discovery-api/Overview.src.html
author Rich Tibbett <richt@opera.com>
Tue, 25 Sep 2012 12:48:42 +0200
changeset 230 3c13dc93cfb1
parent 216 5583626294f6
child 231 a0e6b501258d
permissions -rw-r--r--
Re-write of Section 7: Service Discovery according to feedback @ http://lists.w3.org/Archives/Public/public-device-apis/2012Aug/0017.html
     1 <!DOCTYPE html>
     2 <html>
     3   <head>
     4     <title>Networked Service Discovery and Messaging</title>
     5     <meta http-equiv='Content-Type' content='text/html;charset=utf-8'/>
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     9           //publishDate:  "2012-08-22",
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    13           previousPublishDate: "2012-08-07",
    14           editors: [
    15             {
    16               name:       "Rich Tibbett",
    17               //url:        "http://richt.me/",
    18               company:    "Opera Software ASA",
    19               companyURL: "http://opera.com/"
    20             },
    21             {
    22               name:       "Clarke Stevens",
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    24               company:    "CableLabs",
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    26             }
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    63     </style>
    64   </head>
    65 
    66   <body>
    67     <section id='abstract'>
    68       <p>
    69         This specification defines a mechanism for an HTML document to discover and subsequently communicate with <abbr title="Hypertext Transfer Protocol">HTTP</abbr>-based services
    70         advertised via common discovery protocols within a user's network.
    71       </p>
    72     </section>
    73 
    74     <section id='sotd'>
    75       <p>
    76         This document represents the early consensus of the group on the scope and features of the proposed
    77         API.
    78       </p>
    79     </section>
    80 
    81     <section class="informative">
    82       <h3>Introduction</h3>
    83 
    84       <p>To enable Web pages to connect and communicate with Local-networked Services provided over HTTP, this specification introduces the
    85       <a href="#navigatornetworkservice"><code>NavigatorNetworkService</code></a> interface.</p>
    86 
    87       <p>
    88          Using this <abbr title="Application Programming Interface">API</abbr> consists of requesting a well-known service type, known by developers and advertised by Local-networked Devices. User authorization, where the user connects the web page to one or more discovered services,
    89          is expected before the web page is able to interact with any Local-networked Services.
    90       </p>
    91 
    92       <p>
    93          A web page creates a request to obtain connectivity to services running in the network by specifying a well-known discovery service type that it wishes to interact with.
    94       </p>
    95 
    96       <p>
    97          The user agent, having captured all advertised services on the network from the Service Discovery mechanisms included in this recommendation, attempts to match
    98       the requested service type to a discovered service according to the processing described herein.
    99       </p>
   100 
   101       <p>
   102           If a service connectivity request is successful then the Web page is provided with the necessary information to communicate with the authorized Local-networked Service.
   103           If the request fails then the Web page will receive an error callback containing an error code describing the cause of Local-networked Service connectivity failure.
   104       </p>
   105 
   106       <p>
   107          Once connected to a Local-networked Service the Web page can send requests and receive responses to the Local-networked Service via the messaging format and appropriate channel inferred from the service type
   108          authorized via the provided API.
   109          The Web page, once connected, can also receive service-pushed events, in the messaging format supported by the Local-networked Device, if such event subscription functionality is provided by the
   110          connected Local-networked Service.
   111       </p>
   112 
   113       <div class="example">
   114        <p>Example of requesting a DNS-SD advertised service:</p>
   115        <hr />
   116        <pre class="highlight">function showServices( services ) {
   117   // Show a list of all the services provided to the web page
   118   for(var i = 0, l = services.length; i < l; i++) console.log( services[i].name );
   119 }
   120 
   121 navigator.getNetworkServices('zeroconf:_boxee-jsonrpc._tcp', showServices);</pre>
   122       </div>
   123 
   124       <div class="example">
   125         <p>Example of requesting a UPnP advertised service, also handling error conditions:</p>
   126         <hr />
   127         <pre class="highlight">function showServices( services ) {
   128   // Show a list of all the services provided to the web page
   129   for(var i = 0, l = services.length; i < l; i++) console.log( services[i].name );
   130 }
   131 
   132 function error( e ) {
   133   console.log( "Error occurred: " + e.code );
   134 }
   135 
   136 navigator.getNetworkServices('upnp:urn:schemas-upnp-org:service:ContentDirectory:1', showServices, error);</pre>
   137       </div>
   138 
   139       <div class="example">
   140         <p>Example of requesting either a DNS-SD or UPnP advertised service:</p>
   141         <hr />
   142         <pre class="highlight">function showServices( services ) {
   143   // Show a list of all the services provided to the web page (+ service type)
   144   for(var i = 0, l = services.length; i < l; i++)
   145      console.log( services[i].name + '(' + services[i].type + ')' );
   146 }
   147 
   148 navigator.getNetworkServices([
   149   'zeroconf:_boxee-jsonrpc._tcp',
   150   'upnp:urn:schemas-upnp-org:service:ContentDirectory:1'
   151 ], showServices);</pre>
   152       </div>
   153 
   154       <p>For more detailed examples see the <a href="#examples">Examples</a> section.
   155     </section>
   156 
   157     <section
   158      id='conformance'>
   159 
   160      <p>Requirements phrased in the imperative as part of algorithms (such as "strip any leading space characters" or "return false and abort these steps") are to be interpreted with the
   161      meaning of the key word ("must", "should", "may", etc) used in introducing the algorithm.</p>
   162 
   163      <p>
   164       Some conformance requirements are phrased as requirements on attributes, methods or objects. Such requirements are to be interpreted as requirements on user agents.
   165      </p>
   166 
   167      <p>
   168       Conformance requirements phrased as algorithms or specific steps may be implemented in any manner, so long as the end result is equivalent. (In particular, the algorithms defined in
   169       this specification are intended to be easy to follow, and not intended to be performant.)
   170      </p>
   171 
   172      <p>
   173       The only conformance class defined by this specification is a <dfn>user agent</dfn>.
   174      </p>
   175 
   176      <p>
   177       User agents may impose implementation-specific limits on otherwise unconstrained inputs, e.g. to prevent denial of service attacks, to guard against running out of memory, or to work
   178       around platform-specific limitations.
   179      </p>
   180 
   181      <p>
   182       When support for a feature is disabled (e.g. as an emergency measure to mitigate a security problem, or to aid in development, or for performance reasons), user agents must act as if
   183       they had no support for the feature whatsoever, and as if the feature was not mentioned in this specification. For example, if a particular feature is accessed via an attribute in a Web
   184       IDL interface, the attribute itself would be omitted from the objects that implement that interface - leaving the attribute on the object but making it return null or throw an exception
   185       is insufficient.
   186      </p>
   187 
   188       <section>
   189          <h3>Dependencies</h3>
   190 
   191          This specification relies on several other underlying specifications.
   192 
   193          <dl>
   194             <dt>HTML</dt>
   195             <dd>Many fundamental concepts from HTML are used by this specification. [[!HTML5]]</dd>
   196             <dt>WebIDL</dt>
   197             <dd>The IDL blocks in this specification use the semantics of the WebIDL specification. [[!WEBIDL]]</dd>
   198          </dl>
   199       </section>
   200     </section>
   201 
   202     <section>
   203       <h3>Terminology</h3>
   204 
   205       <p>
   206          The construction "a <code>Foo</code> object", where <code>Foo</code> is actually an interface, is sometimes used instead of the more accurate "an object implementing the interface <code>Foo</code>".
   207       </p>
   208 
   209       <p>
   210          The term DOM is used to refer to the API set made available to scripts in Web applications, and does not necessarily imply the existence of an actual <code>Document</code> object or of any
   211          other <code>Node</code> objects as defined in the DOM Core specifications. [[!DOM4]]
   212       </p>
   213 
   214       <p>
   215          An IDL attribute is said to be <em>getting</em> when its value is being retrieved (e.g. by author script), and is said to be <em>setting</em> when a new value is assigned to it.
   216       </p>
   217 
   218       <p>
   219         A <dfn>valid service type</dfn> is a string that begins with <code>upnp:</code> or <code>zeroconf:</code> 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, U+0030 to U+0039, U+0041 to U+005A, U+005E to U+007E.
   220       </p>
   221       <p></p>
   222 
   223       <p>
   224         A <a>valid service type</a> provided in the <code>type</code> attribute of the <a href="#dom-navigator-getnetworkservices"><code>getNetworkServices()</code></a> method will be matched against the services currently contained in the <a>list of available service records</a> according to the algorithms defined in this specification.
   225       </p>
   226 
   227       <p>
   228         A <dfn>user-agent generated callback url</dfn> is a Local-network accessible URL endpoint that a <a>user agent</a> must generate and maintain for receiving HTTP NOTIFY requests from UPnP Event sources. It is only required when the user agent implements UPnP Service Discovery as defined in
   229         this specification.
   230       </p>
   231 
   232     </section>
   233 
   234     <section>
   235      <h2>Requesting networked services</h2>
   236 
   237 
   238 <pre class="widl">[Supplemental, NoInterfaceObject]
   239 interface <dfn id="navigatornetworkservice">NavigatorNetworkService</dfn> {
   240   // Obtain a Local-networked Service
   241   void <a href="#dom-navigator-getnetworkservices">getNetworkServices</a>( in any type,
   242                            in <a href="#navigatornetworkservicesuccesscallback">NavigatorNetworkServiceSuccessCallback</a> successCallback,
   243                            in optional <a href="#navigatornetworkserviceerrorcallback">NavigatorNetworkServiceErrorCallback</a> errorCallback );
   244 };
   245 <a class="externalDFN" href="http://www.whatwg.org/specs/web-apps/current-work/complete/timers.html#navigator">Navigator</a> implements <a href="#navigatornetworkservice">NavigatorNetworkService</a>;
   246 
   247 [Callback=FunctionOnly, NoInterfaceObject]
   248 interface <dfn id="navigatornetworkservicesuccesscallback">NavigatorNetworkServiceSuccessCallback</dfn> {
   249   void handleEvent( in <a href="#networkservices">NetworkServices</a> services );
   250 };
   251 
   252 [NoInterfaceObject]
   253 interface <dfn id="navigatornetworkserviceerror">NavigatorNetworkServiceError</dfn> {
   254   const unsigned short <a href="#dom-navigatornetworkserviceerror-permission_denied">PERMISSION_DENIED_ERR</a> = 1;
   255   const unsigned short <a href="#dom-navigatornetworkserviceerror-unknown_type_prefix">UNKNOWN_TYPE_PREFIX_ERR</a> = 2;
   256   readonly attribute unsigned short <a href="#dom-navigatornetworkserviceerror-code">code</a>;
   257 };
   258 
   259 [Callback=FunctionOnly, NoInterfaceObject]
   260 interface <dfn id="navigatornetworkserviceerrorcallback">NavigatorNetworkServiceErrorCallback</dfn> {
   261   void handleEvent( in <a href="#navigatornetworkserviceerror">NavigatorNetworkServiceError</a> error );
   262 };
   263 </pre>
   264 
   265   <section>
   266    <h2>Methods</h2>
   267 
   268       <dl class="domintro">
   269         <dt>
   270           <var title="">window</var>
   271            .
   272           <code title="dom-navigator">
   273             <a href="http://www.whatwg.org/specs/web-apps/current-work/complete/timers.html#navigator">navigator</a>
   274           </code>
   275            .
   276           <code title="dom-navigator-getNetworkServices">
   277             <a href="#dom-navigator-getnetworkservices">getNetworkServices</a>
   278           </code>
   279           (
   280           <var title="">type</var>
   281           ,
   282           <var title="">successCallback</var>
   283            [,
   284           <var title="">errorCallback</var>
   285            ] )
   286         </dt>
   287         <dd>
   288           <p>Prompts the user to select one or more discovered network services that have advertised support for the requested service type.</p>
   289           <p>
   290             The
   291             <var title="">type</var>
   292              argument contains one or more <a>valid service type</a> tokens that the web page would like to interact with.
   293           </p>
   294           <p>
   295             If the user accepts, the
   296             <var title="">successCallback</var>
   297              is
   298           invoked, with one or more
   299             <code>
   300               <a href="#networkservice"><code>NetworkService</code></a>
   301             </code>
   302              objects as
   303           its argument.
   304           </p>
   305           <p>
   306             If the user declines, the
   307             <var title="">errorCallback</var>
   308              (if
   309           any) is invoked.
   310           </p>
   311         </dd>
   312       </dl>
   313 
   314        <div>
   315           <p>
   316             When the <dfn id="dom-navigator-getnetworkservices" title="dom-navigator-getnetworkservices"><code>getNetworkServices(type, successCallback[, errorCallback])</code></dfn> method is called, the <a>user agent</a> MUST run the following steps:
   317           </p>
   318 
   319           <ol class="rule">
   320 
   321             <li>
   322               Let <var>requested control types</var> be initially set to an empty array.
   323             </li>
   324 
   325             <li>
   326                If <var>type</var> is an array consisting of one or more <a>valid service type</a> tokens, then let <var>requested control types</var> by the value of <var>type</var>, removing any non-<a>valid service type</a> tokens from the resulting array.
   327             </li>
   328 
   329             <li>
   330                If <var>type</var> is a string consisting of one <a>valid service type</a> token, then let <var>requested control types</var> be an array containing one item with a value of <var>type</var>.
   331             </li>
   332 
   333             <li>
   334                If <var>requested control types</var> is an array that contains at least one or more <a title="valid service type">valid service type</a> tokens then continue to the step labeled <em>process</em> below. Otherwise, the <a>user agent</a> MUST <a href="http://www.whatwg.org/specs/web-apps/current-work/complete/webappapis.html#queue-a-task" class="externalDFN">queue a task</a> to invoke <var>errorCallback</var>, if it is provided and is an object of type <code>Function</code>, with a new <a href="#navigatornetworkserviceerror"><code>NavigatorNetworkServiceError</code></a> object whose
   335                  <a href="#dom-navigatornetworkserviceerror-code"><code>code</code></a> attribute has the numeric value 2
   336                   (<a href="#dom-navigatornetworkserviceerror-unknown_type_prefix"><code>UNKNOWN_TYPE_PREFIX_ERR</code></a>) as its argument,
   337                    abort any remaining steps and return.
   338             </li>
   339 
   340             <li>
   341                <em>Process</em>: Let <var>services found</var> be an empty array.
   342             </li>
   343 
   344             <li>
   345                For each <var>available service</var> in the <a>list of available service records</a> run the following steps:
   346                <ol class="rule">
   347                   <li>
   348                     For each <var>requested control type</var> in <var>requested control types</var>: If <var>available service</var>'s <code>type</code> attribute equals the <var>requested control type</var> then let <var>matched service</var> equal the value of <var>available service</var> and continue at the step labeled <var>attach</var> below.
   349                   </li>
   350                   <li>
   351                      Continue at the next <var>available service</var>.
   352                   </li>
   353                   <li>
   354                      <em>Attach</em>: If <var>matched service</var> is not empty then run the following steps:
   355 
   356                      <ol class="rule">
   357                         <li>
   358                            Let <var>new service object</var> be a new <a href="#networkservice"><code>NetworkService</code></a> object, mapping the parameters of
   359                      <var>matched service</var> to this new object where possible.
   360                         </li>
   361                         <li>
   362                            Append <var>new service object</var> to the <var>services found</var> array.
   363                         </li>
   364                      </ol>
   365                   </li>
   366                </ol>
   367             </li>
   368 
   369             <li>
   370                If <var>services found</var> is an empty array, then the <a>user agent</a> MUST <a href="http://www.whatwg.org/specs/web-apps/current-work/complete/webappapis.html#queue-a-task" class="externalDFN">queue a task</a> to invoke <var>errorCallback</var>, if it is provided and is an object of type <code>Function</code>, with a new <a href="#navigatornetworkserviceerror"><code>NavigatorNetworkServiceError</code></a> object whose
   371                  <a href="#dom-navigatornetworkserviceerror-code"><code>code</code></a> attribute has the numeric value 1
   372                  (<a href="#dom-navigatornetworkserviceerror-permission_denied"><code>PERMISSION_DENIED_ERR</code></a>) as its argument, abort any remaining steps and return.
   373             </li>
   374 
   375             <li>
   376                Return, and run the remaining steps asynchronously.
   377             </li>
   378 
   379             <li>
   380                Optionally, e.g. based on a previously-established user preference, for security reasons, or due to platform limitations, the <a>user agent</a> MAY <a href="http://www.whatwg.org/specs/web-apps/current-work/complete/webappapis.html#queue-a-task" class="externalDFN">queue a task</a> to invoke <var>errorCallback</var>, if it is provided and is an object of type <code>Function</code>, with a new <a href="#navigatornetworkserviceerror"><code>NavigatorNetworkServiceError</code></a> object whose
   381                  <a href="#dom-navigatornetworkserviceerror-code"><code>code</code></a> attribute has the numeric value 1
   382                  (<a href="#dom-navigatornetworkserviceerror-permission_denied"><code>PERMISSION_DENIED_ERR</code></a>) as its argument, abort any remaining steps and return.
   383             </li>
   384 
   385             <li>
   386                   The <a>user agent</a> MUST prompt the user in a user-agent-specific manner for permission to provide the
   387                   <a href="http://www.whatwg.org/specs/web-apps/current-work/complete/browsers.html#entry-script" class="externalDFN">entry script</a>'s
   388                   <a href="http://www.whatwg.org/specs/web-apps/current-work/complete/origin-0.html#origin" class="externalDFN">origin</a> with an array of
   389                   <a href="#networkservice"><code>NetworkService</code></a> objects representing the user-authorized subset of <var>services found</var>.
   390 
   391                <p>
   392                   If the user grants permission to access one or more networked services then the <a>user agent</a> SHOULD include an
   393                   "ongoing local-network communication" indicator.
   394                </p>
   395 
   396                <p>If the user denies permission, then the <a>user agent</a> MUST <a href="http://www.whatwg.org/specs/web-apps/current-work/complete/webappapis.html#queue-a-task" class="externalDFN">queue a task</a> to invoke <var>errorCallback</var>, if it is provided and is an object of type <code>Function</code>, with a new <a href="#navigatornetworkserviceerror"><code>NavigatorNetworkServiceError</code></a> object whose
   397                 <a href="#dom-navigatornetworkserviceerror-code"><code>code</code></a> attribute has the numeric value 1
   398                 (<a href="#dom-navigatornetworkserviceerror-permission_denied"><code>PERMISSION_DENIED_ERR</code></a>) as its argument, abort any remaining steps and return.
   399               </p>
   400 
   401               <p>
   402                 If the user never responds, this algorithm stalls on this step.
   403               </p>
   404 
   405             </li>
   406 
   407             <li>
   408                Let <var>services</var> be the array of one or more <a href="#networkservice"><code>NetworkService</code></a> objects for which the user granted permission.
   409             </li>
   410 
   411             <li>
   412                For each Object <var>service</var> in <var>services</var>, run the following substeps:
   413 
   414                <ol class="rule">
   415                   <li>
   416                      Add the <var>service</var>'s <code>url</code> parameter to the <a>entry script origin's <abbr title="Uniform Resource Locator">URL</abbr> whitelist</a>.
   417                   </li>
   418                   <li>
   419                     If <var>service</var>'s <code>type</code> parameter begins with the DOMString &quot;<code>upnp:</code>&quot; and the <var>service</var>'s <code>eventsUrl</code> parameter is not empty then <a>setup a UPnP Events Subscription</a> for <var>service</var>.
   420                   </li>
   421                </ol>
   422             </li>
   423 
   424             <li>
   425                Let <var>services manager</var> be a new <a href="#networkservices"><code>NetworkServices</code></a> object.
   426             </li>
   427 
   428             <li>
   429                Set <var>services manager</var>'s <a href="#dom-networkservices-servicesavailable"><code>servicesAvailable</code></a> attribute to the length of <var>services</var>.
   430             </li>
   431 
   432             <li>
   433               Add the set of <var>services</var> to the <a>list of authorized service records</a> internally against the newly created <var>services manager</var> object.
   434             </li>
   435 
   436             <li>
   437                The <a>user agent</a> MUST <a href="http://www.whatwg.org/specs/web-apps/current-work/complete/webappapis.html#queue-a-task" class="externalDFN">queue a task</a> to invoke <var>successCallback</var> with
   438                <var>services manager</var> as its argument.
   439             </li>
   440 
   441           </ol>
   442 
   443           <p>
   444             The <a href="http://www.whatwg.org/specs/web-apps/current-work/complete/webappapis.html#task-source" class="externalDFN">task source</a> for these
   445             <a href="http://www.whatwg.org/specs/web-apps/current-work/complete/webappapis.html#concept-task" class="externalDFN">tasks</a> is the
   446             <a href="http://www.whatwg.org/specs/web-apps/current-work/complete/webappapis.html#user-interaction-task-source" class="externalDFN">user interaction task source</a>.
   447           </p>
   448 
   449           <p>
   450             When a <a href="#networkservice"><code>NetworkService</code></a> object is provided to a Web page, the <a>user agent</a> MUST add the <code>url</code> property
   451              to the <dfn>entry script origin's URL whitelist</dfn>. This list enables the
   452             Web page to override and initiate cross-site resource requests towards these URLs, and any sub-resources of these URLs, within the current
   453             <a href="http://www.whatwg.org/specs/web-apps/current-work/complete/browsers.html#entry-script" class="externalDFN">entry script</a>'s
   454             <a href="http://www.whatwg.org/specs/web-apps/current-work/complete/origin-0.html#origin" class="externalDFN">origin</a> via various existing mechanisms (e.g. Web Sockets, Server-Sent Events,
   455             Web Messaging, XMLHttpRequest).
   456          </p>
   457 
   458          <p>
   459             If the user navigates away from the current browsing context, the <a>user agent</a> MUST remove all previously whitelisted urls from the <a>entry script origin's URL whitelist</a>.
   460             There is no persistence to network service selections provided to a web page. It is not possible to access a previously white-listed networked service without the necessary user authorization in all of the following cases:
   461             <ul>
   462               <li>If the current script is reloaded at any point in the same or different window.</li>
   463               <li>if the current script reinvokes the <a href="#dom-navigator-getnetworkservices"><code>getNetworkServices()</code></a> method at any point in its execution.</li>
   464               <li>If the user navigates forward or back in their history to reload the current page.</li>
   465               <li>If a script is running in a different origin.</li>
   466             </ul>
   467          </p>
   468 
   469       </div>
   470       </section>
   471 
   472       <section>
   473          <h3>Error Handling</h3>
   474 
   475       <dl class="domintro">
   476         <dt>
   477           <var title="">error</var>
   478            .
   479           <code title="dom-NavigatorNetworkServiceError-code">
   480             <a href="#dom-navigatornetworkserviceerror-code">code</a>
   481           </code>
   482         </dt>
   483         <dd>
   484           <p>
   485             Returns the current error's error code. At the current time, this may be <code>1</code> or <code>2</code>, for which the
   486             corresponding error constants
   487             <a href="#dom-navigatornetworkserviceerror-permission_denied"><code>PERMISSION_DENIED_ERR</code></a> and
   488             <a href="#dom-navigatornetworkserviceerror-unknown_type_prefix"><code>UNKNOWN_TYPE_PREFIX_ERR</code></a> are defined.
   489           </p>
   490         </dd>
   491       </dl>
   492 
   493          <p>
   494             The <dfn id="dom-navigatornetworkserviceerror-code" title="dom-navigatornetworkserviceerror-code"><code>code</code></dfn> attribute of a
   495             <a href="#navigatornetworkserviceerror"><code>NavigatorNetworkServiceError</code></a> object MUST return the code for the error, which will be one of the following:
   496          </p>
   497 
   498          <dl>
   499             <dt>
   500                <dfn id="dom-navigatornetworkserviceerror-permission_denied" title="dom-navigatornetworkserviceerror-permission_denied"><code>PERMISSION_DENIED_ERR</code></dfn> (numeric value 1)
   501             </dt>
   502             <dd>
   503                The user or user agent denied the page permission to access any services.
   504             </dd>
   505             <dt>
   506                <dfn id="dom-navigatornetworkserviceerror-unknown_type_prefix" title="dom-navigatornetworkserviceerror-unknown_type_prefix"><code>UNKNOWN_TYPE_PREFIX_ERR</code></dfn> (numeric value 2)
   507             </dt>
   508             <dd>
   509                No <a>valid service type</a> tokens were provided in the method invocation.
   510             </dd>
   511          </dl>
   512 
   513       </section>
   514 
   515       </section>
   516       <section>
   517       <h2>Obtaining networked services</h2>
   518 
   519       <p>
   520          The <a href="#networkservices"><code>NetworkServices</code></a> interface is the top-level response object from a call to <a href="#dom-navigator-getnetworkservices"><code>getNetworkServices()</code></a> and provides access to a set of user-authorized <a href="#networkservice"><code>NetworkService</code></a> objects for the given request.
   521       </p>
   522 
   523 <pre class="widl">
   524 [NoInterfaceObject]
   525 interface <dfn id="networkservices">NetworkServices</dfn> {
   526   readonly attribute unsigned long    <a href="#dom-networkservices-length">length</a>;
   527   getter <a href="#networkservice">NetworkService</a> (unsigned long index);
   528   <a href="#networkservice">NetworkService</a>? <a href="#dom-networkservices-getservicebyid">getServiceById</a>(DOMString id);
   529 
   530   readonly attribute unsigned long    <a href="#dom-networkservices-servicesavailable">servicesAvailable</a>;
   531 
   532   // event handler attributes
   533            attribute <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/webappapis.html#eventhandler" class="externalDFN">EventHandler</a>     <a href="#dom-networkservices-onserviceavailable">onserviceavailable</a>;
   534            attribute <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/webappapis.html#eventhandler" class="externalDFN">EventHandler</a>     <a href="#dom-networkservices-onserviceunavailable">onserviceunavailable</a>;
   535 
   536 };
   537 
   538 <a href="#networkservices">NetworkServices</a> implements <a href="http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#interface-eventtarget" class="externalDFN">EventTarget</a>;
   539 </pre>
   540 
   541       <section>
   542       <h2>Attributes</h2>
   543 
   544         <dl class="domintro">
   545           <dt>
   546             <code title="dom-networkservices-length">
   547               <a href="#dom-networkservices-length">length</a>
   548             </code>
   549           </dt>
   550           <dd>
   551             <p>
   552               Returns the current number of services belonging in the respective object's <a>list of authorized service records</a>.
   553             </p>
   554           </dd>
   555           <dt>
   556             <code title="dom-networkservices-servicesavailable">
   557               <a href="#dom-networkservices-servicesavailable">servicesAvailable</a>
   558             </code>
   559           </dt>
   560           <dd>
   561             <p>
   562               Returns the current number of services matching one of the app-requested <a>valid service type</a> tokens that are actively available within the user's current network.
   563             </p>
   564           </dd>
   565         </dl>
   566 
   567         <div>
   568            <p>
   569               The <dfn id="dom-networkservices-length"><code>length</code></dfn> attribute MUST return the number of services represented in the object's corresponding <a>list of authorized service records</a> at the time of getting.
   570            </p>
   571 
   572            <p>
   573               The <dfn id="dom-networkservices-servicesavailable"><code>servicesAvailable</code></dfn> attribute MUST return the number of services available in the
   574               user's network that match the <a>valid service type</a> that was initially used to create the current <a href="#networkservices"><code>NetworkServices</code></a> object.
   575            </p>
   576 
   577            <p>
   578              When a previously unknown instance of a networked service matching one of the requested <a href="#dfn-valid-service-type">valid service types</a> becomes available on the user's current network, the <a>user agent</a> MUST increment the <a href="#dom-networkservices-servicesavailable"><code>servicesAvailable</code></a> attribute by <code>1</code> and then
   579              <a href="http://www.whatwg.org/specs/web-apps/current-work/complete/webappapis.html#queue-a-task" class="externalDFN">queue a task</a>
   580              to dispatch a newly created event with the name <code>serviceavailable</code> that uses the <code>Event</code> interface, which does
   581              not bubble, is not cancellable, and has no default action, at the current <a href="#networkservices"><code>NetworkServices</code></a>
   582              object.
   583            </p>
   584 
   585            <p>
   586              When a previously known instance of a networked service matching one of the requested <a href="#dfn-valid-service-type">valid service types</a> becomes unavailable on the user's current network, the <a>user agent</a> MUST decrement the <a href="#dom-networkservices-servicesavailable"><code>servicesAvailable</code></a> attribute by <code>1</code> and then
   587              <a href="http://www.whatwg.org/specs/web-apps/current-work/complete/webappapis.html#queue-a-task" class="externalDFN">queue a task</a>
   588               to dispatch a newly created event with the name <code>serviceunavailable</code> that uses the <code>Event</code> interface, which does
   589               not bubble, is not cancellable, and has no default action, at the current <a href="#networkservices"><code>NetworkServices</code></a>
   590               object.
   591            </p>
   592         </div>
   593 
   594       </section>
   595 
   596       <section>
   597       <h2>Methods</h2>
   598         <dl class="domintro">
   599         <dt>
   600           <code title="networkservices-getter">
   601             <a href="#networkservices">services</a>
   602           </code>
   603           [
   604           <var title="">index</var>
   605           ]
   606         </dt>
   607         <dd>
   608           <p>
   609             Returns the specified <a href="#networkservice"><code>NetworkService</code></a> object.
   610           </p>
   611         </dd>
   612         <dt>
   613           <code title="networkservices-getter">
   614             <a href="#networkservices">services</a>
   615           </code>
   616           .
   617           <code title="dom-networkservices-getservicebyid">
   618             <a href="#dom-networkservices-getservicebyid">getServiceById</a>
   619           </code>
   620           (
   621           <var title="">id</var>
   622           )
   623         </dt>
   624         <dd>
   625           <p>
   626             Returns the <a href="#networkservice"><code>NetworkService</code></a> object with the given identifier, or null if no
   627             service has that identifier.
   628           </p>
   629         </dd>
   630       </dl>
   631 
   632       <p>
   633         A <a href="#networkservices"><code>NetworkServices</code></a> object represents the current list of one or more current authorized services - the <a>list of authorized service records</a>. Each item in the <a>list of authorized service records</a> is represented by a <a href="#networkservice"><code>NetworkService</code></a> object. The <a>list of authorized service records</a> is <span>immutable</span> meaning that it cannot be modified for the lifetime of a <a href="#networkservices"><code>NetworkServices</code></a> object.
   634       </p>
   635 
   636       <p class="note">
   637         Each service in a <a href="#networkservices"><code>NetworkServices</code></a> object thus has an index; the first has the index 0, and each subsequent service is numbered one higher than the previous one.
   638       </p>
   639 
   640       <p>
   641         The <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/infrastructure.html#supported-property-indices" class="externalDFN">supported property indices</a> of <a href="#networkservices"><code>NetworkServices</code></a> objects at any instant are the numbers from zero to the number of items in the <a>list of authorized service records</a> represented by the respective object minus one, if any services are represented in the <a>list of authorized service records</a>.
   642       </p>
   643 
   644       <p>
   645         To <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/infrastructure.html#determine-the-value-of-an-indexed-property" class="externalDFN">determine the value of an indexed property</a> for a given index <var>index</var> in a <a href="#networkservices"><code>NetworkServices</code></a> object's <a>list of authorized service records</a>, the user agent MUST return the <a href="#networkservice"><code>NetworkService</code></a> object that represents the <var>index</var>th service in the <a>list of authorized service records</a>.
   646       </p>
   647 
   648       <p>
   649         The <dfn id="dom-networkservices-getservicebyid"><code>getServiceById(id)</code></dfn> method MUST return the first <a href="#networkservice"><code>NetworkService</code></a> object in the <a>list of authorized service records</a> represented by the respective object whose <a href="#dom-networkservice-id"><code>id</code></a> attribute is equal to the value of the <var>id</var> argument.
   650         When no services in the <a>list of authorized service records</a> match the given argument, the method MUST return null.
   651       </p>
   652 
   653       <p>
   654          Services available within the local network can connect and disconnect at different times during the execution of a web page. A <a>user agent</a> can
   655          inform a web page when the state of networked services matching the requested <a>valid service type</a> change. Web pages can use this information to enable in-page experiences for communicating the state of networked services
   656          with the ability to change the particular service or set of services the page is connected to by re-invoking the <a href="#dom-navigator-getnetworkservices"><code>getNetworkServices()</code></a> method.
   657       </p>
   658 
   659       </section>
   660 
   661       <section>
   662       <h2>Events</h2>
   663 
   664       <p>
   665          The following are the event handlers (and their corresponding event handler event types) that must be supported, as IDL attributes, by all objects implementing the <a href="#networkservices"><code>NetworkServices</code></a> interface:
   666        </p>
   667 
   668        <table border="1">
   669         <thead>
   670           <tr>
   671             <th>
   672               <span title="event handlers">Event handler</span>
   673             </th>
   674             <th>
   675               <span>Event handler event type</span>
   676             </th>
   677           </tr>
   678         </thead>
   679         <tbody>
   680           <tr>
   681             <td>
   682               <dfn id="dom-networkservices-onserviceavailable" title="dom-NetworkServices-onserviceavailable">
   683                 <code>onserviceavailable</code>
   684               </dfn>
   685             </td>
   686             <td>
   687               <code title="event-serviceavailable">serviceavailable</code>
   688             </td>
   689           </tr>
   690           <tr>
   691             <td>
   692               <dfn id="dom-networkservices-onserviceunavailable" title="dom-NetworkServices-onserviceunavailable">
   693                 <code>onserviceunavailable</code>
   694               </dfn>
   695             </td>
   696             <td>
   697               <code title="event-serviceunavailable">serviceunavailable</code>
   698             </td>
   699           </tr>
   700         </tbody>
   701       </table>
   702 
   703       <p>
   704          Events with an event type of <code>serviceavailable</code> or <code>serviceunavailable</code> defined in this specification are simple <code>Event</code> objects.
   705       </p>
   706 
   707       </section>
   708 
   709     </section>
   710     <section>
   711     <h2>Communicating with a networked service</h3>
   712 
   713 <p>
   714    The <a href="#networkservice"><code>NetworkService</code></a> interface is used to provide a set of connection information for an HTTP service endpoint and if available, service events, running on a networked device.
   715 </p>
   716 
   717 <pre class="widl">
   718 [NoInterfaceObject]
   719 interface <dfn id="networkservice">NetworkService</dfn> {
   720   readonly attribute DOMString        <a href="#dom-networkservice-id">id</a>;
   721   readonly attribute DOMString        <a href="#dom-networkservice-name">name</a>;
   722   readonly attribute DOMString        <a href="#dom-networkservice-type">type</a>;
   723   readonly attribute DOMString        <a href="#dom-networkservice-url">url</a>;
   724   readonly attribute DOMString        <a href="#dom-networkservice-config">config</a>;
   725 
   726   readonly attribute boolean          <a href="#dom-networkservice-online">online</a>;
   727 
   728   // event handler attributes
   729            attribute <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/webappapis.html#eventhandler" class="externalDFN">EventHandler</a>     <a href="#dom-networkservice-onserviceonline">onserviceonline</a>;
   730            attribute <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/webappapis.html#eventhandler" class="externalDFN">EventHandler</a>     <a href="#dom-networkservice-onserviceoffline">onserviceoffline</a>;
   731 
   732            attribute <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/webappapis.html#eventhandler" class="externalDFN">EventHandler</a>     <a href="#dom-networkservice-onnotify">onnotify</a>;
   733 };
   734 
   735 <a href="#networkservice">NetworkService</a> implements <a href="http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#interface-eventtarget" class="externalDFN">EventTarget</a>;
   736 </pre>
   737 
   738 <section>
   739   <h2>Attributes</h2>
   740 
   741       <dl class="domintro">
   742         <dt>
   743           <var title="">service</var>
   744            .
   745           <code title="dom-networkservice-id">
   746             <a href="#dom-networkservice-id">id</a>
   747           </code>
   748         </dt>
   749         <dd>
   750           <p>
   751             A unique identifier for the given user-selected service instance.
   752           </p>
   753         </dd>
   754         <dt>
   755           <var title="">service</var>
   756            .
   757           <code title="dom-networkservice-name">
   758             <a href="#dom-networkservice-name">name</a>
   759           </code>
   760         </dt>
   761         <dd>
   762           <p>
   763             The name of the user-selected service.
   764           </p>
   765         </dd>
   766         <dt>
   767           <var title="">service</var>
   768            .
   769           <code title="dom-networkservice-type">
   770             <a href="#dom-networkservice-type">type</a>
   771           </code>
   772         </dt>
   773         <dd>
   774           <p>
   775             The <a>valid service type</a> token value of the user-selected service.
   776           </p>
   777         </dd>
   778         <dt>
   779           <var title="">service</var>
   780            .
   781           <code title="dom-networkservice-url">
   782             <a href="#dom-networkservice-url">url</a>
   783           </code>
   784         </dt>
   785         <dd>
   786           <p>
   787             The control URL endpoint (including any required port information) of the user-selected control service that has been added to the <a>entry script origin's URL whitelist</a>.
   788           </p>
   789         </dd>
   790         <dt>
   791           <var title="">service</var>
   792            .
   793           <code title="dom-networkservice-config">
   794             <a href="#dom-networkservice-config">config</a>
   795           </code>
   796         </dt>
   797         <dd>
   798           <p>
   799             The configuration information associated with the service depending on the requested service type.
   800           </p>
   801         </dd>
   802       </dl>
   803 
   804           <p>
   805             The <dfn id="dom-networkservice-id"><code>id</code></dfn> attribute is a unique identifier for the service. The same service provided at different times or on different objects MUST have the same <a href="#dom-networkservice-id"><code>id</code></a> value.
   806          </p>
   807 
   808          <p>
   809             The <dfn id="dom-networkservice-name"><code>name</code></dfn> attribute represents a human-readable title for the service.
   810          </p>
   811 
   812          <p>
   813              The <dfn id="dom-networkservice-type"><code>type</code></dfn> attribute reflects the value of the <a>valid service type</a> of the service.
   814           </p>
   815 
   816          <p>
   817             The <dfn id="dom-networkservice-url"><code>url</code></dfn> attribute is an <a href="http://www.w3.org/TR/html5/urls.html#absolute-url" class="externalDFN">absolute URL</a> pointing to the root HTTP
   818             endpoint for the service that has been added to the <a>entry script origin's URL whitelist</a>. Web pages can subsequently use this value for implicit cross-document messaging via various existing mechanisms (e.g. Web Sockets, Server-Sent Events, Web Messaging, XMLHttpRequest).
   819          </p>
   820 
   821          <p>
   822             The <dfn id="dom-networkservice-config"><code>config</code></dfn> attribute provides the raw configuration information extracted from the given network service.
   823          </p>
   824 
   825       </section>
   826 
   827       <section>
   828          <h3>States</h3>
   829 
   830       <dl class="domintro">
   831         <dt>
   832           <var title="">service</var>
   833            .
   834           <code title="dom-networkservice-online">
   835             <a href="#dom-networkservice-online">online</a>
   836           </code>
   837         </dt>
   838         <dd>
   839           <p>
   840             Returns <code>true</code> if the service is reporting that it is accessible on the local network or <code>false</code> if the service is reporting that it is no longer accessible (temporarily or permanently) on the local network.
   841           </p>
   842         </dd>
   843       </dl>
   844 
   845       <p>
   846         The <dfn id="dom-networkservice-online"><code>online</code></dfn> attribute indicates whether the service is reporting itself as being
   847         either <var>online</var>, and therefore accessible on the local network, in which case this attribute will return <code>true</code> or, <var>offline</var>, and therefore not accessible on the local network, either temporarily or permanently, in which case this attribute will return <code>false</code>. This attribute MUST default to <code>true</code>.
   848       </p>
   849 
   850       </section>
   851 
   852       <section>
   853          <h3>Events</h3>
   854 
   855       <p>
   856          The following are the event handlers (and their corresponding event handler event types) that must be supported, as IDL attributes, by all objects implementing the
   857          <a href="#networkservice"><code>NetworkService</code></a> interface:
   858        </p>
   859 
   860        <table border="1">
   861         <thead>
   862           <tr>
   863             <th>
   864               <span title="event handlers">Event handler</span>
   865             </th>
   866             <th>
   867               <span>Event handler event type</span>
   868             </th>
   869           </tr>
   870         </thead>
   871         <tbody>
   872           <tr>
   873             <td>
   874               <dfn id="dom-networkservice-onnotify" title="dom-NetworkService-onnotify">
   875                 <code>onnotify</code>
   876               </dfn>
   877             </td>
   878             <td>
   879               <code title="event-notify">notify</code>
   880             </td>
   881           </tr>
   882           <tr>
   883             <td>
   884               <dfn id="dom-networkservice-onserviceonline" title="dom-NetworkService-onserviceonline">
   885                 <code>onserviceonline</code>
   886               </dfn>
   887             </td>
   888             <td>
   889               <code title="event-onserviceonline">serviceonline</code>
   890             </td>
   891           </tr>
   892           <tr>
   893             <td>
   894               <dfn id="dom-networkservice-onserviceoffline" title="dom-NetworkService-onserviceoffline">
   895                 <code>onserviceoffline</code>
   896               </dfn>
   897             </td>
   898             <td>
   899               <code title="event-onserviceoffline">serviceoffline</code>
   900             </td>
   901           </tr>
   902         </tbody>
   903       </table>
   904 
   905       <p>
   906          Events with an event type of <code>notify</code>, <code>serviceonline</code> or <code>serviceoffline</code> defined in this specification are simple <code>Event</code> objects.
   907       </p>
   908 
   909       </section>
   910    </section>
   911 
   912       <section>
   913             <h2>Service Discovery</h2>
   914 
   915       <p>
   916          A <a>user agent</a> conforming to this specification MAY implement <acronym title="Simple Service Discovery Protocol">SSDP</acronym> [[!UPNP-DEVICEARCH11]] and Zeroconf [[!DNS-SD]] + [[!MDNS]] service discovery mechanisms
   917          to enable Web pages to request and connect with HTTP services running on networked devices, discovered via either mechanism, through this API. When a <a>user agent</a> implements either of these service discovery mechanisms, then it MUST conform to the corresponding algorithms provided in this section of the specification.
   918       </p>
   919       <p>
   920          This section presents how the results of these two service discovery
   921          mechanisms will be matched to requested service types, how the user agent stores available and active services, how their properties are applied to any resulting <a href="#networkservice"><code>NetworkService</code></a> objects.
   922       </p>
   923 
   924       <p>
   925          It is expected that user agents will perform these service discovery mechansisms asynchronously and periodically update the <a>list of networked devices</a> as required. The timing of any
   926          service discovery mechanisms is an implementation detail left to the discretion of the implementer (e.g. once on user agent start-up, every X seconds during user agent execution or on
   927          invocation of this API from a Web page).
   928       </p>
   929 
   930       <p>
   931          The <dfn>list of available service records</dfn> is a single dynamic internal lookup table within user agents that is used to track all the  services that have been discovered and are available in the current network at any given time.
   932          At any point during the running of either of the two service discovery mechanisms then existing entries within this table can be updated, entries can be added and entries can be removed as the status of networked
   933          services changes according to the rules defined in this specification. <!--Each record contained within this table contains the attributes: <code>id</code>, <code>deviceId</code>, <code>name</code>, <code>type</code>, <code>url</code>, <code>config</code> and <code>expiryTimestamp</code>.-->
   934       </p>
   935 
   936       <p>
   937         The <dfn>list of authorized service records</dfn> is a single dynamic internal lookup table within user agents that is used to track the
   938         current services that are being shared with web pages at any given time from the <a>list of available service records</a>. Each record in the <a>list of authorized service records</a> is associated with a <var>services manager</var> object that is assigned as part of the
   939          <a href="#dom-navigator-getnetworkservices"><code>getNetworkServices()</code></a> algorithm.
   940       </p>
   941 
   942       <p>
   943         The rule for <dfn>adding an available service</dfn> is the process of adding a new service or updating an existing service in the <a>list of available service records</a> that is generally available on the user's current network. This rule takes one argument, <var>network service record</var>, and consists of
   944         running the following steps:
   945       </p>
   946 
   947       <ol class="rule">
   948 
   949         <li>
   950           Let <var>new service registration flag</var> be <code>true</code>.
   951         </li>
   952 
   953         <li>
   954            For each <var>existing service record</var> in the current <a>list of available service records</a>, run the following sub-steps:
   955            <ol class="rule">
   956 
   957              <li>
   958               If the <var>existing service record</var>'s <code>id</code> property does not equal <var>network service record</var>'s <code>id</code>
   959                property then abort any remaining sub-steps and continue at the next available <var>existing service record</var>.
   960              </li>
   961 
   962              <li>
   963               Set <var>new service registration flag</var> to <code>false</code>.
   964              </li>
   965 
   966              <li>
   967                Replace the value of <var>existing service record</var> in the current <a>list of available service records</a> with the value of
   968               <var>network service record</var>.
   969              </li>
   970            </ol>
   971         </li>
   972 
   973         <li>
   974            If <var>new service registration flag</var> is set to <code>true</code> then add <var>network service record</var> to the <a>list of available service records</a> as a new entry.
   975         </li>
   976 
   977         <li>
   978           For each <var>active service</var> in the <a>list of authorized service records</a> run the following steps:
   979 
   980           <ol class="rule">
   981 
   982             <li>
   983                If <var>network service record</var>'s <code>type</code> property does not equal the current <var>active service</var>'s
   984                 <code>type</code> attribute then abort any remaining sub-steps for this <var>active service</var> and continue at the next available <var>active service</var>.
   985             </li>
   986 
   987             <li>
   988                If the <var>new service registration flag</var> is set to <code>true</code> then increment the <a href="#dom-networkservices-servicesavailable"><code>servicesAvailable</code></a> attribute of the <var>services manager</var> associated with
   989                the current <var>active service</var>
   990                 object by <code>1</code> and then <a href="http://www.whatwg.org/specs/web-apps/current-work/complete/webappapis.html#queue-a-task" class="externalDFN">queue a task</a>
   991                  to dispatch a newly created event with the name <a href="#dom-networkservices-onserviceavailable"><code>serviceavailable</code></a> that uses the <code>Event</code> interface,
   992                  which does not bubble, is not cancellable, and has no default action, at the <var>services manager</var> associated with
   993                  the current <var>active service</var> object.
   994             </li>
   995 
   996             <li>
   997                <a href="http://www.whatwg.org/specs/web-apps/current-work/complete/webappapis.html#queue-a-task" class="externalDFN">Queue a task</a>
   998                 to dispatch a newly created event with the name <a href="#dom-networkservice-onserviceonline"><code>serviceonline</code></a> that uses the <code>Event</code> interface, which
   999                  does not bubble, is not cancellable, and has no default action, at the current
  1000                 <var>active service</var> object.
  1001             </li>
  1002 
  1003           </ol>
  1004 
  1005         </li>
  1006 
  1007       </ol>
  1008 
  1009 
  1010       <p>
  1011         The rule for <dfn>removing an available service</dfn> is the general process of removing a service from the
  1012         <a>list of available service records</a>
  1013          that has left the user's current network or has otherwise expired. This rule takes one argument, <var>service identifier</var>, and consists of running the following steps:</p>
  1014 
  1015       <ol class="rule">
  1016 
  1017         <li>
  1018            For each <var>existing service record</var> in the current <a>list of available service records</a>, run the following sub-steps:
  1019            <ol class="rule">
  1020 
  1021              <li>
  1022               If the <var>existing service record</var>'s <code>id</code> property does not match <var>service identifier</var> then skip any remaining sub-steps for the current <var>existing service record</var> and continue at the next available <var>existing service record</var>.
  1023              </li>
  1024 
  1025              <li>
  1026                If the <var>existing service record</var>'s <code>type</code> property begins with the DOMString "<code>upnp:</code>" and
  1027                <var>existing service record</var>'s <code>eventsURL</code> property is set then run the rule to
  1028                <a>terminate an existing UPnP Events Subscription</a>, if one is currently active (as a result of having previously called
  1029                <a>setup a UPnP Events Subscription</a> against the current <var>existing service record</var>).
  1030              </li>
  1031 
  1032              <li>
  1033                For each <var>active service</var> in <a>list of authorized service records</a> run the following steps:
  1034 
  1035                <ol class="rule">
  1036 
  1037                  <li>
  1038                     If <var>existing service record</var>'s <code>type</code> property does not equal the current <var>active service</var>'s
  1039                      <code>type</code> attribute then abort any remaining sub-steps for this <var>active service</var> and continue at the next available <var>active service</var>.
  1040                  </li>
  1041 
  1042                  <li>
  1043                     Decrement the <a href="#dom-networkservices-servicesavailable"><code>servicesAvailable</code></a> attribute of the
  1044                     <var>services manager</var> associated with the current <var>active service</var>
  1045                      object by <code>1</code> and then <a href="http://www.whatwg.org/specs/web-apps/current-work/complete/webappapis.html#queue-a-task" class="externalDFN">queue a task</a>
  1046                       to dispatch a newly created event with the name <a href="#dom-networkservices-onserviceunavailable"><code>serviceunavailable</code></a> that uses the <code>Event</code> interface,
  1047                       which does not bubble, is not cancellable, and has no default action, at the <var>services manager</var> associated with
  1048                       the current <var>active service</var> object.
  1049                  </li>
  1050 
  1051                  <li>
  1052                     <a href="http://www.whatwg.org/specs/web-apps/current-work/complete/webappapis.html#queue-a-task" class="externalDFN">Queue a task</a>
  1053                      to dispatch a newly created event with the name <a href="#dom-networkservice-onserviceoffline"><code>serviceoffline</code></a> that uses the <code>Event</code> interface, which
  1054                       does not bubble, is not cancellable, and has no default action, at the current
  1055                      <var>active service</var> object.
  1056                  </li>
  1057 
  1058                </ol>
  1059 
  1060              </li>
  1061 
  1062              <li>
  1063                Remove <var>existing service record</var> from the current <a>list of available service records</a>.
  1064              </li>
  1065 
  1066            </ol>
  1067         </li>
  1068 
  1069       </ol>
  1070 
  1071       <p>
  1072        User agents <em class="ct">SHOULD</em> expire a service record from the <a>list of available service records</a> when its
  1073        <code>expiryTimestamp</code> attribute exceeds the current UTC timestamp. When this condition is met the <a>user agent</a> SHOULD
  1074        run the rule for <a>removing an available service</a>, passing in the expired service record's <code>id</code> attribute as the
  1075        only argument.
  1076       </p>
  1077 
  1078 
  1079       <section>
  1080          <h4>Zeroconf (<abbr title="Multicast DNS">mDNS</abbr> + <abbr title="Domain Name System">DNS</abbr>-<abbr title="Service Discovery">SD</abbr>)</h4>
  1081 
  1082          <p>
  1083             For each DNS response received from a user-agent-initiated Multicast DNS Browse for <abbr title="DNS Pointer Record">PTR</abbr> records with the name <code>_services._dns-sd._udp</code> on the resolved recommended automatic browsing
  1084    domain [[!MDNS]], the <a>user agent</a> MUST run the following steps:
  1085          </p>
  1086 
  1087          <ol class="rule">
  1088 
  1089             <li>Let <var>service mDNS responses</var> be an array of PTR records received by issuing a Multicast DNS Browse for PTR records with the name of the current discovered service type.</li>
  1090 
  1091             <li>For each Object <var>service mDNS response</var> in <var>service mDNS responses</var>, run the following steps:
  1092                <ol>
  1093 
  1094                   <li>
  1095                      Let <var>network service record</var> be an Object consisting of the following empty properties: <code>id</code>, <code>name</code>, <code>type</code>, <code>url</code>, <code>config</code>, <code>expiryTimestamp</code>.
  1096                   </li>
  1097 
  1098                   <li>
  1099                      Set <var>network service record</var>'s <code>id</code> property to the value of the full PTR Service Instance Name [[!MDNS]].
  1100                   </li>
  1101 
  1102                   <li>
  1103                      Set <var>network service record</var>'s <code>name</code> property to the value of the PTR Service Instance Name's <var>Instance</var> component [[!MDNS]].
  1104                   </li>
  1105 
  1106                   <li>
  1107                      Set <var>network service record</var>'s <code>type</code> property to the concatenation of the string <code>zeroconf:</code> followed by the value of the PTR Service Instance Name's <var>Service</var> component [[!MDNS]].
  1108                   </li>
  1109 
  1110                   <li>
  1111                      Set <var>network service record</var>'s <code>url</code> property to the resolvable Service URL obtained from performing an DNS-SD Lookup [[!DNS-SD]] of the current service from the PTR record provided [[!MDNS]].
  1112                   </li>
  1113 
  1114                   <li>
  1115                      Set <var>network service record</var>'s <code>config</code> property to the string value of the contents of the first DNS-SD TXT record associated with the <var>service mDNS response</var> as defined in [[!DNS-SD]].
  1116                   </li>
  1117 
  1118                   <li>
  1119                      Set <var>network service record</var>'s <code>expiryTimestamp</code> property to the value of the current date, in UTC timestamp format, plus a value of <code>120</code> seconds.
  1120                   </li>
  1121 
  1122                   <li>
  1123                      Run the general rule for <a>adding an available service</a>, passing in the current <var>network service record</var> as the
  1124                      only argument.
  1125                   </li>
  1126 
  1127             </ol>
  1128            </li>
  1129          </ol>
  1130 
  1131       </section>
  1132 
  1133       <section>
  1134          <h5>Universal Plug-and-Play (<abbr title="Universal Plug-and-Play">UPnP</abbr>)</h5>
  1135 
  1136          <p>
  1137           A user agent that implements UPnP service discovery must issue an <dfn>advertisement for UPnP root devices</dfn> against the user's
  1138           current local network according to the full normative text and timing provided in 'Section 1.3.2: Search request with M-SEARCH' detailed in [[!UPNP-DEVICEARCH11]].
  1139           </p>
  1140 
  1141           <p>
  1142             The user agent <em class="ct">MUST</em> issue all <a title="advertisement for UPnP root devices">advertisements for UPnP root devices</a> with a HTTP request line equal to <code>M-SEARCH * HTTP/1.1</code>, with a HOST header equal to the reserved multicast address and port of <code>239.255.255.250:1900</code>, a MAN header equal to <code>ssdp:discover</code>, an ST header equal to <code>upnp:rootdevice</code> and a user-agent defined MX header equal to a <dfn>maximum UPnP advertisement response wait time</dfn> value between <code>1</code> and <code>5</code> seconds.
  1143          </p>
  1144 
  1145          <p>
  1146           The user agent <em class="ct">MUST</em> listen for incoming requests and process any incoming responses to any <a>advertisement for UPnP root devices</a> on the <dfn>standard UPnP address and port</dfn>, on all current local network interface addresses with the port <code>1900</code>, according to the rules defined in this section.
  1147          </p>
  1148 
  1149          <p>
  1150           For each <dfn>HTTP Response</dfn> following an initial <a>advertisement for UPnP root devices</a> sent on a <a>standard UPnP address
  1151             and port</a> the user agent <em class="ct">MUST</em> run the following steps:
  1152          </p>
  1153 
  1154          <ol class="rule">
  1155           <li>
  1156             If the <a>HTTP Response</a> is not a HTTP 200 OK response then this response is invalid and the user agent <em class="ct">MUST</em> discard this response, abort any remaining steps and return. The user agent <em class="ct">MAY</em> issue a new <a>advertisement for UPnP root devices</a> as a result of this error occurring.
  1157           </li>
  1158 
  1159           <li>
  1160             If the <a>maximum UPnP advertisement response wait time</a> has been exceeded since the initial <a>advertisement for UPnP root devices</a> was sent then the <a>HTTP Response</a> is invalid and the user agent <em class="ct">MUST</em> discard this response, abort any remaining steps and return.
  1161           </li>
  1162 
  1163           <li>
  1164              Let <var>ssdp device</var> be an Object with a property for each HTTP header received in the <a>HTTP Response</a>, with each key being the name of a HTTP response header and each value being that HTTP response header's value.
  1165           </li>
  1166 
  1167           <li>
  1168             If <var>ssdp device</var> does not contain at least one <var>CACHE-CONTROL</var> entry, at least one <var>USN</var> entry, at least one <var>ST</var> entry and at least one <var>LOCATION</var> entry or the value of its <var>ST</var> entry is not <code>upnp:rootdevice</code>, then the <a>HTTP Response</a> is invalid and the <a>user agent</a> MUST discard this response, abort any remaining steps and return.
  1169           </li>
  1170 
  1171           <li>
  1172             The user agent <em class="ct">MUST</em> run the rule for <a>processing a UPnP Device Description File</a> passing in the first occurrence of <var>LOCATION</var> from <var>ssdp device</var> as the <var>device descriptor</var> argument and the first occurrence of <var>USN</var> from <var>ssdp device</var> as the <var>device identifier</var> argument and the first occurrence of <var>CACHE-CONTROL</var> from <var>ssdp device</var> as the <var>device expiry</var> argument
  1173           </li>
  1174 
  1175         </ol>
  1176 
  1177         <p>
  1178           For each <dfn>HTTP Request</dfn> received on a <a>standard UPnP address and port</a> the user agent <em class="ct">MUST</em> run the following steps:
  1179          </p>
  1180 
  1181         <ol class="rule">
  1182 
  1183           <li>
  1184             If the <a>HTTP Request</a> is not a HTTP NOTIFY request then it is not a valid UPnP Request and the user agent <em class="ct">MUST</em> return a HTTP 200 OK response, discard this request, abort any remaining steps and return.
  1185           </li>
  1186 
  1187           <li>
  1188              Let <var>ssdp device</var> be an Object with a property for each HTTP header received in the <a>HTTP Request</a>, with each key being the name of a HTTP header and each value being that HTTP header's value.
  1189           </li>
  1190 
  1191           <li>
  1192             If <var>ssdp device</var> does not contain at least one <var>CACHE-CONTROL</var> entry, at least one <var>USN</var> entry, at least one <var>NT</var> entry, at least one <var>NTS</var> entry and at least one <var>LOCATION</var> entry or the value of its <var>NT</var> entry is not <code>upnp:rootdevice</code>, then the <a>HTTP Request</a> is a malformed UPnP Request and the <a>user agent</a> MUST return a 400 Bad Request response, discard this request, abort any remaining steps and return.
  1193           </li>
  1194 
  1195           <li>
  1196             If <var>ssdp device</var>'s <var>NTS</var> entry is equal to <code>ssdp:alive</code> or <code>ssdp:update</code> then the user agent <em class="ct">MUST</em> run the rule for <a>processing a UPnP Device Description File</a> passing in the first occurrence of <var>LOCATION</var> from <var>ssdp device</var> as the <var>device descriptor</var> argument and the first occurrence of <var>USN</var> from <var>ssdp device</var> as the <var>device identifier</var> argument and the first occurrence of <var>CACHE-CONTROL</var> from <var>ssdp device</var> as the <var>device expiry</var>. <br/><br/>Otherwise, if <var>ssdp device</var>'s <var>NTS</var> entry is equal to <code>ssdp:byebye</code> then the user agent <em class="ct">MUST</em> run the rule for <a>removing all services from a registered UPnP Device</a> passing in the first occurrence of <var>USN</var> from <var>ssdp device</var> as the <var>device identifier</var> argument.
  1197           </li>
  1198 
  1199         </ol>
  1200 
  1201       <p>
  1202         The rule for <dfn>processing a UPnP Device Description File</dfn> is the process of parsing the contents of a standard UPnP Device Description [[!UPNP-DEVICEARCH11]] and
  1203         registering the UPnP services contained therein within the <a>list of available service records</a>.
  1204       </p>
  1205 
  1206       <p>The rule for <a>processing a UPnP Device Description File</a> takes three arguments - <var>device descriptor</var>, <var>device identifier</var> and <var>device expiry</var> - and when called the user
  1207          agent <em class="ct">MUST</em> run the following steps:</p>
  1208 
  1209       <ol class="rule">
  1210 
  1211           <li>
  1212              Let <var>root device descriptor file</var> contain the contents of the file located at the URL provided in <var>device descriptor</var> obtained according to the rules
  1213              defined in 'Section 2.11: Retrieving a description using HTTP' in [[!UPNP-DEVICEARCH11]]. If the value provided in <var>device descriptor</var> cannot be resolved as a URL on the current network or the <var>root device descriptor file</var> remains empty then the <a>HTTP Response</a> is invalid and the <a>user agent</a> MUST discard this response, abort any remaining steps and return.
  1214           </li>
  1215 
  1216           <li>
  1217              Let <var>advertised services</var> be a <a>list of all advertised services</a> obtained from the <var>root device descriptor file</var> containing the value of the first occurrence of the <code>&lt;serviceList&gt;</code> element as it is defined in 'Section 2.3: Device Description' in [[!UPNP-DEVICEARCH11]].
  1218           </li>
  1219 
  1220           <li>
  1221              For each <code>&lt;service&gt;</code> element - known as an <var>advertised service</var> - in <var>advertised services</var> run the following steps:
  1222 
  1223              <ol class="rule">
  1224 
  1225                 <li>
  1226                    Let <var>network service record</var> be a new Object consisting of the following empty properties: <code>id</code>, <code>deviceId</code>, <code>name</code>, <code>type</code>, <code>url</code>, <code>eventsUrl</code>, <code>config</code>, <code>expiryTimestamp</code>.
  1227                 </li>
  1228 
  1229                 <li>
  1230                    Set <var>network service record</var>'s <code>id</code> property to the concatenated string value of <var>device identifier</var> with the <var>advertised service</var>'s <code>&lt;serviceId&gt;</code> sub-element.
  1231                 </li>
  1232 
  1233                 <li>
  1234                    Set <var>network service record</var>'s <code>deviceId</code> property to the value of <var>device identifier</var>.
  1235                 </li>
  1236 
  1237                 <li>
  1238                    Set <var>network service record</var>'s <code>name</code> property to the string value of the first occurrence of the <var>advertised service</var>'s <code>&lt;serviceId&gt;</code> sub-element.
  1239                 </li>
  1240 
  1241                 <li>
  1242                    Set <var>network service record</var>'s <code>type</code> property to the concatenation of the string <code>upnp:</code> followed by the string value of the first occurrence of the <var>advertised service</var>'s <code>&lt;serviceType&gt;</code> sub-element.
  1243                 </li>
  1244 
  1245                 <li>
  1246                    Set <var>network service record</var>'s <code>url</code> property to the string value of the first occurrence of the <var>advertised service</var>'s <code>&lt;controlURL&gt;</code> sub-element.
  1247                 </li>
  1248 
  1249                 <li>
  1250                    Set <var>network service record</var>'s <code>config</code> property to the string value of the contents of the first occurrence of the <code>&lt;device&gt;</code> element in the <var>root device descriptor file</var>.
  1251                 </li>
  1252 
  1253                 <li>
  1254                    If <var>advertised service</var>'s <code>&lt;eventSubURL&gt;</code> sub-element is not empty, then set <var>network service record</var>'s <code>eventsUrl</code> property to the string value of the first occurrence of the <var>advertised service</var>'s <code>&lt;eventSubURL&gt;</code> sub-element. Otherwise, do not set <var>network service record</var>'s <code>eventsUrl</code> property.
  1255                 </li>
  1256 
  1257                 <li>
  1258                    Set <var>network service record</var>'s <code>expiryTimestamp</code> property to the value of the current date, in UTC timestamp format, plus the value of <var>device expiry</var>.
  1259                 </li>
  1260 
  1261                 <li>
  1262                   Run the general rule for <a>adding an available service</a>, passing in the current <var>network service record</var> as the only argument.
  1263                 </li>
  1264 
  1265               </ol>
  1266 
  1267           </ol>
  1268 
  1269          <p>
  1270            The rule for <dfn>removing all services from a registered UPnP Device</dfn> is the process of removing all services associated with a
  1271            device from the <a>list of available service records</a> that has left the user's current network or has otherwise timed out or expired.
  1272            This rule takes one argument, <var>device identifier</var>, and consists of running the following steps:
  1273         </p>
  1274 
  1275          <ol class="rule">
  1276 
  1277            <li>
  1278               For each <var>existing service record</var> in the current <a>list of available service records</a>, run the following sub-steps:
  1279               <ol class="rule">
  1280 
  1281                 <li>
  1282                  If the <var>existing service record</var>'s <code>deviceId</code> property does not match <var>device identifier</var> then skip any remaining sub-steps for the current <var>existing service record</var> and continue at the next available <var>existing service record</var>.
  1283                 </li>
  1284 
  1285                 <li>
  1286                   Run the general rule for <a>removing an available service</a> passing in <var>existing service record</var>'s <code>id</code>
  1287                   property as the only argument.
  1288                 </li>
  1289 
  1290               </ol>
  1291            </li>
  1292 
  1293          </ol>
  1294 
  1295          <p>When the <a>user agent</a> is to <dfn>setup a UPnP Events Subscription</dfn>, it is to run the following steps with the current <var>network service record</var> object as defined in 'Section 4.1.2: SUBSCRIBE with NT and CALLBACK' in [[!UPNP-DEVICEARCH11]]:</p>
  1296 
  1297          <ol class="rule">
  1298             <li>
  1299                If <var>network service record</var>'s <code>eventsUrl</code> property is empty then the <a>user agent</a> MUST abort these steps.
  1300             </li>
  1301 
  1302             <li>
  1303                Let <var>callback URL</var> be the value of creating a new <a>user-agent generated callback url</a>.
  1304             </li>
  1305 
  1306             <li>
  1307                Send a HTTP SUBSCRIBE request with a <em>NT</em> header with a string value of <code>upnp:event</code>, a <em>TIMEOUT</em> header with a user-agent defined timeout value (in the form <code>Second-XX</code> where <code>XX</code> is the user-agent defined timeout value in seconds) and a <em>CALLBACK</em> header
  1308                with a string value of <var>callback URL</var> towards the <var>network service record</var>'s <code>eventsUrl</code> property.
  1309             </li>
  1310 
  1311             <li>
  1312                If a non-200 OK response is received from the HTTP SUBSCRIBE request then the <a>user agent</a> MUST abort these steps.
  1313             </li>
  1314 
  1315             <li>
  1316                On receiving a valid 200 OK response, run the following steps:
  1317 
  1318                <ol class="rule">
  1319                   <li>
  1320                      Let <var>callback ID</var> equal the string value of the first included <em>SID</em> header, if it exists.
  1321                   </li>
  1322                   <li>
  1323                      Let <var>timeout date</var> equal the sum of the current UTC date value plus the integer value of the first included <em>TIMEOUT</em> header (minus the leading string of <code>Second-</code>), if it exists.
  1324                   </li>
  1325                   <li>
  1326                      Run the following steps aynchronously and continue to the step labeled <em>listen</em> below.
  1327                   </li>
  1328                   <li>
  1329                      <em>Refresh Subscription</em>: Run the following steps at a set interval (X) within the <a>user agent</a>:
  1330 
  1331                      <ol class="rule">
  1332                         <li>
  1333                            Let <var>current date</var> equal the current UTC date.
  1334                         </li>
  1335                         <li>
  1336                            If <var>current date</var> is less than the <var>timeout date</var> then continue to the step labeled <em>refresh subscription</em> above.
  1337                         </li>
  1338                         <li>
  1339                            Send a HTTP SUBSCRIBE request with a <em>SID</em> header with the string value of <var>callback ID</var> and a user-agent defined <em>TIMEOUT</em> header (in the form <code>Second-XX</code> where <code>XX</code> is the user-agent defined timeout value in seconds) towards the <var>network service record</var>'s <code>eventsUrl</code> property.
  1340                         </li>
  1341                         <li>
  1342                            On receiving a valid 200 OK, update <var>callback ID</var> with the string value of the first included <em>SID</em> header, if it exists. All other HTTP
  1343                            responses should cause the <a>user agent</a> to continue from the step labeled <em>refresh subscription</em> above.
  1344                         </li>
  1345                      </ol>
  1346 
  1347                   </li>
  1348 
  1349                   <li>
  1350                      <em>Listen</em>: For each HTTP NOTIFY request received at the <var>callback URL</var> the <a>user agent</a> is to run the following steps:
  1351 
  1352                      <ol class="rule">
  1353                         <li>
  1354                            Let <var>content clone</var> be the result of obtaining the message body of the HTTP NOTIFY request. If <var>content clone</var> is empty, then the <a>user agent</a> MUST abort these steps.
  1355                         </li>
  1356                         <li>
  1357                           Let <var>notification event</var> be a new simple event that uses the <code>Event</code> interface with the name <code>notify</code>,
  1358                            which does not bubble, is not cancellable, and has no default action.
  1359                         </li>
  1360                         <li>
  1361                            Let the <code>data</code> attribute of <var>notification event</var> have the DOMString value of <var>content clone</var>.
  1362                         </li>
  1363                         <li>
  1364                            <a href="http://www.whatwg.org/specs/web-apps/current-work/complete/webappapis.html#queue-a-task" class="externalDFN">Queue a task</a> to
  1365                             dispatch <var>notification event</var> at the current <a><code>NetworkService</code></a> object.
  1366                         </li>
  1367                      </ol>
  1368                   </li>
  1369 
  1370                </ol>
  1371 
  1372             </li>
  1373          </ol>
  1374 
  1375          <p>
  1376            A <a>user agent</a> can <dfn>terminate an existing UPnP Events Subscription</dfn> at any time for any <var>active service</var> in the <a>list of authorized service records</a> by sending an HTTP UNSUBSCRIBE request - as defined in 'Section 4.1.4: Canceling a subscription with UNSUBSCRIBE' in [[!UPNP-DEVICEARCH11]] - with a HOST header set to that <var>active service</var>'s <code>eventsUrl</code> property and a SID header set to the <var>callback ID</var> obtained when the initial <a>setup a UPnP Events Subscription</a> action occurred.
  1377          </p>
  1378 
  1379          </section>
  1380 
  1381          <section>
  1382             <h3>Network Topology Monitoring</h3>
  1383 
  1384                   <div>
  1385                      <p>
  1386                         When the <a>user agent</a> detects that the user has dropped from their connected network then, for each <var>existing service record</var> in the <a>list of available service records</a>, the user agent
  1387                         <em class="ct">MUST</em>
  1388                             run the general rule for <a>removing an available service</a> passing in each <var>existing service record</var>'s
  1389                             <code>id</code> property as the only argument for each call.
  1390                     </p>
  1391 
  1392                      <p>
  1393                         When the <a>user agent</a> detects that the user has connected to a new network or reconnected to an existing network, then it
  1394                         <em class="ct">SHOULD</em> restart its discovery
  1395                          mechanisms as defined in the <a href="#service-discovery">Service Discovery</a> section of this specification, maintaining
  1396                          the existing <a>list of authorized service records</a> currently in use.
  1397                      </p>
  1398                   </div>
  1399          </section>
  1400       </section>
  1401 
  1402    <section>
  1403       <h3>Garbage collection</h3>
  1404 
  1405       <p>
  1406          Only when the user navigates away from the current browsing context can <a><code>NetworkService</code></a> objects be garbage-collected, its records in the <a>entry script origin's URL whitelist</a> be removed and its corresponding entry in the <a>list of authorized service records</a> be removed.
  1407       </p>
  1408 
  1409    </section>
  1410 
  1411 
  1412     <section>
  1413       <h3>Use Cases and Requirements</h3>
  1414 
  1415       <p>This section covers what the requirements are for this API, as well as illustrates some use cases.</p>
  1416 
  1417       <ul class="rule">
  1418          <li>
  1419             Once a user has given permission, user agents should provide the ability for Web pages to communicate directly with a Local-networked Service.
  1420             <ul class="rule">
  1421                <li>
  1422                   Example: A web-based TV remote control. A Web page wants to control the current user's TV, changing the programming shown or increasing/decreasing/muting the
  1423                   volume of the Local-networked Device. The Web page requests a service type that is known to be implemented by television sets to which it has the
  1424                   application logic to communicate. Local devices providing the request service types are discovered and presented to the user for authorization. The user selects one
  1425                   or more of the discovered television sets to be accessible to the current Web page and then clicks 'Share'. The Web page can now communicate directly with
  1426                   the user-authorized Local-networked services.
  1427                </li>
  1428             </ul>
  1429          </li>
  1430 
  1431          <li>
  1432            Web pages should be able to communicate with Local-networked Services using the messaging channel supported by those Devices.
  1433            <ul class="rule">
  1434             <li>
  1435                Example: A Web page advertises that it is capable of controlling multiple Home Media Servers. The user can select their Home Media Server type from a drop-down list, at which point the
  1436                Web page sends a request to the user agent to connect with the associated service type of the Home Media Server. The Media Server selected implements a Web Socket channel for
  1437                bi-directional service communication and so the Web page opens a web socket to the requested Media Server and can communicate as required via that appropriate channel.
  1438             </li>
  1439            </ul>
  1440          </li>
  1441 
  1442          <li>
  1443            Web pages should be able to communicate with Local-networked Services using the messaging format supported by those Devices.
  1444            <ul class="rule">
  1445             <li>
  1446                Example: A Web page advertises that it is capable of interacting with and controlling multiple types of Home Media Server. The user can select their Home Media Server type from a drop-down list or known Media Servers, at which point the
  1447                Web page sends a request to the user agent to connect with the associated service type (and, optionally, the associated event type) of the Home Media Server. The communiciation protocols supported by Home Media Servers typically vary
  1448                between UPnP, JSON-RPC, Protocol Buffers or other messaging formats depending on the Home Media Server requested. The Web page is able to communicate with the user-selected Home Media
  1449                Server in the messaging format supported by that Device, which, in this example is a simple key/value pair text format.
  1450             </li>
  1451            </ul>
  1452          </li>
  1453 
  1454          <li>
  1455            Web pages should not be able to communicate with Local-networked Services that have not been authorized by the user thereby maintaining the user's privacy.
  1456            <ul class="rule">
  1457             <li>
  1458                Example: A Web page requests access to one type of Local-networked service. The user authorizes access to that particular service. Other services running on that same device, and on other devices
  1459                within the network, should not be accessible to the current Web page.
  1460             </li>
  1461            </ul>
  1462          </li>
  1463 
  1464          <li>
  1465            A user should be able to share one or more Local-networked Services based on a particular service type request from a Web page.
  1466            <ul class="rule">
  1467             <li>
  1468                Example: A Web page is capable of interacting with a specific profile of Local-networked Service. As such, it makes a request to the user agent to access those services, of which multiple matches
  1469                are found. The user is capable of selecting one or more of the discovered services to share with the Web page. The Web page can then implement a drag-and-drop interface for the user to drag specific
  1470                actions on to one or more of the authorized Local-networked Services.
  1471             </li>
  1472            </ul>
  1473          </li>
  1474 
  1475          <li>
  1476            User agents should provide an API exposed to script that exposes the features above. The user is notified by UI anytime interaction with Local-networked Services is requested, giving the user
  1477            full ability to cancel or abort the transaction. The user selects the Local-networked Services to be connected to the current Web page, and can cancel these at any time. No invocations to
  1478            these APIs occur silently without user intervention.
  1479          </li>
  1480       </ul>
  1481     </section>
  1482 
  1483           <section class="informative appendix">
  1484              <h3>Examples</h3>
  1485 
  1486            <div class="example">
  1487             <p>This sample code exposes a button. When clicked, this button is disabled and the user is prompted to offer a network service. The user may also select multiple network services. When the user has authorized a network service to be connected to the web page then the web page issues a simple command to get a list of all the albums stored on the connected media player service.
  1488             <p>The button is re-enabled only when the connected network service disconnects for whatever reason (the service becomes unavailable on the network, the user disconnects from their current network or the user revokes access to the service from the current web page). At this point the user can re-click the button to select a new network service to connect to the web page and the above steps are repeated.</p>
  1489             <p>The provided service type identifier and service interaction used in this example is based on the well-defined service type and messaging format supported by the <a href="http://xbmc.org/about/">XBMC Media Server</a>. </p>
  1490             <hr />
  1491             <pre class="highlight">&lt;input type="button" value="Start" onclick="start()" id="startBtn"/&gt;
  1492 &lt;div id="debugconsole">&lt;/div>
  1493 
  1494 &lt;script>
  1495  var startBtn = document.getElementById('startBtn'),
  1496      debug = document.getElementById('debugconsole');
  1497 
  1498  function start() {
  1499    if(navigator.getNetworkServices) {
  1500       navigator.getNetworkServices('zeroconf:_xbmc-jsonrpc._tcp', gotXBMCService, error);
  1501       startBtn.disabled = true;
  1502    } else {
  1503       debug.innerHTML += "&lt;br&gt;Service Discovery not supported!";
  1504    }
  1505  }
  1506 
  1507  function gotXBMCService(services) {
  1508 
  1509 // Listen for service disconnect messages
  1510 
  1511    services[0].addEventListener('serviceoffline', function ( e ) {
  1512        debug.innerHTML += "&lt;br>" + services[0].name + " disconnected.";
  1513        startBtn.disabled = false;
  1514    }, false);
  1515 
  1516 // Send a service message to get albums list (and process the service response)
  1517 
  1518    var svcXhr = new XMLHttpRequest();
  1519    svcXhr.open("POST", services[0].url + "/getAlbums"); // services[0].url and its subresources have been
  1520                                                         // whitelisted for cross-site XHR use in this
  1521                                                         // current browsing context.
  1522 
  1523    svcXhr.setRequestHeader('Content-Type', 'application/json-rpc');
  1524 
  1525    svcXhr.addEventListener('readystatechange', function ( response ) {
  1526      if( response.readyState != 4 || response.status != 200 )
  1527         return;
  1528      debug.innerHTML += "&lt;br>" + services[0].name + " response received: ";
  1529      debug.textContent += JSON.parse(response.responseText);
  1530    }, false);
  1531 
  1532    var svcMsg = [
  1533      { "jsonrpc": "2.0", "method": "AudioLibrary.GetAlbums", "params": { "genreid": -1,
  1534          "artistid": -1, "start": -1, "end": -1 }, "id": "1" }
  1535    ];
  1536 
  1537    svcXhr.send(JSON.stringify(svcMsg));
  1538    debug.innerHTML += "&lt;br>" + services[0].name + " request sent: ";
  1539    debug.textContent += JSON.stringify(svcMsg);
  1540 
  1541  }
  1542 
  1543  function error( err ) {
  1544    debug.innerHTML += "&lt;br>An error occurred obtaining a local network service.";
  1545    startBtn.disabled = false;
  1546  }
  1547 &lt;/script></pre>
  1548            </div>
  1549 
  1550            <div class="example">
  1551             <p>
  1552              This sample exposes a drop-down list containing a number of common Home-based audio devices. When the user selects an audio device from the list provided, they are prompted to authorize a network service
  1553              based on the service type requested. The user may also select multiple network services matching the selected service type.
  1554              In this example, the user selects their make as being <var>Sony</var> and their model as being <var>Bravia S1000</var> from which the Web page can derive a service type
  1555              (<var>urn:schemas-upnp-org:service:RenderingControl:1</var>).
  1556              <br /><br />Once the user has authorized the device, the web page sends a simple mute command according to the messaging format supported by the device.
  1557             </p>
  1558             <hr />
  1559             <pre class="highlight">&lt;select name="make" id="make"&gt;
  1560   &lt;option selected="selected" disabled="disabled"&gt;Select make&lt;/option&gt;
  1561   &lt;option&gt;Sony&lt;/option&gt;
  1562   &lt;option&gt;Philips&lt;/option&gt;
  1563   &lt;option&gt;Alba&lt;/option&gt;
  1564 &lt;/select&gt;
  1565 &lt;select name="model" id="model"&gt;&lt;/select&gt;
  1566 &lt;div id="debugconsole"&gt;&lt;/div&gt;
  1567 
  1568 &lt;script&gt;
  1569   var debug = document.getElementById('debugconsole');
  1570 
  1571   var models = {
  1572     "Sony": [
  1573       {"name": "Bravia TV S1000", "type": "upnp", "service": "urn:schemas-upnp-org:service:RenderingControl:1" },
  1574       {"name": "Bravia TV S2000", "type": "zeroconf", "service": "_mediarenderer._http._tcp" },
  1575       {"name": "HiFi WD10", "type": "upnp", "service": "urn:schemas-upnp-org:service:RenderingControl:1" }
  1576     ],
  1577     "Philips": [ /* ... */ ],
  1578     "Alba": [ /* ... */ ]
  1579   };
  1580 
  1581   var makeEl = document.getElementById("make"),
  1582       modelEl = document.getElementById("model");
  1583 
  1584   makeEl.addEventListener('change', function() {
  1585     modelEl.innerHTML = ""; // reset
  1586     var defaultOption = document.createElement("option");
  1587     defaultOption.textContent = "Select model";
  1588     defaultOption.setAttribute("disabled", "disabled");
  1589     defaultOption.setAttribute("selected", "selected");
  1590     modelEl.appendChild(defaultOption);
  1591     for(var i = 0, l = models[makeEl.value].length; i < l; i++) {
  1592       var option = document.createElement("option");
  1593       option.textContent = models[makeEl.value][i]["name"];
  1594       option.setAttribute("value", models[makeEl.value][i]["type"] + ":" + models[makeEl.value][i]["service"]);
  1595       modelEl.appendChild(option);
  1596     }
  1597   }, false);
  1598 
  1599   modelEl.addEventListener('change', function() {
  1600     if(navigator.getNetworkServices &&
  1601          modelEl.value == "upnp:urn:schemas-upnp-org:service:RenderingControl:1") {
  1602       navigator.getNetworkServices(modelEl.value, successCallback, errorCallback);
  1603     } else if (modelEl.value == "zeroconf:_mediarenderer._http._tcp") {
  1604       debug.innerHTML += "&lt;br&gt;Service type is not implemented by this application.";
  1605     } else {
  1606       debug.innerHTML += "&lt;br&gt;Service Discovery is not supported!";
  1607     }
  1608   }, false);
  1609 &lt;/script&gt;
  1610 
  1611 &lt;script&gt;
  1612   function successCallback( services ) {
  1613 
  1614   // Listen for service push notification messages
  1615 
  1616     services[0].addEventListener('notify', function ( msg ) {
  1617          debug.innerHTML += "&lt;br>" + services[0].name + " event received: ";
  1618          debug.textContent += msg.data;
  1619     }, false);
  1620 
  1621  // Send a control signal to mute the service audio
  1622 
  1623     var svcXhr = new XMLHttpRequest();
  1624     svcXhr.open("POST", services[0].url); // services[0].url and its
  1625                                           // subresources have been whitelisted for
  1626                                           // cross-site XHR use in this current
  1627                                           // browsing context.
  1628 
  1629     svcXhr.setRequestHeader('SOAPAction', 'urn:schemas-upnp-org:service:RenderingControl:1#SetMute');
  1630     svcXhr.setRequestHeader('Content-Type', 'text/xml; charset="utf-8";');
  1631 
  1632     svcXhr.onreadystatechange = function ( response ) {
  1633       if( response.readyState != 4 || response.status != 200 )
  1634         return;
  1635       debug.innerHTML += "&lt;br&gt;" + services[0].name + " response received: ";
  1636       debug.textContent += response.responseXML;
  1637     }
  1638 
  1639     // Service messaging to mute the provided service
  1640     var svcMsg = '&lt;?xml version="1.0" encoding="utf-8"?&gt;' +
  1641                  '&lt;s:Envelope s:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/" ' +
  1642                    'xmlns:s="http://schemas.xmlsoap.org/soap/envelope/"&gt;' +
  1643                    '&lt;s:Body&gt;' +
  1644                      '&lt;u:SetMute xmlns:u="urn:schemas-upnp-org:service:RenderingControl:1"&gt;' +
  1645                        '&lt;InstanceID&gt;0&lt;/InstanceID&gt;' +
  1646                        '&lt;Channel&gt;Master&lt;/Channel&gt;' +
  1647                        '&lt;DesiredMute&gt;true&lt;/DesiredMute&gt;' +
  1648                      '&lt;/u:SetMute&gt;' +
  1649                    '&lt;/s:Body&gt;' +
  1650                  '&lt;/s:Envelope&gt;';
  1651 
  1652     svcXhr.send(svcMsg);
  1653     debug.innerHTML += "&lt;br&gt;" + services[0].name + " request sent: ";
  1654     debug.textContent += svcMsg;
  1655   }
  1656 
  1657   function errorCallback( error ) {
  1658     debug.innerHTML += "&lt;br&gt;An error occurred: " + error.code;
  1659   }
  1660 &lt;/script&gt;</pre>
  1661           </div>
  1662 
  1663        </section>
  1664 
  1665     <section>
  1666       <h3>Acknowledgements</h3>
  1667 
  1668       <p>Thanks are expressed by the editor to the following individuals for their feedback on this specification to date (in alphabetical order):
  1669       <br /><br />
  1670       Gar Bergstedt, Lars-Erik Bolstad, Cathy Chan, Hari G Kumar, Bob Lund, Giuseppe Pascale, Marcin Simonides, Clarke Stevens, Christian S&ouml;derstr&ouml;m, Mark Vickers, ...</p>
  1671 
  1672       <p>Thanks are also expressed by the editor to the following organizations and groups for their support in producing this specification to date (in alphabetical order):
  1673       <br /></br />
  1674       CableLabs, Opera Software ASA, W3C Device APIs Working Group, W3C Web and TV Interest Group, ...</p>
  1675     </section>
  1676 </body>
  1677 </html>