              "#networkservice"><code>NetworkService</code></a> object that represents the <var>index</var>th item in
   825              the collection.
   826         </p>
   827         <p>
   828           The <dfn id="dom-networkservices-getservicebyid"><code>getServiceById(id)</code></dfn> method <em class=
   829           "ct">MUST</em> return the first <a href="#networkservice"><code>NetworkService</code></a> object in the
   830           collection whose <a href="#dom-networkservice-id"><code>id</code></a> attribute is equal to the value of the
   831           <var>id</var> argument provided. When no <a href="#networkservice"><code>NetworkService</code></a> objects
   832           match the given argument, the method MUST return null.
   833         </p>
   834       </section>
   835       <section>
   836         <h2>
   837           Events
   838         </h2>
   839         <p>
   840           The following are the event handlers (and their corresponding event handler event types) that <em class=
   841           "ct">MUST</em> be supported, as IDL attributes, by all objects implementing the <a href=
   842           "#networkservices"><code>NetworkServices</code></a> interface:
   843         </p>
   844         <table border="1">
   845           <thead>
   846             <tr>
   847               <th>
   848                 <span title="event handlers">Event handler</span>
   849               </th>
   850               <th>
   851                 <span>Event handler event type</span>
   852               </th>
   853             </tr>
   854           </thead>
   855           <tbody>
   856             <tr>
   857               <td>
   858                 <dfn id="dom-networkservices-onserviceavailable"
   859                     title="dom-NetworkServices-onserviceavailable"><code>onserviceavailable</code></dfn>
   860               </td>
   861               <td>
   862                 <a href="#event-serviceavailable"><code>serviceavailable</code></a>
   863               </td>
   864             </tr>
   865             <tr>
   866               <td>
   867                 <dfn id="dom-networkservices-onserviceunavailable"
   868                     title="dom-NetworkServices-onserviceunavailable"><code>onserviceunavailable</code></dfn>
   869               </td>
   870               <td>
   871                 <a href="#event-serviceunavailable"><code>serviceunavailable</code></a>
   872               </td>
   873             </tr>
   874           </tbody>
   875         </table>
   876       </section>
   877     </section>
   878     <section>
   879       <h2>
   880         Communicating with a networked service
   881       </h2>
   882       <p>
   883         The <a href="#networkservice"><code>NetworkService</code></a> interface is used to provide a set of connection
   884         information for an HTTP service endpoint and if available, service events, running on a networked device.
   885       </p>
   886       <pre class="widl">
   887 [NoInterfaceObject]
   888 interface <dfn id="networkservice">NetworkService</dfn> {
   889   readonly attribute DOMString        <a href="#dom-networkservice-id">id</a>;
   890   readonly attribute DOMString        <a href="#dom-networkservice-name">name</a>;
   891   readonly attribute DOMString        <a href="#dom-networkservice-type">type</a>;
   892   readonly attribute DOMString        <a href="#dom-networkservice-url">url</a>;
   893   readonly attribute DOMString        <a href="#dom-networkservice-config">config</a>;
   894 
   895   readonly attribute boolean          <a href="#dom-networkservice-online">online</a>;
   896 
   897   // event handler attributes
   898            attribute <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/webappapis.html#eventhandler"
   899      class="externalDFN">EventHandler</a>     <a href="#dom-networkservice-onserviceonline">onserviceonline</a>;
   900            attribute <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/webappapis.html#eventhandler"
   901      class="externalDFN">EventHandler</a>     <a href="#dom-networkservice-onserviceoffline">onserviceoffline</a>;
   902 
   903            attribute <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/webappapis.html#eventhandler"
   904      class="externalDFN">EventHandler</a>     <a href="#dom-networkservice-onnotify">onnotify</a>;
   905 };
   906 
   907 <a href="#networkservice">NetworkService</a> implements <a href=
   908 "http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#interface-eventtarget"
   909      class="externalDFN">EventTarget</a>;
   910 </pre>
   911       <section>
   912         <h2>
   913           Attributes
   914         </h2>
   915         <dl class="domintro">
   916           <dt>
   917             <var title="">service</var> . <code title="dom-networkservice-id"><a href=
   918             "#dom-networkservice-id">id</a></code>
   919           </dt>
   920           <dd>
   921             <p>
   922               A unique identifier for the given user-selected service instance.
   923             </p>
   924           </dd>
   925           <dt>
   926             <var title="">service</var> . <code title="dom-networkservice-name"><a href=
   927             "#dom-networkservice-name">name</a></code>
   928           </dt>
   929           <dd>
   930             <p>
   931               The name of the user-selected service.
   932             </p>
   933           </dd>
   934           <dt>
   935             <var title="">service</var> . <code title="dom-networkservice-type"><a href=
   936             "#dom-networkservice-type">type</a></code>
   937           </dt>
   938           <dd>
   939             <p>
   940               The <a>valid service type</a> token value of the user-selected service.
   941             </p>
   942           </dd>
   943           <dt>
   944             <var title="">service</var> . <code title="dom-networkservice-url"><a href=
   945             "#dom-networkservice-url">url</a></code>
   946           </dt>
   947           <dd>
   948             <p>
   949               The control URL endpoint (including any required port information) of the user-selected control service
   950               that has been added to the <a>entry script origin's URL whitelist</a>.
   951             </p>
   952           </dd>
   953           <dt>
   954             <var title="">service</var> . <code title="dom-networkservice-config"><a href=
   955             "#dom-networkservice-config">config</a></code>
   956           </dt>
   957           <dd>
   958             <p>
   959               The configuration information associated with the service depending on the requested service type.
   960             </p>
   961           </dd>
   962         </dl>
   963         <p>
   964           The <dfn id="dom-networkservice-id"><code>id</code></dfn> attribute is a unique identifier for the service.
   965           The same service provided at different times or on different objects MUST have the same <a href=
   966           "#dom-networkservice-id"><code>id</code></a> value.
   967         </p>
   968         <p>
   969           The <dfn id="dom-networkservice-name"><code>name</code></dfn> attribute represents a human-readable title for
   970           the service.
   971         </p>
   972         <p>
   973           The <dfn id="dom-networkservice-type"><code>type</code></dfn> attribute reflects the value of the <a>valid
   974           service type</a> of the service.
   975         </p>
   976         <p>
   977           The <dfn id="dom-networkservice-url"><code>url</code></dfn> attribute is an <a href=
   978           "http://www.w3.org/TR/html5/urls.html#absolute-url"
   979              class="externalDFN">absolute URL</a> pointing to the root HTTP endpoint for the service that has been
   980              added to the <a>entry script origin's URL whitelist</a>. Web pages can subsequently use this value for
   981              implicit cross-document messaging via various existing mechanisms (e.g. Web Sockets, Server-Sent Events,
   982              Web Messaging, XMLHttpRequest).
   983         </p>
   984         <p>
   985           The <dfn id="dom-networkservice-config"><code>config</code></dfn> attribute provides the raw configuration
   986           information extracted from the given network service.
   987         </p>
   988       </section>
   989       <section>
   990         <h3>
   991           States
   992         </h3>
   993         <dl class="domintro">
   994           <dt>
   995             <var title="">service</var> . <code title="dom-networkservice-online"><a href=
   996             "#dom-networkservice-online">online</a></code>
   997           </dt>
   998           <dd>
   999             <p>
  1000               Returns <code>true</code> if the service is reporting that it is accessible on the local network or
  1001               <code>false</code> if the service is no longer accessible (temporarily or permanently) on the local
  1002               network.
  1003             </p>
  1004           </dd>
  1005         </dl>
  1006         <p>
  1007           The <dfn id="dom-networkservice-online"><code>online</code></dfn> attribute indicates whether the service is
  1008           either <var>online</var>, and therefore accessible on the local network, in which case this attribute will
  1009           return <code>true</code> or, <var>offline</var>, and therefore not accessible on the local network, either
  1010           temporarily or permanently, in which case this attribute will return <code>false</code>. This attribute MUST
  1011           default to <code>true</code>.
  1012         </p>
  1013       </section>
  1014       <section>
  1015         <h3>
  1016           Events
  1017         </h3>
  1018         <p>
  1019           The following are the event handlers (and their corresponding event handler event types) that <em class=
  1020           "ct">MUST</em> be supported, as IDL attributes, by all objects implementing the <a href=
  1021           "#networkservice"><code>NetworkService</code></a> interface:
  1022         </p>
  1023         <table border="1">
  1024           <thead>
  1025             <tr>
  1026               <th>
  1027                 <span title="event handlers">Event handler</span>
  1028               </th>
  1029               <th>
  1030                 <span>Event handler event type</span>
  1031               </th>
  1032             </tr>
  1033           </thead>
  1034           <tbody>
  1035             <tr>
  1036               <td>
  1037                 <dfn id="dom-networkservice-onnotify"
  1038                     title="dom-NetworkService-onnotify"><code>onnotify</code></dfn>
  1039               </td>
  1040               <td>
  1041                 <a href="#event-notify"><code>notify</code></a>
  1042               </td>
  1043             </tr>
  1044             <tr>
  1045               <td>
  1046                 <dfn id="dom-networkservice-onserviceonline"
  1047                     title="dom-NetworkService-onserviceonline"><code>onserviceonline</code></dfn>
  1048               </td>
  1049               <td>
  1050                 <a href="#event-serviceonline"><code>serviceonline</code></a>
  1051               </td>
  1052             </tr>
  1053             <tr>
  1054               <td>
  1055                 <dfn id="dom-networkservice-onserviceoffline"
  1056                     title="dom-NetworkService-onserviceoffline"><code>onserviceoffline</code></dfn>
  1057               </td>
  1058               <td>
  1059                 <a href="#event-serviceoffline"><code>serviceoffline</code></a>
  1060               </td>
  1061             </tr>
  1062           </tbody>
  1063         </table>
  1064       </section>
  1065     </section>
  1066     <section>
  1067       <h2>
  1068         Service Discovery
  1069       </h2>
  1070       <p>
  1071         A <a>user agent</a> conforming to this specification MAY implement <abbr title=
  1072         "Simple Service Discovery Protocol">SSDP</abbr> [[!UPNP-DEVICEARCH11]], Zeroconf [[!DNS-SD]] + [[!MDNS]] and/or
  1073         <abbr title="Discovery and Launch Protocol">DIAL</abbr> [<a href=
  1074         "https://sites.google.com/a/dial-multiscreen.org/dial/dial-protocol-specification">DIAL</a>] <dfn>service
  1075         discovery mechanisms</dfn> - the requirements detailed in this section of the specification - to enable Web
  1076         pages to request and connect with HTTP services running on networked devices, discovered via any of these
  1077         mechanisms, through this API. When a <a>user agent</a> implements any of these <a>service discovery
  1078         mechanisms</a>, then it MUST conform to the corresponding algorithms provided in this section of the
  1079         specification.
  1080       </p>
  1081       <p>
  1082         This section presents how the results of these <a>service discovery mechanisms</a> will be matched to requested
  1083         service types, how the user agent stores available and active services and how their properties are applied to
  1084         any resulting <a href="#networkservice"><code>NetworkService</code></a> objects.
  1085       </p>
  1086       <p>
  1087         It is expected that user agents will perform these <a>service discovery mechanisms</a> asynchronously and
  1088         periodically update the <a>list of available service records</a> as required. The timing of any <a>service
  1089         discovery mechanisms</a> is an implementation detail left to the discretion of the implementer (e.g. by
  1090         continuously monitoring the network as a background process or on invocation of this API from a Web page).
  1091       </p>
  1092       <p>
  1093         The <dfn>list of available service records</dfn> is a single dynamic internal lookup table within user agents
  1094         that is used to track all the services that have been discovered and are available in the current network at
  1095         the current time. At any point during the running of any of the <a>service discovery mechanisms</a> then
  1096         existing entries within this table can be updated, entries can be added and entries can be removed as the
  1097         status of networked services changes according to the rules defined in this specification.
  1098       </p>
  1099       <p>
  1100         The <dfn>list of active service managers</dfn> is an internal list within user agents that is used to track all
  1101         <a href="#networkservices"><code>NetworkServices</code></a> objects currently being shared with any web pages
  1102         at the current time within the user agent. Each <a href="#networkservices"><code>NetworkServices</code></a>
  1103         object in the <a>list of active service managers</a> represents a collection of zero or more <a href=
  1104         "#networkservice"><code>NetworkService</code></a> objects - known as its <dfn>indexed properties</dfn>.
  1105         <a href="#networkservice"><code>NetworkService</code></a> objects are attached as the <a>indexed properties</a>
  1106         of a <a href="#networkservices"><code>NetworkServices</code></a> object as part of the <a href=
  1107         "#dom-navigator-getnetworkservices"><code>getNetworkServices()</code></a> algorithm.
  1108       </p>
  1109       <p>
  1110         The rule for <dfn>adding an available service</dfn> is the process of adding a <a>new service</a> or updating
  1111         an <a>existing service</a> that is generally available on the user's current network in the <a>list of
  1112         available service records</a>. This rule takes one argument, <var>network service record</var>, and consists of
  1113         running the following steps:
  1114       </p>
  1115       <ol class="rule">
  1116         <li>For each <var>existing service record</var> in the current <a>list of available service records</a>, run
  1117         the following sub-steps:
  1118           <ol class="rule">
  1119             <li>If the <var>existing service record</var>'s <code>id</code> property does not equal <var>network
  1120             service record</var>'s <code>id</code> property then abort any remaining sub-steps and continue at the next
  1121             available <var>existing service record</var>.
  1122             </li>
  1123             <li>Replace the value of <var>existing service record</var> in the current <a>list of available service
  1124             records</a> with the value of <var>network service record</var>, aborting any remaining steps in this
  1125             algorithm and return.
  1126             </li>
  1127           </ol>
  1128         </li>
  1129         <li>Add <var>network service record</var> to the <a>list of available service records</a> as a new item.
  1130         </li>
  1131         <li>For each <var>service manager</var> in the <a>list of active service managers</a> run the following steps:
  1132           <ol class="rule">
  1133             <li>For each <var>active service</var> in <var>service manager</var> run the following steps:
  1134               <ol class="rule">
  1135                 <li>If the <var>network service record</var>'s <code>id</code> property equals the <var>active
  1136                 service</var>'s <code>id</code> attribute and <var>active service</var>'s <code>online</code> attribute
  1137                 is currently set to <code>false</code> then set <var>active service</var>'s <a href=
  1138                 "#dom-networkservice-online"><code>online</code></a> attribute to <code>true</code> and then <a href=
  1139                 "http://www.whatwg.org/specs/web-apps/current-work/complete/webappapis.html#queue-a-task"
  1140                       class="externalDFN">queue a task</a> to dispatch a newly created event with the name <a href=
  1141                       "#event-serviceonline"><code>serviceonline</code></a> that uses the <a href=
  1142                       "http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#event"
  1143                       class="externalDFN"><code>Event</code></a> interface, which does not bubble, is not cancellable,
  1144                       and has no default action, at the current <var>active service</var> object.
  1145                 </li>
  1146               </ol>
  1147             </li>
  1148             <li>Let <var>'service type in current service manager' flag</var> be <code>false</code>.
  1149             </li>
  1150             <li>For each <var>requested control type</var> of the <var>requested control types</var> in <var>service
  1151             manager</var> run the following steps:
  1152               <ol class="rule">
  1153                 <li>If <var>network service record</var>'s <code>type</code> property does not equal <var>requested
  1154                 control type</var> then abort any remaining sub-steps and continue at the next available <var>requested
  1155                 control type</var>.
  1156                 </li>
  1157                 <li>Set the <var>'service type in current service manager' flag</var> to <code>true</code>, abort any
  1158                 remaining sub-steps and continue.
  1159                 </li>
  1160               </ol>
  1161             </li>
  1162             <li>If the <var>'service type in current service manager' flag</var> is set to <code>true</code> then
  1163             increment <var>service manager</var>'s <a href=
  1164             "#dom-networkservices-servicesavailable"><code>servicesAvailable</code></a> attribute by <code>1</code> and
  1165             then <a href="http://www.whatwg.org/specs/web-apps/current-work/complete/webappapis.html#queue-a-task"
  1166                   class="externalDFN">queue a task</a> to dispatch a newly created event with the name <a href=
  1167                   "#event-serviceavailable"><code>serviceavailable</code></a> that uses the <a href=
  1168                   "http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#event"
  1169                   class="externalDFN"><code>Event</code></a> interface, which does not bubble, is not cancellable, and
  1170                   has no default action, at the current <var>service manager</var> object.
  1171             </li>
  1172           </ol>
  1173         </li>
  1174       </ol>
  1175       <p>
  1176         The rule for <dfn>removing an available service</dfn> is the general process of removing an <a>existing
  1177         service</a> from the <a>list of available service records</a> that has left the user's current network or has
  1178         otherwise expired. This rule takes one argument, <var>service identifier</var>, and consists of running the
  1179         following steps:
  1180       </p>
  1181       <ol class="rule">
  1182         <li>For each <var>existing service record</var> in the current <a>list of available service records</a>, run
  1183         the following sub-steps:
  1184           <ol class="rule">
  1185             <li>If the <var>existing service record</var>'s <code>id</code> property does not match <var>service
  1186             identifier</var> then skip any remaining sub-steps for the current <var>existing service record</var> and
  1187             continue at the next available <var>existing service record</var>.
  1188             </li>
  1189             <li>Let <var>'service type in use' flag</var> be <code>false</code>.
  1190             </li>
  1191             <li>For each <var>service manager</var> in the <a>list of active service managers</a> run the following
  1192             steps:
  1193               <ol class="rule">
  1194                 <li>Let <var>'service type in current service manager' flag</var> be <code>false</code>.
  1195                 </li>
  1196                 <li>For each <var>active service</var> in <var>service manager</var> run the following steps:
  1197                   <ol class="rule">
  1198                     <li>If <var>existing service record</var>'s <code>id</code> property equals the <var>active
  1199                     service</var>'s <code>id</code> attribute and <var>active service</var>'s <a href=
  1200                     "#dom-networkservice-online"><code>online</code></a> attribute is currently set to
  1201                     <code>true</code> then set <var>active service</var>'s <a href="#dom-networkservice-online"><code>
  1202                       online</code></a> attribute to <code>false</code> and then <a href=
  1203                       "http://www.whatwg.org/specs/web-apps/current-work/complete/webappapis.html#queue-a-task"
  1204                           class="externalDFN">queue a task</a> to dispatch a newly created event with the name <a href=
  1205                           "#event-serviceoffline"><code>serviceoffline</code></a> that uses the <a href=
  1206                           "http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#event"
  1207                           class="externalDFN"><code>Event</code></a> interface, which does not bubble, is not
  1208                           cancellable, and has no default action, at the current <var>active service</var>.
  1209                     </li>
  1210                   </ol>
  1211                 </li>
  1212                 <li>For each <var>requested control type</var> of the <var>requested control types</var> in
  1213                 <var>service manager</var> run the following steps:
  1214                   <ol class="rule">
  1215                     <li>If <var>existing service record</var>'s <code>type</code> property does not equal
  1216                     <var>requested control type</var> then abort any remaining sub-steps and continue at the next
  1217                     available <var>requested control type</var>.
  1218                     </li>
  1219                     <li>Set the <var>'service type in current service manager' flag</var> to <code>true</code> and the
  1220                     <var>'service type in use' flag</var> to <code>true</code>, abort any remaining sub-steps and
  1221                     continue.
  1222                     </li>
  1223                   </ol>
  1224                 </li>
  1225                 <li>If the <var>'service type in current service manager' flag</var> is set to <code>true</code> then
  1226                 decrement <var>service manager</var>'s <a href=
  1227                 "#dom-networkservices-servicesavailable"><code>servicesAvailable</code></a> attribute by <code>1</code>
  1228                 and then <a href=
  1229                 "http://www.whatwg.org/specs/web-apps/current-work/complete/webappapis.html#queue-a-task"
  1230                       class="externalDFN">queue a task</a> to dispatch a newly created event with the name <a href=
  1231                       "#event-serviceunavailable"><code>serviceunavailable</code></a> that uses the <a href=
  1232                       "http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#event"
  1233                       class="externalDFN"><code>Event</code></a> interface, which does not bubble, is not cancellable,
  1234                       and has no default action, at the current <var>service manager</var> object.
  1235                 </li>
  1236               </ol>
  1237             </li>
  1238             <li>If the <var>'service type in use' flag</var> is <code>false</code> and the <var>existing service
  1239             record</var>'s <code>type</code> property begins with the DOMString "<code>upnp:</code>" and <var>existing
  1240             service record</var>'s <code>eventsURL</code> property is set then run the rule to <a>terminate an existing
  1241             UPnP Events Subscription</a>, if one is currently active (as a result of having previously called <a>setup
  1242             a UPnP Events Subscription</a> against the current <var>existing service record</var>).
  1243             </li>
  1244             <li>Remove <var>existing service record</var> from the current <a>list of available service records</a>.
  1245             </li>
  1246           </ol>
  1247         </li>
  1248       </ol>
  1249       <p>
  1250         User agents SHOULD expire a service record from the <a>list of available service records</a> when its
  1251         <code>expiryTimestamp</code> attribute exceeds the current UTC timestamp. When this condition is met the
  1252         <a>user agent</a> SHOULD run the rule for <a>removing an available service</a>, passing in the expired service
  1253         record's <code>id</code> attribute as the only argument.
  1254       </p>
  1255       <section>
  1256         <h4>
  1257           Zeroconf (<abbr title="Multicast DNS">mDNS</abbr> + <abbr title="Domain Name System">DNS</abbr>-<abbr title=
  1258           "Service Discovery">SD</abbr>)
  1259         </h4>
  1260         <p>
  1261           For each DNS response received from a user-agent-initiated Multicast DNS Browse for <abbr title=
  1262           "DNS Pointer Record">PTR</abbr> records with the name <code>_services._dns-sd._udp</code> on the resolved
  1263           recommended automatic browsing domain [[!MDNS]], the <a>user agent</a> MUST run the following steps:
  1264         </p>
  1265         <ol class="rule">
  1266           <li>Let <var>service mDNS responses</var> be an array of PTR records received by issuing a Multicast DNS
  1267           Browse for PTR records with the name of the current discovered service type.
  1268           </li>
  1269           <li>For each Object <var>service mDNS response</var> in <var>service mDNS responses</var>, run the following
  1270           steps:
  1271             <ol>
  1272               <li>Let <var>network service record</var> be an Object consisting of the following empty properties:
  1273               <code>id</code>, <code>name</code>, <code>type</code>, <code>url</code>, <code>config</code>,
  1274               <code>expiryTimestamp</code>.
  1275               </li>
  1276               <li>Set <var>network service record</var>'s <code>id</code> property to the value of the full PTR Service
  1277               Instance Name [[!MDNS]].
  1278               </li>
  1279               <li>Set <var>network service record</var>'s <code>name</code> property to the value of the PTR Service
  1280               Instance Name's <var>Instance</var> component [[!MDNS]].
  1281               </li>
  1282               <li>Set <var>network service record</var>'s <code>type</code> property to the concatenation of the string
  1283               <code>zeroconf:</code> followed be the value of the PTR Service Instance Name's <var>Service</var>
  1284               component [[!MDNS]].
  1285               </li>
  1286               <li>Set <var>network service record</var>'s <code>url</code> property to the resolvable Service URL
  1287               obtained from performing an DNS-SD Lookup [[!DNS-SD]] of the current service from the PTR record provided
  1288               [[!MDNS]].
  1289               </li>
  1290               <li>Set <var>network service record</var>'s <code>config</code> property to the string value of the
  1291               contents of the first DNS-SD TXT record associated with the <var>service mDNS response</var> as defined
  1292               in [[!DNS-SD]].
  1293               </li>
  1294               <li>Set <var>network service record</var>'s <code>expiryTimestamp</code> property to the value of the
  1295               current date, in UTC timestamp format, plus a value of <code>120</code> seconds.
  1296               </li>
  1297               <li>Run the general rule for <a>adding an available service</a>, passing in the current <var>network
  1298               service record</var> as the only argument.
  1299               </li>
  1300             </ol>
  1301           </li>
  1302         </ol>
  1303       </section>
  1304       <section>
  1305         <h5>
  1306           Simple Service Discovery Protocol (<abbr title="Simple Service Discovery Protocol">SSDP</abbr>)
  1307         </h5>
  1308         <p>
  1309           A user agent that implements UPnP service discovery MUST issue a <dfn>search request for UPnP root
  1310           devices</dfn> against the user's current local network according to the full normative text and timing
  1311           provided in 'Section 1.3.2: Search request with M-SEARCH' detailed in [[!UPNP-DEVICEARCH11]].
  1312         </p>
  1313         <p>
  1314           The user agent MUST issue all <a title="search request for UPnP root devices">search requests for UPnP root
  1315           devices</a> with a HTTP request line equal to <code>M-SEARCH * HTTP/1.1</code>, with a HOST header equal to
  1316           the reserved multicast address and port of <code>239.255.255.250:1900</code> and a MAN header equal to
  1317           <code>ssdp:discover</code>. The <a>user agent</a> must also send an ST header with this HTTP request equal to
  1318           the String value of <code>ssdp:all</code> or <code>upnp:rootdevice</code> or a single <a>valid service
  1319           type</a> token beginning with the String value <code>upnp:</code>. If a single <a>valid service type</a>
  1320           token beginning with the String value <code>upnp:</code> is to be used, the user agent MUST strip the leading
  1321           String <code>upnp:</code> before using this value in this HTTP request. The user-agent MUST also send an MX
  1322           header equal to a <dfn>maximum UPnP advertisement response wait time</dfn> value between <code>1</code> and
  1323           <code>5</code> seconds with this HTTP request.
  1324         </p>
  1325         <p>
  1326           The user agent MUST listen for any incoming responses to any <a>search request for UPnP root devices</a>.
  1327         </p>
  1328         <p>
  1329           For each <dfn>HTTP Response</dfn> following an initial <a>search request for UPnP root devices</a> sent on a
  1330           <a>standard UPnP address and port</a> the user agent MUST run the following steps:
  1331         </p>
  1332         <ol class="rule">
  1333           <li>If the <a>HTTP Response</a> is not a HTTP 200 OK response then this response is invalid and the user
  1334           agent MUST discard this response, abort any remaining steps and return. The user agent MAY issue a new
  1335           <a>search request for UPnP root devices</a> as a result of this error occurring.
  1336           </li>
  1337           <li>If the <a>maximum UPnP advertisement response wait time</a> has been exceeded since the initial <a>search
  1338           request for UPnP root devices</a> was sent then the <a>HTTP Response</a> is invalid and the user agent MUST
  1339           discard this response, abort any remaining steps and return. The user agent MAY stop listening for responses
  1340           from the current <a>search request for UPnP root devices</a> as a result of this error occurring. Equally,
  1341           the user agent MAY issue a new <a>search request for UPnP root devices</a> as a result of this error
  1342           occurring.
  1343           </li>
  1344           <li>Let <var>ssdp device</var> be an Object with a property for each HTTP header received in the <a>HTTP
  1345           Response</a>, with each key being the name of a HTTP response header and each value being that HTTP response
  1346           header's value.
  1347           </li>
  1348           <li>If <var>ssdp device</var> does not contain at least one <var>CACHE-CONTROL</var> entry, at least one
  1349           <var>USN</var> entry, at least one <var>ST</var> entry and at least one <var>LOCATION</var> entry then the
  1350           <a>HTTP Response</a> is invalid and the <a>user agent</a> MUST discard this response, abort any remaining
  1351           steps and return.
  1352           </li>
  1353           <li>The user agent MUST run the rule for <a>obtaining a UPnP Device Description File</a> passing in the first
  1354           occurrence of <var>LOCATION</var> from <var>ssdp device</var> as the <var>device descriptor URL</var>
  1355           argument and the first occurrence of <var>USN</var> from <var>ssdp device</var> as the <var>device
  1356           identifier</var> argument and the first occurrence of <var>CACHE-CONTROL</var> from <var>ssdp device</var>
  1357           (minus the leading string of <code>max-age=</code>) as the <var>device expiry</var> argument.
  1358           </li>
  1359         </ol>
  1360         <p>
  1361           The user agent MUST listen for incoming requests on the <dfn>standard UPnP address and port</dfn> on all
  1362           current local network interface addresses with the port <code>1900</code>.
  1363         </p>
  1364         <p>
  1365           For each <dfn>HTTP Request</dfn> received on a <a>standard UPnP address and port</a> the user agent MUST run
  1366           the following steps:
  1367         </p>
  1368         <ol class="rule">
  1369           <li>If the <a>HTTP Request</a> is not a HTTP NOTIFY request then it is not a valid UPnP Request and the user
  1370           agent MUST discard this request, abort any remaining steps and return.
  1371           </li>
  1372           <li>Let <var>ssdp device</var> be an Object with a property for each HTTP header received in the <a>HTTP
  1373           Request</a>, with each key being the name of a HTTP header and each value being that HTTP header's value.
  1374           </li>
  1375           <li>If <var>ssdp device</var>'s <var>NTS</var> entry is equal to <code>ssdp:alive</code> and the <a>HTTP
  1376           Request</a> does not contain at least one <var>CACHE-CONTROL</var> entry, at least one <var>USN</var> entry,
  1377           at least one <var>NT</var> entry, at least one <var>NTS</var> entry and at least one <var>LOCATION</var>
  1378           entry, then the <a>user agent</a> MUST discard this request, abort any remaining steps and return.
  1379           </li>
  1380           <li>If <var>ssdp device</var>'s <var>NTS</var> entry is equal to <code>ssdp:alive</code> then the user agent
  1381           MUST run the rule for <a>obtaining a UPnP Device Description File</a> passing in the first occurrence of
  1382           <var>LOCATION</var> from <var>ssdp device</var> as the <var>device descriptor URL</var> argument and the
  1383           first occurrence of <var>USN</var> from <var>ssdp device</var> as the <var>device identifier</var> argument
  1384           and the first occurrence of <var>CACHE-CONTROL</var> from <var>ssdp device</var> (minus the leading string of
  1385           <code>max-age=</code>) as the <var>device expiry</var>.<br>
  1386             <br>
  1387             Otherwise, if <var>ssdp device</var>'s <var>NTS</var> entry is equal to <code>ssdp:byebye</code> then the
  1388             user agent MUST run the rule for <a>removing all services from a registered UPnP Device</a> passing in the
  1389             first occurrence of <var>USN</var> from <var>ssdp device</var> as the <var>device identifier</var>
  1390             argument.
  1391           </li>
  1392         </ol>
  1393         <p>
  1394           The rule for <dfn>obtaining a UPnP Device Description File</dfn> is the process of obtaining the contents of
  1395           a standard UPnP Device Description [[!UPNP-DEVICEARCH11]] from a URL-based resource. This rule takes three
  1396           arguments - <var>device descriptor URL</var>, <var>device identifier</var> and <var>device expiry</var> - and
  1397           when called the user agent MUST run the following steps:
  1398         </p>
  1399         <ol class="rule">
  1400           <li>Let <var>device descriptor file</var> contain the contents of the file located at the URL provided in
  1401           <var>device descriptor URL</var> obtained according to the rules defined in 'Section 2.11: Retrieving a
  1402           description using HTTP' in [[!UPNP-DEVICEARCH11]].
  1403           </li>
  1404           <li>If the value provided in <var>device descriptor URL</var> cannot be resolved as a reachable URL on the
  1405           current network or the <var>device descriptor file</var> remains empty then it is invalid and the <a>user
  1406           agent</a> MUST abort any remaining steps and return.
  1407           </li>
  1408           <li>Run the rule for <a>processing a UPnP Device Description File</a>, passing in the current <var>device
  1409           descriptor file</var>, <var>device identifier</var> and <var>device expiry</var> arguments.
  1410           </li>
  1411         </ol>
  1412         <p>
  1413           The rule for <dfn>processing a UPnP Device Description File</dfn> is the process of parsing the contents of a
  1414           standard UPnP Device Description [[!UPNP-DEVICEARCH11]] and registering the UPnP services contained therein
  1415           within the <a>list of available service records</a>.
  1416         </p>
  1417         <p>
  1418           The rule for <a>processing a UPnP Device Description File</a> takes three arguments - <var>device descriptor
  1419           file</var>, <var>device identifier</var> and <var>device expiry</var> - and when called the user agent MUST
  1420           run the following steps:
  1421         </p>
  1422         <ol class="rule">
  1423           <li>Let <var>advertised services</var> be a list of all advertised services obtained from the <var>device
  1424           descriptor file</var> containing the value of the first occurrence of the <code>&lt;serviceList&gt;</code>
  1425           element as it is defined in 'Section 2.3: Device Description' in [[!UPNP-DEVICEARCH11]].
  1426           </li>
  1427           <li>For each <code>&lt;service&gt;</code> element - known as an <var>advertised service</var> - in
  1428           <var>advertised services</var> run the following steps:
  1429             <ol class="rule">
  1430               <li>Let <var>network service record</var> be a new Object consisting of the following empty properties:
  1431               <code>id</code>, <code>deviceId</code>, <code>name</code>, <code>type</code>, <code>url</code>,
  1432               <code>eventsUrl</code>, <code>config</code>, <code>expiryTimestamp</code>.
  1433               </li>
  1434               <li>Set <var>network service record</var>'s <code>id</code> property to the concatenated string value of
  1435               the first occurrence of the <code>&lt;UDN&gt;</code> element in the <var>device descriptor file</var>
  1436               with the <var>advertised service</var>'s <code>&lt;serviceId&gt;</code> sub-element.
  1437               </li>
  1438               <li>Set <var>network service record</var>'s <code>deviceId</code> property to the value of <var>device
  1439               identifier</var>.
  1440               </li>
  1441               <li>Set <var>network service record</var>'s <code>name</code> property to the string value of the first
  1442               occurrence of the <var>advertised service</var>'s <code>&lt;serviceId&gt;</code> sub-element.
  1443               </li>
  1444               <li>Set <var>network service record</var>'s <code>type</code> property to the concatenation of the string
  1445               <code>upnp:</code> followed by the string value of the first occurrence of the <var>advertised
  1446               service</var>'s <code>&lt;serviceType&gt;</code> sub-element.
  1447               </li>
  1448               <li>Set <var>network service record</var>'s <code>url</code> property to the string value of the first
  1449               occurrence of the <var>advertised service</var>'s <code>&lt;controlURL&gt;</code> sub-element.
  1450               </li>
  1451               <li>Set <var>network service record</var>'s <code>config</code> property to the string value of the
  1452               contents of the first occurrence of the <code>&lt;device&gt;</code> element in the <var>device descriptor
  1453               file</var>.
  1454               </li>
  1455               <li>If <var>advertised service</var>'s <code>&lt;eventSubURL&gt;</code> sub-element is not empty, then
  1456               set <var>network service record</var>'s <code>eventsUrl</code> property to the string value of the first
  1457               occurrence of the <var>advertised service</var>'s <code>&lt;eventSubURL&gt;</code> sub-element.
  1458               Otherwise, do not set <var>network service record</var>'s <code>eventsUrl</code> property.
  1459               </li>
  1460               <li>Set <var>network service record</var>'s <code>expiryTimestamp</code> property to the value of the
  1461               current date, in UTC timestamp format, plus the value of <var>device expiry</var>.
  1462               </li>
  1463               <li>Run the general rule for <a>adding an available service</a>, passing in the current <var>network
  1464               service record</var> as the only argument.
  1465               </li>
  1466             </ol>
  1467           </li>
  1468           <li>If <var>device descriptor file</var> contains a <code>&lt;deviceList&gt;</code> element then for each
  1469           <code>&lt;device&gt;</code> element within <code>&lt;deviceList&gt;</code> - herein known as an <var>embedded
  1470           device descriptor file</var> - the user agent MUST run the rule for <a>processing a UPnP Device Description
  1471           File</a>, passing in the current <var>embedded device descriptor file</var> as the <var>device descriptor
  1472           file</var> argument, along with the current <var>device identifier</var> and <var>device expiry</var>
  1473           arguments.
  1474           </li>
  1475         </ol>
  1476         <p>
  1477           The rule for <dfn>removing all services from a registered UPnP Device</dfn> is the process of removing all
  1478           services associated with a device from the <a>list of available service records</a> that has left the user's
  1479           current network or has otherwise timed out or expired. This rule takes one argument, <var>device
  1480           identifier</var>, and consists of running the following steps:
  1481         </p>
  1482         <ol class="rule">
  1483           <li>For each <var>existing service record</var> in the current <a>list of available service records</a>, run
  1484           the following sub-steps:
  1485             <ol class="rule">
  1486               <li>If the <var>existing service record</var>'s <code>deviceId</code> property does not match <var>device
  1487               identifier</var> then skip any remaining sub-steps for the current <var>existing service record</var> and
  1488               continue at the next available <var>existing service record</var>.
  1489               </li>
  1490               <li>Run the general rule for <a>removing an available service</a> passing in <var>existing service
  1491               record</var>'s <code>id</code> property as the only argument.
  1492               </li>
  1493             </ol>
  1494           </li>
  1495         </ol>
  1496         <p>
  1497           When the <a>user agent</a> is to <dfn>setup a UPnP Events Subscription</dfn>, it is to run the following
  1498           steps with the current <var>network service record</var> object as defined in 'Section 4.1.2: SUBSCRIBE with
  1499           NT and CALLBACK' in [[!UPNP-DEVICEARCH11]]:
  1500         </p>
  1501         <ol class="rule">
  1502           <li>If <var>network service record</var>'s <code>eventsUrl</code> property is empty then the <a>user
  1503           agent</a> MUST abort these steps.
  1504           </li>
  1505           <li>Let <var>callback URL</var> be the value of creating a new <a>user-agent generated callback url</a>.
  1506           </li>
  1507           <li>Send a HTTP SUBSCRIBE request with a <em>NT</em> header with a string value of <code>upnp:event</code>, a
  1508           <em>TIMEOUT</em> header with a user-agent defined timeout value (in the form <code>Second-XX</code> where
  1509           <code>XX</code> is the user-agent defined timeout value in seconds) and a <em>CALLBACK</em> header with a
  1510           string value of <var>callback URL</var> towards the <var>network service record</var>'s
  1511           <code>eventsUrl</code> property.
  1512           </li>
  1513           <li>If a non-200 OK response is received from the HTTP SUBSCRIBE request then the <a>user agent</a> MUST
  1514           abort these steps.
  1515           </li>
  1516           <li>On receiving a valid 200 OK response, run the following steps:
  1517             <ol class="rule">
  1518               <li>Let <var>callback ID</var> equal the string value of the first included <em>SID</em> header, if it
  1519               exists.
  1520               </li>
  1521               <li>Let <var>timeout date</var> equal the sum of the current UTC date value plus the integer value of the
  1522               first included <em>TIMEOUT</em> header (minus the leading string of <code>Second-</code>), if it exists.
  1523               </li>
  1524               <li>Run the following steps asynchronously and continue to the step labeled <em>listen</em> below.
  1525               </li>
  1526               <li>
  1527                 <em>Refresh Subscription</em>: Run the following steps at a set interval (X) within the <a>user
  1528                 agent</a>:
  1529                 <ol class="rule">
  1530                   <li>Let <var>current date</var> equal the current UTC date.
  1531                   </li>
  1532                   <li>If <var>current date</var> is less than the <var>timeout date</var> then continue to the step
  1533                   labeled <em>refresh subscription</em> above.
  1534                   </li>
  1535                   <li>Send a HTTP SUBSCRIBE request with a <em>SID</em> header with the string value of <var>callback
  1536                   ID</var> and a user-agent defined <em>TIMEOUT</em> header (in the form <code>Second-XX</code> where
  1537                   <code>XX</code> is the user-agent defined timeout value in seconds) towards the <var>network service
  1538                   record</var>'s <code>eventsUrl</code> property.
  1539                   </li>
  1540                   <li>On receiving a valid 200 OK, update <var>callback ID</var> with the string value of the first
  1541                   included <em>SID</em> header and set <var>timeout date</var> to the sum of the current UTC date value
  1542                   plus the integer value of the first included <em>TIMEOUT</em> header (minus the leading string of
  1543                   <code>Second-</code>), if it exists. If the current date is greater than or equal to <var>timeout
  1544                   date</var> then the <a>user agent</a> SHOULD continue from the step labeled <em>refresh
  1545                   subscription</em> above. For all non 200 OK responses the <a>user agent</a> SHOULD continue from the
  1546                   step labeled <em>refresh subscription</em> above.
  1547                   </li>
  1548                 </ol>
  1549               </li>
  1550               <li>
  1551                 <em>Listen</em>: For each HTTP NOTIFY request received at the <var>callback URL</var> the <a>user
  1552                 agent</a> is to run the following steps:
  1553                 <ol class="rule">
  1554                   <li>Let <var>content clone</var> be the result of obtaining the message body of the HTTP NOTIFY
  1555                   request. If <var>content clone</var> is empty, then the <a>user agent</a> MUST abort these steps.
  1556                   </li>
  1557                   <li>Let <var>notification event</var> be a new simple event that uses the <a href=
  1558                   "http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#event"
  1559                         class="externalDFN"><code>Event</code></a> interface with the name <a href=
  1560                         "#event-notify"><code>notify</code></a>, which does not bubble, is not cancellable, and has no
  1561                         default action.
  1562                   </li>
  1563                   <li>Let the <code>data</code> attribute of <var>notification event</var> have the DOMString value of
  1564                   <var>content clone</var>.
  1565                   </li>
  1566                   <li>
  1567                     <a href="http://www.whatwg.org/specs/web-apps/current-work/complete/webappapis.html#queue-a-task"
  1568                         class="externalDFN">Queue a task</a> to dispatch <var>notification event</var> at the current
  1569                         <a><code>NetworkService</code></a> object.
  1570                   </li>
  1571                   <li>Return a HTTP 200 OK response to the sender of the HTTP NOTIFY request.
  1572                   </li>
  1573                 </ol>
  1574               </li>
  1575             </ol>
  1576           </li>
  1577         </ol>
  1578         <p>
  1579           A <a>user agent</a> can <dfn>terminate an existing UPnP Events Subscription</dfn> at any time for a
  1580           <var>network service record</var> by sending an HTTP UNSUBSCRIBE request - as defined in 'Section 4.1.4:
  1581           Cancelling a subscription with UNSUBSCRIBE' in [[!UPNP-DEVICEARCH11]] - with a HOST header set to that
  1582           <var>active service</var>'s <code>eventsUrl</code> property and a SID header set to the <var>callback
  1583           ID</var> obtained when the initial <a>setup a UPnP Events Subscription</a> action occurred.
  1584         </p>
  1585       </section>
  1586       <section>
  1587         <h5>
  1588           Discovery and Launch Protocol (<abbr title="Discovery and Launch Protocol">DIAL</abbr>)
  1589         </h5>
  1590         <p>
  1591           A user agent that implements DIAL service discovery MUST issue a <dfn>search request for DIAL-enabled
  1592           devices</dfn> against the user's current local network according to the full normative text and timing
  1593           provided in 'Section 1.3.2: Search request with M-SEARCH' detailed in [[!UPNP-DEVICEARCH11]].
  1594         </p>
  1595         <p>
  1596           Let <var>dial version</var> be the version number specified in the <a>valid service type</a> token. Let
  1597           <var>dial search target</var> be the concatentation of the
  1598           <code>urn:dial-multiscreen-org:service:dial:</code> string constant with the <var>dial version</var>
  1599           (currently, <var>dial version</var> can only be <code>1</code>)
  1600         </p>
  1601         <p>
  1602           The user agent MUST issue all <a title="search request for DIAL devices">search requests for DIAL devices</a>
  1603           with a HTTP request line equal to <code>M-SEARCH * HTTP/1.1</code>, with a HOST header equal to the reserved
  1604           multicast address and port of <code>239.255.255.250:1900</code>, a MAN header equal to
  1605           <code>ssdp:discover</code>, an ST header equal to <var>dial search target</var> and a user-agent defined MX
  1606           header equal to a <dfn>maximum DIAL advertisement response wait time</dfn> value between <code>1</code> and
  1607           <code>5</code> seconds.
  1608         </p>
  1609         <p>
  1610           The user agent MUST listen for any incoming responses to a <a>search request for DIAL devices</a>.
  1611         </p>
  1612         <p>
  1613           For each HTTP Response following an initial <a>search request for DIAL devices</a> sent on a <a>standard UPnP
  1614           address and port</a> the user agent MUST run the following steps:
  1615         </p>
  1616         <ol class="rule">
  1617           <li>If the HTTP Response is not a HTTP 200 OK response then this response is invalid and the user agent MUST
  1618           discard this response, abort any remaining steps and return. The user agent MAY issue a new <a>search request
  1619           for DIAL devices</a> as a result of this error occurring.
  1620           </li>
  1621           <li>If the <a>maximum DIAL advertisement response wait time</a> has been exceeded since the initial <a>search
  1622           request for DIAL devices</a> was sent then the <a>HTTP Response</a> is invalid and the user agent MUST
  1623           discard this response, abort any remaining steps and return. The user agent MAY stop listening for responses
  1624           from the current <a>search request for DIAL devices</a> as a result of this error occurring. Equally, the
  1625           user agent MAY issue a new <a>search request for DIAL devices</a> as a result of this error occurring.
  1626           </li>
  1627           <li>Let <var>dial device</var> be an Object with a property for each HTTP header received in the <a>HTTP
  1628           Response</a>, with each key being the name of a HTTP response header and each value being that HTTP response
  1629           header's value.
  1630           </li>
  1631           <li>If <var>dial device</var> does not contain at least one <var>CACHE-CONTROL</var> entry, at least one
  1632           <var>USN</var> entry, at least one <var>ST</var> entry and at least one <var>LOCATION</var> entry or the
  1633           value of its <var>ST</var> entry is not <var>dial search target</var>, then the <a>HTTP Response</a> is
  1634           invalid and the <a>user agent</a> MUST discard this response, abort any remaining steps and return.
  1635           </li>
  1636           <li>The user agent MUST run the rule for <a>obtaining a UPnP Device Description File</a> passing in the first
  1637           occurrence of <var>LOCATION</var> from <var>dial device</var> as the <var>device descriptor URL</var>
  1638           argument and the first occurrence of <var>USN</var> from <var>dial device</var> as the <var>device
  1639           identifier</var> argument and the first occurrence of <var>CACHE-CONTROL</var> from <var>dial device</var>
  1640           (minus the leading string of <code>max-age=</code>) as the <var>device expiry</var> argument.
  1641           </li>
  1642         </ol>
  1643         <p>
  1644           The rule for <dfn>obtaining a DIAL Device Description File</dfn> is the process of obtaining the contents of
  1645           a standard UPnP Device Description [[!UPNP-DEVICEARCH11]] from a URL-based resource. This rule takes three
  1646           arguments - <var>device descriptor URL</var>, <var>device identifier</var> and <var>device expiry</var> - and
  1647           when called the user agent MUST run the following steps:
  1648         </p>
  1649         <ol class="rule">
  1650           <li>Let <var>device descriptor file</var> contain the contents of the file located at the URL provided in
  1651           <var>device descriptor URL</var> obtained according to the rules defined in 'Section 2.11: Retrieving a
  1652           description using HTTP' in [[!UPNP-DEVICEARCH11]].
  1653           </li>
  1654           <li>Let <var>application url</var> be the value of the first occurrence of the <code>Application-URL</code>
  1655           response header field obtained according to the rules defined in 'Section 5.4: Device Description Response'
  1656           in [<a href="https://sites.google.com/a/dial-multiscreen.org/dial/dial-protocol-specification">DIAL</a>]
  1657           </li>
  1658           <li>If the value provided in <var>device descriptor URL</var> cannot be resolved as a reachable URL on the
  1659           current network or the <var>device descriptor file</var> remains empty or <var>application url</var> is
  1660           undefined then it is invalid and the <a>user agent</a> MUST abort any remaining steps and return.
  1661           </li>
  1662           <li>Run the following steps to add the newly discovered DIAL service:
  1663             <ol class="rule">
  1664               <li>Let <var>network service record</var> be a new Object consisting of the following empty properties:
  1665               <code>id</code>, <code>deviceId</code>, <code>name</code>, <code>type</code>, <code>url</code>,
  1666               <code>expiryTimestamp</code>.
  1667               </li>
  1668               <li>Set <var>network service record</var>'s <code>id</code> property to the first occurrence of the
  1669               <code>&lt;UDN&gt;</code> element in the <var>descriptor file</var> prefixed with the <code>dial:</code>
  1670               string constant
  1671               </li>
  1672               <li>Set <var>network service record</var>'s <code>deviceId</code> property to the value of <var>device
  1673               identifier</var>.
  1674               </li>
  1675               <li>Set <var>network service record</var>'s <code>name</code> property to the string value of the first
  1676               occurrence of the <code>&lt;friendlyName&gt;</code> element in the <var>descriptor file</var>.
  1677               </li>
  1678               <li>Set <var>network service record</var>'s <code>type</code> property to <var>dial search target</var>.
  1679               </li>
  1680               <li>Set <var>network service record</var>'s <code>url</code> property to the string value of the
  1681               <var>application url</var>.
  1682               </li>
  1683               <li>Set <var>network service record</var>'s <code>expiryTimestamp</code> property to the value of the
  1684               current date, in UTC timestamp format, plus the value of <var>device expiry</var>.
  1685               </li>
  1686               <li>Run the general rule for <a>adding an available service</a>, passing in the current <var>network
  1687               service record</var> as the only argument.
  1688               </li>
  1689             </ol>
  1690           </li>
  1691         </ol>
  1692       </section>
  1693       <section>
  1694         <h3>
  1695           Network Topology Monitoring
  1696         </h3>
  1697         <div>
  1698           <p>
  1699             When the <a>user agent</a> detects that the user has dropped from a connected network then, for each
  1700             <var>existing service record</var> in the <a>list of available service records</a> discovered via that
  1701             network connection, the <a>user agent</a> MUST run the general rule for <a>removing an available
  1702             service</a> passing in each <var>existing service record</var>'s <code>id</code> property as the only
  1703             argument for each call.
  1704           </p>
  1705           <p>
  1706             When the <a>user agent</a> detects that the user has connected to a new network or reconnected to an
  1707             existing network, then it SHOULD restart its discovery mechanisms as defined in the <a href=
  1708             "#service-discovery">Service Discovery</a> section of this specification, maintaining the existing <a>list
  1709             of active service managers</a> currently in use.
  1710           </p>
  1711         </div>
  1712       </section>
  1713     </section>
  1714     <section>
  1715       <h3>
  1716         Events Summary
  1717       </h3>
  1718       <p>
  1719         The following events are dispatched on the <a href="#networkservices"><code>NetworkServices</code></a> and/or
  1720         <a href="#networkservice"><code>NetworkService</code></a> objects:
  1721       </p>
  1722       <table border="1">
  1723         <thead>
  1724           <tr>
  1725             <th>
  1726               <span>Event name</span>
  1727             </th>
  1728             <th>
  1729               <span>Interface</span>
  1730             </th>
  1731             <th>
  1732               <span>Dispatched when...</span>
  1733             </th>
  1734           </tr>
  1735         </thead>
  1736         <tbody>
  1737           <tr>
  1738             <td>
  1739               <dfn id="event-serviceavailable"><code>serviceavailable</code></dfn>
  1740             </td>
  1741             <td>
  1742               <a href="http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#event"
  1743                   class="externalDFN"><code>Event</code></a>
  1744             </td>
  1745             <td>
  1746               When a <a>new service</a> that matches one of the <a>requested type tokens</a> is found in the current
  1747               network.
  1748             </td>
  1749           </tr>
  1750           <tr>
  1751             <td>
  1752               <dfn id="event-serviceunavailable"><code>serviceunavailable</code></dfn>
  1753             </td>
  1754             <td>
  1755               <a href="http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#event"
  1756                   class="externalDFN"><code>Event</code></a>
  1757             </td>
  1758             <td>
  1759               When an <a>existing service</a> that matches one of the <a>requested type tokens</a> gracefully leaves or
  1760               expires from the current network.
  1761             </td>
  1762           </tr>
  1763           <tr>
  1764             <td>
  1765               <dfn id="event-serviceonline"><code>serviceonline</code></dfn>
  1766             </td>
  1767             <td>
  1768               <a href="http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#event"
  1769                   class="externalDFN"><code>Event</code></a>
  1770             </td>
  1771             <td>
  1772               When a <a>current service</a> renews its service registration within the current network.
  1773             </td>
  1774           </tr>
  1775           <tr>
  1776             <td>
  1777               <dfn id="event-serviceoffline"><code>serviceoffline</code></dfn>
  1778             </td>
  1779             <td>
  1780               <a href="http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#event"
  1781                   class="externalDFN"><code>Event</code></a>
  1782             </td>
  1783             <td>
  1784               When a <a>current service</a> gracefully leaves or otherwise expires from the current network.
  1785             </td>
  1786           </tr>
  1787           <tr>
  1788             <td>
  1789               <dfn id="event-notify"><code>notify</code></dfn>
  1790             </td>
  1791             <td>
  1792               <a href="http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#event"
  1793                   class="externalDFN"><code>Event</code></a>
  1794             </td>
  1795             <td>
  1796               When a valid UPnP Events Subscription Message is received on a <a>user-agent generated callback url</a>
  1797               for a <a>current service</a>. This event never fires for Zeroconf-based services.
  1798             </td>
  1799           </tr>
  1800         </tbody>
  1801       </table>
  1802     </section>
  1803     <section>
  1804       <h3>
  1805         Garbage collection
  1806       </h3>
  1807       <p>
  1808         There is an <dfn>implied strong reference</dfn> from any IDL attribute in this API that returns a pre-existing
  1809         object to that object.
  1810       </p>
  1811       <p class="note">
  1812         For example, if a <a><code>NetworkServices</code></a> object has one or more <a>indexed properties</a> attached
  1813         to it then there is a strong reference from that <a><code>NetworkServices</code></a> object toward each of its
  1814         <a>indexed properties</a>.
  1815       </p>
  1816       <p>
  1817         If a <a>user agent</a> is to <dfn>make disappear</dfn> a <a><code>NetworkServices</code></a> object (this
  1818         happens when a <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/dom.html#document"
  1819            class="externalDFN"><code>Document</code></a> object goes away), the <a>user agent</a> MUST remove this
  1820            object from the <a>list of active service managers</a> and remove the <a href=
  1821            "#dom-networkservice-url"><code>url</code></a> of each of its <a>indexed properties</a> from the <a>entry
  1822            script origin's URL whitelist</a>.
  1823       </p>
  1824     </section>
  1825     <section>
  1826       <h3>
  1827         Use Cases and Requirements
  1828       </h3>
  1829       <p>
  1830         This section covers what the requirements are for this API, as well as illustrates some use cases.
  1831       </p>
  1832       <ul class="rule">
  1833         <li>Once a user has given permission, user agents should provide the ability for Web pages to communicate
  1834         directly with a Local-networked Service.
  1835           <ul class="rule">
  1836             <li>Example: A web-based TV remote control. A Web page wants to control the current user's TV, changing the
  1837             programming shown or increasing/decreasing/muting the volume of the Local-networked Device. The Web page
  1838             requests a service type that is known to be implemented by television sets to which it has the application
  1839             logic to communicate. Local devices providing the request service types are discovered and presented to the
  1840             user for authorization. The user selects one or more of the discovered television sets to be accessible to
  1841             the current Web page and then clicks 'Share'. The Web page can now communicate directly with the
  1842             user-authorized Local-networked services.
  1843             </li>
  1844           </ul>
  1845         </li>
  1846         <li>Web pages should be able to communicate with Local-networked Services using the messaging channel supported
  1847         by those Devices.
  1848           <ul class="rule">
  1849             <li>Example: A Web page advertises that it is capable of controlling multiple Home Media Servers. The user
  1850             can select their Home Media Server type from a drop-down list, at which point the Web page sends a request
  1851             to the user agent to connect with the associated service type of the Home Media Server. The Media Server
  1852             selected implements a Web Socket channel for bi-directional service communication and so the Web page opens
  1853             a web socket to the requested Media Server and can communicate as required via that appropriate channel.
  1854             </li>
  1855           </ul>
  1856         </li>
  1857         <li>Web pages should be able to communicate with Local-networked Services using the messaging format supported
  1858         by those Devices.
  1859           <ul class="rule">
  1860             <li>Example: A Web page advertises that it is capable of interacting with and controlling multiple types of
  1861             Home Media Server. The user can select their Home Media Server type from a drop-down list or known Media
  1862             Servers, at which point the Web page sends a request to the user agent to connect with the associated
  1863             service type (and, optionally, the associated event type) of the Home Media Server. The communication
  1864             protocols supported by Home Media Servers typically vary between UPnP, JSON-RPC, Protocol Buffers or other
  1865             messaging formats depending on the Home Media Server requested. The Web page is able to communicate with
  1866             the user-selected Home Media Server in the messaging format supported by that Device, which, in this
  1867             example is a simple key/value pair text format.
  1868             </li>
  1869           </ul>
  1870         </li>
  1871         <li>Web pages should not be able to communicate with Local-networked Services that have not been authorized by
  1872         the user thereby maintaining the user's privacy.
  1873           <ul class="rule">
  1874             <li>Example: A Web page requests access to one type of Local-networked service. The user authorizes access
  1875             to that particular service. Other services running on that same device, and on other devices within the
  1876             network, should not be accessible to the current Web page.
  1877             </li>
  1878           </ul>
  1879         </li>
  1880         <li>A user should be able to share one or more Local-networked Services based on a particular service type
  1881         request from a Web page.
  1882           <ul class="rule">
  1883             <li>Example: A Web page is capable of interacting with a specific profile of Local-networked Service. As
  1884             such, it makes a request to the user agent to access those services, of which multiple matches are found.
  1885             The user is capable of selecting one or more of the discovered services to share with the Web page. The Web
  1886             page can then implement a drag-and-drop interface for the user to drag specific actions on to one or more
  1887             of the authorized Local-networked Services.
  1888             </li>
  1889           </ul>
  1890         </li>
  1891         <li>User agents should provide an API exposed to script that exposes the features above. The user is notified
  1892         by UI anytime interaction with Local-networked Services is requested, giving the user full ability to cancel or
  1893         abort the transaction. The user selects the Local-networked Services to be connected to the current Web page,
  1894         and can cancel these at any time. No invocations to these APIs occur silently without user intervention.
  1895         </li>
  1896       </ul>
  1897     </section>
  1898     <section class="informative appendix">
  1899       <h3>
  1900         Examples
  1901       </h3>
  1902       <div class="example">
  1903         <p>
  1904           This sample code exposes a button. When clicked, this button is disabled and the user is prompted to offer a
  1905           network service. The user may also select multiple network services. When the user has authorized a network
  1906           service to be connected to the web page then the web page issues a simple command to get a list of all the
  1907           albums stored on the connected media player service.
  1908         </p>
  1909         <p>
  1910           The button is re-enabled only when the connected network service disconnects for whatever reason (the service
  1911           becomes unavailable on the network, the user disconnects from their current network or the user revokes
  1912           access to the service from the current web page). At this point the user can re-click the button to select a
  1913           new network service to connect to the web page and the above steps are repeated.
  1914         </p>
  1915         <p>
  1916           The provided service type identifier and service interaction used in this example is based on the
  1917           well-defined service type and messaging format supported by the <a href="http://xbmc.org/about/">XBMC Media
  1918           Server</a>.
  1919         </p>
  1920         <hr>
  1921         <pre class="highlight">
  1922 &lt;input type="button" value="Start" onclick="start()" id="startBtn"/&gt;
  1923 &lt;div id="debugconsole"&gt;&lt;/div&gt;
  1924 
  1925 &lt;script&gt;
  1926  var startBtn = document.getElementById('startBtn'),
  1927      debug = document.getElementById('debugconsole');
  1928 
  1929  function start() {
  1930    if(navigator.getNetworkServices) {
  1931       navigator.getNetworkServices('zeroconf:_xbmc-jsonrpc._tcp').then(gotXBMCService).catch(error);
  1932       startBtn.disabled = true;
  1933    } else {
  1934       debug.innerHTML += "&lt;br&gt;Service Discovery not supported!";
  1935    }
  1936  }
  1937 
  1938  function gotXBMCService(services) {
  1939 
  1940 // Listen for service disconnect messages
  1941 
  1942    services[0].addEventListener('serviceoffline', function ( e ) {
  1943        debug.innerHTML += "&lt;br&gt;" + services[0].name + " disconnected.";
  1944        startBtn.disabled = false;
  1945    }, false);
  1946 
  1947 // Send a service message to get albums list (and process the service response)
  1948 
  1949    var svcXhr = new XMLHttpRequest();
  1950    svcXhr.open("POST", services[0].url + "/getAlbums"); // services[0].url and its sub-resources have been
  1951                                                         // whitelisted for cross-site XHR use in this
  1952                                                         // current browsing context.
  1953 
  1954    svcXhr.setRequestHeader('Content-Type', 'application/json-rpc');
  1955 
  1956    svcXhr.addEventListener('readystatechange', function ( response ) {
  1957      if( response.readyState != 4 || response.status != 200 )
  1958         return;
  1959      debug.innerHTML += "&lt;br&gt;" + services[0].name + " response received: ";
  1960      debug.textContent += JSON.parse(response.responseText);
  1961    }, false);
  1962 
  1963    var svcMsg = [
  1964      { "jsonrpc": "2.0", "method": "AudioLibrary.GetAlbums", "params": { "genreid": -1,
  1965          "artistid": -1, "start": -1, "end": -1 }, "id": "1" }
  1966    ];
  1967 
  1968    svcXhr.send(JSON.stringify(svcMsg));
  1969    debug.innerHTML += "&lt;br&gt;" + services[0].name + " request sent: ";
  1970    debug.textContent += JSON.stringify(svcMsg);
  1971 
  1972  }
  1973 
  1974  function error( err ) {
  1975    debug.innerHTML += "&lt;br&gt;An error occurred obtaining a local network service.";
  1976    startBtn.disabled = false;
  1977  }
  1978 &lt;/script&gt;
  1979 </pre>
  1980       </div>
  1981       <div class="example">
  1982         <p>
  1983           This sample exposes a drop-down list containing a number of common Home-based audio devices. When the user
  1984           selects an audio device from the list provided, they are prompted to authorize a network service based on the
  1985           service type requested. The user may also select multiple network services matching the selected service
  1986           type. In this example, the user selects their make as being <var>Sony</var> and their model as being
  1987           <var>Bravia S1000</var> from which the Web page can derive a service type
  1988           (<var>urn:schemas-upnp-org:service:RenderingControl:1</var>).<br>
  1989           <br>
  1990           Once the user has authorized the device, the web page sends a simple mute command according to the messaging
  1991           format supported by the device.
  1992         </p>
  1993         <hr>
  1994         <pre class="highlight">
  1995 &lt;select name="make" id="make"&gt;
  1996   &lt;option selected="selected" disabled="disabled"&gt;Select make&lt;/option&gt;
  1997   &lt;option&gt;Sony&lt;/option&gt;
  1998   &lt;option&gt;Philips&lt;/option&gt;
  1999   &lt;option&gt;Alba&lt;/option&gt;
  2000 &lt;/select&gt;
  2001 &lt;select name="model" id="model"&gt;&lt;/select&gt;
  2002 &lt;div id="debugconsole"&gt;&lt;/div&gt;
  2003 
  2004 &lt;script&gt;
  2005   var debug = document.getElementById('debugconsole');
  2006 
  2007   var models = {
  2008     "Sony": [
  2009       {"name": "Bravia TV S1000", "type": "upnp", "service": "urn:schemas-upnp-org:service:RenderingControl:1" },
  2010       {"name": "Bravia TV S2000", "type": "zeroconf", "service": "_mediarenderer._http._tcp" },
  2011       {"name": "HiFi WD10", "type": "upnp", "service": "urn:schemas-upnp-org:service:RenderingControl:1" }
  2012     ],
  2013     "Philips": [ /* ... */ ],
  2014     "Alba": [ /* ... */ ]
  2015   };
  2016 
  2017   var makeEl = document.getElementById("make"),
  2018       modelEl = document.getElementById("model");
  2019 
  2020   makeEl.addEventListener('change', function() {
  2021     modelEl.innerHTML = ""; // reset
  2022     var defaultOption = document.createElement("option");
  2023     defaultOption.textContent = "Select model";
  2024     defaultOption.setAttribute("disabled", "disabled");
  2025     defaultOption.setAttribute("selected", "selected");
  2026     modelEl.appendChild(defaultOption);
  2027     for(var i = 0, l = models[makeEl.value].length; i &lt; l; i++) {
  2028       var option = document.createElement("option");
  2029       option.textContent = models[makeEl.value][i]["name"];
  2030       option.setAttribute("value", models[makeEl.value][i]["type"] + ":" + models[makeEl.value][i]["service"]);
  2031       modelEl.appendChild(option);
  2032     }
  2033   }, false);
  2034 
  2035   modelEl.addEventListener('change', function() {
  2036     if(navigator.getNetworkServices &amp;&amp;
  2037          modelEl.value == "upnp:urn:schemas-upnp-org:service:RenderingControl:1") {
  2038       var servicesPromise = navigator.getNetworkServices(modelEl.value).then(successCallback, errorCallback);
  2039     } else if (modelEl.value == "zeroconf:_mediarenderer._http._tcp") {
  2040       debug.innerHTML += "&lt;br&gt;Service type is not implemented by this application.";
  2041     } else {
  2042       debug.innerHTML += "&lt;br&gt;Service Discovery is not supported!";
  2043     }
  2044   }, false);
  2045 &lt;/script&gt;
  2046 
  2047 &lt;script&gt;
  2048   function successCallback( services ) {
  2049 
  2050   // Listen for service push notification messages
  2051 
  2052     services[0].addEventListener('notify', function ( msg ) {
  2053          debug.innerHTML += "&lt;br&gt;" + services[0].name + " event received: ";
  2054          debug.textContent += msg.data;
  2055     }, false);
  2056 
  2057  // Send a control signal to mute the service audio
  2058 
  2059     var svcXhr = new XMLHttpRequest();
  2060     svcXhr.open("POST", services[0].url); // services[0].url and its
  2061                                           // sub-resources have been whitelisted for
  2062                                           // cross-site XHR use in this current
  2063                                           // browsing context.
  2064 
  2065     svcXhr.setRequestHeader('SOAPAction', 'urn:schemas-upnp-org:service:RenderingControl:1#SetMute');
  2066     svcXhr.setRequestHeader('Content-Type', 'text/xml; charset="utf-8";');
  2067 
  2068     svcXhr.onreadystatechange = function ( response ) {
  2069       if( response.readyState != 4 || response.status != 200 )
  2070         return;
  2071       debug.innerHTML += "&lt;br&gt;" + services[0].name + " response received: ";
  2072       debug.textContent += response.responseXML;
  2073     }
  2074 
  2075     // Service messaging to mute the provided service
  2076     var svcMsg = '&lt;?xml version="1.0" encoding="utf-8"?&gt;' +
  2077                  '&lt;s:Envelope s:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/" ' +
  2078                    'xmlns:s="http://schemas.xmlsoap.org/soap/envelope/"&gt;' +
  2079                    '&lt;s:Body&gt;' +
  2080                      '&lt;u:SetMute xmlns:u="urn:schemas-upnp-org:service:RenderingControl:1"&gt;' +
  2081                        '&lt;InstanceID&gt;0&lt;/InstanceID&gt;' +
  2082                        '&lt;Channel&gt;Master&lt;/Channel&gt;' +
  2083                        '&lt;DesiredMute&gt;true&lt;/DesiredMute&gt;' +
  2084                      '&lt;/u:SetMute&gt;' +
  2085                    '&lt;/s:Body&gt;' +
  2086                  '&lt;/s:Envelope&gt;';
  2087 
  2088     svcXhr.send(svcMsg);
  2089     debug.innerHTML += "&lt;br&gt;" + services[0].name + " request sent: ";
  2090     debug.textContent += svcMsg;
  2091   }
  2092 
  2093   function errorCallback( error ) {
  2094     debug.innerHTML += "&lt;br&gt;An error occurred: " + error.code;
  2095   }
  2096 &lt;/script&gt;
  2097 </pre>
  2098       </div>
  2099     </section>
  2100     <section>
  2101       <h3>
  2102         Acknowledgements
  2103       </h3>
  2104       <p>
  2105         Thanks are expressed by the editor to the following individuals for their feedback on this specification to
  2106         date (in alphabetical order):<br>
  2107         <br>
  2108         Gar Bergstedt, Lars-Erik Bolstad, Cathy Chan, Hari G Kumar, Bob Lund, Giuseppe Pascale, Marcin Simonides,
  2109         Clarke Stevens, Christian Söderström, Mark Vickers.
  2110       </p>
  2111       <p>
  2112         Thanks are also expressed by the editor to the following organizations and groups for their support in
  2113         producing this specification to date (in alphabetical order):<br>
  2114         <br>
  2115         CableLabs, Opera Software ASA, W3C Device APIs Working Group, W3C Web and TV Interest Group.
  2116       </p>
  2117     </section>
  2118   </body>
  2119 </html>