This specification defines a mechanism for an HTML document to discover and subsequently communicate with HTTP-based services advertised via common discovery protocols within a user's network.

This document represents the early consensus of the group on the scope and features of the proposed API.

Introduction

To enable Web pages to connect and communicate with Local-networked Services provided over HTTP, this specification introduces the NavigatorNetworkService interface.

Using this API consists of requesting a well-known service type, known by developers and advertised by Local-networked Devices. User authorization, where the user connects the web page to one or more discovered services, is expected before the web page is able to interact with any Local-networked Services.

A web page creates a request to obtain connectivity to services running in the network by specifying a well-known discovery service type that it wishes to interact with.

The user agent, having captured all advertised services on the network from the Service Discovery mechanisms included in this recommendation, attempts to match the requested service type to a discovered service according to the processing described herein.

If a service connectivity request is successful then the Web page is provided with the necessary information to communicate with the authorized Local-networked Service. If the request fails then the Web page will receive an error callback containing an error code describing the cause of Local-networked Service connectivity failure.

Once connected to a Local-networked Service the Web page can send requests and receive responses to the Local-networked Service via the messaging format and appropriate channel inferred from the service type authorized via the provided API. The Web page, once connected, can also receive service-pushed events, in the messaging format supported by the Local-networked Device, if such event subscription functionality is provided by the connected Local-networked Service.

Example of requesting a DNS-SD advertised service:


function showServices( services ) {
  // Show a list of all the services provided to the web page
  for(var i = 0, l = services.length; i < l; i++) console.log( services[i].name );
}

navigator.getNetworkServices('zeroconf:_boxee-jsonrpc._tcp', showServices);

Example of requesting a UPnP advertised service, also handling error conditions:


function showServices( services ) {
  // Show a list of all the services provided to the web page
  for(var i = 0, l = services.length; i < l; i++) console.log( services[i].name );
}

function error( e ) {
  console.log( "Error occurred: " + e.code );
}

navigator.getNetworkServices('upnp:urn:schemas-upnp-org:service:ContentDirectory:1', showServices, error);

Example of requesting either a DNS-SD or UPnP advertised service:


function showServices( services ) {
  // Show a list of all the services provided to the web page (+ service type)
  for(var i = 0, l = services.length; i < l; i++)
     console.log( services[i].name + '(' + services[i].type + ')' );
}

navigator.getNetworkServices([
  'zeroconf:_boxee-jsonrpc._tcp',
  'upnp:urn:schemas-upnp-org:service:ContentDirectory:1'
], showServices);

For more detailed examples see the Examples section.

Requirements phrased in the imperative as part of algorithms (such as "strip any leading space characters" or "return false and abort these steps") are to be interpreted with the meaning of the key word ("must", "should", "may", etc) used in introducing the algorithm.

Some conformance requirements are phrased as requirements on attributes, methods or objects. Such requirements are to be interpreted as requirements on user agents.

Conformance requirements phrased as algorithms or specific steps may be implemented in any manner, so long as the end result is equivalent. (In particular, the algorithms defined in this specification are intended to be easy to follow, and not intended to be performant.)

The only conformance class defined by this specification is a user agent.

User agents may impose implementation-specific limits on otherwise unconstrained inputs, e.g. to prevent denial of service attacks, to guard against running out of memory, or to work around platform-specific limitations.

When support for a feature is disabled (e.g. as an emergency measure to mitigate a security problem, or to aid in development, or for performance reasons), user agents must act as if they had no support for the feature whatsoever, and as if the feature was not mentioned in this specification. For example, if a particular feature is accessed via an attribute in a Web IDL interface, the attribute itself would be omitted from the objects that implement that interface - leaving the attribute on the object but making it return null or throw an exception is insufficient.

Dependencies

This specification relies on several other underlying specifications.
HTML
Many fundamental concepts from HTML are used by this specification. [[!HTML5]]
WebIDL
The IDL blocks in this specification use the semantics of the WebIDL specification. [[!WEBIDL]]

Terminology

The construction "a Foo object", where Foo is actually an interface, is sometimes used instead of the more accurate "an object implementing the interface Foo".

The term DOM is used to refer to the API set made available to scripts in Web applications, and does not necessarily imply the existence of an actual Document object or of any other Node objects as defined in the DOM Core specifications. [[!DOM-CORE]]

An IDL attribute is said to be getting when its value is being retrieved (e.g. by author script), and is said to be setting when a new value is assigned to it.

A valid service type is a string that begins with upnp: or zeroconf: followed by one or more characters in the ranges U+0021, U+0023 to U+0027, U+002A to U+002B, U+002D to U+002E, U+0030 to U+0039, U+0041 to U+005A, U+005E to U+007E.

A valid service type provided in the type attribute of the getNetworkServices() method will be matched against the services currently contained in the list of available service records according to the algorithms defined in this specification.

Requesting networked services

[Supplemental, NoInterfaceObject]
interface NavigatorNetworkService {
  // Obtain a Local-networked Service
  void getNetworkServices( in any type,
                           in NavigatorNetworkServiceSuccessCallback successCallback,
                           in optional NavigatorNetworkServiceErrorCallback errorCallback );
};
Navigator implements NavigatorNetworkService;

[Callback=FunctionOnly, NoInterfaceObject]
interface NavigatorNetworkServiceSuccessCallback {
  void handleEvent( in NetworkServices services );
};

[NoInterfaceObject]
interface NavigatorNetworkServiceError {
  const unsigned short PERMISSION_DENIED_ERR = 1;
  const unsigned short UNKNOWN_TYPE_PREFIX_ERR = 2;
  readonly attribute unsigned short code;
};

[Callback=FunctionOnly, NoInterfaceObject]
interface NavigatorNetworkServiceErrorCallback {
  void handleEvent( in NavigatorNetworkServiceError error );
};

Methods

window . navigator . getNetworkServices ( type , successCallback [, errorCallback ] )

Prompts the user to select one or more discovered network services that have advertised support for the requested service type.

The type argument contains one or more valid service type tokens that the web page would like to interact with.

If the user accepts, the successCallback is invoked, with one or more NetworkService objects as its argument.

If the user declines, the errorCallback (if any) is invoked.

When the getNetworkServices(type, successCallback[, errorCallback]) method is called, the user agent MUST run the following steps:

  1. If successCallback is empty or is not an object of type Function then the user agent MUST abort these steps.
  2. Let requested control types be initially set to an empty array.
  3. If type is an array consisting of one or more valid service type tokens, then let requested control types by the value of type, removing any non-valid service type tokens from the resulting array.
  4. If type is a string consisting of one valid service type token, then let requested control types be an array containing one item with a value of type.
  5. If requested control types is an array that contains at least one or more valid service type tokens then continue to the step labeled process below. Otherwise, the user agent MUST queue a task to invoke errorCallback, if it is provided and is an object of type Function, with a new NavigatorNetworkServiceError object whose code attribute has the numeric value 2 (UNKNOWN_TYPE_PREFIX_ERR) as its argument, abort any remaining steps and return.
  6. Process: Let services found be an empty array.
  7. For each available service in the list of available service records run the following steps:
    1. For each requested control type in requested control types: If available service's type attribute equals the requested control type then let matched service equal the value of available service and continue at the step labeled attach below.
    2. Continue at the next available service.
    3. Attach: If matched service is not empty then run the following steps:
      1. Let new service object be a new NetworkService object, mapping the parameters of matched service to this new object where possible.
      2. Append new service object to the services found array.
  8. If services found is an empty array, then the user agent MUST queue a task to invoke errorCallback, if it is provided and is an object of type Function, with a new NavigatorNetworkServiceError object whose code attribute has the numeric value 1 (PERMISSION_DENIED_ERR) as its argument, abort any remaining steps and return.
  9. Return, and run the remaining steps asynchronously.
  10. Optionally, e.g. based on a previously-established user preference, for security reasons, or due to platform limitations, the user agent MAY queue a task to invoke errorCallback, if it is provided and is an object of type Function, with a new NavigatorNetworkServiceError object whose code attribute has the numeric value 1 (PERMISSION_DENIED_ERR) as its argument, abort any remaining steps and return.
  11. The user agent MUST prompt the user in a user-agent-specific manner for permission to provide the entry script's origin with an array of NetworkService objects representing the user-authorized subset of services found.

    If the user grants permission to access one or more networked services then the user agent SHOULD include an "ongoing local-network communication" indicator.

    If the user denies permission, then the user agent MUST queue a task to invoke errorCallback, if it is provided and is an object of type Function, with a new NavigatorNetworkServiceError object whose code attribute has the numeric value 1 (PERMISSION_DENIED_ERR) as its argument, abort any remaining steps and return.

    If the user never responds, this algorithm stalls on this step.

  12. Let services be the array of one or more NetworkService objects for which the user granted permission.
  13. For each Object service in services, run the following substeps:
    1. Add the service's url parameter to the entry script origin's URL whitelist.
    2. If service was originally created from a UPnP discovery process and the service's eventsUrl parameter is not empty then setup a UPnP Events Subscription for service.
  14. Let services manager be a new NetworkServices object.
  15. Set services manager's servicesAvailable attribute to the length of services.
  16. Store the set of services as current authorized services internally against the newly created services manager object.
  17. The user agent MUST queue a task to invoke successCallback with services manager as its argument.

The task source for these tasks is the user interaction task source.

When a NetworkService object is provided to a Web page, the user agent MUST add the url property to the entry script origin's URL whitelist. This list enables the Web page to override and initiate cross-site resource requests towards these URLs, and any sub-resources of these URLs, within the current entry script's origin via various existing mechanisms (e.g. Web Sockets, Server-Sent Events, Web Messaging, XMLHttpRequest).

If the user navigates away from the current browsing context, the user agent MUST remove all previously whitelisted urls from the entry script origin's URL whitelist. There is no persistence to network service selections provided to a web page. It is not possible to access a previously white-listed networked service without the necessary user authorization in all of the following cases:

  • If the current script is reloaded at any point in the same or different window.
  • if the current script reinvokes the getNetworkServices() method at any point in its execution.
  • If the user navigates forward or back in their history to reload the current page.
  • If a script is running in a different origin.

Error Handling

error . code

Returns the current error's error code. At the current time, this may be 1 or 2, for which the corresponding error constants PERMISSION_DENIED_ERR and UNKNOWN_TYPE_PREFIX_ERR are defined.

The code attribute of a NavigatorNetworkServiceError object MUST return the code for the error, which will be one of the following:

PERMISSION_DENIED_ERR (numeric value 1)
The user denied the page permission to access any services.
UNKNOWN_TYPE_PREFIX_ERR (numeric value 2)
No valid service type tokens were provided in the method invocation.

Obtaining networked services

The NetworkServices interface is the top-level response object from a call to getNetworkServices() and provides access to a set of user-authorized NetworkService objects for the given request.

[NoInterfaceObject]
interface NetworkServices {
  readonly attribute unsigned long    length;
  getter NetworkService (unsigned long index);
  NetworkService? getServiceById(DOMString id);

  readonly attribute unsigned long    servicesAvailable;

  // event handler attributes
           attribute EventHandler     onserviceavailable;
           attribute EventHandler     onserviceunavailable;

};

NetworkServices implements EventTarget;

Attributes

length

Returns the current number of services in the respective object's current authorized services.

servicesAvailable

Returns the current number of services matching one of the app-requested valid service type tokens that are actively available within the user's current network.

The length attribute MUST return the number of services represented in the object's corresponding current authorized services list at the time of getting.

The servicesAvailable attribute MUST return the number of services available in the user's network that match the valid service type that was initially used to create the current NetworkServices object. By default, servicesAvailable MUST be set to 1.

When a previously unknown instance of a networked service matching one or the requested valid service types becomes available on the user's current network, the user agent MUST fire a new simple event at the onserviceavailable event handler.

When a previously known instance of a networked service matching one or the requested valid service types becomes unavailable on the user's current network, the user agent MUST fire a new simple event at the onserviceunavailable event handler.

Methods

services [ index ]

Returns the specified NetworkService object.

services . getServiceById ( id )

Returns the NetworkService object with the given identifier, or null if no service has that identifier.

A NetworkServices object represents the current list of zero or more current authorized services, of which zero or more can be available at a time. Each item in current authorized services is represented by a NetworkService object.

Each service in a NetworkServices object thus has an index; the first has the index 0, and each subsequent service is numbered one higher than the previous one. If the user agent dynamically adds or removes network services for any reason, then the indices of the services in current authorized services will change dynamically. If the set of network services changes entirely, then all the previous services will be removed from current authorized services and replaced with new services.

The supported property indices of NetworkServices objects at any instant are the numbers from zero to the number of items in current authorized services represented by the respective object minus one, if any services are represented in current authorized services. If a NetworkServices object represents no current authorized services, it has no supported property indices.

To determine the value of an indexed property for a given index index in a NetworkServices object's current authorized services, the user agent MUST return the NetworkService object that represents the indexth service in current authorized services.

The getServiceById(id) method MUST return the first NetworkService object in current authorized services represented by the respective object whose id attribute is equal to the value of the id argument. When no services in current authorized services match the given argument, the method MUST return null.

Services available within the local network can connect and disconnect at different times during the execution of a web page. A user agent can inform a web page when the state of networked services matching the requested valid service type change. Web pages can use this information to enable in-page experiences for communicating the state of networked services with the ability to change the particular service or set of services the page is connected to by re-invoking the getNetworkServices() method.

Events

The following are the event handlers (and their corresponding event handler event types) that must be supported, as IDL attributes, by all objects implementing the NetworkServices interface:

Event handler Event handler event type
onserviceavailable serviceavailable
onserviceunavailable serviceunavailable

Events with an event type of serviceavailable or serviceunavailable defined in this specification are simple Event objects.

Communicating with a networked service

The NetworkService interface is used to provide a set of connection information for an HTTP service endpoint and if available, service events, running on a networked device.

[NoInterfaceObject]
interface NetworkService {
  readonly attribute DOMString        id;
  readonly attribute DOMString        name;
  readonly attribute DOMString        type;
  readonly attribute DOMString        url;
  readonly attribute DOMString        config;

  const unsigned short AVAILABLE      = 1;
  const unsigned short UNAVAILABLE    = 2;
  readonly attribute unsigned short   readyState;

  // event handler attributes
           attribute EventHandler     onreadystatechange;
           attribute EventHandler     onmessage;
};

NetworkService implements EventTarget;

Attributes

service . id

A unique identifier for the given user-selected service instance.

service . name

The name of the user-selected service.

service . type

The valid service type token value of the user-selected service.

service . url

The control URL endpoint (including any required port information) of the user-selected control service that has been added to the entry script origin's URL whitelist.

service . config

The configuration information associated with the service depending on the requested service type.

The id attribute is a unique identifier for the service. Two services provided at different times or on different objects MUST have the same id value.

The name attribute represents a human-readable title for the service.

The type attribute reflects the value of the valid service type of the service.

The url attribute is an absolute URL pointing to the root HTTP endpoint for the service that has been added to the entry script origin's URL whitelist. Web pages can subsequently use this value for implicit cross-document messaging via various existing mechanisms (e.g. Web Sockets, Server-Sent Events, Web Messaging, XMLHttpRequest).

The config attribute provides the raw configuration information extracted from the given network service.

States

service . readyState

Returns the current state.

A NetworkService object can be in several states. The readyState attribute MUST return the current state of the networked service, which MUST be one of the following values:
AVAILABLE (numeric value 1)

The object is connected to its service endpoint.

UNAVAILABLE (numeric value 2)

The object is not connected to its service endpoint.

Events

The following are the event handlers (and their corresponding event handler event types) that must be supported, as IDL attributes, by all objects implementing the NetworkService interface:

Event handler Event handler event type
onmessage message
onreadystatechange readystatechange

Events with an event type of message defined in this specification are MessageEvent objects as defined in [[!WEBMESSAGING]].

Events with an event type of readystatechange defined in this specification are simple Event objects.

Service Discovery

A user agent conforming to this specification MAY implement SSDP [[!UPNP]] and Zeroconf [[!ZEROCONF]] service discovery mechanisms to enable Web pages to request and connect with HTTP services running on networked devices, discovered via either mechanism, through this API. When a user agent implements either of these service discovery mechanisms, then it MUST conform to the corresponding algorithms provided in this section of the specification.

This section presents how the results of these two service discovery mechanisms will be matched to requested service types and how their properties will be applied to any resulting NetworkService objects.

It is expected that user agents will perform these service discovery mechansisms asynchronously and periodically update the list of networked devices as required. The timing of any service discovery mechanisms is an implementation detail left to the discretion of the implementer (e.g. once on user agent start-up, every X seconds during user agent execution or on invocation of this API from a Web page).

The list of available service records is a single dynamic internal lookup table within user agents that is used to track the current services available in the network at any given time. At any point during the running of either of the two service discovery mechanisms then existing entries within this table can be updated, entries can be added and entries can be removed as the status of networked services changes. Each record contained within this table contains the attributes: id, name, type, url and config.

Zeroconf (mDNS + DNS-SD)

For each DNS response received from a user-agent-initiated Multicast DNS Browse for PTR records with the name _services._dns-sd._udp on the resolved recommended automatic browsing domain [[!MDNS]], the user agent MUST run the following steps:

  1. Let service mDNS responses be an array of PTR records received by issuing a Multicast DNS Browse for PTR records with the name of the current discovered service type.
  2. For each Object service mDNS response in service mDNS responses, run the following steps:
    1. Let network service record be an Object consisting of the following empty properties: id, name, type, url, config.
    2. Set network service record's id property to the value of the full PTR Service Instance Name [[!MDNS]].
    3. Set network service record's name property to the value of the PTR Service Instance Name's Instance component [[!MDNS]].
    4. Set network service record's type property to the concatenation of the string zeroconf: followed by the value of the PTR Service Instance Name's Service component [[!MDNS]].
    5. Set network service record's url property to the resolvable Service URL obtained from performing an DNS-SD Lookup [[!DNS-SD]] of the current service from the PTR record provided [[!MDNS]].
    6. Set network service record's config property to the string value of the contents of the first DNS-SD TXT record associated with the service mDNS response as defined in [[!DNS-SD]].
    7. For each Object existing service record in the current list of available service records, run the following sub-steps:
      1. If the existing service record's id property matches the value of the network service record's id, then set the value of existing service record in the current list of available service records to the value of the network service record and skip the next step.
    8. Add network service record to the list of available service records.
    9. For each non-garbage collected NetworkService object run the following steps:
      1. If the NetworkService object's type attribute does not equal the current network service record's type property then continue at the next available active NetworkService object.
      2. Increment the servicesAvailable attribute of the NetworkServices object by 1.
Universal Plug-and-Play (UPnP)

For each SSDP Presence Announcement [[!UPNP]] - a HTTP NOTIFY request - received from a user-agent-initiated SSDP Discovery Request [[!UPNP]], the user agent MUST run the following steps:

  1. Let ssdp device be an Object with a property for each HTTP header received in the received SSDP Presence Announcement, with each key being the name of a HTTP header and its value being that HTTP header's accompanying value.
  2. If ssdp device does not contain at least one NTS, USN and Location parameter, then the user agent MUST abort these steps.
  3. If the first occurrence of NTS has a value other than ssdp:alive, then continue to the step labeled update service monitor below.
  4. Let root device descriptor file contain the contents of the file located at the URL provided in the first occurrence of Location obtained according to the rules defined in the section 'Retrieving a description using HTTP' [[!UPNP]].
  5. If root device descriptor file is empty, then the user agent MUST abort these steps.
  6. Let advertised services be a list of all advertised services obtained from the root device descriptor file containing all sub-nodes of the serviceList node as described in the section 'Device Description' [[!UPNP]].
  7. For each Object advertised service in advertised services run the following steps:
    1. Let network service record be an Object consisting of the following empty properties: id, name, type, url, eventsUrl, config.
    2. Set network service record's id property to the string value of the first occurrence of ssdp device's USN parameter.
    3. Set network service record's name property to the string value of the first occurrence of the service's serviceId property.
    4. Set network service record's type property to the concatenation of the string upnp: followed by the string value of the first occurrence of the service's serviceType property.
    5. Set network service record's url property to the string value of the first occurrence of the service's controlURL property.
    6. Set network service record's config property to the string value of the first occurrence of the device property.
    7. If service's eventSubURL property is empty, then continue to the step labeled register below.
    8. Set network service record's eventsUrl property to the string value of the first occurrence of the service's eventSubURL property.
    9. Register: For each Object existing service record in the current list of available service records, run the following sub-steps:
      1. If the existing service record's id property matches the value of the first occurrence of USN and the existing service record's type property matches the value of network service record's type, then set the value of existing service record in the current list of available service records to the value of the network service record and skip the next step.
    10. Add network service record to the list of available service records.
  8. Update Service Monitor: For each non-garbage collected NetworkService object run the following steps:
    1. If this NetworkService object's type attribute does not equal the current network service record's type property then continue at the next available active NetworkService object.
    2. If the announcement type equals ssdp:alive then Increment the servicesAvailable attribute of the NetworkServices object by 1. Otherwise, decrement the servicesAvailable attribute of the NetworkServices object by 1.

A user-agent generated callback url is a Local-network accessible URL endpoint that a user agent must generate and maintain for receiving HTTP NOTIFY requests from UPnP Event sources.

When the user agent is to setup a UPnP Events Subscription, it is to run the following steps with the current network service record object:

  1. If network service record's eventsUrl property is empty then the user agent MUST abort these steps.
  2. Let callback URL be the value of creating a new user-agent generated callback url.
  3. Send a HTTP SUBSCRIBE request with a NT header with a string value of upnp:event, a TIMEOUT header with an integer value of 86400 and a CALLBACK header with a string value of callback URL towards the network service record's eventsUrl property.
  4. If a non-200 OK response is received from the HTTP SUBSCRIBE request then the user agent MUST abort these steps.
  5. On receiving a valid 200 OK response, run the following steps:
    1. Let callback ID equal the string value of the first included SID header, if it exists.
    2. Let timeout date equal the sum of the current UTC date value plus the integer value of the first included TIMEOUT header, if it exists.
    3. Run the following steps aynchronously and continue to the step labeled listen below.
    4. Refresh Subscription: Run the following steps at a set interval (X) within the user agent:
      1. Let current date equal the current UTC date.
      2. If current date is less than the timeout date then continue to the step labeled refresh subscription above.
      3. Send a HTTP SUBSCRIBE request with a SID header with the string value of callback ID and a TIMEOUT header with an integer value of 86400 towards the network service record's eventsUrl property.
      4. On receiving a valid 200 OK, update callback ID with the string value of the first included SID header, if it exists. All other HTTP responses should cause the user agent to continue from the step labeled refresh subscription above.
    5. Listen: For each HTTP NOTIFY request received at the callback URL the user agent is to run the following steps:
      1. Let content clone be the result of obtaining the message body of the HTTP NOTIFY request. If content clone is empty, then the user agent MUST abort these steps.
      2. Create a new message event that uses the MessageEvent interface [[!WEBMESSAGING]], with the name message, which does not bubble, is not cancelable, and has no default action.
      3. Let the data attribute of the event have the DOMString value of content clone.
      4. Queue a task to dispatch the newly created event at the current NetworkService object.

Network Topology Monitoring

When the user agent detects that the user has dropped from their connected network, then it MUST run the following steps:

  1. Flush all entries from the list of available service records.
  2. For each NetworkService object currently active in the user agent perform the following steps:
    1. Set the readyState attribute to 2 (UNAVAILABLE).
    2. Create a new readystatechange event that uses the Event interface which does not bubble, is not cancelable, and has no default action.
    3. Queue a task to dispatch the newly created event at the NetworkService object.

When the user agent detects that the user has connected to a new network, then it SHOULD run the following steps:

  1. Re-issue an mDNS search and SSDP discovery search and handle the responses according to the processing defined in Section 6: Service Discovery.

Garbage collection

A NetworkService object containing a url parameter currently in the entry script origin's URL whitelist MUST NOT be garbage collected.

Only when the user navigates away from the current browsing context can NetworkService objects be garbage-collected and records in the entry script origin's URL whitelist be removed.

Use Cases and Requirements

This section covers what the requirements are for this API, as well as illustrates some use cases.

Examples

This sample code exposes a button. When clicked, this button is disabled and the user is prompted to offer a network service. The user may also select multiple network services. When the user has authorized a network service to be connected to the web page then the web page issues a simple command to get a list of all the albums stored on the connected media player service.

The button is re-enabled only when the connected network service disconnects for whatever reason (the service becomes unavailable on the network, the user disconnects from their current network or the user revokes access to the service from the current web page). At this point the user can re-click the button to select a new network service to connect to the web page and the above steps are repeated.

The provided service type identifier and service interaction used in this example is based on the well-defined service type and messaging format supported by the XBMC Media Server.


<input type="button" value="Start" onclick="start()" id="startBtn"/>
<div id="debugconsole"></div>

<script>
 var startBtn = document.getElementById('startBtn'),
     debug = document.getElementById('debugconsole');

 function start() {
   if(navigator.getNetworkServices) {
      navigator.getNetworkServices('zeroconf:_xbmc-jsonrpc._tcp', gotXBMCService, error);
      startBtn.disabled = true;
   } else {
      debug.innerHTML += "<br>Service Discovery API not supported!";
   }
 }

 function gotXBMCService(services) {

// Listen for service disconnect messages

   services[0].addEventListener('readystatechange', function ( e ) {
     if(services[0].readyState === services[0].UNAVAILABLE) {
       debug.innerHTML += "<br>" + services[0].name + " disconnected.";
       startBtn.disabled = false;
     }
   }, false);

// Send a service message to get albums list (and process the service response)

   var svcXhr = new XMLHttpRequest();
   svcXhr.open("POST", services[0].url + "/getAlbums"); // services[0].url and its subresources have been
                                                        // whitelisted for cross-site XHR use in this
                                                        // current browsing context.

   svcXhr.setRequestHeader('Content-Type', 'application/json-rpc');

   svcXhr.addEventListener('readystatechange', function ( response ) {
     if( response.readyState != 4 || response.status != 200 )
        return;
     debug.innerHTML += "<br>" + services[0].name + " response received: ";
     debug.textContent += JSON.parse(response.responseText);
   }, false);

   var svcMsg = [
     { "jsonrpc": "2.0", "method": "AudioLibrary.GetAlbums", "params": { "genreid": -1,
         "artistid": -1, "start": -1, "end": -1 }, "id": "1" }
   ];

   svcXhr.send(JSON.stringify(svcMsg));
   debug.innerHTML += "<br>" + services[0].name + " request sent: ";
   debug.textContent += JSON.stringify(svcMsg);

 }

 function error( err ) {
   debug.innerHTML += "<br>An error occurred obtaining a local network service.";
   startBtn.disabled = false;
 }
</script>

This sample exposes a drop-down list containing a number of common Home-based audio devices. When the user selects an audio device from the list provided, they are prompted to authorize a network service based on the service type requested. The user may also select multiple network services matching the selected service type. In this example, the user selects their make as being Sony and their model as being Bravia S1000 from which the Web page can derive a service type (urn:schemas-upnp-org:service:RenderingControl:1).

Once the user has authorized the device, the web page sends a simple mute command according to the messaging format supported by the device.


<select name="make" id="make">
  <option selected="selected" disabled="disabled">Select make</option>
  <option>Sony</option>
  <option>Philips</option>
  <option>Alba</option>
</select>
<select name="model" id="model"></select>
<div id="debugconsole"></div>

<script>
  var debug = document.getElementById('debugconsole');

  var models = {
    "Sony": [
      {"name": "Bravia TV S1000", "type": "upnp", "service": "urn:schemas-upnp-org:service:RenderingControl:1" },
      {"name": "Bravia TV S2000", "type": "zeroconf", "service": "_mediarenderer._http._tcp" },
      {"name": "HiFi WD10", "type": "upnp", "service": "urn:schemas-upnp-org:service:RenderingControl:1" }
    ],
    "Philips": [ /* ... */ ],
    "Alba": [ /* ... */ ]
  };

  var makeEl = document.getElementById("make"),
      modelEl = document.getElementById("model");

  makeEl.addEventListener('change', function() {
    modelEl.innerHTML = ""; // reset
    var defaultOption = document.createElement("option");
    defaultOption.textContent = "Select model";
    defaultOption.setAttribute("disabled", "disabled");
    defaultOption.setAttribute("selected", "selected");
    modelEl.appendChild(defaultOption);
    for(var i = 0, l = models[makeEl.value].length; i < l; i++) {
      var option = document.createElement("option");
      option.textContent = models[makeEl.value][i]["name"];
      option.setAttribute("value", models[makeEl.value][i]["type"] + ":" + models[makeEl.value][i]["service"]);
      modelEl.appendChild(option);
    }
  }, false);

  modelEl.addEventListener('change', function() {
    if(navigator.getNetworkServices &&
         modelEl.value == "upnp:urn:schemas-upnp-org:service:RenderingControl:1") {
      navigator.getNetworkServices(modelEl.value, successCallback, errorCallback);
    } else if (modelEl.value == "zeroconf:_mediarenderer._http._tcp") {
      debug.innerHTML += "<br>Service type is not implemented by this application.";
    } else {
      debug.innerHTML += "<br>Service Discovery is not supported!";
    }
  }, false);
</script>

<script>
  function successCallback( services ) {

  // Listen for service push messages

    services[0].addEventListener('message', function ( msg ) {
         debug.innerHTML += "<br>" + services[0].name + " event received: ";
         debug.textContent += msg.data;
    }, false);

 // Send a control signal to mute the service audio

    var svcXhr = new XMLHttpRequest();
    svcXhr.open("POST", services[0].url); // services[0].url and its
                                          // subresources have been whitelisted for
                                          // cross-site XHR use in this current
                                          // browsing context.

    svcXhr.setRequestHeader('SOAPAction', 'urn:schemas-upnp-org:service:RenderingControl:1#SetMute');
    svcXhr.setRequestHeader('Content-Type', 'text/xml; charset="utf-8";');

    svcXhr.onreadystatechange = function ( response ) {
      if( response.readyState != 4 || response.status != 200 )
        return;
      debug.innerHTML += "<br>" + services[0].name + " response received: ";
      debug.textContent += response.responseXML;
    }

    // Service messaging to mute the provided service
    var svcMsg = '<?xml version="1.0" encoding="utf-8"?>' +
                 '<s:Envelope s:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/" ' +
                   'xmlns:s="http://schemas.xmlsoap.org/soap/envelope/">' +
                   '<s:Body>' +
                     '<u:SetMute xmlns:u="urn:schemas-upnp-org:service:RenderingControl:1">' +
                       '<InstanceID>0</InstanceID>' +
                       '<Channel>Master</Channel>' +
                       '<DesiredMute>true</DesiredMute>' +
                     '</u:SetMute>' +
                   '</s:Body>' +
                 '</s:Envelope>';

    svcXhr.send(svcMsg);
    debug.innerHTML += "<br>" + services[0].name + " request sent: ";
    debug.textContent += svcMsg;
  }

  function errorCallback( error ) {
    debug.innerHTML += "<br>An error occurred: " + error.code;
  }
</script>

Acknowledgements

Thanks are expressed by the editor to the following individuals for their feedback on this specification to date (in alphabetical order):

Gar Bergstedt, Lars-Erik Bolstad, Hari G Kumar, Bob Lund, Giuseppe Pascale, Marcin Simonides, Clarke Stevens, Christian Söderström, Mark Vickers, ...

Thanks are also expressed by the editor to the following organizations and groups for their support in producing this specification to date (in alphabetical order):

CableLabs, Opera Software ASA, W3C Device APIs Working Group, W3C Web and TV Interest Group, ...