discovery-api/Overview.src.html
author Rich Tibbett <richt@opera.com>
Thu, 17 Jan 2013 15:08:37 +0100
changeset 332 e19dc529aacc
parent 331 43b139afeba9
child 371 8b03e17da083
permissions -rw-r--r--
Minor editorial changes to DIAL protocol support section
     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
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    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"
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    37           specStatus:   "ED",
    38           //publishDate:  "2012-10-04",
    39           shortName:    "discovery-api",
    40           edDraftURI:   "http://dvcs.w3.org/hg/dap/raw-file/tip/discovery-api/Overview.html",
    41           previousMaturity: "FPWD",
    42           previousPublishDate: "2012-08-07",
    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               name:       "Clarke Stevens",
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    55             }
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   100     </style>
   101   </head>
   102   <body>
   103     <section id='abstract'>
   104       <p>
   105         This specification defines a mechanism for an HTML document to discover and subsequently communicate with
   106         <abbr title="Hypertext Transfer Protocol">HTTP</abbr>-based services advertised via common discovery protocols
   107         within the current network.
   108       </p>
   109     </section>
   110     <section id='sotd'>
   111       <p>
   112         This document represents the early consensus of the group on the scope and features of the proposed API.
   113       </p>
   114     </section>
   115     <section class="informative">
   116       <h3>
   117         Introduction
   118       </h3>
   119       <p>
   120         To enable Web pages to connect and communicate with Local-networked Services provided over HTTP, this
   121         specification introduces the <a href="#navigatornetworkservice"><code>NavigatorNetworkService</code></a>
   122         interface.
   123       </p>
   124       <p>
   125         Using this <abbr title="Application Programming Interface">API</abbr> consists of requesting a well-known
   126         service type, known by developers and advertised by Local-networked Devices. User authorization, where the user
   127         connects the web page to discovered services, is expected before the web page is able to interact
   128         with any Local-networked Services.
   129       </p>
   130       <p>
   131         A web page creates a request to obtain connectivity to services running in the network by specifying a
   132         well-known discovery service type that it wishes to interact with.
   133       </p>
   134       <p>
   135         The user agent, having captured all advertised services on the network from the <a>service discovery
   136         mechanisms</a> included in this recommendation, attempts to match the requested service type to a discovered
   137         service according to the processing described herein.
   138       </p>
   139       <p>
   140         If a service connectivity request is successful then the Web page is provided with the necessary information to
   141         communicate with the authorized Local-networked Service. If the request fails then the Web page will receive an
   142         error callback containing an error code describing the cause of Local-networked Service connectivity failure.
   143       </p>
   144       <p>
   145         Once connected to a Local-networked Service the Web page can send requests and receive responses to the
   146         Local-networked Service via the messaging format and appropriate channel inferred from the service type
   147         authorized via the provided API. The Web page, once connected, can also receive service-pushed events, in the
   148         messaging format supported by the Local-networked Device, if such event subscription functionality is provided
   149         by the connected Local-networked Service.
   150       </p>
   151       <div class="example">
   152         <p>
   153           Example of requesting a DNS-SD advertised service:
   154         </p>
   155         <hr>
   156         <pre class="highlight">
   157 function showServices( services ) {
   158   // Show a list of all the services provided to the web page
   159   for(var i = 0, l = services.length; i &lt; l; i++) console.log( services[i].name );
   160 }
   161 
   162 navigator.getNetworkServices('zeroconf:_boxee-jsonrpc._tcp', showServices);
   163 </pre>
   164       </div>
   165       <div class="example">
   166         <p>
   167           Example of requesting a UPnP advertised service, also handling error conditions:
   168         </p>
   169         <hr>
   170         <pre class="highlight">
   171 function showServices( services ) {
   172   // Show a list of all the services provided to the web page
   173   for(var i = 0, l = services.length; i &lt; l; i++) console.log( services[i].name );
   174 }
   175 
   176 function error( e ) {
   177   console.log( "Error occurred: " + e.code );
   178 }
   179 
   180 navigator.getNetworkServices('upnp:urn:schemas-upnp-org:service:ContentDirectory:1', showServices, error);
   181 </pre>
   182       </div>
   183       <div class="example">
   184         <p>
   185           Example of requesting either a DNS-SD or UPnP advertised service:
   186         </p>
   187         <hr>
   188         <pre class="highlight">
   189 function showServices( services ) {
   190   // Show a list of all the services provided to the web page (+ service type)
   191   for(var i = 0, l = services.length; i &lt; l; i++)
   192      console.log( services[i].name + '(' + services[i].type + ')' );
   193 }
   194 
   195 navigator.getNetworkServices([
   196   'zeroconf:_boxee-jsonrpc._tcp',
   197   'upnp:urn:schemas-upnp-org:service:ContentDirectory:1'
   198 ], showServices);
   199 </pre>
   200       </div>
   201       <p>
   202         For more detailed examples see the <a href="#examples">Examples</a> section.
   203       </p>
   204     </section>
   205     <section id='conformance'>
   206       <p>
   207         Requirements phrased in the imperative as part of algorithms (such as "strip any leading space characters" or
   208         "return false and abort these steps") are to be interpreted with the meaning of the key word ("must", "should",
   209         "may", etc) used in introducing the algorithm.
   210       </p>
   211       <p>
   212         Some conformance requirements are phrased as requirements on attributes, methods or objects. Such requirements
   213         are to be interpreted as requirements on user agents.
   214       </p>
   215       <p>
   216         Conformance requirements phrased as algorithms or specific steps MAY be implemented in any manner, so long as
   217         the end result is equivalent. (In particular, the algorithms defined in this specification are intended to be
   218         easy to follow, and not intended to be performant.)
   219       </p>
   220       <p>
   221         The only conformance class defined by this specification is a <dfn>user agent</dfn>.
   222       </p>
   223       <p>
   224         User agents MAY impose implementation-specific limits on otherwise unconstrained inputs, e.g. to prevent denial
   225         of service attacks, to guard against running out of memory, or to work around platform-specific limitations.
   226       </p>
   227       <p>
   228         When support for a feature is disabled (e.g. as an emergency measure to mitigate a security problem, or to aid
   229         in development, or for performance reasons), user agents MUST act as if they had no support for the feature
   230         whatsoever, and as if the feature was not mentioned in this specification. For example, if a particular feature
   231         is accessed via an attribute in a Web IDL interface, the attribute itself would be omitted from the objects
   232         that implement that interface - leaving the attribute on the object but making it return null or throw an
   233         exception is insufficient.
   234       </p>
   235       <section>
   236         <h3>
   237           Dependencies
   238         </h3>This specification relies on several other underlying specifications.
   239         <dl>
   240           <dt>
   241             HTML
   242           </dt>
   243           <dd>
   244             Many fundamental concepts from HTML are used by this specification. [[!HTML5]]
   245           </dd>
   246           <dt>
   247             WebIDL
   248           </dt>
   249           <dd>
   250             The IDL blocks in this specification use the semantics of the WebIDL specification. [[!WEBIDL]]
   251           </dd>
   252         </dl>
   253       </section>
   254     </section>
   255     <section>
   256       <h3>
   257         Terminology
   258       </h3>
   259       <p>
   260         The construction "a <code>Foo</code> object", where <code>Foo</code> is actually an interface, is sometimes
   261         used instead of the more accurate "an object implementing the interface <code>Foo</code>".
   262       </p>
   263       <p>
   264         The term DOM is used to refer to the API set made available to scripts in Web applications, and does not
   265         necessarily imply the existence of an actual <code>Document</code> object or of any other <code>Node</code>
   266         objects as defined in the DOM Core specifications. [[!DOM4]]
   267       </p>
   268       <p>
   269         An IDL attribute is said to be <em>getting</em> when its value is being retrieved (e.g. by author script), and
   270         is said to be <em>setting</em> when a new value is assigned to it.
   271       </p>
   272       <p>
   273         A <dfn>valid service type</dfn> is any of the following:
   274         <ul>
   275            <li>
   276               a string that begins with <code>upnp:</code> or <code>zeroconf:</code>
   277               followed by one or more characters in the ranges U+0021, U+0023 to U+0027, U+002A to U+002B, U+002D to U+002E,
   278               U+0030 to U+0039, U+0041 to U+005A, U+005E to U+007E.
   279            </li>
   280            <li>
   281               a string that begins with <code>dial:</code> followed by an integer version.
   282            </li>
   283         </ul>
   284       </p>
   285       <p>
   286         A <a>valid service type</a> provided in the <code>type</code> attribute of the <a href=
   287         "#dom-navigator-getnetworkservices"><code>getNetworkServices()</code></a> method will be matched against the
   288         services currently contained in the <a>list of available service records</a> according to the algorithms
   289         defined in this specification.
   290       </p>
   291       <p>
   292         A <dfn>user-agent generated callback url</dfn> is a Local-network accessible URL endpoint that a <a>user
   293         agent</a> generates and maintains for receiving HTTP NOTIFY requests from UPnP Event sources. It is only
   294         required when the user agent implements UPnP Service Discovery as defined in this specification.
   295       </p>
   296     </section>
   297     <section>
   298       <h2>
   299         Requesting networked services
   300       </h2>
   301       <pre class="widl">
   302 [Supplemental, NoInterfaceObject]
   303 interface <dfn id="navigatornetworkservice">NavigatorNetworkService</dfn> {
   304   // Obtain a Local-networked Service
   305   void <a href="#dom-navigator-getnetworkservices">getNetworkServices</a>( in any type,
   306                            in <a href=
   307 "#navigatornetworkservicesuccesscallback">NavigatorNetworkServiceSuccessCallback</a> successCallback,
   308                            in optional <a href=
   309 "#navigatornetworkserviceerrorcallback">NavigatorNetworkServiceErrorCallback</a> errorCallback );
   310 };
   311 <a class="externalDFN"
   312      href=
   313      "http://www.whatwg.org/specs/web-apps/current-work/complete/timers.html#navigator">Navigator</a> implements <a href=
   314      "#navigatornetworkservice">NavigatorNetworkService</a>;
   315 
   316 [Callback=FunctionOnly, NoInterfaceObject]
   317 interface <dfn id="navigatornetworkservicesuccesscallback">NavigatorNetworkServiceSuccessCallback</dfn> {
   318   void handleEvent( in <a href="#networkservices">NetworkServices</a> services );
   319 };
   320 
   321 [NoInterfaceObject]
   322 interface <dfn id="navigatornetworkserviceerror">NavigatorNetworkServiceError</dfn> {
   323   const unsigned short <a href="#dom-navigatornetworkserviceerror-permission_denied">PERMISSION_DENIED_ERR</a> = 1;
   324   const unsigned short <a href="#dom-navigatornetworkserviceerror-unknown_type_prefix">UNKNOWN_TYPE_PREFIX_ERR</a> = 2;
   325   readonly attribute unsigned short <a href="#dom-navigatornetworkserviceerror-code">code</a>;
   326 };
   327 
   328 [Callback=FunctionOnly, NoInterfaceObject]
   329 interface <dfn id="navigatornetworkserviceerrorcallback">NavigatorNetworkServiceErrorCallback</dfn> {
   330   void handleEvent( in <a href="#navigatornetworkserviceerror">NavigatorNetworkServiceError</a> error );
   331 };
   332 </pre>
   333       <section>
   334         <h2>
   335           Methods
   336         </h2>
   337         <dl class="domintro">
   338           <dt>
   339             <var title="">window</var> . <code title="dom-navigator"><a href=
   340             "http://www.whatwg.org/specs/web-apps/current-work/complete/timers.html#navigator">navigator</a></code> .
   341             <code title="dom-navigator-getNetworkServices"><a href=
   342             "#dom-navigator-getnetworkservices">getNetworkServices</a></code> ( <var title="">type</var> , <var title=
   343             "">successCallback</var> [, <var title="">errorCallback</var> ] )
   344           </dt>
   345           <dd>
   346             <p>
   347               Prompts the user to select discovered network services that have advertised support for the
   348               requested service type.
   349             </p>
   350             <p>
   351               The <var title="">type</var> argument contains one or more <a>valid service type</a> tokens that the web
   352               page would like to interact with.
   353             </p>
   354             <p>
   355               If the user accepts, the <var title="">successCallback</var> is invoked, with zero or more <a href=
   356               "#networkservice"><code>NetworkService</code></a> objects as its argument.
   357             </p>
   358             <p>
   359               If the user declines, the <var title="">errorCallback</var> (if any) is invoked.
   360             </p>
   361           </dd>
   362         </dl>
   363         <div>
   364           <p>
   365             When the <dfn id="dom-navigator-getnetworkservices"
   366                title="dom-navigator-getnetworkservices"><code>getNetworkServices(type, successCallback[,
   367                errorCallback])</code></dfn> method is called, the <a>user agent</a> MUST run the following steps:
   368           </p>
   369           <ol class="rule">
   370             <li>Let <var>requested control types</var> be initially set to an empty array.
   371             </li>
   372             <li>If <var>type</var> is an array consisting of one or more <a>valid service type</a> tokens, then let
   373             <var>requested control types</var> by the value of <var>type</var>, removing any non-<a>valid service
   374             type</a> tokens from the resulting array.
   375             </li>
   376             <li>If <var>type</var> is a string consisting of one <a>valid service type</a> token, then let
   377             <var>requested control types</var> be an array containing one item with a value of <var>type</var>.
   378             </li>
   379             <li>If <var>requested control types</var> is an array that contains at least one or more <a title=
   380             "valid service type">valid service type</a> tokens then continue to the step labeled <em>process</em>
   381             below. Otherwise, the <a>user agent</a> MUST <a href=
   382             "http://www.whatwg.org/specs/web-apps/current-work/complete/webappapis.html#queue-a-task"
   383                   class="externalDFN">queue a task</a> to invoke <var>errorCallback</var>, if it is provided and is an
   384                   object of type <code>Function</code>, with a new <a href=
   385                   "#navigatornetworkserviceerror"><code>NavigatorNetworkServiceError</code></a> object whose <a href=
   386                   "#dom-navigatornetworkserviceerror-code"><code>code</code></a> attribute has the numeric value 2
   387                   (<a href=
   388                   "#dom-navigatornetworkserviceerror-unknown_type_prefix"><code>UNKNOWN_TYPE_PREFIX_ERR</code></a>) as
   389                   its argument, abort any remaining steps and return.
   390             </li>
   391             <li>
   392               <em>Process</em>: Let <var>services found</var> be an empty array.
   393             </li>
   394             <li>For each <var>available service</var> in the <a>list of available service records</a> run the following
   395             steps:
   396               <ol class="rule">
   397                 <li>For each <var>requested control type</var> in <var>requested control types</var>: If <var>available
   398                 service</var>'s <code>type</code> attribute equals the <var>requested control type</var> then let <var>
   399                   matched service</var> equal the value of <var>available service</var> and continue at the step
   400                   labeled <var>attach</var> below.
   401                 </li>
   402                 <li>Continue at the next <var>available service</var>.
   403                 </li>
   404                 <li>
   405                   <em>Attach</em>: If <var>matched service</var> is not empty then run the following steps:
   406                   <ol class="rule">
   407                     <li>Let <var>new service object</var> be a new <a href=
   408                     "#networkservice"><code>NetworkService</code></a> object, mapping the parameters of <var>matched
   409                     service</var> to this new object where possible.
   410                     </li>
   411                     <li>Append <var>new service object</var> to the <var>services found</var> array.
   412                     </li>
   413                   </ol>
   414                 </li>
   415               </ol>
   416             </li>
   417             <li>Return, and run the remaining steps asynchronously.
   418             </li>
   419             <li>Optionally, e.g. based on a previously-established user preference, for security reasons, or due to
   420             platform limitations, the <a>user agent</a> MAY <a href=
   421             "http://www.whatwg.org/specs/web-apps/current-work/complete/webappapis.html#queue-a-task"
   422                   class="externalDFN">queue a task</a> to invoke <var>errorCallback</var>, if it is provided and is an
   423                   object of type <code>Function</code>, with a new <a href=
   424                   "#navigatornetworkserviceerror"><code>NavigatorNetworkServiceError</code></a> object whose <a href=
   425                   "#dom-navigatornetworkserviceerror-code"><code>code</code></a> attribute has the numeric value 1
   426                   (<a href=
   427                   "#dom-navigatornetworkserviceerror-permission_denied"><code>PERMISSION_DENIED_ERR</code></a>) as its
   428                   argument, abort any remaining steps and return.
   429             </li>
   430             <li>If <var>services found</var> is not an empty array then the <a>user agent</a> MUST prompt the user in a
   431               user-agent-specific manner for permission to provide
   432             the <a href="http://www.whatwg.org/specs/web-apps/current-work/complete/browsers.html#entry-script"
   433                   class="externalDFN">entry script</a>'s <a href=
   434                   "http://www.whatwg.org/specs/web-apps/current-work/complete/origin-0.html#origin"
   435                   class="externalDFN">origin</a> with an array of <a href=
   436                   "#networkservice"><code>NetworkService</code></a> objects representing the <a>user-authorized</a> subset
   437                   of <var>services found</var>.
   438               <p>
   439                 If the user grants permission to access one or more networked services then the <a>user agent</a>
   440                 SHOULD include an "ongoing local-network communication" indicator.
   441               </p>
   442               <p>
   443                 If the user denies permission, then the <a>user agent</a> MUST <a href=
   444                 "http://www.whatwg.org/specs/web-apps/current-work/complete/webappapis.html#queue-a-task"
   445                    class="externalDFN">queue a task</a> to invoke <var>errorCallback</var>, if it is provided and is an
   446                    object of type <code>Function</code>, with a new <a href=
   447                    "#navigatornetworkserviceerror"><code>NavigatorNetworkServiceError</code></a> object whose <a href=
   448                    "#dom-navigatornetworkserviceerror-code"><code>code</code></a> attribute has the numeric value 1
   449                    (<a href=
   450                    "#dom-navigatornetworkserviceerror-permission_denied"><code>PERMISSION_DENIED_ERR</code></a>) as its
   451                    argument, abort any remaining steps and return.
   452               </p>
   453               <p>
   454                 If the user never responds, this algorithm stalls on this step.
   455               </p>
   456             </li>
   457             <li>Let <var>services</var> be an empty array.
   458             </li>
   459             <li>
   460                If <var>services found</var> is not an empty array then set <var>services</var> to be an array of one or more <a href=
   461             "#networkservice"><code>NetworkService</code></a> objects for which the user granted permission above - known as the
   462             current objects <dfn>user-authorized</dfn> services.
   463             </li>
   464             <li>For each Object <var>service</var> in <var>services</var>, if any, run the following sub-steps:
   465               <ol class="rule">
   466                 <li>Add the <var>service</var>'s <code>url</code> parameter to the <a>entry script origin's
   467                   <abbr title="Uniform Resource Locator">URL</abbr> whitelist</a>.
   468                 </li>
   469                 <li>If <var>service</var>'s <code>type</code> parameter begins with the DOMString "<code>upnp:</code>"
   470                 and the <var>service</var>'s <code>eventsUrl</code> parameter is not empty then <a>setup a UPnP Events
   471                 Subscription</a> for <var>service</var>.
   472                 </li>
   473               </ol>
   474             </li>
   475             <li>Let <var>services manager</var> be a new <a href="#networkservices"><code>NetworkServices</code></a>
   476             object.
   477             </li>
   478             <li>Set <var>services manager</var>'s <a href=
   479             "#dom-networkservices-servicesavailable"><code>servicesAvailable</code></a> attribute to the number of
   480             items currently found in the <a>list of available service records</a> whose <code>type</code> property
   481             matches any of the tokens requested in <var>requested control types</var>.
   482             </li>
   483             <li>Add <var>services</var>, if any, to the <var>services manager</var> object as its collection of <a>indexed
   484             properties</a>. If <var>services</var> is an empty array then the <var>services manager</var> does not have any
   485             <var>indexed properties</var>.
   486             </li>
   487             <li>Set <var>services manager</var>'s <a href="#dom-networkservices-length"><code>length</code></a>
   488             attribute to the number of items in <var>services</var>.
   489             </li>
   490             <li>Add <var>services manager</var> to the <a>list of active service managers</a>.
   491             </li>
   492             <li>The <a>user agent</a> MUST <a href=
   493             "http://www.whatwg.org/specs/web-apps/current-work/complete/webappapis.html#queue-a-task"
   494                   class="externalDFN">queue a task</a> to invoke <var>successCallback</var> with <var>services
   495                   manager</var> as its argument.
   496             </li>
   497           </ol>
   498           <p>
   499             The <a href="http://www.whatwg.org/specs/web-apps/current-work/complete/webappapis.html#task-source"
   500                class="externalDFN">task source</a> for these <a href=
   501                "http://www.whatwg.org/specs/web-apps/current-work/complete/webappapis.html#concept-task"
   502                class="externalDFN">tasks</a> is the <a href=
   503                "http://www.whatwg.org/specs/web-apps/current-work/complete/webappapis.html#user-interaction-task-source"
   504                class="externalDFN">user interaction task source</a>.
   505           </p>
   506           <p>
   507             When a <a href="#networkservice"><code>NetworkService</code></a> object is provided to a Web page, the
   508             <a>user agent</a> MUST add the <code>url</code> property to the <dfn>entry script origin's URL
   509             whitelist</dfn>. This list enables the Web page to override and initiate cross-site resource requests
   510             towards these URLs, and any sub-resources of these URLs, within the current <a href=
   511             "http://www.whatwg.org/specs/web-apps/current-work/complete/browsers.html#entry-script"
   512                class="externalDFN">entry script</a>'s <a href=
   513                "http://www.whatwg.org/specs/web-apps/current-work/complete/origin-0.html#origin"
   514                class="externalDFN">origin</a> via various existing mechanisms (e.g. Web Sockets, Server-Sent Events,
   515                Web Messaging, XMLHttpRequest).
   516           </p>
   517           <p>
   518             If the user navigates away from the
   519             <a href="http://www.whatwg.org/specs/web-apps/current-work/complete/browsers.html#entry-script"
   520                   class="externalDFN">entry script</a>'s <a href=
   521                   "http://www.whatwg.org/specs/web-apps/current-work/complete/origin-0.html#origin"
   522                   class="externalDFN">origin</a> then the <a>user agent</a> <em class=
   523             "ct">MUST</em> remove all previously whitelisted urls from the <a>entry script origin's URL whitelist</a>.
   524             There is no persistence to network service selections provided to a web page. It is not possible to access
   525             a previously white-listed networked service without the necessary user authorization in all of the
   526             following cases:
   527           </p>
   528           <ul>
   529             <li>If the current script is reloaded at any point in the same or different window.
   530             </li>
   531             <li>if the current script reinvokes the <a href=
   532             "#dom-navigator-getnetworkservices"><code>getNetworkServices()</code></a> method at any point in its
   533             execution.
   534             </li>
   535             <li>If the user navigates forward or back in their history to reload the current page.
   536             </li>
   537             <li>If a script is running in a different origin.
   538             </li>
   539           </ul>
   540         </div>
   541       </section>
   542       <section>
   543         <h3>
   544           Error Handling
   545         </h3>
   546         <dl class="domintro">
   547           <dt>
   548             <var title="">error</var> . <code title="dom-NavigatorNetworkServiceError-code"><a href=
   549             "#dom-navigatornetworkserviceerror-code">code</a></code>
   550           </dt>
   551           <dd>
   552             <p>
   553               Returns the current error's error code. At the current time, this will be <code>1</code> or
   554               <code>2</code>, for which the corresponding error constants <a href=
   555               "#dom-navigatornetworkserviceerror-permission_denied"><code>PERMISSION_DENIED_ERR</code></a> and <a href=
   556               "#dom-navigatornetworkserviceerror-unknown_type_prefix"><code>UNKNOWN_TYPE_PREFIX_ERR</code></a> are
   557               defined.
   558             </p>
   559           </dd>
   560         </dl>
   561         <p>
   562           The <dfn id="dom-navigatornetworkserviceerror-code"
   563              title="dom-navigatornetworkserviceerror-code"><code>code</code></dfn> attribute of a <a href=
   564              "#navigatornetworkserviceerror"><code>NavigatorNetworkServiceError</code></a> object <em class=
   565              "ct">MUST</em> return the code for the error, which will be one of the following:
   566         </p>
   567         <dl>
   568           <dt>
   569             <dfn id="dom-navigatornetworkserviceerror-permission_denied"
   570                 title="dom-navigatornetworkserviceerror-permission_denied"><code>PERMISSION_DENIED_ERR</code></dfn>
   571                 (numeric value 1)
   572           </dt>
   573           <dd>
   574             The user or user agent denied the page permission to access any services.
   575           </dd>
   576           <dt>
   577             <dfn id="dom-navigatornetworkserviceerror-unknown_type_prefix"
   578                 title="dom-navigatornetworkserviceerror-unknown_type_prefix"><code>UNKNOWN_TYPE_PREFIX_ERR</code></dfn>
   579                 (numeric value 2)
   580           </dt>
   581           <dd>
   582             No <a>valid service type</a> tokens were provided in the method invocation.
   583           </dd>
   584         </dl>
   585       </section>
   586     </section>
   587     <section>
   588       <h2>
   589         Obtaining networked services
   590       </h2>
   591       <p>
   592         The <a href="#networkservices"><code>NetworkServices</code></a> interface represents a collection of zero
   593         or more <dfn>indexed properties</dfn> that are
   594         each a <a>user-authorized</a> <a href="#networkservice"><code>NetworkService</code></a> object.
   595       </p>
   596       <p>
   597         A <a href="#networkservices"><code>NetworkServices</code></a> object is the top level success callback
   598         parameter from a call to
   599         <a href="#dom-navigator-getnetworkservices"><code>getNetworkServices()</code></a>.
   600       </p>
   601       <pre class="widl">
   602 [NoInterfaceObject]
   603 interface <dfn id="networkservices">NetworkServices</dfn> {
   604   readonly attribute unsigned long    <a href="#dom-networkservices-length">length</a>;
   605   getter <a href="#networkservice">NetworkService</a> (unsigned long index);
   606   <a href="#networkservice">NetworkService</a>? <a href=
   607 "#dom-networkservices-getservicebyid">getServiceById</a>(DOMString id);
   608 
   609   readonly attribute unsigned long    <a href="#dom-networkservices-servicesavailable">servicesAvailable</a>;
   610 
   611   // event handler attributes
   612            attribute <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/webappapis.html#eventhandler"
   613      class="externalDFN">EventHandler</a>     <a href="#dom-networkservices-onserviceavailable">onserviceavailable</a>;
   614            attribute <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/webappapis.html#eventhandler"
   615      class="externalDFN">EventHandler</a>     <a href=
   616      "#dom-networkservices-onserviceunavailable">onserviceunavailable</a>;
   617 
   618 };
   619 
   620 <a href="#networkservices">NetworkServices</a> implements <a href=
   621 "http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#interface-eventtarget"
   622      class="externalDFN">EventTarget</a>;
   623 </pre>
   624       <section>
   625         <h2>
   626           Attributes
   627         </h2>
   628         <dl class="domintro">
   629           <dt>
   630             <code title="dom-networkservices-length"><a href="#dom-networkservices-length">length</a></code>
   631           </dt>
   632           <dd>
   633             <p>
   634               Returns the current number of items in the current object's collection of <a href=
   635               "#networkservice"><code>NetworkService</code></a> objects.
   636             </p>
   637           </dd>
   638           <dt>
   639             <code title="dom-networkservices-servicesavailable"><a href=
   640             "#dom-networkservices-servicesavailable">servicesAvailable</a></code>
   641           </dt>
   642           <dd>
   643             <p>
   644               Returns the current number of items matching one of the app-requested <a>valid service type</a> tokens in
   645               the <a>list of available service records</a>.
   646             </p>
   647           </dd>
   648         </dl>
   649         <div>
   650           <p>
   651             The <dfn id="dom-networkservices-length"><code>length</code></dfn> attribute MUST return the number of
   652             <a href="#networkservice"><code>NetworkService</code></a> objects represented by the collection.
   653           </p>
   654           <p>
   655             The <dfn id="dom-networkservices-servicesavailable"><code>servicesAvailable</code></dfn> attribute MUST
   656             return the number of services in the <a>list of available service records</a> whose <code>type</code>
   657             attribute matches any of the <a>valid service type</a> tokens that was initially used to create the current
   658             <a href="#networkservices"><code>NetworkServices</code></a> object.
   659           </p>
   660         </div>
   661       </section>
   662       <section>
   663         <h2>
   664           Methods
   665         </h2>
   666         <dl class="domintro">
   667           <dt>
   668             <code title="networkservices-getter"><a href="#networkservices">services</a></code> [ <var title=
   669             "">index</var> ]
   670           </dt>
   671           <dd>
   672             <p>
   673               Returns the specified <a href="#networkservice"><code>NetworkService</code></a> object.
   674             </p>
   675           </dd>
   676           <dt>
   677             <code title="networkservices-getter"><a href="#networkservices">services</a></code> . <code title=
   678             "dom-networkservices-getservicebyid"><a href=
   679             "#dom-networkservices-getservicebyid">getServiceById</a></code> ( <var title="">id</var> )
   680           </dt>
   681           <dd>
   682             <p>
   683               Returns the <a href="#networkservice"><code>NetworkService</code></a> object with the given identifier,
   684               or null if no service has that identifier.
   685             </p>
   686           </dd>
   687         </dl>
   688         <p>
   689           A <a href="#networkservices"><code>NetworkServices</code></a> object represents the current collection of zero
   690           or more <a href="#networkservice"><code>NetworkService</code></a> objects - its <a>indexed properties</a>. A <a href=
   691           "#networkservices"><code>NetworkServices</code></a> object is <span>immutable</span> meaning that
   692           <a>indexed properties</a> cannot be added and <a>indexed properties</a> cannot be removed for the lifetime of
   693           a <a href="#networkservices"><code>NetworkServices</code></a> object.
   694         </p>
   695         <p class="note">
   696           Each service in a <a href="#networkservices"><code>NetworkServices</code></a> object thus has an index; the
   697           first has the index 0, and each subsequent service is numbered one higher than the previous one.
   698         </p>
   699         <p>
   700           The <a href=
   701           "http://www.whatwg.org/specs/web-apps/current-work/multipage/infrastructure.html#supported-property-indices"
   702              class="externalDFN">supported property indices</a> of <a href=
   703              "#networkservices"><code>NetworkServices</code></a> objects at any instant are the numbers from zero to
   704              the number of the <a href="#networkservice"><code>NetworkService</code></a> objects in the collection
   705              minus one.
   706         </p>
   707         <p>
   708           To <a href=
   709           "http://www.whatwg.org/specs/web-apps/current-work/multipage/infrastructure.html#determine-the-value-of-an-indexed-property"
   710              class="externalDFN">determine the value of an indexed property</a> for a given index <var>index</var> in a
   711              <a href="#networkservices"><code>NetworkServices</code></a> object the user agent MUST return the <a href=
   712              "#networkservice"><code>NetworkService</code></a> object that represents the <var>index</var>th item in
   713              the collection.
   714         </p>
   715         <p>
   716           The <dfn id="dom-networkservices-getservicebyid"><code>getServiceById(id)</code></dfn> method <em class=
   717           "ct">MUST</em> return the first <a href="#networkservice"><code>NetworkService</code></a> object in the
   718           collection whose <a href="#dom-networkservice-id"><code>id</code></a> attribute is equal to the value of the
   719           <var>id</var> argument provided. When no <a href="#networkservice"><code>NetworkService</code></a> objects
   720           match the given argument, the method MUST return null.
   721         </p>
   722         <p>
   723           Services available within the local network can connect and disconnect at different times during the
   724           execution of a web page. A <a>user agent</a> can inform a web page when the state of networked services
   725           matching the requested <a>valid service type</a> change. Web pages can use this information to enable in-page
   726           experiences for communicating the state of networked services with the ability to change the particular
   727           service or set of services the page is connected to by re-invoking the <a href=
   728           "#dom-navigator-getnetworkservices"><code>getNetworkServices()</code></a> method.
   729         </p>
   730       </section>
   731       <section>
   732         <h2>
   733           Events
   734         </h2>
   735         <p>
   736           The following are the event handlers (and their corresponding event handler event types) that <em class=
   737           "ct">MUST</em> be supported, as IDL attributes, by all objects implementing the <a href=
   738           "#networkservices"><code>NetworkServices</code></a> interface:
   739         </p>
   740         <table border="1">
   741           <thead>
   742             <tr>
   743               <th>
   744                 <span title="event handlers">Event handler</span>
   745               </th>
   746               <th>
   747                 <span>Event handler event type</span>
   748               </th>
   749             </tr>
   750           </thead>
   751           <tbody>
   752             <tr>
   753               <td>
   754                 <dfn id="dom-networkservices-onserviceavailable"
   755                     title="dom-NetworkServices-onserviceavailable"><code>onserviceavailable</code></dfn>
   756               </td>
   757               <td>
   758                 <a href="#event-serviceavailable"><code>serviceavailable</code></a>
   759               </td>
   760             </tr>
   761             <tr>
   762               <td>
   763                 <dfn id="dom-networkservices-onserviceunavailable"
   764                     title="dom-NetworkServices-onserviceunavailable"><code>onserviceunavailable</code></dfn>
   765               </td>
   766               <td>
   767                 <a href="#event-serviceunavailable"><code>serviceunavailable</code></a>
   768               </td>
   769             </tr>
   770           </tbody>
   771         </table>
   772       </section>
   773     </section>
   774     <section>
   775       <h2>
   776         Communicating with a networked service
   777       </h2>
   778       <p>
   779         The <a href="#networkservice"><code>NetworkService</code></a> interface is used to provide a set of connection
   780         information for an HTTP service endpoint and if available, service events, running on a networked device.
   781       </p>
   782       <pre class="widl">
   783 [NoInterfaceObject]
   784 interface <dfn id="networkservice">NetworkService</dfn> {
   785   readonly attribute DOMString        <a href="#dom-networkservice-id">id</a>;
   786   readonly attribute DOMString        <a href="#dom-networkservice-name">name</a>;
   787   readonly attribute DOMString        <a href="#dom-networkservice-type">type</a>;
   788   readonly attribute DOMString        <a href="#dom-networkservice-url">url</a>;
   789   readonly attribute DOMString        <a href="#dom-networkservice-config">config</a>;
   790 
   791   readonly attribute boolean          <a href="#dom-networkservice-online">online</a>;
   792 
   793   // event handler attributes
   794            attribute <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/webappapis.html#eventhandler"
   795      class="externalDFN">EventHandler</a>     <a href="#dom-networkservice-onserviceonline">onserviceonline</a>;
   796            attribute <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/webappapis.html#eventhandler"
   797      class="externalDFN">EventHandler</a>     <a href="#dom-networkservice-onserviceoffline">onserviceoffline</a>;
   798 
   799            attribute <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/webappapis.html#eventhandler"
   800      class="externalDFN">EventHandler</a>     <a href="#dom-networkservice-onnotify">onnotify</a>;
   801 };
   802 
   803 <a href="#networkservice">NetworkService</a> implements <a href=
   804 "http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#interface-eventtarget"
   805      class="externalDFN">EventTarget</a>;
   806 </pre>
   807       <section>
   808         <h2>
   809           Attributes
   810         </h2>
   811         <dl class="domintro">
   812           <dt>
   813             <var title="">service</var> . <code title="dom-networkservice-id"><a href=
   814             "#dom-networkservice-id">id</a></code>
   815           </dt>
   816           <dd>
   817             <p>
   818               A unique identifier for the given user-selected service instance.
   819             </p>
   820           </dd>
   821           <dt>
   822             <var title="">service</var> . <code title="dom-networkservice-name"><a href=
   823             "#dom-networkservice-name">name</a></code>
   824           </dt>
   825           <dd>
   826             <p>
   827               The name of the user-selected service.
   828             </p>
   829           </dd>
   830           <dt>
   831             <var title="">service</var> . <code title="dom-networkservice-type"><a href=
   832             "#dom-networkservice-type">type</a></code>
   833           </dt>
   834           <dd>
   835             <p>
   836               The <a>valid service type</a> token value of the user-selected service.
   837             </p>
   838           </dd>
   839           <dt>
   840             <var title="">service</var> . <code title="dom-networkservice-url"><a href=
   841             "#dom-networkservice-url">url</a></code>
   842           </dt>
   843           <dd>
   844             <p>
   845               The control URL endpoint (including any required port information) of the user-selected control service
   846               that has been added to the <a>entry script origin's URL whitelist</a>.
   847             </p>
   848           </dd>
   849           <dt>
   850             <var title="">service</var> . <code title="dom-networkservice-config"><a href=
   851             "#dom-networkservice-config">config</a></code>
   852           </dt>
   853           <dd>
   854             <p>
   855               The configuration information associated with the service depending on the requested service type.
   856             </p>
   857           </dd>
   858         </dl>
   859         <p>
   860           The <dfn id="dom-networkservice-id"><code>id</code></dfn> attribute is a unique identifier for the service.
   861           The same service provided at different times or on different objects MUST have the same <a href=
   862           "#dom-networkservice-id"><code>id</code></a> value.
   863         </p>
   864         <p>
   865           The <dfn id="dom-networkservice-name"><code>name</code></dfn> attribute represents a human-readable title for
   866           the service.
   867         </p>
   868         <p>
   869           The <dfn id="dom-networkservice-type"><code>type</code></dfn> attribute reflects the value of the <a>valid
   870           service type</a> of the service.
   871         </p>
   872         <p>
   873           The <dfn id="dom-networkservice-url"><code>url</code></dfn> attribute is an <a href=
   874           "http://www.w3.org/TR/html5/urls.html#absolute-url"
   875              class="externalDFN">absolute URL</a> pointing to the root HTTP endpoint for the service that has been
   876              added to the <a>entry script origin's URL whitelist</a>. Web pages can subsequently use this value for
   877              implicit cross-document messaging via various existing mechanisms (e.g. Web Sockets, Server-Sent Events,
   878              Web Messaging, XMLHttpRequest).
   879         </p>
   880         <p>
   881           The <dfn id="dom-networkservice-config"><code>config</code></dfn> attribute provides the raw configuration
   882           information extracted from the given network service.
   883         </p>
   884       </section>
   885       <section>
   886         <h3>
   887           States
   888         </h3>
   889         <dl class="domintro">
   890           <dt>
   891             <var title="">service</var> . <code title="dom-networkservice-online"><a href=
   892             "#dom-networkservice-online">online</a></code>
   893           </dt>
   894           <dd>
   895             <p>
   896               Returns <code>true</code> if the service is reporting that it is accessible on the local network or
   897               <code>false</code> if the service is reporting that it is no longer accessible (temporarily or
   898               permanently) on the local network.
   899             </p>
   900           </dd>
   901         </dl>
   902         <p>
   903           The <dfn id="dom-networkservice-online"><code>online</code></dfn> attribute indicates whether the service is
   904           reporting itself as being either <var>online</var>, and therefore accessible on the local network, in which
   905           case this attribute will return <code>true</code> or, <var>offline</var>, and therefore not accessible on the
   906           local network, either temporarily or permanently, in which case this attribute will return
   907           <code>false</code>. This attribute MUST default to <code>true</code>.
   908         </p>
   909       </section>
   910       <section>
   911         <h3>
   912           Events
   913         </h3>
   914         <p>
   915           The following are the event handlers (and their corresponding event handler event types) that <em class=
   916           "ct">MUST</em> be supported, as IDL attributes, by all objects implementing the <a href=
   917           "#networkservice"><code>NetworkService</code></a> interface:
   918         </p>
   919         <table border="1">
   920           <thead>
   921             <tr>
   922               <th>
   923                 <span title="event handlers">Event handler</span>
   924               </th>
   925               <th>
   926                 <span>Event handler event type</span>
   927               </th>
   928             </tr>
   929           </thead>
   930           <tbody>
   931             <tr>
   932               <td>
   933                 <dfn id="dom-networkservice-onnotify"
   934                     title="dom-NetworkService-onnotify"><code>onnotify</code></dfn>
   935               </td>
   936               <td>
   937                 <a href="#event-notify"><code>notify</code></a>
   938               </td>
   939             </tr>
   940             <tr>
   941               <td>
   942                 <dfn id="dom-networkservice-onserviceonline"
   943                     title="dom-NetworkService-onserviceonline"><code>onserviceonline</code></dfn>
   944               </td>
   945               <td>
   946                 <a href="#event-serviceonline"><code>serviceonline</code></a>
   947               </td>
   948             </tr>
   949             <tr>
   950               <td>
   951                 <dfn id="dom-networkservice-onserviceoffline"
   952                     title="dom-NetworkService-onserviceoffline"><code>onserviceoffline</code></dfn>
   953               </td>
   954               <td>
   955                 <a href="#event-serviceoffline"><code>serviceoffline</code></a>
   956               </td>
   957             </tr>
   958           </tbody>
   959         </table>
   960       </section>
   961     </section>
   962     <section>
   963       <h2>
   964         Service Discovery
   965       </h2>
   966       <p>
   967         A <a>user agent</a> conforming to this specification MAY implement <abbr title=
   968         "Simple Service Discovery Protocol">SSDP</abbr> [[!UPNP-DEVICEARCH11]], Zeroconf [[!DNS-SD]] + [[!MDNS]] or
   969         <abbr title="Discovery and Launch Protocol">DIAL</abbr> [<a href = "https://sites.google.com/a/dial-multiscreen.org/dial/dial-protocol-specification">DIAL</a>]
   970         <dfn>service discovery mechanisms</dfn> - the requirements detailed in this section of the specification - to
   971         enable Web pages to request and connect with HTTP services running on networked devices, discovered via either
   972         mechanism, through this API. When a <a>user agent</a> implements either of these <a>service discovery
   973         mechanisms</a>, then it MUST conform to the corresponding algorithms provided in this section of the
   974         specification.
   975       </p>
   976       <p>
   977         This section presents how the results of these two <a>service discovery mechanisms</a> will be matched to
   978         requested service types, how the user agent stores available and active services and how their properties are
   979         applied to any resulting <a href="#networkservice"><code>NetworkService</code></a> objects.
   980       </p>
   981       <p>
   982         It is expected that user agents will perform these <a>service discovery mechanisms</a> asynchronously and
   983         periodically update the <a>list of available service records</a> as required. The timing of any <a>service
   984         discovery mechanisms</a> is an implementation detail left to the discretion of the implementer (e.g. by
   985         continuously monitoring the network as a background process or on invocation of this API from a Web page).
   986       </p>
   987       <p>
   988         The <dfn>list of available service records</dfn> is a single dynamic internal lookup table within user agents
   989         that is used to track all the services that have been discovered and are available in the current network at
   990         any given time. At any point during the running of either of the two <a>service discovery mechanisms</a> then
   991         existing entries within this table can be updated, entries can be added and entries can be removed as the
   992         status of networked services changes according to the rules defined in this specification.
   993       </p>
   994       <p>
   995         The <dfn>list of active service managers</dfn> is an internal list within user agents that is used to track all
   996         <a href="#networkservices"><code>NetworkServices</code></a> objects currently being shared with any web pages
   997         at the current time within the user agent. Each <a href="#networkservices"><code>NetworkServices</code></a> object
   998         in the <a>list of
   999         active service managers</a> represents a collection of zero or more <a href=
  1000         "#networkservice"><code>NetworkService</code></a> objects - known as its <dfn>indexed properties</dfn>.
  1001         <a href="#networkservice"><code>NetworkService</code></a> objects are attached as the <a>indexed properties</a>
  1002         of a <a href="#networkservices"><code>NetworkServices</code></a> object as part of the <a href=
  1003         "#dom-navigator-getnetworkservices"><code>getNetworkServices()</code></a> algorithm.
  1004       </p>
  1005       <p>
  1006         The rule for <dfn>adding an available service</dfn> is the process of adding a new service or updating an
  1007         existing service in the <a>list of available service records</a> that is generally available on the user's
  1008         current network. This rule takes one argument, <var>network service record</var>, and consists of running the
  1009         following steps:
  1010       </p>
  1011       <ol class="rule">
  1012         <li>Let <var>new service registration flag</var> be <code>true</code>.
  1013         </li>
  1014         <li>For each <var>existing service record</var> in the current <a>list of available service records</a>, run
  1015         the following sub-steps:
  1016           <ol class="rule">
  1017             <li>If the <var>existing service record</var>'s <code>id</code> property does not equal <var>network
  1018             service record</var>'s <code>id</code> property then abort any remaining sub-steps and continue at the next
  1019             available <var>existing service record</var>.
  1020             </li>
  1021             <li>Set <var>new service registration flag</var> to <code>false</code>.
  1022             </li>
  1023             <li>Replace the value of <var>existing service record</var> in the current <a>list of available service
  1024             records</a> with the value of <var>network service record</var>.
  1025             </li>
  1026           </ol>
  1027         </li>
  1028         <li>If <var>new service registration flag</var> is set to <code>true</code> then add <var>network service
  1029         record</var> to the <a>list of available service records</a> as a new item.
  1030         </li>
  1031         <li>For each <var>service manager</var> in the <a>list of active service managers</a> run the following steps:
  1032           <ol class="rule">
  1033             <li>Let <var>service type in current service manager flag</var> be <code>false</code>.
  1034             </li>
  1035             <li>For each <var>active service</var> in <var>service manager</var> run the following steps:
  1036               <ol class="rule">
  1037                 <li>If <var>network service record</var>'s <code>type</code> property does not equal <var>active
  1038                 service</var>'s <code>type</code> attribute then abort any remaining sub-steps for this <var>active
  1039                 service</var> and continue at the next available <var>active service</var>.
  1040                 </li>
  1041                 <li>Set the <var>service type in current service manager flag</var> to <code>true</code>.
  1042                 </li>
  1043                 <li>If the <var>new service registration flag</var> is set to <code>false</code>, the <var>network
  1044                 service record</var>'s <code>id</code> property equals the <var>active service</var>'s <code>id</code>
  1045                 attribute and <var>active service</var>'s <a href="#dom-networkservice-online"><code>online</code></a>
  1046                 attribute is currently set to <code>false</code> then set <var>active service</var>'s <a href=
  1047                 "#dom-networkservice-online"><code>online</code></a> attribute to <code>true</code> and then <a href=
  1048                 "http://www.whatwg.org/specs/web-apps/current-work/complete/webappapis.html#queue-a-task"
  1049                       class="externalDFN">queue a task</a> to dispatch a newly created event with the name <a href=
  1050                       "#event-serviceonline"><code>serviceonline</code></a> that uses the <a href=
  1051                       "http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#event"
  1052                       class="externalDFN"><code>Event</code></a> interface, which does not bubble, is not cancellable,
  1053                       and has no default action, at the current <var>active service</var> object.
  1054                 </li>
  1055               </ol>
  1056             </li>
  1057             <li>If the <var>new service registration flag</var> is set to <code>true</code> and the <var>service type
  1058             in current service manager flag</var> is also set to <code>true</code> then increment <var>service
  1059             manager</var>'s <a href="#dom-networkservices-servicesavailable"><code>servicesAvailable</code></a>
  1060             attribute by <code>1</code> and then <a href=
  1061             "http://www.whatwg.org/specs/web-apps/current-work/complete/webappapis.html#queue-a-task"
  1062                   class="externalDFN">queue a task</a> to dispatch a newly created event with the name <a href=
  1063                   "#event-serviceavailable"><code>serviceavailable</code></a> that uses the <a href=
  1064                   "http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#event"
  1065                   class="externalDFN"><code>Event</code></a> interface, which does not bubble, is not cancellable, and
  1066                   has no default action, at the current <var>service manager</var> object.
  1067             </li>
  1068           </ol>
  1069         </li>
  1070       </ol>
  1071       <p>
  1072         The rule for <dfn>removing an available service</dfn> is the general process of removing a service from the
  1073         <a>list of available service records</a> that has left the user's current network or has otherwise expired.
  1074         This rule takes one argument, <var>service identifier</var>, and consists of running the following steps:
  1075       </p>
  1076       <ol class="rule">
  1077         <li>For each <var>existing service record</var> in the current <a>list of available service records</a>, run
  1078         the following sub-steps:
  1079           <ol class="rule">
  1080             <li>If the <var>existing service record</var>'s <code>id</code> property does not match <var>service
  1081             identifier</var> then skip any remaining sub-steps for the current <var>existing service record</var> and
  1082             continue at the next available <var>existing service record</var>.
  1083             </li>
  1084             <li>If the <var>existing service record</var>'s <code>type</code> property begins with the DOMString
  1085             "<code>upnp:</code>" and <var>existing service record</var>'s <code>eventsURL</code> property is set then
  1086             run the rule to <a>terminate an existing UPnP Events Subscription</a>, if one is currently active (as a
  1087             result of having previously called <a>setup a UPnP Events Subscription</a> against the current
  1088             <var>existing service record</var>).
  1089             </li>
  1090             <li>For each <var>service manager</var> in the <a>list of active service managers</a> run the following
  1091             steps:
  1092               <ol class="rule">
  1093                 <li>Let <var>service type in current service manager flag</var> be <code>false</code>.
  1094                 </li>
  1095                 <li>For each <var>active service</var> in <var>service manager</var> run the following steps:
  1096                   <ol class="rule">
  1097                     <li>If <var>existing service record</var>'s <code>type</code> property does not equal the
  1098                     <var>active service</var>'s <code>type</code> attribute then abort any remaining sub-steps for this
  1099                     <var>active service</var> and continue at the next available <var>active service</var>.
  1100                     </li>
  1101                     <li>Set the <var>service type in current service manager flag</var> to <code>true</code>.
  1102                     </li>
  1103                     <li>If <var>existing service record</var>'s <code>id</code> property equals the <var>active
  1104                     service</var>'s <code>id</code> attribute and <var>active service</var>'s <a href=
  1105                     "#dom-networkservice-online"><code>online</code></a> attribute is currently set to
  1106                     <code>true</code> then set <var>active service</var>'s <a href="#dom-networkservice-online"><code>
  1107                       online</code></a> attribute to <code>false</code> and then <a href=
  1108                       "http://www.whatwg.org/specs/web-apps/current-work/complete/webappapis.html#queue-a-task"
  1109                           class="externalDFN">queue a task</a> to dispatch a newly created event with the name <a href=
  1110                           "#event-serviceoffline"><code>serviceoffline</code></a> that uses the <a href=
  1111                           "http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#event"
  1112                           class="externalDFN"><code>Event</code></a> interface, which does not bubble, is not
  1113                           cancellable, and has no default action, at the current <var>active service</var>.
  1114                     </li>
  1115                   </ol>
  1116                 </li>
  1117                 <li>If the <var>service type in current service manager flag</var> is set to <code>true</code> then
  1118                 decrement <var>service manager</var>'s <a href=
  1119                 "#dom-networkservices-servicesavailable"><code>servicesAvailable</code></a> attribute by <code>1</code>
  1120                 and then <a href=
  1121                 "http://www.whatwg.org/specs/web-apps/current-work/complete/webappapis.html#queue-a-task"
  1122                       class="externalDFN">queue a task</a> to dispatch a newly created event with the name <a href=
  1123                       "#event-serviceunavailable"><code>serviceunavailable</code></a> that uses the <a href=
  1124                       "http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#event"
  1125                       class="externalDFN"><code>Event</code></a> interface, which does not bubble, is not cancellable,
  1126                       and has no default action, at the current <var>service manager</var> object.
  1127                 </li>
  1128               </ol>
  1129             </li>
  1130             <li>Remove <var>existing service record</var> from the current <a>list of available service records</a>.
  1131             </li>
  1132           </ol>
  1133         </li>
  1134       </ol>
  1135       <p>
  1136         User agents SHOULD expire a service record from the <a>list of available service records</a> when its
  1137         <code>expiryTimestamp</code> attribute exceeds the current UTC timestamp. When this condition is met the
  1138         <a>user agent</a> SHOULD run the rule for <a>removing an available service</a>, passing in the expired service
  1139         record's <code>id</code> attribute as the only argument.
  1140       </p>
  1141       <section>
  1142         <h4>
  1143           Zeroconf (<abbr title="Multicast DNS">mDNS</abbr> + <abbr title="Domain Name System">DNS</abbr>-<abbr title=
  1144           "Service Discovery">SD</abbr>)
  1145         </h4>
  1146         <p>
  1147           For each DNS response received from a user-agent-initiated Multicast DNS Browse for <abbr title=
  1148           "DNS Pointer Record">PTR</abbr> records with the name <code>_services._dns-sd._udp</code> on the resolved
  1149           recommended automatic browsing domain [[!MDNS]], the <a>user agent</a> MUST run the following steps:
  1150         </p>
  1151         <ol class="rule">
  1152           <li>Let <var>service mDNS responses</var> be an array of PTR records received by issuing a Multicast DNS
  1153           Browse for PTR records with the name of the current discovered service type.
  1154           </li>
  1155           <li>For each Object <var>service mDNS response</var> in <var>service mDNS responses</var>, run the following
  1156           steps:
  1157             <ol>
  1158               <li>Let <var>network service record</var> be an Object consisting of the following empty properties:
  1159               <code>id</code>, <code>name</code>, <code>type</code>, <code>url</code>, <code>config</code>,
  1160               <code>expiryTimestamp</code>.
  1161               </li>
  1162               <li>Set <var>network service record</var>'s <code>id</code> property to the value of the full PTR Service
  1163               Instance Name [[!MDNS]].
  1164               </li>
  1165               <li>Set <var>network service record</var>'s <code>name</code> property to the value of the PTR Service
  1166               Instance Name's <var>Instance</var> component [[!MDNS]].
  1167               </li>
  1168               <li>Set <var>network service record</var>'s <code>type</code> property to the concatenation of the string
  1169               <code>zeroconf:</code> followed be the value of the PTR Service Instance Name's <var>Service</var>
  1170               component [[!MDNS]].
  1171               </li>
  1172               <li>Set <var>network service record</var>'s <code>url</code> property to the resolvable Service URL
  1173               obtained from performing an DNS-SD Lookup [[!DNS-SD]] of the current service from the PTR record provided
  1174               [[!MDNS]].
  1175               </li>
  1176               <li>Set <var>network service record</var>'s <code>config</code> property to the string value of the
  1177               contents of the first DNS-SD TXT record associated with the <var>service mDNS response</var> as defined
  1178               in [[!DNS-SD]].
  1179               </li>
  1180               <li>Set <var>network service record</var>'s <code>expiryTimestamp</code> property to the value of the
  1181               current date, in UTC timestamp format, plus a value of <code>120</code> seconds.
  1182               </li>
  1183               <li>Run the general rule for <a>adding an available service</a>, passing in the current <var>network
  1184               service record</var> as the only argument.
  1185               </li>
  1186             </ol>
  1187           </li>
  1188         </ol>
  1189       </section>
  1190       <section>
  1191         <h5>
  1192           Simple Service Discovery Protocol (<abbr title="Simple Service Discovery Protocol">SSDP</abbr>)
  1193         </h5>
  1194         <p>
  1195           A user agent that implements UPnP service discovery MUST issue a <dfn>search request for UPnP root
  1196           devices</dfn> against the user's current local network according to the full normative text and timing
  1197           provided in 'Section 1.3.2: Search request with M-SEARCH' detailed in [[!UPNP-DEVICEARCH11]].
  1198         </p>
  1199         <p>
  1200           The user agent MUST issue all <a title="search request for UPnP root devices">search requests for UPnP root
  1201           devices</a> with a HTTP request line equal to <code>M-SEARCH * HTTP/1.1</code>, with a HOST header equal to
  1202           the reserved multicast address and port of <code>239.255.255.250:1900</code>, a MAN header equal to
  1203           <code>ssdp:discover</code>, an ST header equal to <code>upnp:rootdevice</code> and a user-agent defined MX
  1204           header equal to a <dfn>maximum UPnP advertisement response wait time</dfn> value between <code>1</code> and
  1205           <code>5</code> seconds.
  1206         </p>
  1207         <p>
  1208           The user agent MUST listen for any incoming responses to any <a>search request for UPnP root devices</a>.
  1209         </p>
  1210         <p>
  1211           For each <dfn>HTTP Response</dfn> following an initial <a>search request for UPnP root devices</a> sent on a
  1212           <a>standard UPnP address and port</a> the user agent MUST run the following steps:
  1213         </p>
  1214         <ol class="rule">
  1215           <li>If the <a>HTTP Response</a> is not a HTTP 200 OK response then this response is invalid and the user
  1216           agent MUST discard this response, abort any remaining steps and return. The user agent MAY issue a new
  1217           <a>search request for UPnP root devices</a> as a result of this error occurring.
  1218           </li>
  1219           <li>If the <a>maximum UPnP advertisement response wait time</a> has been exceeded since the initial <a>search
  1220           request for UPnP root devices</a> was sent then the <a>HTTP Response</a> is invalid and the user agent MUST
  1221           discard this response, abort any remaining steps and return. The user agent MAY stop listening for responses
  1222           from the current <a>search request for UPnP root devices</a> as a result of this error occurring. Equally,
  1223           the user agent MAY issue a new <a>search request for UPnP root devices</a> as a result of this error
  1224           occurring.
  1225           </li>
  1226           <li>Let <var>ssdp device</var> be an Object with a property for each HTTP header received in the <a>HTTP
  1227           Response</a>, with each key being the name of a HTTP response header and each value being that HTTP response
  1228           header's value.
  1229           </li>
  1230           <li>If <var>ssdp device</var> does not contain at least one <var>CACHE-CONTROL</var> entry, at least one
  1231           <var>USN</var> entry, at least one <var>ST</var> entry and at least one <var>LOCATION</var> entry or the
  1232           value of its <var>ST</var> entry is not <code>upnp:rootdevice</code>, then the <a>HTTP Response</a> is
  1233           invalid and the <a>user agent</a> MUST discard this response, abort any remaining steps and return.
  1234           </li>
  1235           <li>The user agent MUST run the rule for <a>obtaining a UPnP Device Description File</a> passing in the first
  1236           occurrence of <var>LOCATION</var> from <var>ssdp device</var> as the <var>device descriptor URL</var>
  1237           argument and the first occurrence of <var>USN</var> from <var>ssdp device</var> as the <var>device
  1238           identifier</var> argument and the first occurrence of <var>CACHE-CONTROL</var> from <var>ssdp device</var>
  1239           (minus the leading string of <code>max-age=</code>) as the <var>device expiry</var> argument.
  1240           </li>
  1241         </ol>
  1242         <p>
  1243           The user agent MUST listen for incoming requests on the <dfn>standard UPnP address and port</dfn> on all
  1244           current local network interface addresses with the port <code>1900</code>.
  1245         </p>
  1246         <p>
  1247           For each <dfn>HTTP Request</dfn> received on a <a>standard UPnP address and port</a> the user agent MUST run
  1248           the following steps:
  1249         </p>
  1250         <ol class="rule">
  1251           <li>If the <a>HTTP Request</a> is not a HTTP NOTIFY request then it is not a valid UPnP Request and the user
  1252           agent MUST discard this request, abort any remaining steps and return.
  1253           </li>
  1254           <li>Let <var>ssdp device</var> be an Object with a property for each HTTP header received in the <a>HTTP
  1255           Request</a>, with each key being the name of a HTTP header and each value being that HTTP header's value.
  1256           </li>
  1257           <li>If <var>ssdp device</var> does not contain at least one <var>CACHE-CONTROL</var> entry, at least one
  1258           <var>USN</var> entry, at least one <var>NT</var> entry, at least one <var>NTS</var> entry and at least one
  1259           <var>LOCATION</var> entry or the value of its <var>NT</var> entry is not <code>upnp:rootdevice</code>, then
  1260           the <a>HTTP Request</a> is a malformed UPnP Request and the <a>user agent</a> MUST discard this request,
  1261           abort any remaining steps and return.
  1262           </li>
  1263           <li>If <var>ssdp device</var>'s <var>NTS</var> entry is equal to <code>ssdp:alive</code> then the user agent
  1264           MUST run the rule for <a>obtaining a UPnP Device Description File</a> passing in the first occurrence of
  1265           <var>LOCATION</var> from <var>ssdp device</var> as the <var>device descriptor URL</var> argument and the
  1266           first occurrence of <var>USN</var> from <var>ssdp device</var> as the <var>device identifier</var> argument
  1267           and the first occurrence of <var>CACHE-CONTROL</var> from <var>ssdp device</var> (minus the leading string of
  1268           <code>max-age=</code>) as the <var>device expiry</var>.<br>
  1269             <br>
  1270             Otherwise, if <var>ssdp device</var>'s <var>NTS</var> entry is equal to <code>ssdp:byebye</code> then the
  1271             user agent MUST run the rule for <a>removing all services from a registered UPnP Device</a> passing in the
  1272             first occurrence of <var>USN</var> from <var>ssdp device</var> as the <var>device identifier</var>
  1273             argument.
  1274           </li>
  1275         </ol>
  1276         <p>
  1277           The rule for <dfn>obtaining a UPnP Device Description File</dfn> is the process of obtaining the contents of
  1278           a standard UPnP Device Description [[!UPNP-DEVICEARCH11]] from a URL-based resource. This rule takes three
  1279           arguments - <var>device descriptor URL</var>, <var>device identifier</var> and <var>device expiry</var> - and
  1280           when called the user agent MUST run the following steps:
  1281         </p>
  1282         <ol class="rule">
  1283           <li>Let <var>device descriptor file</var> contain the contents of the file located at the URL provided in
  1284           <var>device descriptor URL</var> obtained according to the rules defined in 'Section 2.11: Retrieving a
  1285           description using HTTP' in [[!UPNP-DEVICEARCH11]].
  1286           </li>
  1287           <li>If the value provided in <var>device descriptor URL</var> cannot be resolved as a reachable URL on the
  1288           current network or the <var>device descriptor file</var> remains empty then it is invalid and the <a>user
  1289           agent</a> MUST abort any remaining steps and return.
  1290           </li>
  1291           <li>Run the rule for <a>processing a UPnP Device Description File</a>, passing in the current <var>device
  1292           descriptor file</var>, <var>device identifier</var> and <var>device expiry</var> arguments.
  1293           </li>
  1294         </ol>
  1295         <p>
  1296           The rule for <dfn>processing a UPnP Device Description File</dfn> is the process of parsing the contents of a
  1297           standard UPnP Device Description [[!UPNP-DEVICEARCH11]] and registering the UPnP services contained therein
  1298           within the <a>list of available service records</a>.
  1299         </p>
  1300         <p>
  1301           The rule for <a>processing a UPnP Device Description File</a> takes three arguments - <var>device descriptor
  1302           file</var>, <var>device identifier</var> and <var>device expiry</var> - and when called the user agent MUST
  1303           run the following steps:
  1304         </p>
  1305         <ol class="rule">
  1306           <li>Let <var>advertised services</var> be a list of all advertised services obtained from the <var>device
  1307           descriptor file</var> containing the value of the first occurrence of the <code>&lt;serviceList&gt;</code>
  1308           element as it is defined in 'Section 2.3: Device Description' in [[!UPNP-DEVICEARCH11]].
  1309           </li>
  1310           <li>For each <code>&lt;service&gt;</code> element - known as an <var>advertised service</var> - in
  1311           <var>advertised services</var> run the following steps:
  1312             <ol class="rule">
  1313               <li>Let <var>network service record</var> be a new Object consisting of the following empty properties:
  1314               <code>id</code>, <code>deviceId</code>, <code>name</code>, <code>type</code>, <code>url</code>,
  1315               <code>eventsUrl</code>, <code>config</code>, <code>expiryTimestamp</code>.
  1316               </li>
  1317               <li>Set <var>network service record</var>'s <code>id</code> property to the concatenated string value of
  1318               the first occurrence of the <code>&lt;UDN&gt;</code> element in the <var>device descriptor file</var>
  1319               with the <var>advertised service</var>'s <code>&lt;serviceId&gt;</code> sub-element.
  1320               </li>
  1321               <li>Set <var>network service record</var>'s <code>deviceId</code> property to the value of <var>device
  1322               identifier</var>.
  1323               </li>
  1324               <li>Set <var>network service record</var>'s <code>name</code> property to the string value of the first
  1325               occurrence of the <var>advertised service</var>'s <code>&lt;serviceId&gt;</code> sub-element.
  1326               </li>
  1327               <li>Set <var>network service record</var>'s <code>type</code> property to the concatenation of the string
  1328               <code>upnp:</code> followed by the string value of the first occurrence of the <var>advertised
  1329               service</var>'s <code>&lt;serviceType&gt;</code> sub-element.
  1330               </li>
  1331               <li>Set <var>network service record</var>'s <code>url</code> property to the string value of the first
  1332               occurrence of the <var>advertised service</var>'s <code>&lt;controlURL&gt;</code> sub-element.
  1333               </li>
  1334               <li>Set <var>network service record</var>'s <code>config</code> property to the string value of the
  1335               contents of the first occurrence of the <code>&lt;device&gt;</code> element in the <var>device descriptor
  1336               file</var>.
  1337               </li>
  1338               <li>If <var>advertised service</var>'s <code>&lt;eventSubURL&gt;</code> sub-element is not empty, then
  1339               set <var>network service record</var>'s <code>eventsUrl</code> property to the string value of the first
  1340               occurrence of the <var>advertised service</var>'s <code>&lt;eventSubURL&gt;</code> sub-element.
  1341               Otherwise, do not set <var>network service record</var>'s <code>eventsUrl</code> property.
  1342               </li>
  1343               <li>Set <var>network service record</var>'s <code>expiryTimestamp</code> property to the value of the
  1344               current date, in UTC timestamp format, plus the value of <var>device expiry</var>.
  1345               </li>
  1346               <li>Run the general rule for <a>adding an available service</a>, passing in the current <var>network
  1347               service record</var> as the only argument.
  1348               </li>
  1349             </ol>
  1350           </li>
  1351           <li>If <var>device descriptor file</var> contains a <code>&lt;deviceList&gt;</code> element then for each
  1352           <code>&lt;device&gt;</code> element within <code>&lt;deviceList&gt;</code> - herein known as an <var>embedded
  1353           device descriptor file</var> - the user agent MUST run the rule for <a>processing a UPnP Device Description
  1354           File</a>, passing in the current <var>embedded device descriptor file</var> as the <var>device descriptor
  1355           file</var> argument, along with the current <var>device identifier</var> and <var>device expiry</var>
  1356           arguments.
  1357           </li>
  1358         </ol>
  1359         <p>
  1360           The rule for <dfn>removing all services from a registered UPnP Device</dfn> is the process of removing all
  1361           services associated with a device from the <a>list of available service records</a> that has left the user's
  1362           current network or has otherwise timed out or expired. This rule takes one argument, <var>device
  1363           identifier</var>, and consists of running the following steps:
  1364         </p>
  1365         <ol class="rule">
  1366           <li>For each <var>existing service record</var> in the current <a>list of available service records</a>, run
  1367           the following sub-steps:
  1368             <ol class="rule">
  1369               <li>If the <var>existing service record</var>'s <code>deviceId</code> property does not match <var>device
  1370               identifier</var> then skip any remaining sub-steps for the current <var>existing service record</var> and
  1371               continue at the next available <var>existing service record</var>.
  1372               </li>
  1373               <li>Run the general rule for <a>removing an available service</a> passing in <var>existing service
  1374               record</var>'s <code>id</code> property as the only argument.
  1375               </li>
  1376             </ol>
  1377           </li>
  1378         </ol>
  1379         <p>
  1380           When the <a>user agent</a> is to <dfn>setup a UPnP Events Subscription</dfn>, it is to run the following
  1381           steps with the current <var>network service record</var> object as defined in 'Section 4.1.2: SUBSCRIBE with
  1382           NT and CALLBACK' in [[!UPNP-DEVICEARCH11]]:
  1383         </p>
  1384         <ol class="rule">
  1385           <li>If <var>network service record</var>'s <code>eventsUrl</code> property is empty then the <a>user
  1386           agent</a> MUST abort these steps.
  1387           </li>
  1388           <li>Let <var>callback URL</var> be the value of creating a new <a>user-agent generated callback url</a>.
  1389           </li>
  1390           <li>Send a HTTP SUBSCRIBE request with a <em>NT</em> header with a string value of <code>upnp:event</code>, a
  1391           <em>TIMEOUT</em> header with a user-agent defined timeout value (in the form <code>Second-XX</code> where
  1392           <code>XX</code> is the user-agent defined timeout value in seconds) and a <em>CALLBACK</em> header with a
  1393           string value of <var>callback URL</var> towards the <var>network service record</var>'s
  1394           <code>eventsUrl</code> property.
  1395           </li>
  1396           <li>If a non-200 OK response is received from the HTTP SUBSCRIBE request then the <a>user agent</a> MUST
  1397           abort these steps.
  1398           </li>
  1399           <li>On receiving a valid 200 OK response, run the following steps:
  1400             <ol class="rule">
  1401               <li>Let <var>callback ID</var> equal the string value of the first included <em>SID</em> header, if it
  1402               exists.
  1403               </li>
  1404               <li>Let <var>timeout date</var> equal the sum of the current UTC date value plus the integer value of the
  1405               first included <em>TIMEOUT</em> header (minus the leading string of <code>Second-</code>), if it exists.
  1406               </li>
  1407               <li>Run the following steps asynchronously and continue to the step labeled <em>listen</em> below.
  1408               </li>
  1409               <li>
  1410                 <em>Refresh Subscription</em>: Run the following steps at a set interval (X) within the <a>user
  1411                 agent</a>:
  1412                 <ol class="rule">
  1413                   <li>Let <var>current date</var> equal the current UTC date.
  1414                   </li>
  1415                   <li>If <var>current date</var> is less than the <var>timeout date</var> then continue to the step
  1416                   labeled <em>refresh subscription</em> above.
  1417                   </li>
  1418                   <li>Send a HTTP SUBSCRIBE request with a <em>SID</em> header with the string value of <var>callback
  1419                   ID</var> and a user-agent defined <em>TIMEOUT</em> header (in the form <code>Second-XX</code> where
  1420                   <code>XX</code> is the user-agent defined timeout value in seconds) towards the <var>network service
  1421                   record</var>'s <code>eventsUrl</code> property.
  1422                   </li>
  1423                   <li>On receiving a valid 200 OK, update <var>callback ID</var> with the string value of the first
  1424                   included <em>SID</em> header and set <var>timeout date</var> to the sum of the current UTC date value
  1425                   plus the integer value of the first included <em>TIMEOUT</em> header (minus the leading string of
  1426                   <code>Second-</code>), if it exists. If the current date is greater than or equal to <var>timeout
  1427                   date</var> then the <a>user agent</a> SHOULD continue from the step labeled <em>refresh
  1428                   subscription</em> above. For all non 200 OK responses the <a>user agent</a> SHOULD continue from the
  1429                   step labeled <em>refresh subscription</em> above.
  1430                   </li>
  1431                 </ol>
  1432               </li>
  1433               <li>
  1434                 <em>Listen</em>: For each HTTP NOTIFY request received at the <var>callback URL</var> the <a>user
  1435                 agent</a> is to run the following steps:
  1436                 <ol class="rule">
  1437                   <li>Let <var>content clone</var> be the result of obtaining the message body of the HTTP NOTIFY
  1438                   request. If <var>content clone</var> is empty, then the <a>user agent</a> MUST abort these steps.
  1439                   </li>
  1440                   <li>Let <var>notification event</var> be a new simple event that uses the <a href=
  1441                   "http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#event"
  1442                         class="externalDFN"><code>Event</code></a> interface with the name <a href=
  1443                         "#event-notify"><code>notify</code></a>, which does not bubble, is not cancellable, and has no
  1444                         default action.
  1445                   </li>
  1446                   <li>Let the <code>data</code> attribute of <var>notification event</var> have the DOMString value of
  1447                   <var>content clone</var>.
  1448                   </li>
  1449                   <li>
  1450                     <a href="http://www.whatwg.org/specs/web-apps/current-work/complete/webappapis.html#queue-a-task"
  1451                         class="externalDFN">Queue a task</a> to dispatch <var>notification event</var> at the current
  1452                         <a><code>NetworkService</code></a> object.
  1453                   </li>
  1454                   <li>Return a HTTP 200 OK response to the sender of the HTTP NOTIFY request.
  1455                   </li>
  1456                 </ol>
  1457               </li>
  1458             </ol>
  1459           </li>
  1460         </ol>
  1461         <p>
  1462           A <a>user agent</a> can <dfn>terminate an existing UPnP Events Subscription</dfn> at any time for a
  1463           <var>network service record</var> by sending an HTTP UNSUBSCRIBE request - as defined in 'Section 4.1.4:
  1464           Cancelling a subscription with UNSUBSCRIBE' in [[!UPNP-DEVICEARCH11]] - with a HOST header set to that
  1465           <var>active service</var>'s <code>eventsUrl</code> property and a SID header set to the <var>callback
  1466           ID</var> obtained when the initial <a>setup a UPnP Events Subscription</a> action occurred.
  1467         </p>
  1468       </section>
  1469       <section>
  1470         <h5>
  1471           Discovery and Launch Protocol (<abbr title="Discovery and Launch Protocol">DIAL</abbr>)
  1472         </h5>
  1473          <p>
  1474           A user agent that implements DIAL service discovery MUST issue a <dfn>search request for DIAL-enabled
  1475           devices</dfn> against the user's current local network according to the full normative text and timing
  1476           provided in 'Section 1.3.2: Search request with M-SEARCH' detailed in [[!UPNP-DEVICEARCH11]].
  1477         </p>
  1478         <p>
  1479           Let <var>dial version</var> be the version number specified in the <a>valid service type</a> token.
  1480           Let <var>dial search target</var> be the concatentation of the
  1481           <code>urn:dial-multiscreen-org:service:dial:</code> string constant with the <var>dial version</var>
  1482           (currently, <var>dial version</var> can only be <code>1</code>)
  1483         </p>
  1484         <p>
  1485           The user agent MUST issue all <a title="search request for DIAL devices">search requests for DIAL
  1486           devices</a> with a HTTP request line equal to <code>M-SEARCH * HTTP/1.1</code>, with a HOST header equal to
  1487           the reserved multicast address and port of <code>239.255.255.250:1900</code>, a MAN header equal to
  1488           <code>ssdp:discover</code>, an ST header equal to <var>dial search target</var>
  1489           and a user-agent defined MX header equal to a <dfn>maximum DIAL advertisement response wait time</dfn>
  1490           value between <code>1</code> and <code>5</code> seconds.
  1491         </p>
  1492         <p>
  1493           The user agent MUST listen for any incoming responses to a <a>search request for DIAL devices</a>.
  1494         </p>
  1495         <p>
  1496           For each HTTP Response following an initial <a>search request for DIAL devices</a> sent on a
  1497           <a>standard UPnP address and port</a> the user agent MUST run the following steps:
  1498         </p>
  1499         <ol class="rule">
  1500           <li>If the HTTP Response is not a HTTP 200 OK response then this response is invalid and the user
  1501           agent MUST discard this response, abort any remaining steps and return. The user agent MAY issue a new
  1502           <a>search request for DIAL devices</a> as a result of this error occurring.
  1503           </li>
  1504           <li>If the <a>maximum DIAL advertisement response wait time</a> has been exceeded since the initial <a>search
  1505           request for DIAL devices</a> was sent then the <a>HTTP Response</a> is invalid and the user agent MUST
  1506           discard this response, abort any remaining steps and return. The user agent MAY stop listening for responses
  1507           from the current <a>search request for DIAL devices</a> as a result of this error occurring. Equally,
  1508           the user agent MAY issue a new <a>search request for DIAL devices</a> as a result of this error
  1509           occurring.
  1510           </li>
  1511           <li>Let <var>dial device</var> be an Object with a property for each HTTP header received in the <a>HTTP
  1512           Response</a>, with each key being the name of a HTTP response header and each value being that HTTP response
  1513           header's value.
  1514           </li>
  1515           <li>If <var>dial device</var> does not contain at least one <var>CACHE-CONTROL</var> entry, at least one
  1516           <var>USN</var> entry, at least one <var>ST</var> entry and at least one <var>LOCATION</var> entry or the
  1517           value of its <var>ST</var> entry is not <var>dial search target</var>, then the
  1518           <a>HTTP Response</a> is invalid and the <a>user agent</a> MUST discard this response, abort any remaining
  1519           steps and return.
  1520           </li>
  1521           <li>The user agent MUST run the rule for <a>obtaining a UPnP Device Description File</a> passing in the first
  1522           occurrence of <var>LOCATION</var> from <var>dial device</var> as the <var>device descriptor URL</var>
  1523           argument and the first occurrence of <var>USN</var> from <var>dial device</var> as the <var>device
  1524           identifier</var> argument and the first occurrence of <var>CACHE-CONTROL</var> from <var>dial device</var>
  1525           (minus the leading string of <code>max-age=</code>) as the <var>device expiry</var> argument.
  1526           </li>
  1527         </ol>
  1528         <p>
  1529           The rule for <dfn>obtaining a DIAL Device Description File</dfn> is the process of obtaining the contents of
  1530           a standard UPnP Device Description [[!UPNP-DEVICEARCH11]] from a URL-based resource. This rule takes three
  1531           arguments - <var>device descriptor URL</var>, <var>device identifier</var> and <var>device expiry</var> - and
  1532           when called the user agent MUST run the following steps:
  1533         </p>
  1534         <ol class="rule">
  1535           <li>Let <var>device descriptor file</var> contain the contents of the file located at the URL provided in
  1536           <var>device descriptor URL</var> obtained according to the rules defined in 'Section 2.11: Retrieving a
  1537           description using HTTP' in [[!UPNP-DEVICEARCH11]].
  1538           </li>
  1539           <li>Let <var>application url</var> be the value of the first occurrence of the <code>Application-URL</code>
  1540           response header field obtained according to the rules defined in 'Section 5.4: Device Description Response' in
  1541           [<a href = "https://sites.google.com/a/dial-multiscreen.org/dial/dial-protocol-specification">DIAL</a>]
  1542           </li>
  1543           <li>If the value provided in <var>device descriptor URL</var> cannot be resolved as a reachable URL on the
  1544           current network or the <var>device descriptor file</var> remains empty or <var>application url</var> is undefined
  1545           then it is invalid and the <a>user agent</a> MUST abort any remaining steps and return.
  1546           </li>
  1547           <li>Run the following steps to add the newly discovered DIAL service:
  1548             <ol class="rule">
  1549               <li>Let <var>network service record</var> be a new Object consisting of the following empty properties:
  1550               <code>id</code>, <code>deviceId</code>, <code>name</code>, <code>type</code>, <code>url</code>,
  1551               <code>expiryTimestamp</code>.
  1552               </li>
  1553               <li>Set <var>network service record</var>'s <code>id</code> property to the first occurrence of the
  1554               <code>&lt;UDN&gt;</code> element in the <var>descriptor file</var> prefixed with the <code>dial:</code>
  1555               string constant
  1556               </li>
  1557               <li>Set <var>network service record</var>'s <code>deviceId</code> property to the value of <var>device
  1558               identifier</var>.
  1559               </li>
  1560               <li>Set <var>network service record</var>'s <code>name</code> property to the string value of the first
  1561               occurrence of the <code>&lt;friendlyName&gt;</code> element in the <var>descriptor file</var>.
  1562               </li>
  1563               <li>Set <var>network service record</var>'s <code>type</code> property to <var>dial search target</var>.
  1564               </li>
  1565               <li>Set <var>network service record</var>'s <code>url</code> property to the string value of the <var>
  1566               application url</var>.
  1567               </li>
  1568               <li>Set <var>network service record</var>'s <code>expiryTimestamp</code> property to the value of the
  1569               current date, in UTC timestamp format, plus the value of <var>device expiry</var>.
  1570               </li>
  1571               <li>Run the general rule for <a>adding an available service</a>, passing in the current <var>network
  1572               service record</var> as the only argument.
  1573               </li>
  1574             </ol>
  1575           </li>
  1576         </ol>
  1577       </section>
  1578       <section>
  1579         <h3>
  1580           Network Topology Monitoring
  1581         </h3>
  1582         <div>
  1583           <p>
  1584             When the <a>user agent</a> detects that the user has dropped from their connected network then, for each
  1585             <var>existing service record</var> in the <a>list of available service records</a>, the user agent MUST run
  1586             the general rule for <a>removing an available service</a> passing in each <var>existing service
  1587             record</var>'s <code>id</code> property as the only argument for each call.
  1588           </p>
  1589           <p>
  1590             When the <a>user agent</a> detects that the user has connected to a new network or reconnected to an
  1591             existing network, then it SHOULD restart its discovery mechanisms as defined in the <a href=
  1592             "#service-discovery">Service Discovery</a> section of this specification, maintaining the existing <a>list
  1593             of active service managers</a> currently in use.
  1594           </p>
  1595         </div>
  1596       </section>
  1597     </section>
  1598     <section>
  1599       <h3>
  1600         Events Summary
  1601       </h3>
  1602       <p>
  1603         The following events are dispatched on the <a href="#networkservices"><code>NetworkServices</code></a> and/or
  1604         <a href="#networkservice"><code>NetworkService</code></a> objects:
  1605       </p>
  1606       <table border="1">
  1607         <thead>
  1608           <tr>
  1609             <th>
  1610               <span>Event name</span>
  1611             </th>
  1612             <th>
  1613               <span>Interface</span>
  1614             </th>
  1615             <th>
  1616               <span>Dispatched when...</span>
  1617             </th>
  1618           </tr>
  1619         </thead>
  1620         <tbody>
  1621           <tr>
  1622             <td>
  1623               <dfn id="event-serviceavailable"><code>serviceavailable</code></dfn>
  1624             </td>
  1625             <td>
  1626               <a href="http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#event"
  1627                   class="externalDFN"><code>Event</code></a>
  1628             </td>
  1629             <td>
  1630               When a new service that matches one of the <a>requested type tokens</a> is found in the current network.
  1631             </td>
  1632           </tr>
  1633           <tr>
  1634             <td>
  1635               <dfn id="event-serviceunavailable"><code>serviceunavailable</code></dfn>
  1636             </td>
  1637             <td>
  1638               <a href="http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#event"
  1639                   class="externalDFN"><code>Event</code></a>
  1640             </td>
  1641             <td>
  1642               When an existing service that matches one of the <a>requested type tokens</a> gracefully leaves or
  1643               expires from the current network.
  1644             </td>
  1645           </tr>
  1646           <tr>
  1647             <td>
  1648               <dfn id="event-serviceonline"><code>serviceonline</code></dfn>
  1649             </td>
  1650             <td>
  1651               <a href="http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#event"
  1652                   class="externalDFN"><code>Event</code></a>
  1653             </td>
  1654             <td>
  1655               When a current service renews its service registration within the current network.
  1656             </td>
  1657           </tr>
  1658           <tr>
  1659             <td>
  1660               <dfn id="event-serviceoffline"><code>serviceoffline</code></dfn>
  1661             </td>
  1662             <td>
  1663               <a href="http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#event"
  1664                   class="externalDFN"><code>Event</code></a>
  1665             </td>
  1666             <td>
  1667               When a current service gracefully leaves or otherwise expires from the current network.
  1668             </td>
  1669           </tr>
  1670           <tr>
  1671             <td>
  1672               <dfn id="event-notify"><code>notify</code></dfn>
  1673             </td>
  1674             <td>
  1675               <a href="http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#event"
  1676                   class="externalDFN"><code>Event</code></a>
  1677             </td>
  1678             <td>
  1679               When a valid UPnP Events Subscription Message is received on a <a>user-agent generated callback url</a>
  1680               for a current service. This event never fires for Zeroconf-based services.
  1681             </td>
  1682           </tr>
  1683         </tbody>
  1684       </table>
  1685     </section>
  1686     <section>
  1687       <h3>
  1688         Garbage collection
  1689       </h3>
  1690       <p>
  1691         A user agent MUST only garbage collect a <a><code>NetworkServices</code></a> object and remove its entry from
  1692         the <a>list of active service managers</a> when the user has navigated away from the
  1693         <a href="http://www.whatwg.org/specs/web-apps/current-work/complete/browsers.html#entry-script"
  1694               class="externalDFN">entry script</a>'s <a href=
  1695               "http://www.whatwg.org/specs/web-apps/current-work/complete/origin-0.html#origin"
  1696               class="externalDFN">origin</a> in which
  1697         the current <a><code>NetworkServices</code></a> object was provided.
  1698       </p>
  1699       <p>
  1700         A user agent MUST NOT garbage collect individual <a><code>NetworkService</code></a> objects until their parent
  1701         <a><code>NetworkServices</code></a> object has been garbage collected.
  1702       </p>
  1703       <p>
  1704         A user agent MUST garbage collect the <a><code>NetworkService</code></a> <a>indexed properties</a> of a
  1705         <a><code>NetworkServices</code></a> object when that <a><code>NetworkServices</code></a> object itself has been
  1706         garbage-collected.
  1707       </p>
  1708     </section>
  1709     <section>
  1710       <h3>
  1711         Use Cases and Requirements
  1712       </h3>
  1713       <p>
  1714         This section covers what the requirements are for this API, as well as illustrates some use cases.
  1715       </p>
  1716       <ul class="rule">
  1717         <li>Once a user has given permission, user agents should provide the ability for Web pages to communicate
  1718         directly with a Local-networked Service.
  1719           <ul class="rule">
  1720             <li>Example: A web-based TV remote control. A Web page wants to control the current user's TV, changing the
  1721             programming shown or increasing/decreasing/muting the volume of the Local-networked Device. The Web page
  1722             requests a service type that is known to be implemented by television sets to which it has the application
  1723             logic to communicate. Local devices providing the request service types are discovered and presented to the
  1724             user for authorization. The user selects one or more of the discovered television sets to be accessible to
  1725             the current Web page and then clicks 'Share'. The Web page can now communicate directly with the
  1726             user-authorized Local-networked services.
  1727             </li>
  1728           </ul>
  1729         </li>
  1730         <li>Web pages should be able to communicate with Local-networked Services using the messaging channel supported
  1731         by those Devices.
  1732           <ul class="rule">
  1733             <li>Example: A Web page advertises that it is capable of controlling multiple Home Media Servers. The user
  1734             can select their Home Media Server type from a drop-down list, at which point the Web page sends a request
  1735             to the user agent to connect with the associated service type of the Home Media Server. The Media Server
  1736             selected implements a Web Socket channel for bi-directional service communication and so the Web page opens
  1737             a web socket to the requested Media Server and can communicate as required via that appropriate channel.
  1738             </li>
  1739           </ul>
  1740         </li>
  1741         <li>Web pages should be able to communicate with Local-networked Services using the messaging format supported
  1742         by those Devices.
  1743           <ul class="rule">
  1744             <li>Example: A Web page advertises that it is capable of interacting with and controlling multiple types of
  1745             Home Media Server. The user can select their Home Media Server type from a drop-down list or known Media
  1746             Servers, at which point the Web page sends a request to the user agent to connect with the associated
  1747             service type (and, optionally, the associated event type) of the Home Media Server. The communication
  1748             protocols supported by Home Media Servers typically vary between UPnP, JSON-RPC, Protocol Buffers or other
  1749             messaging formats depending on the Home Media Server requested. The Web page is able to communicate with
  1750             the user-selected Home Media Server in the messaging format supported by that Device, which, in this
  1751             example is a simple key/value pair text format.
  1752             </li>
  1753           </ul>
  1754         </li>
  1755         <li>Web pages should not be able to communicate with Local-networked Services that have not been authorized by
  1756         the user thereby maintaining the user's privacy.
  1757           <ul class="rule">
  1758             <li>Example: A Web page requests access to one type of Local-networked service. The user authorizes access
  1759             to that particular service. Other services running on that same device, and on other devices within the
  1760             network, should not be accessible to the current Web page.
  1761             </li>
  1762           </ul>
  1763         </li>
  1764         <li>A user should be able to share one or more Local-networked Services based on a particular service type
  1765         request from a Web page.
  1766           <ul class="rule">
  1767             <li>Example: A Web page is capable of interacting with a specific profile of Local-networked Service. As
  1768             such, it makes a request to the user agent to access those services, of which multiple matches are found.
  1769             The user is capable of selecting one or more of the discovered services to share with the Web page. The Web
  1770             page can then implement a drag-and-drop interface for the user to drag specific actions on to one or more
  1771             of the authorized Local-networked Services.
  1772             </li>
  1773           </ul>
  1774         </li>
  1775         <li>User agents should provide an API exposed to script that exposes the features above. The user is notified
  1776         by UI anytime interaction with Local-networked Services is requested, giving the user full ability to cancel or
  1777         abort the transaction. The user selects the Local-networked Services to be connected to the current Web page,
  1778         and can cancel these at any time. No invocations to these APIs occur silently without user intervention.
  1779         </li>
  1780       </ul>
  1781     </section>
  1782     <section class="informative appendix">
  1783       <h3>
  1784         Examples
  1785       </h3>
  1786       <div class="example">
  1787         <p>
  1788           This sample code exposes a button. When clicked, this button is disabled and the user is prompted to offer a
  1789           network service. The user may also select multiple network services. When the user has authorized a network
  1790           service to be connected to the web page then the web page issues a simple command to get a list of all the
  1791           albums stored on the connected media player service.
  1792         </p>
  1793         <p>
  1794           The button is re-enabled only when the connected network service disconnects for whatever reason (the service
  1795           becomes unavailable on the network, the user disconnects from their current network or the user revokes
  1796           access to the service from the current web page). At this point the user can re-click the button to select a
  1797           new network service to connect to the web page and the above steps are repeated.
  1798         </p>
  1799         <p>
  1800           The provided service type identifier and service interaction used in this example is based on the
  1801           well-defined service type and messaging format supported by the <a href="http://xbmc.org/about/">XBMC Media
  1802           Server</a>.
  1803         </p>
  1804         <hr>
  1805         <pre class="highlight">
  1806 &lt;input type="button" value="Start" onclick="start()" id="startBtn"/&gt;
  1807 &lt;div id="debugconsole"&gt;&lt;/div&gt;
  1808 
  1809 &lt;script&gt;
  1810  var startBtn = document.getElementById('startBtn'),
  1811      debug = document.getElementById('debugconsole');
  1812 
  1813  function start() {
  1814    if(navigator.getNetworkServices) {
  1815       navigator.getNetworkServices('zeroconf:_xbmc-jsonrpc._tcp', gotXBMCService, error);
  1816       startBtn.disabled = true;
  1817    } else {
  1818       debug.innerHTML += "&lt;br&gt;Service Discovery not supported!";
  1819    }
  1820  }
  1821 
  1822  function gotXBMCService(services) {
  1823 
  1824 // Listen for service disconnect messages
  1825 
  1826    services[0].addEventListener('serviceoffline', function ( e ) {
  1827        debug.innerHTML += "&lt;br&gt;" + services[0].name + " disconnected.";
  1828        startBtn.disabled = false;
  1829    }, false);
  1830 
  1831 // Send a service message to get albums list (and process the service response)
  1832 
  1833    var svcXhr = new XMLHttpRequest();
  1834    svcXhr.open("POST", services[0].url + "/getAlbums"); // services[0].url and its sub-resources have been
  1835                                                         // whitelisted for cross-site XHR use in this
  1836                                                         // current browsing context.
  1837 
  1838    svcXhr.setRequestHeader('Content-Type', 'application/json-rpc');
  1839 
  1840    svcXhr.addEventListener('readystatechange', function ( response ) {
  1841      if( response.readyState != 4 || response.status != 200 )
  1842         return;
  1843      debug.innerHTML += "&lt;br&gt;" + services[0].name + " response received: ";
  1844      debug.textContent += JSON.parse(response.responseText);
  1845    }, false);
  1846 
  1847    var svcMsg = [
  1848      { "jsonrpc": "2.0", "method": "AudioLibrary.GetAlbums", "params": { "genreid": -1,
  1849          "artistid": -1, "start": -1, "end": -1 }, "id": "1" }
  1850    ];
  1851 
  1852    svcXhr.send(JSON.stringify(svcMsg));
  1853    debug.innerHTML += "&lt;br&gt;" + services[0].name + " request sent: ";
  1854    debug.textContent += JSON.stringify(svcMsg);
  1855 
  1856  }
  1857 
  1858  function error( err ) {
  1859    debug.innerHTML += "&lt;br&gt;An error occurred obtaining a local network service.";
  1860    startBtn.disabled = false;
  1861  }
  1862 &lt;/script&gt;
  1863 </pre>
  1864       </div>
  1865       <div class="example">
  1866         <p>
  1867           This sample exposes a drop-down list containing a number of common Home-based audio devices. When the user
  1868           selects an audio device from the list provided, they are prompted to authorize a network service based on the
  1869           service type requested. The user may also select multiple network services matching the selected service
  1870           type. In this example, the user selects their make as being <var>Sony</var> and their model as being
  1871           <var>Bravia S1000</var> from which the Web page can derive a service type
  1872           (<var>urn:schemas-upnp-org:service:RenderingControl:1</var>).<br>
  1873           <br>
  1874           Once the user has authorized the device, the web page sends a simple mute command according to the messaging
  1875           format supported by the device.
  1876         </p>
  1877         <hr>
  1878         <pre class="highlight">
  1879 &lt;select name="make" id="make"&gt;
  1880   &lt;option selected="selected" disabled="disabled"&gt;Select make&lt;/option&gt;
  1881   &lt;option&gt;Sony&lt;/option&gt;
  1882   &lt;option&gt;Philips&lt;/option&gt;
  1883   &lt;option&gt;Alba&lt;/option&gt;
  1884 &lt;/select&gt;
  1885 &lt;select name="model" id="model"&gt;&lt;/select&gt;
  1886 &lt;div id="debugconsole"&gt;&lt;/div&gt;
  1887 
  1888 &lt;script&gt;
  1889   var debug = document.getElementById('debugconsole');
  1890 
  1891   var models = {
  1892     "Sony": [
  1893       {"name": "Bravia TV S1000", "type": "upnp", "service": "urn:schemas-upnp-org:service:RenderingControl:1" },
  1894       {"name": "Bravia TV S2000", "type": "zeroconf", "service": "_mediarenderer._http._tcp" },
  1895       {"name": "HiFi WD10", "type": "upnp", "service": "urn:schemas-upnp-org:service:RenderingControl:1" }
  1896     ],
  1897     "Philips": [ /* ... */ ],
  1898     "Alba": [ /* ... */ ]
  1899   };
  1900 
  1901   var makeEl = document.getElementById("make"),
  1902       modelEl = document.getElementById("model");
  1903 
  1904   makeEl.addEventListener('change', function() {
  1905     modelEl.innerHTML = ""; // reset
  1906     var defaultOption = document.createElement("option");
  1907     defaultOption.textContent = "Select model";
  1908     defaultOption.setAttribute("disabled", "disabled");
  1909     defaultOption.setAttribute("selected", "selected");
  1910     modelEl.appendChild(defaultOption);
  1911     for(var i = 0, l = models[makeEl.value].length; i &lt; l; i++) {
  1912       var option = document.createElement("option");
  1913       option.textContent = models[makeEl.value][i]["name"];
  1914       option.setAttribute("value", models[makeEl.value][i]["type"] + ":" + models[makeEl.value][i]["service"]);
  1915       modelEl.appendChild(option);
  1916     }
  1917   }, false);
  1918 
  1919   modelEl.addEventListener('change', function() {
  1920     if(navigator.getNetworkServices &amp;&amp;
  1921          modelEl.value == "upnp:urn:schemas-upnp-org:service:RenderingControl:1") {
  1922       navigator.getNetworkServices(modelEl.value, successCallback, errorCallback);
  1923     } else if (modelEl.value == "zeroconf:_mediarenderer._http._tcp") {
  1924       debug.innerHTML += "&lt;br&gt;Service type is not implemented by this application.";
  1925     } else {
  1926       debug.innerHTML += "&lt;br&gt;Service Discovery is not supported!";
  1927     }
  1928   }, false);
  1929 &lt;/script&gt;
  1930 
  1931 &lt;script&gt;
  1932   function successCallback( services ) {
  1933 
  1934   // Listen for service push notification messages
  1935 
  1936     services[0].addEventListener('notify', function ( msg ) {
  1937          debug.innerHTML += "&lt;br&gt;" + services[0].name + " event received: ";
  1938          debug.textContent += msg.data;
  1939     }, false);
  1940 
  1941  // Send a control signal to mute the service audio
  1942 
  1943     var svcXhr = new XMLHttpRequest();
  1944     svcXhr.open("POST", services[0].url); // services[0].url and its
  1945                                           // sub-resources have been whitelisted for
  1946                                           // cross-site XHR use in this current
  1947                                           // browsing context.
  1948 
  1949     svcXhr.setRequestHeader('SOAPAction', 'urn:schemas-upnp-org:service:RenderingControl:1#SetMute');
  1950     svcXhr.setRequestHeader('Content-Type', 'text/xml; charset="utf-8";');
  1951 
  1952     svcXhr.onreadystatechange = function ( response ) {
  1953       if( response.readyState != 4 || response.status != 200 )
  1954         return;
  1955       debug.innerHTML += "&lt;br&gt;" + services[0].name + " response received: ";
  1956       debug.textContent += response.responseXML;
  1957     }
  1958 
  1959     // Service messaging to mute the provided service
  1960     var svcMsg = '&lt;?xml version="1.0" encoding="utf-8"?&gt;' +
  1961                  '&lt;s:Envelope s:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/" ' +
  1962                    'xmlns:s="http://schemas.xmlsoap.org/soap/envelope/"&gt;' +
  1963                    '&lt;s:Body&gt;' +
  1964                      '&lt;u:SetMute xmlns:u="urn:schemas-upnp-org:service:RenderingControl:1"&gt;' +
  1965                        '&lt;InstanceID&gt;0&lt;/InstanceID&gt;' +
  1966                        '&lt;Channel&gt;Master&lt;/Channel&gt;' +
  1967                        '&lt;DesiredMute&gt;true&lt;/DesiredMute&gt;' +
  1968                      '&lt;/u:SetMute&gt;' +
  1969                    '&lt;/s:Body&gt;' +
  1970                  '&lt;/s:Envelope&gt;';
  1971 
  1972     svcXhr.send(svcMsg);
  1973     debug.innerHTML += "&lt;br&gt;" + services[0].name + " request sent: ";
  1974     debug.textContent += svcMsg;
  1975   }
  1976 
  1977   function errorCallback( error ) {
  1978     debug.innerHTML += "&lt;br&gt;An error occurred: " + error.code;
  1979   }
  1980 &lt;/script&gt;
  1981 </pre>
  1982       </div>
  1983     </section>
  1984     <section>
  1985       <h3>
  1986         Acknowledgements
  1987       </h3>
  1988       <p>
  1989         Thanks are expressed by the editor to the following individuals for their feedback on this specification to
  1990         date (in alphabetical order):<br>
  1991         <br>
  1992         Gar Bergstedt, Lars-Erik Bolstad, Cathy Chan, Hari G Kumar, Bob Lund, Giuseppe Pascale, Marcin Simonides,
  1993         Clarke Stevens, Christian Söderström, Mark Vickers.
  1994       </p>
  1995       <p>
  1996         Thanks are also expressed by the editor to the following organizations and groups for their support in
  1997         producing this specification to date (in alphabetical order):<br>
  1998         <br>
  1999         CableLabs, Opera Software ASA, W3C Device APIs Working Group, W3C Web and TV Interest Group.
  2000       </p>
  2001     </section>
  2002   </body>
  2003 </html>