discovery-api/Overview.src.html
author Rich Tibbett <richt@opera.com>
Fri, 30 Aug 2013 11:56:42 +0200
changeset 448 865b6f93faac
parent 447 5e36d90b8960
child 449 41aeb68f3f12
permissions -rw-r--r--
Fix [DAP-ISSUE-134]: Rename NetworkServices and NetworkService events
     1 <!DOCTYPE html>
     2 <!--
     3 
     4   THIS IS THE WORKING VERSION OF THE CURRENT SPECIFICATION!
     5 
     6   This specification is built using ReSpec.js <http://dev.w3.org/2009/dap/ReSpec.js/documentation.html>
     7 
     8   From time to time it's necessary to HTML5 Tidy this document using the tool @ <http://w3c.github.com/tidy-html5/>.
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    10   The command used to format this document (Overview.src.html) is as follows (replacing all = signs with - signs!):
    11 
    12   @> tidy ==new-blocklevel-tags section ==char-encoding utf8 ==tidy-mark no ==indent yes ==indent-spaces 2 ==indent-attributes yes ==wrap 120 ==fix-bad-comments yes -m Overview.src.html
    13 
    14   To publish a new compiled version (Overview.html), we need to open this file (Overview.src.html) in any web browser.
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    20   Next we run HTML5 Tidy over our new Overview.html file with the following command (replacing all = signs with - signs!):
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    22   @> tidy ==new-blocklevel-tags section ==char-encoding utf8 ==tidy-mark no ==indent yes ==indent-spaces 2 ==indent-attributes yes ==wrap 120 ==hide-comments yes -m Overview.html
    23 
    24   Now the specification is ready to be published :)
    25 
    26 -->
    27 <html>
    28   <head>
    29     <title>
    30       Network Service Discovery
    31     </title>
    32     <meta http-equiv='Content-Type'
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    44             {
    45               name:       "Rich Tibbett",
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    47               company:    "Opera Software ASA",
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   107   </head>
   108   <body>
   109     <section id='abstract'>
   110       <p>
   111         This specification defines a mechanism for an HTML document to discover and subsequently communicate with
   112         <abbr title="Hypertext Transfer Protocol">HTTP</abbr>-based services advertised via common discovery protocols
   113         within the current network.
   114       </p>
   115     </section>
   116     <section id='sotd'>
   117       <p>
   118         This document represents the early consensus of the group on the scope and features of the proposed API.
   119       </p>
   120     </section>
   121     <section class="informative">
   122       <h3>
   123         Introduction
   124       </h3>
   125       <p>
   126         To enable Web pages to connect and communicate with Local-networked Services provided over HTTP, this
   127         specification introduces the <a href="#navigatornetworkservice"><code>NavigatorNetworkService</code></a>
   128         interface.
   129       </p>
   130       <p>
   131         Using this <abbr title="Application Programming Interface">API</abbr> consists of requesting a well-known
   132         service type, known by developers and advertised by Local-networked Devices. User authorization, where the user
   133         connects the web page to discovered services, is expected before the web page is able to interact with any
   134         Local-networked Services.
   135       </p>
   136       <p>
   137         A web page creates a request to obtain connectivity to services running in the network by specifying a
   138         well-known discovery service type that it wishes to interact with.
   139       </p>
   140       <p>
   141         The user agent, having captured all advertised services on the network from the <a>service discovery
   142         mechanisms</a> included in this recommendation, attempts to match the requested service type to a discovered
   143         service according to the processing described herein.
   144       </p>
   145       <p>
   146         If a service connectivity request is successful then the Web page is provided with a promise-based success
   147         callback with the all necessary information to communicate with the authorized Local-networked Service. If the
   148         request fails then the Web page will receive a promise-based error callback containing an error string
   149         describing the cause of Local-networked Service connectivity failure.
   150       </p>
   151       <p>
   152         Once connected to a Local-networked Service the Web page can send requests and receive responses to the
   153         Local-networked Service via the messaging format and appropriate channel inferred from the service type
   154         authorized via the provided API. The Web page, once connected, can also receive service-pushed events, in the
   155         messaging format supported by the Local-networked Device, if such event subscription functionality is provided
   156         by the connected Local-networked Service.
   157       </p>
   158       <p>
   159         Services available within the local network can connect and disconnect at different times during the execution
   160         of a web page. The user agent can inform a web page when the state of networked services matching any of the
   161         requested valid service types change. Web pages can use this information to enable in-page experiences for
   162         communicating the state of networked services with the ability to change the particular service or set of
   163         services the page is connected to (by re-invoking the <a href=
   164         "#dom-navigator-getnetworkservices"><code>getNetworkServices()</code></a> method defined herein).
   165       </p>
   166       <div class="example">
   167         <p>
   168           Example of requesting a DNS-SD advertised service:
   169         </p>
   170         <hr>
   171         <pre class="highlight">
   172 function showServices( services ) {
   173   // Show a list of all the services provided to the web page
   174   for(var i = 0, l = services.length; i &lt; l; i++) console.log( services[i].name );
   175 }
   176 
   177 navigator.getNetworkServices('zeroconf:_boxee-jsonrpc._tcp').then(showServices);
   178 </pre>
   179       </div>
   180       <div class="example">
   181         <p>
   182           Example of requesting a UPnP advertised service, also handling error conditions:
   183         </p>
   184         <hr>
   185         <pre class="highlight">
   186 function showServices( services ) {
   187   // Show a list of all the services provided to the web page
   188   for(var i = 0, l = services.length; i &lt; l; i++) console.log( services[i].name );
   189 }
   190 
   191 function error( e ) {
   192   console.log( "Error occurred: " + e.name );
   193 }
   194 
   195 navigator.getNetworkServices('upnp:urn:schemas-upnp-org:service:ContentDirectory:1').then(showServices, error);
   196 </pre>
   197       </div>
   198       <div class="example">
   199         <p>
   200           Example of requesting either a DNS-SD or UPnP advertised service:
   201         </p>
   202         <hr>
   203         <pre class="highlight">
   204 function showServices( services ) {
   205   // Show a list of all the services provided to the web page (+ service type)
   206   for(var i = 0, l = services.length; i &lt; l; i++)
   207      console.log( services[i].name + '(' + services[i].type + ')' );
   208 }
   209 
   210 navigator.getNetworkServices([
   211   'zeroconf:_boxee-jsonrpc._tcp',
   212   'upnp:urn:schemas-upnp-org:service:ContentDirectory:1'
   213 ]).then(showServices);
   214 </pre>
   215       </div>
   216       <p>
   217         For more detailed examples, including examples of communicating with obtained networked services, see the
   218         <a href="#examples">Examples</a> section.
   219       </p>
   220     </section>
   221     <section id='conformance'>
   222       <p>
   223         Requirements phrased in the imperative as part of algorithms (such as "strip any leading space characters" or
   224         "return false and abort these steps") are to be interpreted with the meaning of the key word ("must", "should",
   225         "may", etc) used in introducing the algorithm.
   226       </p>
   227       <p>
   228         Some conformance requirements are phrased as requirements on attributes, methods or objects. Such requirements
   229         are to be interpreted as requirements on user agents.
   230       </p>
   231       <p>
   232         Conformance requirements phrased as algorithms or specific steps MAY be implemented in any manner, so long as
   233         the end result is equivalent. (In particular, the algorithms defined in this specification are intended to be
   234         easy to follow, and not intended to be performant.)
   235       </p>
   236       <p>
   237         The only conformance class defined by this specification is a <dfn>user agent</dfn>.
   238       </p>
   239       <p>
   240         User agents MAY impose implementation-specific limits on otherwise unconstrained inputs, e.g. to prevent denial
   241         of service attacks, to guard against running out of memory, or to work around platform-specific limitations.
   242       </p>
   243       <p>
   244         When support for a feature is disabled (e.g. as an emergency measure to mitigate a security problem, or to aid
   245         in development, or for performance reasons), user agents MUST act as if they had no support for the feature
   246         whatsoever, and as if the feature was not mentioned in this specification. For example, if a particular feature
   247         is accessed via an attribute in a Web IDL interface, the attribute itself would be omitted from the objects
   248         that implement that interface - leaving the attribute on the object but making it return null or throw an
   249         exception is insufficient.
   250       </p>
   251       <section>
   252         <h3>
   253           Dependencies
   254         </h3>This specification relies on several other underlying specifications.
   255         <dl>
   256           <dt>
   257             HTML
   258           </dt>
   259           <dd>
   260             Many fundamental concepts from HTML are used by this specification. [[!HTML5]]
   261           </dd>
   262           <dt>
   263             WebIDL
   264           </dt>
   265           <dd>
   266             The IDL blocks in this specification use the semantics of the WebIDL specification. [[!WEBIDL]]
   267           </dd>
   268         </dl>
   269       </section>
   270     </section>
   271     <section>
   272       <h3>
   273         Terminology
   274       </h3>
   275       <p>
   276         The construction "a <code>Foo</code> object", where <code>Foo</code> is actually an interface, is sometimes
   277         used instead of the more accurate "an object implementing the interface <code>Foo</code>".
   278       </p>
   279       <p>
   280         The term DOM is used to refer to the API set made available to scripts in Web applications, and does not
   281         necessarily imply the existence of an actual <code>Document</code> object or of any other <code>Node</code>
   282         objects as defined in the DOM Core specifications. [[!DOM4]]
   283       </p>
   284       <p>
   285         An IDL attribute is said to be <em>getting</em> when its value is being retrieved (e.g. by author script), and
   286         is said to be <em>setting</em> when a new value is assigned to it.
   287       </p>
   288       <p>
   289         A <dfn>valid service type</dfn> is any of the following:
   290       </p>
   291       <ul>
   292         <li>a string that begins with <code>upnp:</code> or <code>zeroconf:</code> followed by one or more characters
   293         in the ranges U+0021, U+0023 to U+0027, U+002A to U+002B, U+002D to U+002E, U+0030 to U+0039, U+0041 to U+005A,
   294         U+005E to U+007E.
   295         </li>
   296         <li>a string that begins with <code>dial:</code> followed by an integer version.
   297         </li>
   298       </ul>
   299       <p>
   300         A <a>valid service type</a> provided in the <code>type</code> attribute of the <a href=
   301         "#dom-navigator-getnetworkservices"><code>getNetworkServices()</code></a> method will be matched against the
   302         services currently contained in the <a>list of available service records</a> according to the algorithms
   303         defined in this specification.
   304       </p>
   305       <p>
   306         A <dfn>user-agent generated callback url</dfn> is a Local-network accessible URL endpoint that a <a>user
   307         agent</a> generates and maintains for receiving HTTP NOTIFY requests from UPnP Event sources. It is only
   308         required when the user agent implements UPnP Service Discovery as defined in this specification.
   309       </p>
   310       <p>
   311         In this specification we use the following terms to describe the processes required for Local-networked
   312         Services management:
   313       </p>
   314       <ul>
   315         <li>A <dfn>new service</dfn> is a Local-networked Service that has not previously been discovered or registered
   316         in the <a>list of available service records</a>.
   317         </li>
   318         <li>An <dfn>existing service</dfn> is a Local-networked Service that has previously been discovered and is
   319         registered in the <a>list of available service records</a>.
   320         </li>
   321         <li>A <dfn>current service</dfn> is a Local-networked Service, represented by a <a href=
   322         "#networkservice"><code>NetworkService</code></a> object, that is currently being shared with a web page via a
   323         <a href="#networkservices"><code>NetworkServices</code></a> object registered in the <a>list of active service
   324         managers</a>.
   325         </li>
   326       </ul>
   327     </section>
   328     <section>
   329       <h2>
   330         Security and privacy considerations
   331       </h2>
   332       <p>
   333         The API defined in this specification can be used to find and connect to devices and services within a user's
   334         current network. This discloses information related to a user's network: devices available on their network and
   335         the publicly-accessible services ("networked services") currently running and available on those devices. The
   336         distribution of this information could potentially compromise the user's privacy. A conforming implementation
   337         of this specification MUST provide a mechanism that protects the user's privacy. This mechanism MUST ensure
   338         that no networked service information is retrievable without the user's express permission.
   339       </p>
   340       <section>
   341         <h3>
   342           Privacy considerations for API implementations
   343         </h3>
   344         <p>
   345           A <a>user agent</a> MUST NOT provide networked service information to web sites without the express
   346           permission of the user. A user agent MUST acquire permission through a user interface, unless they have
   347           prearranged trust relationships with users, as described below. The user interface MUST include the document
   348           base URL. Those permissions that are acquired through the user interface and that are preserved beyond the
   349           current browsing session (i.e. beyond the time when the browsing context is navigated to another URL) MUST be
   350           revocable and a user agent MUST respect revoked permissions.
   351         </p>
   352         <p>
   353           Obtaining the user's express permission to access one API method does not imply the user has granted
   354           permission for the same web site to access any other methods that may be provided by this API, or to access
   355           the same method with a different set of arguments, as part of the same permission context. If a user has
   356           expressed permission for an implementation to, e.g. find a set of existing networked services, the
   357           implementation MUST seek the user's express permission if and when any subsequent functions are called on
   358           this API.
   359         </p>
   360         <p>
   361           A user agent MAY have prearranged trust relationships that do not require such user interfaces. For example,
   362           while a web browser will present a user interface when a web site performs a networked service lookup, a
   363           different runtime may have a prearranged, delegated security relationship with the user and, as such, a
   364           suitable alternative security and privacy mechanism with which to authorise the retrieval of networked
   365           service information.
   366         </p>
   367       </section>
   368       <section class="informative">
   369         <h3>
   370           Additional API implementation considerations
   371         </h3>
   372         <p>
   373           Further to the requirements listed in the previous section, implementors of the Network Service Discovery API
   374           are also advised to consider the following aspects that can negatively affect the privacy of their users: in
   375           certain cases, users can inadvertently grant permission to the user agent to disclose networked services to
   376           Web sites. In other cases, the content hosted at a certain URL changes in such a way that previously granted
   377           networked service permissions no longer apply as far as the user is concerned. Or the users might simply
   378           change their minds.
   379         </p>
   380         <p>
   381           Predicting or preventing these situations is inherently difficult. Mitigation and in-depth defensive measures
   382           are an implementation responsibility and not prescribed by this specification. However, in designing these
   383           measures, implementers are advised to enable user awareness of networked service sharing, and to provide easy
   384           access to interfaces that enable revocation of permissions that web applications have for accessing networked
   385           services via this API.
   386         </p>
   387       </section>
   388     </section>
   389     <section>
   390       <h2>
   391         Requesting networked services
   392       </h2>
   393       <pre class="widl">
   394 [Supplemental, NoInterfaceObject]
   395 interface <dfn id="navigatornetworkservice">NavigatorNetworkService</dfn> {
   396   <a class="externalDFN"
   397      href="http://dom.spec.whatwg.org/#promise">Promise</a> <a href=
   398      "#dom-navigator-getnetworkservices">getNetworkServices</a>( in any type );
   399 };
   400 
   401 <a class="externalDFN"
   402      href=
   403      "http://www.whatwg.org/specs/web-apps/current-work/complete/timers.html#navigator">Navigator</a> implements <a href=
   404      "#navigatornetworkservice">NavigatorNetworkService</a>;
   405 </pre>
   406       <section>
   407         <h2>
   408           Methods
   409         </h2>
   410         <dl class="domintro">
   411           <dt>
   412             <var title="">promise</var> = <var title="">window</var> . <code title="dom-navigator"><a href=
   413             "http://www.whatwg.org/specs/web-apps/current-work/complete/timers.html#navigator">navigator</a></code> .
   414             <code title="dom-navigator-getNetworkServices"><a href=
   415             "#dom-navigator-getnetworkservices">getNetworkServices</a></code> ( <var title="">type</var> )
   416           </dt>
   417           <dd>
   418             <p>
   419               Immediately returns a new <a href="http://dom.spec.whatwg.org/#promise"
   420                  class="externalDFN">Promise</a> object and then the user is prompted to select discovered network
   421                  services that have advertised support for the requested service type(s).
   422             </p>
   423             <p>
   424               The <var title="">type</var> argument contains one or more <a>valid service type</a> tokens that the web
   425               page would like to interact with.
   426             </p>
   427             <p>
   428               If the user accepts, the <var title="">promise</var> object is <a class="externalDFN"
   429                  href="http://dom.spec.whatwg.org/#concept-resolver-resolve">resolved</a>, with a <a href=
   430                  "#networkservices"><code>NetworkServices</code></a> object as its argument.
   431             </p>
   432             <p>
   433               If the user declines, or an error occurs, the <var title="">promise</var> object is <a class=
   434               "externalDFN"
   435                  href="http://dom.spec.whatwg.org/#concept-resolver-reject">rejected</a>.
   436             </p>
   437           </dd>
   438         </dl>
   439         <div>
   440           <p>
   441             When the <dfn id="dom-navigator-getnetworkservices"
   442                title="dom-navigator-getnetworkservices"><code>getNetworkServices(type)</code></dfn> method is called,
   443                the <a>user agent</a> MUST run the following steps:
   444           </p>
   445           <ol class="rule">
   446             <li>Let <var>Network Service Promise</var> be a new <a href="http://dom.spec.whatwg.org/#promise"
   447                   class="externalDFN"><code>Promise</code></a> object.
   448             </li>
   449             <li>Let <var>Network Service Promise's Resolver</var> be the default <a href=
   450             "http://dom.spec.whatwg.org/#concept-resolver"
   451                   class="externalDFN">resolver</a> of <var>Network Service Promise</var>.
   452             </li>
   453             <li>Return <var>Network Service Promise</var>, and run the remaining steps asynchronously.
   454             </li>
   455             <li>Let <var>requested control types</var> be initially set to an empty array.
   456             </li>
   457             <li>If <var>type</var> is an array consisting of one or more <a>valid service type</a> tokens, then let
   458             <var>requested control types</var> by the value of <var>type</var>, removing any non-<a>valid service
   459             type</a> tokens from the resulting array.
   460             </li>
   461             <li>If <var>type</var> is a string consisting of one <a>valid service type</a> token, then let
   462             <var>requested control types</var> be an array containing one item with a value of <var>type</var>.
   463             </li>
   464             <li>If <var>requested control types</var> is an array that contains at least one or more <a title=
   465             "valid service type">valid service type</a> tokens then continue to the step labeled <em>process</em>
   466             below. Otherwise, reject <var>Network Service Promise</var> by running the <a href=
   467             "http://dom.spec.whatwg.org/#concept-resolver-reject"
   468                   class="externalDFN">resolver reject algorithm</a> against the <var>Network Service Promise's
   469                   Resolver</var>, passing in a newly constructed <a href="http://dom.spec.whatwg.org/#domerror"
   470                   class="externalDFN"><code>DOMError</code></a> object whose <code>name</code> attribute has the string
   471                   value "UnknownTypePrefixError" (<a href=
   472                   "#dom-domerror-extensions-unknown_type_prefix"><code>UNKNOWN_TYPE_PREFIX_ERR</code></a>) and whose
   473                   <code>message</code> attribute has a helpful implementation-dependent message that explains this
   474                   error, abort any remaining steps and return.
   475             </li>
   476             <li>
   477               <em>Process</em>: Let <var>services found</var> be an empty array.
   478             </li>
   479             <li>For each <var>available service</var> in the <a>list of available service records</a> run the following
   480             steps:
   481               <ol class="rule">
   482                 <li>For each <var>requested control type</var> in <var>requested control types</var>: If <var>available
   483                 service</var>'s <code>type</code> attribute equals the <var>requested control type</var> then let <var>
   484                   matched service</var> equal the value of <var>available service</var> and continue at the step
   485                   labeled <var>attach</var> below.
   486                 </li>
   487                 <li>Continue at the next <var>available service</var>.
   488                 </li>
   489                 <li>
   490                   <em>Attach</em>: If <var>matched service</var> is not empty then run the following steps:
   491                   <ol class="rule">
   492                     <li>Let <var>new service object</var> be a new <a href=
   493                     "#networkservice"><code>NetworkService</code></a> object, mapping the parameters of <var>matched
   494                     service</var> to this new object where possible.
   495                     </li>
   496                     <li>Append <var>new service object</var> to the <var>services found</var> array.
   497                     </li>
   498                   </ol>
   499                 </li>
   500               </ol>
   501             </li>
   502             <li>Optionally, e.g. based on a previously-established user preference, for security reasons, or due to
   503             platform limitations, the <a>user agent</a> MAY reject <var>Network Service Promise</var> by running the
   504             <a href="http://dom.spec.whatwg.org/#concept-resolver-reject"
   505                   class="externalDFN">resolver reject algorithm</a> against the <var>Network Service Promise's
   506                   Resolver</var>, passing in a newly constructed <a href="http://dom.spec.whatwg.org/#domerror"
   507                   class="externalDFN"><code>DOMError</code></a> object whose <code>name</code> attribute has the string
   508                   value "PermissionDeniedError" (<a href=
   509                   "#dom-domerror-extensions-permission_denied"><code>PERMISSION_DENIED_ERR</code></a>) and whose
   510                   <code>message</code> attribute has a helpful implementation-dependent message that explains this
   511                   error, abort any remaining steps and return.
   512             </li>
   513             <li>The user agent MUST NOT provide the entry script's origin with a <a href=
   514             "#networkservices"><code>NetworkServices</code></a> object without prior permission given by the user.
   515               <p>
   516                 If <var>services found</var> is not an empty array then the <a>user agent</a> MAY choose to prompt the
   517                 user in a user-agent-specific manner for permission to provide the <a href=
   518                 "http://www.whatwg.org/specs/web-apps/current-work/complete/browsers.html#entry-script"
   519                    class="externalDFN">entry script</a>'s <a href=
   520                    "http://www.whatwg.org/specs/web-apps/current-work/complete/origin-0.html#origin"
   521                    class="externalDFN">origin</a> with a <a href="#networkservices"><code>NetworkServices</code></a>
   522                    object representing the <a>user-authorized</a> subset of <var>services found</var>.
   523               </p>
   524               <p>
   525                 Alternatively, the user agent MAY wish to skip this user opt-in step and choose to fulfill <var>Network
   526                 Service Promise</var> immediately based on a previously-established user preference, for security
   527                 reasons, or due to platform limitations. In such an implementation, if <var>Network Service
   528                 Promise</var> is to be fulfilled as a result of a previously-established user preference then the
   529                 <a>user agent</a> MUST continue at the next step of this algorithm.
   530               </p>
   531               <p>
   532                 If permission has been granted by the user to access one or more networked services then the <a>user
   533                 agent</a> SHOULD include an "ongoing local-network communication" indicator.
   534               </p>
   535               <p>
   536                 If permission has been denied by the user, <a>user agent</a> or platform, then the <a>user agent</a>
   537                 MUST reject <var>Network Service Promise</var> by running the <a href=
   538                 "http://dom.spec.whatwg.org/#concept-resolver-reject"
   539                    class="externalDFN">resolver reject algorithm</a> against the <var>Network Service Promise's
   540                    Resolver</var>, passing in a newly constructed <a href="http://dom.spec.whatwg.org/#domerror"
   541                    class="externalDFN"><code>DOMError</code></a> object whose <code>name</code> attribute has the
   542                    string value "PermissionDeniedError" (<a href=
   543                    "#dom-domerror-extensions-permission_denied"><code>PERMISSION_DENIED_ERR</code></a>) and whose
   544                    <code>message</code> attribute has a helpful implementation-dependent message that explains this
   545                    error, abort any remaining steps and return.
   546               </p>
   547               <p>
   548                 If the user never responds or no previously-established user preference has been met, this algorithm
   549                 stalls on this step.
   550               </p>
   551             </li>
   552             <li>Let <var>services</var> be an empty array.
   553             </li>
   554             <li>If <var>services found</var> is not an empty array then set <var>services</var> to be an array of one
   555             or more <a href="#networkservice"><code>NetworkService</code></a> objects for which the user granted
   556             permission above - known as the current objects <dfn>user-authorized</dfn> services.
   557             </li>
   558             <li>Remove all previously whitelisted urls from the <a>entry script origin's URL whitelist</a> granted in
   559             the current <a href="http://www.whatwg.org/specs/web-apps/current-work/complete/browsers.html#entry-script"
   560                   class="externalDFN">entry script</a>'s <a href=
   561                   "http://www.whatwg.org/specs/web-apps/current-work/complete/origin-0.html#origin"
   562                   class="externalDFN">origin</a>.
   563             </li>
   564             <li>For each Object <var>service</var> in <var>services</var>, if any, run the following sub-steps:
   565               <ol class="rule">
   566                 <li>Add the <var>service</var>'s <code>url</code> parameter to the <a>entry script origin's
   567                   <abbr title="Uniform Resource Locator">URL</abbr> whitelist</a>.
   568                 </li>
   569                 <li>If <var>service</var>'s <code>type</code> parameter begins with the DOMString "<code>upnp:</code>"
   570                 and the <var>service</var>'s <code>eventsUrl</code> parameter is not empty then <a>setup a UPnP Events
   571                 Subscription</a> for <var>service</var>.
   572                 </li>
   573               </ol>
   574             </li>
   575             <li>Let <var>services manager</var> be a new <a href="#networkservices"><code>NetworkServices</code></a>
   576             object.
   577             </li>
   578             <li>Store <var>requested control types</var> against <var>services manager</var> as an internal variable.
   579             </li>
   580             <li>Set <var>services manager</var>'s <a href=
   581             "#dom-networkservices-servicesavailable"><code>servicesAvailable</code></a> attribute to the number of
   582             items currently found in the <a>list of available service records</a> whose <code>type</code> property
   583             matches any of the tokens requested in <var>requested control types</var>.
   584             </li>
   585             <li>Add <var>services</var>, if any, to the <var>services manager</var> object as its collection of
   586             <a>indexed properties</a>. If <var>services</var> is an empty array then the <var>services manager</var>
   587             does not have any <var>indexed properties</var>.
   588             </li>
   589             <li>Set <var>services manager</var>'s <a href="#dom-networkservices-length"><code>length</code></a>
   590             attribute to the number of items in <var>services</var>.
   591             </li>
   592             <li>Add <var>services manager</var> to the <a>list of active service managers</a>.
   593             </li>
   594             <li>The <a>user agent</a> MUST fulfill <var>Network Service Promise</var> by running the <a href=
   595             "http://dom.spec.whatwg.org/#concept-resolver-fulfill"
   596                   class="externalDFN">resolver fulfill algorithm</a> against the <var>Network Service Promise's
   597                   Resolver</var>, passing in <var>services manager</var> as its argument.
   598             </li>
   599           </ol>
   600           <p>
   601             The <a href="http://www.whatwg.org/specs/web-apps/current-work/complete/webappapis.html#task-source"
   602                class="externalDFN">task source</a> for these <a href=
   603                "http://www.whatwg.org/specs/web-apps/current-work/complete/webappapis.html#concept-task"
   604                class="externalDFN">tasks</a> is the <a href=
   605                "http://www.whatwg.org/specs/web-apps/current-work/complete/webappapis.html#user-interaction-task-source"
   606                class="externalDFN">user interaction task source</a>.
   607           </p>
   608           <p>
   609             When a <a href="#networkservice"><code>NetworkService</code></a> object is provided to a Web page, the
   610             <a>user agent</a> MUST add its <a href="#dom-networkservice-url"><code>url</code></a> to the <dfn>entry
   611             script origin's URL whitelist</dfn>. This list enables the Web page to override and initiate cross-site
   612             resource requests towards these URLs, and any sub-resources of these URLs, within the current <a href=
   613             "http://www.whatwg.org/specs/web-apps/current-work/complete/browsers.html#entry-script"
   614                class="externalDFN">entry script</a>'s <a href=
   615                "http://www.whatwg.org/specs/web-apps/current-work/complete/origin-0.html#origin"
   616                class="externalDFN">origin</a> via various existing mechanisms (e.g. Web Sockets, Server-Sent Events,
   617                Web Messaging, XMLHttpRequest).
   618           </p>
   619           <p>
   620             If the user navigates away from the <a href=
   621             "http://www.whatwg.org/specs/web-apps/current-work/complete/browsers.html#entry-script"
   622                class="externalDFN">entry script</a>'s <a href=
   623                "http://www.whatwg.org/specs/web-apps/current-work/complete/origin-0.html#origin"
   624                class="externalDFN">origin</a> or permission to access a given networked service is revoked at any time
   625                by the platform or user then the <a>user agent</a> <em class="ct">MUST</em> remove its previously
   626                whitelisted urls from the <a>entry script origin's URL whitelist</a>.
   627           </p>
   628           <p>
   629             There is no implied persistence to networked service sharing provided to a web page. It MUST NOT be
   630             possible to access a previously white-listed networked service without user authorization in all of the
   631             following cases:
   632           </p>
   633           <ul>
   634             <li>If the current script is reloaded at any point in the same or different window.
   635             </li>
   636             <li>if the current script reinvokes the <a href=
   637             "#dom-navigator-getnetworkservices"><code>getNetworkServices()</code></a> method at any point in its
   638             execution.
   639             </li>
   640             <li>If the user navigates forward or back in their history to reload the current page.
   641             </li>
   642             <li>If a script is running in a different origin.
   643             </li>
   644           </ul>
   645         </div>
   646       </section>
   647       <section>
   648         <h3>
   649           Error Handling
   650         </h3>
   651         <dl class="domintro">
   652           <dt>
   653             <var title="">error</var> . <code title="dom-NavigatorNetworkServiceError-name"><a href=
   654             "#dom-domerror-extensions-name">name</a></code>
   655           </dt>
   656           <dd>
   657             <p>
   658               Returns the current error's error name. At the current time, this will be "PermissionDeniedError" or
   659               "UnknownTypePrefixError", for which the corresponding error constants <a href=
   660               "#dom-domerror-extensions-permission_denied"><code>PERMISSION_DENIED_ERR</code></a> and <a href=
   661               "#dom-domerror-extensions-unknown_type_prefix"><code>UNKNOWN_TYPE_PREFIX_ERR</code></a> are defined.
   662             </p>
   663           </dd>
   664         </dl>
   665         <p>
   666           The <dfn id="dom-domerror-extensions-name"
   667              title="dom-domerror-extensions-name"><code>name</code></dfn> attribute of a <a href=
   668              "http://dom.spec.whatwg.org/#domerror"
   669              class="externalDFN"><code>DOMError</code></a> object returned from this API <em class="ct">MUST</em>
   670              return the name for the error, which will be one of the following:
   671         </p>
   672         <dl>
   673           <dt>
   674             <dfn id="dom-domerror-extensions-permission_denied"
   675                 title="dom-domerror-extensions-permission_denied"><code>PERMISSION_DENIED_ERR</code></dfn> (DOMString
   676                 value "PermissionDeniedError")
   677           </dt>
   678           <dd>
   679             The user or user agent denied the page permission to access any services.
   680           </dd>
   681           <dt>
   682             <dfn id="dom-domerror-extensions-unknown_type_prefix"
   683                 title="dom-domerror-extensions-unknown_type_prefix"><code>UNKNOWN_TYPE_PREFIX_ERR</code></dfn>
   684                 (DOMString value "UnknownTypePrefixError")
   685           </dt>
   686           <dd>
   687             No <a>valid service type</a> tokens were provided in the method invocation.
   688           </dd>
   689         </dl>
   690       </section>
   691     </section>
   692     <section>
   693       <h2>
   694         Obtaining networked services
   695       </h2>
   696       <p>
   697         The <a href="#networkservices"><code>NetworkServices</code></a> interface represents a collection of zero or
   698         more <dfn>indexed properties</dfn> that are each a <a>user-authorized</a> <a href=
   699         "#networkservice"><code>NetworkService</code></a> object.
   700       </p>
   701       <p>
   702         A <a href="#networkservices"><code>NetworkServices</code></a> object is the <a href=
   703         "http://dom.spec.whatwg.org/#concept-promise-result"
   704            class="externalDFN">promise result</a> from a call to <a href=
   705            "#dom-navigator-getnetworkservices"><code>getNetworkServices()</code></a>.
   706       </p>
   707       <pre class="widl">
   708 [NoInterfaceObject]
   709 interface <dfn id="networkservices">NetworkServices</dfn> {
   710   readonly attribute unsigned long    <a href="#dom-networkservices-length">length</a>;
   711   getter <a href="#networkservice">NetworkService</a> (unsigned long index);
   712   <a href="#networkservice">NetworkService</a>? <a href=
   713 "#dom-networkservices-getservicebyid">getServiceById</a>(DOMString id);
   714 
   715   readonly attribute unsigned long    <a href="#dom-networkservices-servicesavailable">servicesAvailable</a>;
   716 
   717   // event handler attributes
   718            attribute <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/webappapis.html#eventhandler"
   719      class="externalDFN">EventHandler</a>     <a href="#dom-networkservices-onservicefound">onservicefound</a>;
   720            attribute <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/webappapis.html#eventhandler"
   721      class="externalDFN">EventHandler</a>     <a href="#dom-networkservices-onservicelost">onservicelost</a>;
   722 
   723 };
   724 
   725 <a href="#networkservices">NetworkServices</a> implements <a href=
   726 "http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#interface-eventtarget"
   727      class="externalDFN">EventTarget</a>;
   728 </pre>
   729       <section>
   730         <h2>
   731           Attributes
   732         </h2>
   733         <dl class="domintro">
   734           <dt>
   735             <code title="dom-networkservices-length"><a href="#dom-networkservices-length">length</a></code>
   736           </dt>
   737           <dd>
   738             <p>
   739               Returns the current number of <a>indexed properties</a> in the current object's collection.
   740             </p>
   741           </dd>
   742           <dt>
   743             <code title="dom-networkservices-servicesavailable"><a href=
   744             "#dom-networkservices-servicesavailable">servicesAvailable</a></code>
   745           </dt>
   746           <dd>
   747             <p>
   748               Returns the current number of items matching one of the app-requested <a>valid service type</a> tokens in
   749               the <a>list of available service records</a>.
   750             </p>
   751           </dd>
   752         </dl>
   753         <div>
   754           <p>
   755             The <dfn id="dom-networkservices-length"><code>length</code></dfn> attribute MUST return the number of
   756             <a href="#networkservice"><code>NetworkService</code></a> objects represented by the collection.
   757           </p>
   758           <p>
   759             The <dfn id="dom-networkservices-servicesavailable"><code>servicesAvailable</code></dfn> attribute MUST
   760             return the number of services in the <a>list of available service records</a> whose <code>type</code>
   761             attribute matches any of the <a>valid service type</a> tokens that were initially used to create the
   762             current <a href="#networkservices"><code>NetworkServices</code></a> object.
   763           </p>
   764         </div>
   765       </section>
   766       <section>
   767         <h2>
   768           Methods
   769         </h2>
   770         <dl class="domintro">
   771           <dt>
   772             <code title="networkservices-getter"><a href="#networkservices">services</a></code> [ <var title=
   773             "">index</var> ]
   774           </dt>
   775           <dd>
   776             <p>
   777               Returns the specified <a href="#networkservice"><code>NetworkService</code></a> object.
   778             </p>
   779           </dd>
   780           <dt>
   781             <code title="networkservices-getter"><a href="#networkservices">services</a></code> . <code title=
   782             "dom-networkservices-getservicebyid"><a href=
   783             "#dom-networkservices-getservicebyid">getServiceById</a></code> ( <var title="">id</var> )
   784           </dt>
   785           <dd>
   786             <p>
   787               Returns the <a href="#networkservice"><code>NetworkService</code></a> object with the given identifier,
   788               or null if no service has that identifier.
   789             </p>
   790           </dd>
   791         </dl>
   792         <p>
   793           A <a href="#networkservices"><code>NetworkServices</code></a> object represents the current collection of
   794           zero or more <a href="#networkservice"><code>NetworkService</code></a> objects - its <a>indexed
   795           properties</a>. The <a>indexed properties</a> of a <a href=
   796           "#networkservices"><code>NetworkServices</code></a> object are <span>immutable</span> meaning that <a>indexed
   797           properties</a> cannot be added and <a>indexed properties</a> cannot be removed for the lifetime of a <a href=
   798           "#networkservices"><code>NetworkServices</code></a> object.
   799         </p>
   800         <p>
   801           The <a href=
   802           "http://www.whatwg.org/specs/web-apps/current-work/multipage/infrastructure.html#supported-property-indices"
   803              class="externalDFN">supported property indices</a> of <a href=
   804              "#networkservices"><code>NetworkServices</code></a> objects at any instant are the numbers from zero to
   805              the number of the <a href="#networkservice"><code>NetworkService</code></a> objects in the collection
   806              minus one.
   807         </p>
   808         <p class="note">
   809           Each service in a <a href="#networkservices"><code>NetworkServices</code></a> object thus has an index; the
   810           first has the index 0, and each subsequent service is numbered one higher than the previous one.
   811         </p>
   812         <p>
   813           To <a href=
   814           "http://www.whatwg.org/specs/web-apps/current-work/multipage/infrastructure.html#determine-the-value-of-an-indexed-property"
   815              class="externalDFN">determine the value of an indexed property</a> for a given index <var>index</var> in a
   816              <a href="#networkservices"><code>NetworkServices</code></a> object the user agent MUST return the <a href=
   817              "#networkservice"><code>NetworkService</code></a> object that represents the <var>index</var>th item in
   818              the collection.
   819         </p>
   820         <p>
   821           The <dfn id="dom-networkservices-getservicebyid"><code>getServiceById(id)</code></dfn> method <em class=
   822           "ct">MUST</em> return the first <a href="#networkservice"><code>NetworkService</code></a> object in the
   823           collection whose <a href="#dom-networkservice-id"><code>id</code></a> attribute is equal to the value of the
   824           <var>id</var> argument provided. When no <a href="#networkservice"><code>NetworkService</code></a> objects
   825           match the given argument, the method MUST return null.
   826         </p>
   827       </section>
   828       <section>
   829         <h2>
   830           Events
   831         </h2>
   832         <p>
   833           The following are the event handlers (and their corresponding event handler event types) that <em class=
   834           "ct">MUST</em> be supported, as IDL attributes, by all objects implementing the <a href=
   835           "#networkservices"><code>NetworkServices</code></a> interface:
   836         </p>
   837         <table border="1">
   838           <thead>
   839             <tr>
   840               <th>
   841                 <span title="event handlers">Event handler</span>
   842               </th>
   843               <th>
   844                 <span>Event handler event type</span>
   845               </th>
   846             </tr>
   847           </thead>
   848           <tbody>
   849             <tr>
   850               <td>
   851                 <dfn id="dom-networkservices-onservicefound"
   852                     title="dom-NetworkServices-onservicefound"><code>onservicefound</code></dfn>
   853               </td>
   854               <td>
   855                 <a href="#event-servicefound"><code>servicefound</code></a>
   856               </td>
   857             </tr>
   858             <tr>
   859               <td>
   860                 <dfn id="dom-networkservices-onservicelost"
   861                     title="dom-NetworkServices-onservicelost"><code>onservicelost</code></dfn>
   862               </td>
   863               <td>
   864                 <a href="#event-servicelost"><code>servicelost</code></a>
   865               </td>
   866             </tr>
   867           </tbody>
   868         </table>
   869       </section>
   870     </section>
   871     <section>
   872       <h2>
   873         Communicating with a networked service
   874       </h2>
   875       <p>
   876         The <a href="#networkservice"><code>NetworkService</code></a> interface is used to provide a set of connection
   877         information for an HTTP service endpoint and if available, service events, running on a networked device.
   878       </p>
   879       <pre class="widl">
   880 [NoInterfaceObject]
   881 interface <dfn id="networkservice">NetworkService</dfn> {
   882   readonly attribute DOMString        <a href="#dom-networkservice-id">id</a>;
   883   readonly attribute DOMString        <a href="#dom-networkservice-name">name</a>;
   884   readonly attribute DOMString        <a href="#dom-networkservice-type">type</a>;
   885   readonly attribute DOMString        <a href="#dom-networkservice-url">url</a>;
   886   readonly attribute DOMString        <a href="#dom-networkservice-config">config</a>;
   887 
   888   readonly attribute boolean          <a href="#dom-networkservice-online">online</a>;
   889 
   890   // event handler attributes
   891            attribute <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/webappapis.html#eventhandler"
   892      class="externalDFN">EventHandler</a>     <a href="#dom-networkservice-onavailable">onavailable</a>;
   893            attribute <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/webappapis.html#eventhandler"
   894      class="externalDFN">EventHandler</a>     <a href="#dom-networkservice-onunavailable">onunavailable</a>;
   895 
   896            attribute <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/webappapis.html#eventhandler"
   897      class="externalDFN">EventHandler</a>     <a href="#dom-networkservice-onnotify">onnotify</a>;
   898 };
   899 
   900 <a href="#networkservice">NetworkService</a> implements <a href=
   901 "http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#interface-eventtarget"
   902      class="externalDFN">EventTarget</a>;
   903 </pre>
   904       <section>
   905         <h2>
   906           Attributes
   907         </h2>
   908         <dl class="domintro">
   909           <dt>
   910             <var title="">service</var> . <code title="dom-networkservice-id"><a href=
   911             "#dom-networkservice-id">id</a></code>
   912           </dt>
   913           <dd>
   914             <p>
   915               A unique identifier for the given user-selected service instance.
   916             </p>
   917           </dd>
   918           <dt>
   919             <var title="">service</var> . <code title="dom-networkservice-name"><a href=
   920             "#dom-networkservice-name">name</a></code>
   921           </dt>
   922           <dd>
   923             <p>
   924               The name of the user-selected service.
   925             </p>
   926           </dd>
   927           <dt>
   928             <var title="">service</var> . <code title="dom-networkservice-type"><a href=
   929             "#dom-networkservice-type">type</a></code>
   930           </dt>
   931           <dd>
   932             <p>
   933               The <a>valid service type</a> token value of the user-selected service.
   934             </p>
   935           </dd>
   936           <dt>
   937             <var title="">service</var> . <code title="dom-networkservice-url"><a href=
   938             "#dom-networkservice-url">url</a></code>
   939           </dt>
   940           <dd>
   941             <p>
   942               The control URL endpoint (including any required port information) of the user-selected control service
   943               that has been added to the <a>entry script origin's URL whitelist</a>.
   944             </p>
   945           </dd>
   946           <dt>
   947             <var title="">service</var> . <code title="dom-networkservice-config"><a href=
   948             "#dom-networkservice-config">config</a></code>
   949           </dt>
   950           <dd>
   951             <p>
   952               The configuration information associated with the service depending on the requested service type.
   953             </p>
   954           </dd>
   955         </dl>
   956         <p>
   957           The <dfn id="dom-networkservice-id"><code>id</code></dfn> attribute is a unique identifier for the service.
   958           The same service provided at different times or on different objects MUST have the same <a href=
   959           "#dom-networkservice-id"><code>id</code></a> value.
   960         </p>
   961         <p>
   962           The <dfn id="dom-networkservice-name"><code>name</code></dfn> attribute represents a human-readable title for
   963           the service.
   964         </p>
   965         <p>
   966           The <dfn id="dom-networkservice-type"><code>type</code></dfn> attribute reflects the value of the <a>valid
   967           service type</a> of the service.
   968         </p>
   969         <p>
   970           The <dfn id="dom-networkservice-url"><code>url</code></dfn> attribute is an <a href=
   971           "http://www.w3.org/TR/html5/urls.html#absolute-url"
   972              class="externalDFN">absolute URL</a> pointing to the root HTTP endpoint for the service that has been
   973              added to the <a>entry script origin's URL whitelist</a>. Web pages can subsequently use this value for
   974              implicit cross-document messaging via various existing mechanisms (e.g. Web Sockets, Server-Sent Events,
   975              Web Messaging, XMLHttpRequest).
   976         </p>
   977         <p>
   978           The <dfn id="dom-networkservice-config"><code>config</code></dfn> attribute provides the raw configuration
   979           information extracted from the given network service.
   980         </p>
   981       </section>
   982       <section>
   983         <h3>
   984           States
   985         </h3>
   986         <dl class="domintro">
   987           <dt>
   988             <var title="">service</var> . <code title="dom-networkservice-online"><a href=
   989             "#dom-networkservice-online">online</a></code>
   990           </dt>
   991           <dd>
   992             <p>
   993               Returns <code>true</code> if the service is reporting that it is accessible on the local network or
   994               <code>false</code> if the service is no longer accessible (temporarily or permanently) on the local
   995               network.
   996             </p>
   997           </dd>
   998         </dl>
   999         <p>
  1000           The <dfn id="dom-networkservice-online"><code>online</code></dfn> attribute indicates whether the service is
  1001           either <var>online</var>, and therefore accessible on the local network, in which case this attribute will
  1002           return <code>true</code> or, <var>offline</var>, and therefore not accessible on the local network, either
  1003           temporarily or permanently, in which case this attribute will return <code>false</code>. This attribute MUST
  1004           default to <code>true</code>.
  1005         </p>
  1006       </section>
  1007       <section>
  1008         <h3>
  1009           Events
  1010         </h3>
  1011         <p>
  1012           The following are the event handlers (and their corresponding event handler event types) that <em class=
  1013           "ct">MUST</em> be supported, as IDL attributes, by all objects implementing the <a href=
  1014           "#networkservice"><code>NetworkService</code></a> interface:
  1015         </p>
  1016         <table border="1">
  1017           <thead>
  1018             <tr>
  1019               <th>
  1020                 <span title="event handlers">Event handler</span>
  1021               </th>
  1022               <th>
  1023                 <span>Event handler event type</span>
  1024               </th>
  1025             </tr>
  1026           </thead>
  1027           <tbody>
  1028             <tr>
  1029               <td>
  1030                 <dfn id="dom-networkservice-onnotify"
  1031                     title="dom-NetworkService-onnotify"><code>onnotify</code></dfn>
  1032               </td>
  1033               <td>
  1034                 <a href="#event-notify"><code>notify</code></a>
  1035               </td>
  1036             </tr>
  1037             <tr>
  1038               <td>
  1039                 <dfn id="dom-networkservice-onavailable"
  1040                     title="dom-NetworkService-onavailable"><code>onavailable</code></dfn>
  1041               </td>
  1042               <td>
  1043                 <a href="#event-available"><code>available</code></a>
  1044               </td>
  1045             </tr>
  1046             <tr>
  1047               <td>
  1048                 <dfn id="dom-networkservice-onunavailable"
  1049                     title="dom-NetworkService-onunavailable"><code>onunavailable</code></dfn>
  1050               </td>
  1051               <td>
  1052                 <a href="#event-unavailable"><code>unavailable</code></a>
  1053               </td>
  1054             </tr>
  1055           </tbody>
  1056         </table>
  1057       </section>
  1058     </section>
  1059     <section>
  1060       <h2>
  1061         Service Discovery
  1062       </h2>
  1063       <p>
  1064         A <a>user agent</a> conforming to this specification MAY implement <abbr title=
  1065         "Simple Service Discovery Protocol">SSDP</abbr> [[!UPNP-DEVICEARCH11]], Zeroconf [[!DNS-SD]] + [[!MDNS]] and/or
  1066         <abbr title="Discovery and Launch Protocol">DIAL</abbr> [<a href=
  1067         "https://sites.google.com/a/dial-multiscreen.org/dial/dial-protocol-specification">DIAL</a>] <dfn>service
  1068         discovery mechanisms</dfn> - the requirements detailed in this section of the specification - to enable Web
  1069         pages to request and connect with HTTP services running on networked devices, discovered via any of these
  1070         mechanisms, through this API. When a <a>user agent</a> implements any of these <a>service discovery
  1071         mechanisms</a>, then it MUST conform to the corresponding algorithms provided in this section of the
  1072         specification.
  1073       </p>
  1074       <p>
  1075         This section presents how the results of these <a>service discovery mechanisms</a> will be matched to requested
  1076         service types, how the user agent stores available and active services and how their properties are applied to
  1077         any resulting <a href="#networkservice"><code>NetworkService</code></a> objects.
  1078       </p>
  1079       <p>
  1080         It is expected that user agents will perform these <a>service discovery mechanisms</a> asynchronously and
  1081         periodically update the <a>list of available service records</a> as required. The timing of any <a>service
  1082         discovery mechanisms</a> is an implementation detail left to the discretion of the implementer (e.g. by
  1083         continuously monitoring the network as a background process or on invocation of this API from a Web page).
  1084       </p>
  1085       <p>
  1086         The <dfn>list of available service records</dfn> is a single dynamic internal lookup table within user agents
  1087         that is used to track all the services that have been discovered and are available in the current network at
  1088         the current time. At any point during the running of any of the <a>service discovery mechanisms</a> then
  1089         existing entries within this table can be updated, entries can be added and entries can be removed as the
  1090         status of networked services changes according to the rules defined in this specification.
  1091       </p>
  1092       <p>
  1093         The <dfn>list of active service managers</dfn> is an internal list within user agents that is used to track all
  1094         <a href="#networkservices"><code>NetworkServices</code></a> objects currently being shared with any web pages
  1095         at the current time within the user agent. Each <a href="#networkservices"><code>NetworkServices</code></a>
  1096         object in the <a>list of active service managers</a> represents a collection of zero or more <a href=
  1097         "#networkservice"><code>NetworkService</code></a> objects - known as its <dfn>indexed properties</dfn>.
  1098         <a href="#networkservice"><code>NetworkService</code></a> objects are attached as the <a>indexed properties</a>
  1099         of a <a href="#networkservices"><code>NetworkServices</code></a> object as part of the <a href=
  1100         "#dom-navigator-getnetworkservices"><code>getNetworkServices()</code></a> algorithm.
  1101       </p>
  1102       <p>
  1103         The rule for <dfn>adding an available service</dfn> is the process of adding a <a>new service</a> or updating
  1104         an <a>existing service</a> that is generally available on the user's current network in the <a>list of
  1105         available service records</a>. This rule takes one argument, <var>network service record</var>, and consists of
  1106         running the following steps:
  1107       </p>
  1108       <ol class="rule">
  1109         <li>For each <var>existing service record</var> in the current <a>list of available service records</a>, run
  1110         the following sub-steps:
  1111           <ol class="rule">
  1112             <li>If the <var>existing service record</var>'s <code>id</code> property does not equal <var>network
  1113             service record</var>'s <code>id</code> property then abort any remaining sub-steps and continue at the next
  1114             available <var>existing service record</var>.
  1115             </li>
  1116             <li>Replace the value of <var>existing service record</var> in the current <a>list of available service
  1117             records</a> with the value of <var>network service record</var>, aborting any remaining steps in this
  1118             algorithm and return.
  1119             </li>
  1120           </ol>
  1121         </li>
  1122         <li>Add <var>network service record</var> to the <a>list of available service records</a> as a new item.
  1123         </li>
  1124         <li>For each <var>service manager</var> in the <a>list of active service managers</a> run the following steps:
  1125           <ol class="rule">
  1126             <li>For each <var>active service</var> in <var>service manager</var> run the following steps:
  1127               <ol class="rule">
  1128                 <li>If the <var>network service record</var>'s <code>id</code> property equals the <var>active
  1129                 service</var>'s <code>id</code> attribute and <var>active service</var>'s <code>online</code> attribute
  1130                 is currently set to <code>false</code> then set <var>active service</var>'s <a href=
  1131                 "#dom-networkservice-online"><code>online</code></a> attribute to <code>true</code> and then <a href=
  1132                 "http://www.whatwg.org/specs/web-apps/current-work/complete/webappapis.html#queue-a-task"
  1133                       class="externalDFN">queue a task</a> to dispatch a newly created event with the name <a href=
  1134                       "#event-available"><code>available</code></a> that uses the <a href=
  1135                       "http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#event"
  1136                       class="externalDFN"><code>Event</code></a> interface, which does not bubble, is not cancellable,
  1137                       and has no default action, at the current <var>active service</var> object.
  1138                 </li>
  1139               </ol>
  1140             </li>
  1141             <li>Let <var>'service type in current service manager' flag</var> be <code>false</code>.
  1142             </li>
  1143             <li>For each <var>requested control type</var> of the <var>requested control types</var> in <var>service
  1144             manager</var> run the following steps:
  1145               <ol class="rule">
  1146                 <li>If <var>network service record</var>'s <code>type</code> property does not equal <var>requested
  1147                 control type</var> then abort any remaining sub-steps and continue at the next available <var>requested
  1148                 control type</var>.
  1149                 </li>
  1150                 <li>Set the <var>'service type in current service manager' flag</var> to <code>true</code>, abort any
  1151                 remaining sub-steps and continue.
  1152                 </li>
  1153               </ol>
  1154             </li>
  1155             <li>If the <var>'service type in current service manager' flag</var> is set to <code>true</code> then
  1156             increment <var>service manager</var>'s <a href=
  1157             "#dom-networkservices-servicesavailable"><code>servicesAvailable</code></a> attribute by <code>1</code> and
  1158             then <a href="http://www.whatwg.org/specs/web-apps/current-work/complete/webappapis.html#queue-a-task"
  1159                   class="externalDFN">queue a task</a> to dispatch a newly created event with the name <a href=
  1160                   "#event-servicefound"><code>servicefound</code></a> that uses the <a href=
  1161                   "http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#event"
  1162                   class="externalDFN"><code>Event</code></a> interface, which does not bubble, is not cancellable, and
  1163                   has no default action, at the current <var>service manager</var> object.
  1164             </li>
  1165           </ol>
  1166         </li>
  1167       </ol>
  1168       <p>
  1169         The rule for <dfn>removing an available service</dfn> is the general process of removing an <a>existing
  1170         service</a> from the <a>list of available service records</a> that has left the user's current network or has
  1171         otherwise expired. This rule takes one argument, <var>service identifier</var>, and consists of running the
  1172         following steps:
  1173       </p>
  1174       <ol class="rule">
  1175         <li>For each <var>existing service record</var> in the current <a>list of available service records</a>, run
  1176         the following sub-steps:
  1177           <ol class="rule">
  1178             <li>If the <var>existing service record</var>'s <code>id</code> property does not match <var>service
  1179             identifier</var> then skip any remaining sub-steps for the current <var>existing service record</var> and
  1180             continue at the next available <var>existing service record</var>.
  1181             </li>
  1182             <li>Let <var>'service type in use' flag</var> be <code>false</code>.
  1183             </li>
  1184             <li>For each <var>service manager</var> in the <a>list of active service managers</a> run the following
  1185             steps:
  1186               <ol class="rule">
  1187                 <li>Let <var>'service type in current service manager' flag</var> be <code>false</code>.
  1188                 </li>
  1189                 <li>For each <var>active service</var> in <var>service manager</var> run the following steps:
  1190                   <ol class="rule">
  1191                     <li>If <var>existing service record</var>'s <code>id</code> property equals the <var>active
  1192                     service</var>'s <code>id</code> attribute and <var>active service</var>'s <a href=
  1193                     "#dom-networkservice-online"><code>online</code></a> attribute is currently set to
  1194                     <code>true</code> then set <var>active service</var>'s <a href="#dom-networkservice-online"><code>
  1195                       online</code></a> attribute to <code>false</code> and then <a href=
  1196                       "http://www.whatwg.org/specs/web-apps/current-work/complete/webappapis.html#queue-a-task"
  1197                           class="externalDFN">queue a task</a> to dispatch a newly created event with the name <a href=
  1198                           "#event-unavailable"><code>unavailable</code></a> that uses the <a href=
  1199                           "http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#event"
  1200                           class="externalDFN"><code>Event</code></a> interface, which does not bubble, is not
  1201                           cancellable, and has no default action, at the current <var>active service</var>.
  1202                     </li>
  1203                   </ol>
  1204                 </li>
  1205                 <li>For each <var>requested control type</var> of the <var>requested control types</var> in
  1206                 <var>service manager</var> run the following steps:
  1207                   <ol class="rule">
  1208                     <li>If <var>existing service record</var>'s <code>type</code> property does not equal
  1209                     <var>requested control type</var> then abort any remaining sub-steps and continue at the next
  1210                     available <var>requested control type</var>.
  1211                     </li>
  1212                     <li>Set the <var>'service type in current service manager' flag</var> to <code>true</code> and the
  1213                     <var>'service type in use' flag</var> to <code>true</code>, abort any remaining sub-steps and
  1214                     continue.
  1215                     </li>
  1216                   </ol>
  1217                 </li>
  1218                 <li>If the <var>'service type in current service manager' flag</var> is set to <code>true</code> then
  1219                 decrement <var>service manager</var>'s <a href=
  1220                 "#dom-networkservices-servicesavailable"><code>servicesAvailable</code></a> attribute by <code>1</code>
  1221                 and then <a href=
  1222                 "http://www.whatwg.org/specs/web-apps/current-work/complete/webappapis.html#queue-a-task"
  1223                       class="externalDFN">queue a task</a> to dispatch a newly created event with the name <a href=
  1224                       "#event-servicelost"><code>servicelost</code></a> that uses the <a href=
  1225                       "http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#event"
  1226                       class="externalDFN"><code>Event</code></a> interface, which does not bubble, is not cancellable,
  1227                       and has no default action, at the current <var>service manager</var> object.
  1228                 </li>
  1229               </ol>
  1230             </li>
  1231             <li>If the <var>'service type in use' flag</var> is <code>false</code> and the <var>existing service
  1232             record</var>'s <code>type</code> property begins with the DOMString "<code>upnp:</code>" and <var>existing
  1233             service record</var>'s <code>eventsURL</code> property is set then run the rule to <a>terminate an existing
  1234             UPnP Events Subscription</a>, if one is currently active (as a result of having previously called <a>setup
  1235             a UPnP Events Subscription</a> against the current <var>existing service record</var>).
  1236             </li>
  1237             <li>Remove <var>existing service record</var> from the current <a>list of available service records</a>.
  1238             </li>
  1239           </ol>
  1240         </li>
  1241       </ol>
  1242       <p>
  1243         User agents SHOULD expire a service record from the <a>list of available service records</a> when its
  1244         <code>expiryTimestamp</code> attribute exceeds the current UTC timestamp. When this condition is met the
  1245         <a>user agent</a> SHOULD run the rule for <a>removing an available service</a>, passing in the expired service
  1246         record's <code>id</code> attribute as the only argument.
  1247       </p>
  1248       <section>
  1249         <h4>
  1250           Zeroconf (<abbr title="Multicast DNS">mDNS</abbr> + <abbr title="Domain Name System">DNS</abbr>-<abbr title=
  1251           "Service Discovery">SD</abbr>)
  1252         </h4>
  1253         <p>
  1254           For each DNS response received from a user-agent-initiated Multicast DNS Browse for <abbr title=
  1255           "DNS Pointer Record">PTR</abbr> records with the name <code>_services._dns-sd._udp</code> on the resolved
  1256           recommended automatic browsing domain [[!MDNS]], the <a>user agent</a> MUST run the following steps:
  1257         </p>
  1258         <ol class="rule">
  1259           <li>Let <var>service mDNS responses</var> be an array of PTR records received by issuing a Multicast DNS
  1260           Browse for PTR records with the name of the current discovered service type.
  1261           </li>
  1262           <li>For each Object <var>service mDNS response</var> in <var>service mDNS responses</var>, run the following
  1263           steps:
  1264             <ol>
  1265               <li>Let <var>network service record</var> be an Object consisting of the following empty properties:
  1266               <code>id</code>, <code>name</code>, <code>type</code>, <code>url</code>, <code>config</code>,
  1267               <code>expiryTimestamp</code>.
  1268               </li>
  1269               <li>Set <var>network service record</var>'s <code>id</code> property to the value of the full PTR Service
  1270               Instance Name [[!MDNS]].
  1271               </li>
  1272               <li>Set <var>network service record</var>'s <code>name</code> property to the value of the PTR Service
  1273               Instance Name's <var>Instance</var> component [[!MDNS]].
  1274               </li>
  1275               <li>Set <var>network service record</var>'s <code>type</code> property to the concatenation of the string
  1276               <code>zeroconf:</code> followed be the value of the PTR Service Instance Name's <var>Service</var>
  1277               component [[!MDNS]].
  1278               </li>
  1279               <li>Set <var>network service record</var>'s <code>url</code> property to the resolvable Service URL
  1280               obtained from performing an DNS-SD Lookup [[!DNS-SD]] of the current service from the PTR record provided
  1281               [[!MDNS]].
  1282               </li>
  1283               <li>Set <var>network service record</var>'s <code>config</code> property to the string value of the
  1284               contents of the first DNS-SD TXT record associated with the <var>service mDNS response</var> as defined
  1285               in [[!DNS-SD]].
  1286               </li>
  1287               <li>Set <var>network service record</var>'s <code>expiryTimestamp</code> property to the value of the
  1288               current date, in UTC timestamp format, plus a value of <code>120</code> seconds.
  1289               </li>
  1290               <li>Run the general rule for <a>adding an available service</a>, passing in the current <var>network
  1291               service record</var> as the only argument.
  1292               </li>
  1293             </ol>
  1294           </li>
  1295         </ol>
  1296       </section>
  1297       <section>
  1298         <h5>
  1299           Simple Service Discovery Protocol (<abbr title="Simple Service Discovery Protocol">SSDP</abbr>)
  1300         </h5>
  1301         <p>
  1302           A user agent that implements UPnP service discovery MUST issue a <dfn>search request for UPnP root
  1303           devices</dfn> against the user's current local network according to the full normative text and timing
  1304           provided in 'Section 1.3.2: Search request with M-SEARCH' detailed in [[!UPNP-DEVICEARCH11]].
  1305         </p>
  1306         <p>
  1307           The user agent MUST issue all <a title="search request for UPnP root devices">search requests for UPnP root
  1308           devices</a> with a HTTP request line equal to <code>M-SEARCH * HTTP/1.1</code>, with a HOST header equal to
  1309           the reserved multicast address and port of <code>239.255.255.250:1900</code> and a MAN header equal to
  1310           <code>ssdp:discover</code>. The <a>user agent</a> must also send an ST header with this HTTP request equal to
  1311           the String value of <code>ssdp:all</code> or <code>upnp:rootdevice</code> or a single <a>valid service
  1312           type</a> token beginning with the String value <code>upnp:</code>. If a single <a>valid service type</a>
  1313           token beginning with the String value <code>upnp:</code> is to be used, the user agent MUST strip the leading
  1314           String <code>upnp:</code> before using this value in this HTTP request. The user-agent MUST also send an MX
  1315           header equal to a <dfn>maximum UPnP advertisement response wait time</dfn> value between <code>1</code> and
  1316           <code>5</code> seconds with this HTTP request.
  1317         </p>
  1318         <p>
  1319           The user agent MUST listen for any incoming responses to any <a>search request for UPnP root devices</a>.
  1320         </p>
  1321         <p>
  1322           For each <dfn>HTTP Response</dfn> following an initial <a>search request for UPnP root devices</a> sent on a
  1323           <a>standard UPnP address and port</a> the user agent MUST run the following steps:
  1324         </p>
  1325         <ol class="rule">
  1326           <li>If the <a>HTTP Response</a> is not a HTTP 200 OK response then this response is invalid and the user
  1327           agent MUST discard this response, abort any remaining steps and return. The user agent MAY issue a new
  1328           <a>search request for UPnP root devices</a> as a result of this error occurring.
  1329           </li>
  1330           <li>If the <a>maximum UPnP advertisement response wait time</a> has been exceeded since the initial <a>search
  1331           request for UPnP root devices</a> was sent then the <a>HTTP Response</a> is invalid and the user agent MUST
  1332           discard this response, abort any remaining steps and return. The user agent MAY stop listening for responses
  1333           from the current <a>search request for UPnP root devices</a> as a result of this error occurring. Equally,
  1334           the user agent MAY issue a new <a>search request for UPnP root devices</a> as a result of this error
  1335           occurring.
  1336           </li>
  1337           <li>Let <var>ssdp device</var> be an Object with a property for each HTTP header received in the <a>HTTP
  1338           Response</a>, with each key being the name of a HTTP response header and each value being that HTTP response
  1339           header's value.
  1340           </li>
  1341           <li>If <var>ssdp device</var> does not contain at least one <var>CACHE-CONTROL</var> entry, at least one
  1342           <var>USN</var> entry, at least one <var>ST</var> entry and at least one <var>LOCATION</var> entry then the
  1343           <a>HTTP Response</a> is invalid and the <a>user agent</a> MUST discard this response, abort any remaining
  1344           steps and return.
  1345           </li>
  1346           <li>The user agent MUST run the rule for <a>obtaining a UPnP Device Description File</a> passing in the first
  1347           occurrence of <var>LOCATION</var> from <var>ssdp device</var> as the <var>device descriptor URL</var>
  1348           argument and the first occurrence of <var>USN</var> from <var>ssdp device</var> as the <var>device
  1349           identifier</var> argument and the first occurrence of <var>CACHE-CONTROL</var> from <var>ssdp device</var>
  1350           (minus the leading string of <code>max-age=</code>) as the <var>device expiry</var> argument.
  1351           </li>
  1352         </ol>
  1353         <p>
  1354           The user agent MUST listen for incoming requests on the <dfn>standard UPnP address and port</dfn> on all
  1355           current local network interface addresses with the port <code>1900</code>.
  1356         </p>
  1357         <p>
  1358           For each <dfn>HTTP Request</dfn> received on a <a>standard UPnP address and port</a> the user agent MUST run
  1359           the following steps:
  1360         </p>
  1361         <ol class="rule">
  1362           <li>If the <a>HTTP Request</a> is not a HTTP NOTIFY request then it is not a valid UPnP Request and the user
  1363           agent MUST discard this request, abort any remaining steps and return.
  1364           </li>
  1365           <li>Let <var>ssdp device</var> be an Object with a property for each HTTP header received in the <a>HTTP
  1366           Request</a>, with each key being the name of a HTTP header and each value being that HTTP header's value.
  1367           </li>
  1368           <li>If <var>ssdp device</var>'s <var>NTS</var> entry is equal to <code>ssdp:alive</code> and the <a>HTTP
  1369           Request</a> does not contain at least one <var>CACHE-CONTROL</var> entry, at least one <var>USN</var> entry,
  1370           at least one <var>NT</var> entry, at least one <var>NTS</var> entry and at least one <var>LOCATION</var>
  1371           entry, then the <a>user agent</a> MUST discard this request, abort any remaining steps and return.
  1372           </li>
  1373           <li>If <var>ssdp device</var>'s <var>NTS</var> entry is equal to <code>ssdp:alive</code> then the user agent
  1374           MUST run the rule for <a>obtaining a UPnP Device Description File</a> passing in the first occurrence of
  1375           <var>LOCATION</var> from <var>ssdp device</var> as the <var>device descriptor URL</var> argument and the
  1376           first occurrence of <var>USN</var> from <var>ssdp device</var> as the <var>device identifier</var> argument
  1377           and the first occurrence of <var>CACHE-CONTROL</var> from <var>ssdp device</var> (minus the leading string of
  1378           <code>max-age=</code>) as the <var>device expiry</var>.<br>
  1379             <br>
  1380             Otherwise, if <var>ssdp device</var>'s <var>NTS</var> entry is equal to <code>ssdp:byebye</code> then the
  1381             user agent MUST run the rule for <a>removing all services from a registered UPnP Device</a> passing in the
  1382             first occurrence of <var>USN</var> from <var>ssdp device</var> as the <var>device identifier</var>
  1383             argument.
  1384           </li>
  1385         </ol>
  1386         <p>
  1387           The rule for <dfn>obtaining a UPnP Device Description File</dfn> is the process of obtaining the contents of
  1388           a standard UPnP Device Description [[!UPNP-DEVICEARCH11]] from a URL-based resource. This rule takes three
  1389           arguments - <var>device descriptor URL</var>, <var>device identifier</var> and <var>device expiry</var> - and
  1390           when called the user agent MUST run the following steps:
  1391         </p>
  1392         <ol class="rule">
  1393           <li>Let <var>device descriptor file</var> contain the contents of the file located at the URL provided in
  1394           <var>device descriptor URL</var> obtained according to the rules defined in 'Section 2.11: Retrieving a
  1395           description using HTTP' in [[!UPNP-DEVICEARCH11]].
  1396           </li>
  1397           <li>If the value provided in <var>device descriptor URL</var> cannot be resolved as a reachable URL on the
  1398           current network or the <var>device descriptor file</var> remains empty then it is invalid and the <a>user
  1399           agent</a> MUST abort any remaining steps and return.
  1400           </li>
  1401           <li>Run the rule for <a>processing a UPnP Device Description File</a>, passing in the current <var>device
  1402           descriptor file</var>, <var>device identifier</var> and <var>device expiry</var> arguments.
  1403           </li>
  1404         </ol>
  1405         <p>
  1406           The rule for <dfn>processing a UPnP Device Description File</dfn> is the process of parsing the contents of a
  1407           standard UPnP Device Description [[!UPNP-DEVICEARCH11]] and registering the UPnP services contained therein
  1408           within the <a>list of available service records</a>.
  1409         </p>
  1410         <p>
  1411           The rule for <a>processing a UPnP Device Description File</a> takes three arguments - <var>device descriptor
  1412           file</var>, <var>device identifier</var> and <var>device expiry</var> - and when called the user agent MUST
  1413           run the following steps:
  1414         </p>
  1415         <ol class="rule">
  1416           <li>Let <var>advertised services</var> be a list of all advertised services obtained from the <var>device
  1417           descriptor file</var> containing the value of the first occurrence of the <code>&lt;serviceList&gt;</code>
  1418           element as it is defined in 'Section 2.3: Device Description' in [[!UPNP-DEVICEARCH11]].
  1419           </li>
  1420           <li>For each <code>&lt;service&gt;</code> element - known as an <var>advertised service</var> - in
  1421           <var>advertised services</var> run the following steps:
  1422             <ol class="rule">
  1423               <li>Let <var>network service record</var> be a new Object consisting of the following empty properties:
  1424               <code>id</code>, <code>deviceId</code>, <code>name</code>, <code>type</code>, <code>url</code>,
  1425               <code>eventsUrl</code>, <code>config</code>, <code>expiryTimestamp</code>.
  1426               </li>
  1427               <li>Set <var>network service record</var>'s <code>id</code> property to the concatenated string value of
  1428               the first occurrence of the <code>&lt;UDN&gt;</code> element in the <var>device descriptor file</var>
  1429               with the <var>advertised service</var>'s <code>&lt;serviceId&gt;</code> sub-element.
  1430               </li>
  1431               <li>Set <var>network service record</var>'s <code>deviceId</code> property to the value of <var>device
  1432               identifier</var>.
  1433               </li>
  1434               <li>Set <var>network service record</var>'s <code>name</code> property to the string value of the first
  1435               occurrence of the <var>advertised service</var>'s <code>&lt;serviceId&gt;</code> sub-element.
  1436               </li>
  1437               <li>Set <var>network service record</var>'s <code>type</code> property to the concatenation of the string
  1438               <code>upnp:</code> followed by the string value of the first occurrence of the <var>advertised
  1439               service</var>'s <code>&lt;serviceType&gt;</code> sub-element.
  1440               </li>
  1441               <li>Set <var>network service record</var>'s <code>url</code> property to the string value of the first
  1442               occurrence of the <var>advertised service</var>'s <code>&lt;controlURL&gt;</code> sub-element.
  1443               </li>
  1444               <li>Set <var>network service record</var>'s <code>config</code> property to the string value of the
  1445               contents of the first occurrence of the <code>&lt;device&gt;</code> element in the <var>device descriptor
  1446               file</var>.
  1447               </li>
  1448               <li>If <var>advertised service</var>'s <code>&lt;eventSubURL&gt;</code> sub-element is not empty, then
  1449               set <var>network service record</var>'s <code>eventsUrl</code> property to the string value of the first
  1450               occurrence of the <var>advertised service</var>'s <code>&lt;eventSubURL&gt;</code> sub-element.
  1451               Otherwise, do not set <var>network service record</var>'s <code>eventsUrl</code> property.
  1452               </li>
  1453               <li>Set <var>network service record</var>'s <code>expiryTimestamp</code> property to the value of the
  1454               current date, in UTC timestamp format, plus the value of <var>device expiry</var>.
  1455               </li>
  1456               <li>Run the general rule for <a>adding an available service</a>, passing in the current <var>network
  1457               service record</var> as the only argument.
  1458               </li>
  1459             </ol>
  1460           </li>
  1461           <li>If <var>device descriptor file</var> contains a <code>&lt;deviceList&gt;</code> element then for each
  1462           <code>&lt;device&gt;</code> element within <code>&lt;deviceList&gt;</code> - herein known as an <var>embedded
  1463           device descriptor file</var> - the user agent MUST run the rule for <a>processing a UPnP Device Description
  1464           File</a>, passing in the current <var>embedded device descriptor file</var> as the <var>device descriptor
  1465           file</var> argument, along with the current <var>device identifier</var> and <var>device expiry</var>
  1466           arguments.
  1467           </li>
  1468         </ol>
  1469         <p>
  1470           The rule for <dfn>removing all services from a registered UPnP Device</dfn> is the process of removing all
  1471           services associated with a device from the <a>list of available service records</a> that has left the user's
  1472           current network or has otherwise timed out or expired. This rule takes one argument, <var>device
  1473           identifier</var>, and consists of running the following steps:
  1474         </p>
  1475         <ol class="rule">
  1476           <li>For each <var>existing service record</var> in the current <a>list of available service records</a>, run
  1477           the following sub-steps:
  1478             <ol class="rule">
  1479               <li>If the <var>existing service record</var>'s <code>deviceId</code> property does not match <var>device
  1480               identifier</var> then skip any remaining sub-steps for the current <var>existing service record</var> and
  1481               continue at the next available <var>existing service record</var>.
  1482               </li>
  1483               <li>Run the general rule for <a>removing an available service</a> passing in <var>existing service
  1484               record</var>'s <code>id</code> property as the only argument.
  1485               </li>
  1486             </ol>
  1487           </li>
  1488         </ol>
  1489         <p>
  1490           When the <a>user agent</a> is to <dfn>setup a UPnP Events Subscription</dfn>, it is to run the following
  1491           steps with the current <var>network service record</var> object as defined in 'Section 4.1.2: SUBSCRIBE with
  1492           NT and CALLBACK' in [[!UPNP-DEVICEARCH11]]:
  1493         </p>
  1494         <ol class="rule">
  1495           <li>If <var>network service record</var>'s <code>eventsUrl</code> property is empty then the <a>user
  1496           agent</a> MUST abort these steps.
  1497           </li>
  1498           <li>Let <var>callback URL</var> be the value of creating a new <a>user-agent generated callback url</a>.
  1499           </li>
  1500           <li>Send a HTTP SUBSCRIBE request with a <em>NT</em> header with a string value of <code>upnp:event</code>, a
  1501           <em>TIMEOUT</em> header with a user-agent defined timeout value (in the form <code>Second-XX</code> where
  1502           <code>XX</code> is the user-agent defined timeout value in seconds) and a <em>CALLBACK</em> header with a
  1503           string value of <var>callback URL</var> towards the <var>network service record</var>'s
  1504           <code>eventsUrl</code> property.
  1505           </li>
  1506           <li>If a non-200 OK response is received from the HTTP SUBSCRIBE request then the <a>user agent</a> MUST
  1507           abort these steps.
  1508           </li>
  1509           <li>On receiving a valid 200 OK response, run the following steps:
  1510             <ol class="rule">
  1511               <li>Let <var>callback ID</var> equal the string value of the first included <em>SID</em> header, if it
  1512               exists.
  1513               </li>
  1514               <li>Let <var>timeout date</var> equal the sum of the current UTC date value plus the integer value of the
  1515               first included <em>TIMEOUT</em> header (minus the leading string of <code>Second-</code>), if it exists.
  1516               </li>
  1517               <li>Run the following steps asynchronously and continue to the step labeled <em>listen</em> below.
  1518               </li>
  1519               <li>
  1520                 <em>Refresh Subscription</em>: Run the following steps at a set interval (X) within the <a>user
  1521                 agent</a>:
  1522                 <ol class="rule">
  1523                   <li>Let <var>current date</var> equal the current UTC date.
  1524                   </li>
  1525                   <li>If <var>current date</var> is less than the <var>timeout date</var> then continue to the step
  1526                   labeled <em>refresh subscription</em> above.
  1527                   </li>
  1528                   <li>Send a HTTP SUBSCRIBE request with a <em>SID</em> header with the string value of <var>callback
  1529                   ID</var> and a user-agent defined <em>TIMEOUT</em> header (in the form <code>Second-XX</code> where
  1530                   <code>XX</code> is the user-agent defined timeout value in seconds) towards the <var>network service
  1531                   record</var>'s <code>eventsUrl</code> property.
  1532                   </li>
  1533                   <li>On receiving a valid 200 OK, update <var>callback ID</var> with the string value of the first
  1534                   included <em>SID</em> header and set <var>timeout date</var> to the sum of the current UTC date value
  1535                   plus the integer value of the first included <em>TIMEOUT</em> header (minus the leading string of
  1536                   <code>Second-</code>), if it exists. If the current date is greater than or equal to <var>timeout
  1537                   date</var> then the <a>user agent</a> SHOULD continue from the step labeled <em>refresh
  1538                   subscription</em> above. For all non 200 OK responses the <a>user agent</a> SHOULD continue from the
  1539                   step labeled <em>refresh subscription</em> above.
  1540                   </li>
  1541                 </ol>
  1542               </li>
  1543               <li>
  1544                 <em>Listen</em>: For each HTTP NOTIFY request received at the <var>callback URL</var> the <a>user
  1545                 agent</a> is to run the following steps:
  1546                 <ol class="rule">
  1547                   <li>Let <var>content clone</var> be the result of obtaining the message body of the HTTP NOTIFY
  1548                   request. If <var>content clone</var> is empty, then the <a>user agent</a> MUST abort these steps.
  1549                   </li>
  1550                   <li>Let <var>notification event</var> be a new simple event that uses the <a href=
  1551                   "http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#event"
  1552                         class="externalDFN"><code>Event</code></a> interface with the name <a href=
  1553                         "#event-notify"><code>notify</code></a>, which does not bubble, is not cancellable, and has no
  1554                         default action.
  1555                   </li>
  1556                   <li>Let the <code>data</code> attribute of <var>notification event</var> have the DOMString value of
  1557                   <var>content clone</var>.
  1558                   </li>
  1559                   <li>
  1560                     <a href="http://www.whatwg.org/specs/web-apps/current-work/complete/webappapis.html#queue-a-task"
  1561                         class="externalDFN">Queue a task</a> to dispatch <var>notification event</var> at the current
  1562                         <a><code>NetworkService</code></a> object.
  1563                   </li>
  1564                   <li>Return a HTTP 200 OK response to the sender of the HTTP NOTIFY request.
  1565                   </li>
  1566                 </ol>
  1567               </li>
  1568             </ol>
  1569           </li>
  1570         </ol>
  1571         <p>
  1572           A <a>user agent</a> can <dfn>terminate an existing UPnP Events Subscription</dfn> at any time for a
  1573           <var>network service record</var> by sending an HTTP UNSUBSCRIBE request - as defined in 'Section 4.1.4:
  1574           Cancelling a subscription with UNSUBSCRIBE' in [[!UPNP-DEVICEARCH11]] - with a HOST header set to that
  1575           <var>active service</var>'s <code>eventsUrl</code> property and a SID header set to the <var>callback
  1576           ID</var> obtained when the initial <a>setup a UPnP Events Subscription</a> action occurred.
  1577         </p>
  1578       </section>
  1579       <section>
  1580         <h5>
  1581           Discovery and Launch Protocol (<abbr title="Discovery and Launch Protocol">DIAL</abbr>)
  1582         </h5>
  1583         <p>
  1584           A user agent that implements DIAL service discovery MUST issue a <dfn>search request for DIAL-enabled
  1585           devices</dfn> against the user's current local network according to the full normative text and timing
  1586           provided in 'Section 1.3.2: Search request with M-SEARCH' detailed in [[!UPNP-DEVICEARCH11]].
  1587         </p>
  1588         <p>
  1589           Let <var>dial version</var> be the version number specified in the <a>valid service type</a> token. Let
  1590           <var>dial search target</var> be the concatentation of the
  1591           <code>urn:dial-multiscreen-org:service:dial:</code> string constant with the <var>dial version</var>
  1592           (currently, <var>dial version</var> can only be <code>1</code>)
  1593         </p>
  1594         <p>
  1595           The user agent MUST issue all <a title="search request for DIAL devices">search requests for DIAL devices</a>
  1596           with a HTTP request line equal to <code>M-SEARCH * HTTP/1.1</code>, with a HOST header equal to the reserved
  1597           multicast address and port of <code>239.255.255.250:1900</code>, a MAN header equal to
  1598           <code>ssdp:discover</code>, an ST header equal to <var>dial search target</var> and a user-agent defined MX
  1599           header equal to a <dfn>maximum DIAL advertisement response wait time</dfn> value between <code>1</code> and
  1600           <code>5</code> seconds.
  1601         </p>
  1602         <p>
  1603           The user agent MUST listen for any incoming responses to a <a>search request for DIAL devices</a>.
  1604         </p>
  1605         <p>
  1606           For each HTTP Response following an initial <a>search request for DIAL devices</a> sent on a <a>standard UPnP
  1607           address and port</a> the user agent MUST run the following steps:
  1608         </p>
  1609         <ol class="rule">
  1610           <li>If the HTTP Response is not a HTTP 200 OK response then this response is invalid and the user agent MUST
  1611           discard this response, abort any remaining steps and return. The user agent MAY issue a new <a>search request
  1612           for DIAL devices</a> as a result of this error occurring.
  1613           </li>
  1614           <li>If the <a>maximum DIAL advertisement response wait time</a> has been exceeded since the initial <a>search
  1615           request for DIAL devices</a> was sent then the <a>HTTP Response</a> is invalid and the user agent MUST
  1616           discard this response, abort any remaining steps and return. The user agent MAY stop listening for responses
  1617           from the current <a>search request for DIAL devices</a> as a result of this error occurring. Equally, the
  1618           user agent MAY issue a new <a>search request for DIAL devices</a> as a result of this error occurring.
  1619           </li>
  1620           <li>Let <var>dial device</var> be an Object with a property for each HTTP header received in the <a>HTTP
  1621           Response</a>, with each key being the name of a HTTP response header and each value being that HTTP response
  1622           header's value.
  1623           </li>
  1624           <li>If <var>dial device</var> does not contain at least one <var>CACHE-CONTROL</var> entry, at least one
  1625           <var>USN</var> entry, at least one <var>ST</var> entry and at least one <var>LOCATION</var> entry or the
  1626           value of its <var>ST</var> entry is not <var>dial search target</var>, then the <a>HTTP Response</a> is
  1627           invalid and the <a>user agent</a> MUST discard this response, abort any remaining steps and return.
  1628           </li>
  1629           <li>The user agent MUST run the rule for <a>obtaining a UPnP Device Description File</a> passing in the first
  1630           occurrence of <var>LOCATION</var> from <var>dial device</var> as the <var>device descriptor URL</var>
  1631           argument and the first occurrence of <var>USN</var> from <var>dial device</var> as the <var>device
  1632           identifier</var> argument and the first occurrence of <var>CACHE-CONTROL</var> from <var>dial device</var>
  1633           (minus the leading string of <code>max-age=</code>) as the <var>device expiry</var> argument.
  1634           </li>
  1635         </ol>
  1636         <p>
  1637           The rule for <dfn>obtaining a DIAL Device Description File</dfn> is the process of obtaining the contents of
  1638           a standard UPnP Device Description [[!UPNP-DEVICEARCH11]] from a URL-based resource. This rule takes three
  1639           arguments - <var>device descriptor URL</var>, <var>device identifier</var> and <var>device expiry</var> - and
  1640           when called the user agent MUST run the following steps:
  1641         </p>
  1642         <ol class="rule">
  1643           <li>Let <var>device descriptor file</var> contain the contents of the file located at the URL provided in
  1644           <var>device descriptor URL</var> obtained according to the rules defined in 'Section 2.11: Retrieving a
  1645           description using HTTP' in [[!UPNP-DEVICEARCH11]].
  1646           </li>
  1647           <li>Let <var>application url</var> be the value of the first occurrence of the <code>Application-URL</code>
  1648           response header field obtained according to the rules defined in 'Section 5.4: Device Description Response'
  1649           in [<a href="https://sites.google.com/a/dial-multiscreen.org/dial/dial-protocol-specification">DIAL</a>]
  1650           </li>
  1651           <li>If the value provided in <var>device descriptor URL</var> cannot be resolved as a reachable URL on the
  1652           current network or the <var>device descriptor file</var> remains empty or <var>application url</var> is
  1653           undefined then it is invalid and the <a>user agent</a> MUST abort any remaining steps and return.
  1654           </li>
  1655           <li>Run the following steps to add the newly discovered DIAL service:
  1656             <ol class="rule">
  1657               <li>Let <var>network service record</var> be a new Object consisting of the following empty properties:
  1658               <code>id</code>, <code>deviceId</code>, <code>name</code>, <code>type</code>, <code>url</code>,
  1659               <code>expiryTimestamp</code>.
  1660               </li>
  1661               <li>Set <var>network service record</var>'s <code>id</code> property to the first occurrence of the
  1662               <code>&lt;UDN&gt;</code> element in the <var>descriptor file</var> prefixed with the <code>dial:</code>
  1663               string constant
  1664               </li>
  1665               <li>Set <var>network service record</var>'s <code>deviceId</code> property to the value of <var>device
  1666               identifier</var>.
  1667               </li>
  1668               <li>Set <var>network service record</var>'s <code>name</code> property to the string value of the first
  1669               occurrence of the <code>&lt;friendlyName&gt;</code> element in the <var>descriptor file</var>.
  1670               </li>
  1671               <li>Set <var>network service record</var>'s <code>type</code> property to <var>dial search target</var>.
  1672               </li>
  1673               <li>Set <var>network service record</var>'s <code>url</code> property to the string value of the
  1674               <var>application url</var>.
  1675               </li>
  1676               <li>Set <var>network service record</var>'s <code>expiryTimestamp</code> property to the value of the
  1677               current date, in UTC timestamp format, plus the value of <var>device expiry</var>.
  1678               </li>
  1679               <li>Run the general rule for <a>adding an available service</a>, passing in the current <var>network
  1680               service record</var> as the only argument.
  1681               </li>
  1682             </ol>
  1683           </li>
  1684         </ol>
  1685       </section>
  1686       <section>
  1687         <h3>
  1688           Network Topology Monitoring
  1689         </h3>
  1690         <div>
  1691           <p>
  1692             When the <a>user agent</a> detects that the user has dropped from a connected network then, for each
  1693             <var>existing service record</var> in the <a>list of available service records</a> discovered via that
  1694             network connection, the <a>user agent</a> MUST run the general rule for <a>removing an available
  1695             service</a> passing in each <var>existing service record</var>'s <code>id</code> property as the only
  1696             argument for each call.
  1697           </p>
  1698           <p>
  1699             When the <a>user agent</a> detects that the user has connected to a new network or reconnected to an
  1700             existing network, then it SHOULD restart its discovery mechanisms as defined in the <a href=
  1701             "#service-discovery">Service Discovery</a> section of this specification, maintaining the existing <a>list
  1702             of active service managers</a> currently in use.
  1703           </p>
  1704         </div>
  1705       </section>
  1706     </section>
  1707     <section>
  1708       <h3>
  1709         Events Summary
  1710       </h3>
  1711       <p>
  1712         The following events are dispatched on the <a href="#networkservices"><code>NetworkServices</code></a> and/or
  1713         <a href="#networkservice"><code>NetworkService</code></a> objects:
  1714       </p>
  1715       <table border="1">
  1716         <thead>
  1717           <tr>
  1718             <th>
  1719               <span>Event name</span>
  1720             </th>
  1721             <th>
  1722               <span>Interface</span>
  1723             </th>
  1724             <th>
  1725               <span>Dispatched when...</span>
  1726             </th>
  1727           </tr>
  1728         </thead>
  1729         <tbody>
  1730           <tr>
  1731             <td>
  1732               <dfn id="event-servicefound"><code>servicefound</code></dfn>
  1733             </td>
  1734             <td>
  1735               <a href="http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#event"
  1736                   class="externalDFN"><code>Event</code></a>
  1737             </td>
  1738             <td>
  1739               When a <a>new service</a> that matches one of the <a>requested type tokens</a> is found in the current
  1740               network.
  1741             </td>
  1742           </tr>
  1743           <tr>
  1744             <td>
  1745               <dfn id="event-servicelost"><code>servicelost</code></dfn>
  1746             </td>
  1747             <td>
  1748               <a href="http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#event"
  1749                   class="externalDFN"><code>Event</code></a>
  1750             </td>
  1751             <td>
  1752               When an <a>existing service</a> that matches one of the <a>requested type tokens</a> gracefully leaves or
  1753               expires from the current network.
  1754             </td>
  1755           </tr>
  1756           <tr>
  1757             <td>
  1758               <dfn id="event-available"><code>available</code></dfn>
  1759             </td>
  1760             <td>
  1761               <a href="http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#event"
  1762                   class="externalDFN"><code>Event</code></a>
  1763             </td>
  1764             <td>
  1765               When a <a>current service</a> renews its service registration within the current network.
  1766             </td>
  1767           </tr>
  1768           <tr>
  1769             <td>
  1770               <dfn id="event-unavailable"><code>unavailable</code></dfn>
  1771             </td>
  1772             <td>
  1773               <a href="http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#event"
  1774                   class="externalDFN"><code>Event</code></a>
  1775             </td>
  1776             <td>
  1777               When a <a>current service</a> gracefully leaves or otherwise expires from the current network.
  1778             </td>
  1779           </tr>
  1780           <tr>
  1781             <td>
  1782               <dfn id="event-notify"><code>notify</code></dfn>
  1783             </td>
  1784             <td>
  1785               <a href="http://dvcs.w3.org/hg/domcore/raw-file/tip/Overview.html#event"
  1786                   class="externalDFN"><code>Event</code></a>
  1787             </td>
  1788             <td>
  1789               When a valid UPnP Events Subscription Message is received on a <a>user-agent generated callback url</a>
  1790               for a <a>current service</a>. This event never fires for Zeroconf-based services.
  1791             </td>
  1792           </tr>
  1793         </tbody>
  1794       </table>
  1795     </section>
  1796     <section>
  1797       <h3>
  1798         Garbage collection
  1799       </h3>
  1800       <p>
  1801         There is an <dfn>implied strong reference</dfn> from any IDL attribute in this API that returns a pre-existing
  1802         object to that object.
  1803       </p>
  1804       <p class="note">
  1805         For example, if a <a><code>NetworkServices</code></a> object has one or more <a>indexed properties</a> attached
  1806         to it then there is a strong reference from that <a><code>NetworkServices</code></a> object toward each of its
  1807         <a>indexed properties</a>.
  1808       </p>
  1809       <p>
  1810         If a <a>user agent</a> is to <dfn>make disappear</dfn> a <a><code>NetworkServices</code></a> object (this
  1811         happens when a <a href="http://www.whatwg.org/specs/web-apps/current-work/multipage/dom.html#document"
  1812            class="externalDFN"><code>Document</code></a> object goes away), the <a>user agent</a> MUST remove this
  1813            object from the <a>list of active service managers</a> and remove the <a href=
  1814            "#dom-networkservice-url"><code>url</code></a> of each of its <a>indexed properties</a> from the <a>entry
  1815            script origin's URL whitelist</a>.
  1816       </p>
  1817     </section>
  1818     <section>
  1819       <h3>
  1820         Use Cases and Requirements
  1821       </h3>
  1822       <p>
  1823         This section covers what the requirements are for this API, as well as illustrates some use cases.
  1824       </p>
  1825       <ul class="rule">
  1826         <li>Once a user has given permission, user agents should provide the ability for Web pages to communicate
  1827         directly with a Local-networked Service.
  1828           <ul class="rule">
  1829             <li>Example: A web-based TV remote control. A Web page wants to control the current user's TV, changing the
  1830             programming shown or increasing/decreasing/muting the volume of the Local-networked Device. The Web page
  1831             requests a service type that is known to be implemented by television sets to which it has the application
  1832             logic to communicate. Local devices providing the request service types are discovered and presented to the
  1833             user for authorization. The user selects one or more of the discovered television sets to be accessible to
  1834             the current Web page and then clicks 'Share'. The Web page can now communicate directly with the
  1835             user-authorized Local-networked services.
  1836             </li>
  1837           </ul>
  1838         </li>
  1839         <li>Web pages should be able to communicate with Local-networked Services using the messaging channel supported
  1840         by those Devices.
  1841           <ul class="rule">
  1842             <li>Example: A Web page advertises that it is capable of controlling multiple Home Media Servers. The user
  1843             can select their Home Media Server type from a drop-down list, at which point the Web page sends a request
  1844             to the user agent to connect with the associated service type of the Home Media Server. The Media Server
  1845             selected implements a Web Socket channel for bi-directional service communication and so the Web page opens
  1846             a web socket to the requested Media Server and can communicate as required via that appropriate channel.
  1847             </li>
  1848           </ul>
  1849         </li>
  1850         <li>Web pages should be able to communicate with Local-networked Services using the messaging format supported
  1851         by those Devices.
  1852           <ul class="rule">
  1853             <li>Example: A Web page advertises that it is capable of interacting with and controlling multiple types of
  1854             Home Media Server. The user can select their Home Media Server type from a drop-down list or known Media
  1855             Servers, at which point the Web page sends a request to the user agent to connect with the associated
  1856             service type (and, optionally, the associated event type) of the Home Media Server. The communication
  1857             protocols supported by Home Media Servers typically vary between UPnP, JSON-RPC, Protocol Buffers or other
  1858             messaging formats depending on the Home Media Server requested. The Web page is able to communicate with
  1859             the user-selected Home Media Server in the messaging format supported by that Device, which, in this
  1860             example is a simple key/value pair text format.
  1861             </li>
  1862           </ul>
  1863         </li>
  1864         <li>Web pages should not be able to communicate with Local-networked Services that have not been authorized by
  1865         the user thereby maintaining the user's privacy.
  1866           <ul class="rule">
  1867             <li>Example: A Web page requests access to one type of Local-networked service. The user authorizes access
  1868             to that particular service. Other services running on that same device, and on other devices within the
  1869             network, should not be accessible to the current Web page.
  1870             </li>
  1871           </ul>
  1872         </li>
  1873         <li>A user should be able to share one or more Local-networked Services based on a particular service type
  1874         request from a Web page.
  1875           <ul class="rule">
  1876             <li>Example: A Web page is capable of interacting with a specific profile of Local-networked Service. As
  1877             such, it makes a request to the user agent to access those services, of which multiple matches are found.
  1878             The user is capable of selecting one or more of the discovered services to share with the Web page. The Web
  1879             page can then implement a drag-and-drop interface for the user to drag specific actions on to one or more
  1880             of the authorized Local-networked Services.
  1881             </li>
  1882           </ul>
  1883         </li>
  1884         <li>User agents should provide an API exposed to script that exposes the features above. The user is notified
  1885         by UI anytime interaction with Local-networked Services is requested, giving the user full ability to cancel or
  1886         abort the transaction. The user selects the Local-networked Services to be connected to the current Web page,
  1887         and can cancel these at any time. No invocations to these APIs occur silently without user intervention.
  1888         </li>
  1889       </ul>
  1890     </section>
  1891     <section class="informative appendix">
  1892       <h3>
  1893         Examples
  1894       </h3>
  1895       <div class="example">
  1896         <p>
  1897           This sample code exposes a button. When clicked, this button is disabled and the user is prompted to offer a
  1898           network service. The user may also select multiple network services. When the user has authorized a network
  1899           service to be connected to the web page then the web page issues a simple command to get a list of all the
  1900           albums stored on the connected media player service.
  1901         </p>
  1902         <p>
  1903           The button is re-enabled only when the connected network service disconnects for whatever reason (the service
  1904           becomes unavailable on the network, the user disconnects from their current network or the user revokes
  1905           access to the service from the current web page). At this point the user can re-click the button to select a
  1906           new network service to connect to the web page and the above steps are repeated.
  1907         </p>
  1908         <p>
  1909           The provided service type identifier and service interaction used in this example is based on the
  1910           well-defined service type and messaging format supported by the <a href="http://xbmc.org/about/">XBMC Media
  1911           Server</a>.
  1912         </p>
  1913         <hr>
  1914         <pre class="highlight">
  1915 &lt;input type="button" value="Start" onclick="start()" id="startBtn"/&gt;
  1916 &lt;div id="debugconsole"&gt;&lt;/div&gt;
  1917 
  1918 &lt;script&gt;
  1919  var startBtn = document.getElementById('startBtn'),
  1920      debug = document.getElementById('debugconsole');
  1921 
  1922  function start() {
  1923    if(navigator.getNetworkServices) {
  1924       navigator.getNetworkServices('zeroconf:_xbmc-jsonrpc._tcp').then(gotXBMCService).catch(error);
  1925       startBtn.disabled = true;
  1926    } else {
  1927       debug.innerHTML += "&lt;br&gt;Service Discovery not supported!";
  1928    }
  1929  }
  1930 
  1931  function gotXBMCService(services) {
  1932 
  1933 // Listen for service disconnect messages
  1934 
  1935    services[0].addEventListener('unavailable', function ( e ) {
  1936        debug.innerHTML += "&lt;br&gt;" + services[0].name + " disconnected.";
  1937        startBtn.disabled = false;
  1938    }, false);
  1939 
  1940 // Send a service message to get albums list (and process the service response)
  1941 
  1942    var svcXhr = new XMLHttpRequest();
  1943    svcXhr.open("POST", services[0].url + "/getAlbums"); // services[0].url and its sub-resources have been
  1944                                                         // whitelisted for cross-site XHR use in this
  1945                                                         // current browsing context.
  1946 
  1947    svcXhr.setRequestHeader('Content-Type', 'application/json-rpc');
  1948 
  1949    svcXhr.addEventListener('readystatechange', function ( response ) {
  1950      if( response.readyState != 4 || response.status != 200 )
  1951         return;
  1952      debug.innerHTML += "&lt;br&gt;" + services[0].name + " response received: ";
  1953      debug.textContent += JSON.parse(response.responseText);
  1954    }, false);
  1955 
  1956    var svcMsg = [
  1957      { "jsonrpc": "2.0", "method": "AudioLibrary.GetAlbums", "params": { "genreid": -1,
  1958          "artistid": -1, "start": -1, "end": -1 }, "id": "1" }
  1959    ];
  1960 
  1961    svcXhr.send(JSON.stringify(svcMsg));
  1962    debug.innerHTML += "&lt;br&gt;" + services[0].name + " request sent: ";
  1963    debug.textContent += JSON.stringify(svcMsg);
  1964 
  1965  }
  1966 
  1967  function error( err ) {
  1968    debug.innerHTML += "&lt;br&gt;An error occurred obtaining a local network service.";
  1969    startBtn.disabled = false;
  1970  }
  1971 &lt;/script&gt;
  1972 </pre>
  1973       </div>
  1974       <div class="example">
  1975         <p>
  1976           This sample exposes a drop-down list containing a number of common Home-based audio devices. When the user
  1977           selects an audio device from the list provided, they are prompted to authorize a network service based on the
  1978           service type requested. The user may also select multiple network services matching the selected service
  1979           type. In this example, the user selects their make as being <var>Sony</var> and their model as being
  1980           <var>Bravia S1000</var> from which the Web page can derive a service type
  1981           (<var>urn:schemas-upnp-org:service:RenderingControl:1</var>).<br>
  1982           <br>
  1983           Once the user has authorized the device, the web page sends a simple mute command according to the messaging
  1984           format supported by the device.
  1985         </p>
  1986         <hr>
  1987         <pre class="highlight">
  1988 &lt;select name="make" id="make"&gt;
  1989   &lt;option selected="selected" disabled="disabled"&gt;Select make&lt;/option&gt;
  1990   &lt;option&gt;Sony&lt;/option&gt;
  1991   &lt;option&gt;Philips&lt;/option&gt;
  1992   &lt;option&gt;Alba&lt;/option&gt;
  1993 &lt;/select&gt;
  1994 &lt;select name="model" id="model"&gt;&lt;/select&gt;
  1995 &lt;div id="debugconsole"&gt;&lt;/div&gt;
  1996 
  1997 &lt;script&gt;
  1998   var debug = document.getElementById('debugconsole');
  1999 
  2000   var models = {
  2001     "Sony": [
  2002       {"name": "Bravia TV S1000", "type": "upnp", "service": "urn:schemas-upnp-org:service:RenderingControl:1" },
  2003       {"name": "Bravia TV S2000", "type": "zeroconf", "service": "_mediarenderer._http._tcp" },
  2004       {"name": "HiFi WD10", "type": "upnp", "service": "urn:schemas-upnp-org:service:RenderingControl:1" }
  2005     ],
  2006     "Philips": [ /* ... */ ],
  2007     "Alba": [ /* ... */ ]
  2008   };
  2009 
  2010   var makeEl = document.getElementById("make"),
  2011       modelEl = document.getElementById("model");
  2012 
  2013   makeEl.addEventListener('change', function() {
  2014     modelEl.innerHTML = ""; // reset
  2015     var defaultOption = document.createElement("option");
  2016     defaultOption.textContent = "Select model";
  2017     defaultOption.setAttribute("disabled", "disabled");
  2018     defaultOption.setAttribute("selected", "selected");
  2019     modelEl.appendChild(defaultOption);
  2020     for(var i = 0, l = models[makeEl.value].length; i &lt; l; i++) {
  2021       var option = document.createElement("option");
  2022       option.textContent = models[makeEl.value][i]["name"];
  2023       option.setAttribute("value", models[makeEl.value][i]["type"] + ":" + models[makeEl.value][i]["service"]);
  2024       modelEl.appendChild(option);
  2025     }
  2026   }, false);
  2027 
  2028   modelEl.addEventListener('change', function() {
  2029     if(navigator.getNetworkServices &amp;&amp;
  2030          modelEl.value == "upnp:urn:schemas-upnp-org:service:RenderingControl:1") {
  2031       var servicesPromise = navigator.getNetworkServices(modelEl.value).then(successCallback, errorCallback);
  2032     } else if (modelEl.value == "zeroconf:_mediarenderer._http._tcp") {
  2033       debug.innerHTML += "&lt;br&gt;Service type is not implemented by this application.";
  2034     } else {
  2035       debug.innerHTML += "&lt;br&gt;Service Discovery is not supported!";
  2036     }
  2037   }, false);
  2038 &lt;/script&gt;
  2039 
  2040 &lt;script&gt;
  2041   function successCallback( services ) {
  2042 
  2043   // Listen for service push notification messages
  2044 
  2045     services[0].addEventListener('notify', function ( msg ) {
  2046          debug.innerHTML += "&lt;br&gt;" + services[0].name + " event received: ";
  2047          debug.textContent += msg.data;
  2048     }, false);
  2049 
  2050  // Send a control signal to mute the service audio
  2051 
  2052     var svcXhr = new XMLHttpRequest();
  2053     svcXhr.open("POST", services[0].url); // services[0].url and its
  2054                                           // sub-resources have been whitelisted for
  2055                                           // cross-site XHR use in this current
  2056                                           // browsing context.
  2057 
  2058     svcXhr.setRequestHeader('SOAPAction', 'urn:schemas-upnp-org:service:RenderingControl:1#SetMute');
  2059     svcXhr.setRequestHeader('Content-Type', 'text/xml; charset="utf-8";');
  2060 
  2061     svcXhr.onreadystatechange = function ( response ) {
  2062       if( response.readyState != 4 || response.status != 200 )
  2063         return;
  2064       debug.innerHTML += "&lt;br&gt;" + services[0].name + " response received: ";
  2065       debug.textContent += response.responseXML;
  2066     }
  2067 
  2068     // Service messaging to mute the provided service
  2069     var svcMsg = '&lt;?xml version="1.0" encoding="utf-8"?&gt;' +
  2070                  '&lt;s:Envelope s:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/" ' +
  2071                    'xmlns:s="http://schemas.xmlsoap.org/soap/envelope/"&gt;' +
  2072                    '&lt;s:Body&gt;' +
  2073                      '&lt;u:SetMute xmlns:u="urn:schemas-upnp-org:service:RenderingControl:1"&gt;' +
  2074                        '&lt;InstanceID&gt;0&lt;/InstanceID&gt;' +
  2075                        '&lt;Channel&gt;Master&lt;/Channel&gt;' +
  2076                        '&lt;DesiredMute&gt;true&lt;/DesiredMute&gt;' +
  2077                      '&lt;/u:SetMute&gt;' +
  2078                    '&lt;/s:Body&gt;' +
  2079                  '&lt;/s:Envelope&gt;';
  2080 
  2081     svcXhr.send(svcMsg);
  2082     debug.innerHTML += "&lt;br&gt;" + services[0].name + " request sent: ";
  2083     debug.textContent += svcMsg;
  2084   }
  2085 
  2086   function errorCallback( error ) {
  2087     debug.innerHTML += "&lt;br&gt;An error occurred: " + error.name;
  2088   }
  2089 &lt;/script&gt;
  2090 </pre>
  2091       </div>
  2092     </section>
  2093     <section>
  2094       <h3>
  2095         Acknowledgements
  2096       </h3>
  2097       <p>
  2098         Thanks are expressed by the editor to the following individuals for their feedback on this specification to
  2099         date (in alphabetical order):<br>
  2100         <br>
  2101         Gar Bergstedt, Lars-Erik Bolstad, Cathy Chan, Hari G Kumar, Bob Lund, Giuseppe Pascale, Marcin Simonides,
  2102         Clarke Stevens, Christian Söderström, Mark Vickers.
  2103       </p>
  2104       <p>
  2105         Thanks are also expressed by the editor to the following organizations and groups for their support in
  2106         producing this specification to date (in alphabetical order):<br>
  2107         <br>
  2108         CableLabs, Opera Software ASA, W3C Device APIs Working Group, W3C Web and TV Interest Group.
  2109       </p>
  2110     </section>
  2111   </body>
  2112 </html>