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Re: Mapping WebIntents to Network Service Discovery API

From: Dave Raggett <dsr@w3.org>
Date: Sat, 14 Jan 2012 13:43:35 +0000
Message-ID: <4F118687.4070203@w3.org>
To: Cathy.Chan@nokia.com
CC: timeless@gmail.com, public-web-intents@w3.org
On 13/01/12 21:15, Cathy.Chan@nokia.com wrote:
>> Dave Raggett wrote:
>> 
>> My guess is that the browser would only have limited knowledge of
>> the basic UPnP mechanisms. In which case it would need a way to
>> communicate UPnP events to the web page scripts to act upon.

> I think that would most likely be the case. The UA (or an extension)
> will simply relay the complete message from the UPnP device to the
> web page. If the web page is aiming to use UPnP devices, it would be
> able to parse and interpret UPnP messages properly.

Here is a Java UPnPEventListener interface:


http://www.osgi.org/javadoc/r4v42/org/osgi/service/upnp/UPnPEventListener.html

We could define something similar for web page scripts. A UPnP event has
a device Id, a service Id and a set of name/value pairs for state
variables. This could be passed to the script as a couple of strings for
the Ids, and an associative array for the name/value pairs.

What did you think of my suggestion that the web page passes a handler
interface to startActivity:

 var intent = new Intent("http://webintents.org/print");
 window.navigator.startActivity(intent, handler);

where the web page script previously declares "handler" as an object
with the notification interface as suggested above, e.g.

var handler = {

  UPnPEventListener: function (deviceId, serviceId, state)
  {
     // do something useful with the notification
  },

};

A basic print template for UPnP can be found at:

  http://www.upnp.org/specs/pntr/UPnP-pntr-PrintBasic-v1-Service.pdf

This shows that, for example, the PrinterStateReasons variable is a list
of values such as "media-jam", "media-empty" and "marker-supply-empty".

The basic printer template supports a number of actions such as
CreateJob, CancelJob, GetPrinterAttributes and GetJobAttributes. The
CreateJob action takes a set of name value pairs and returns with values
for the JobId and DataSink. The latter is a URL for the client to send
the print data to via HTTP POST.

A UPnP action takes the name of the action and a set of name value
pairs, and returns a set of name value pairs. There are a number of ways
this could be mapped into JavaScript. The returned values will need to
handled asynchronously to avoid the risk of stalling the UA.

In principle, the UA could read the UPnP service description and
dynamically set a function for each action as part of the above handler
object. Alternatively, there could be a generic function for all
actions, together with some kind of service handle set by the UA.

We could choose to define print is a standard web intent along with a
standard interface for notifications, cancelling a job, etc. I would be
happy to explore that in more detail. In principle, support for standard
intents could be built into the UA or provided via an extension.

We also need to think about non-standard web intents and how these can
be supported over UPnP. For these, the UA would need to expose the UPnP
service to scripts. This presents a range of possibilities for us to
explore. The UA could provide a generic means to invoke actions and to
process notifications. The UPnP service description could be exposed in
its raw XML form, or there could be lighter weight means for scripts to
determine the list of actions and state variables. The ServiceId could
be used as a basis for a predetermined API without the need for reflection.

When it comes to standardizing web intents, we could define a generic
means to create an Intent and start an activity, and defer the
standardization of the interfaces for particular events to separate
standardization efforts. In this way we just need agreement on an
optional second argument to history.startActivity, and can define the
interfaces that argument supports in separate W3C Working Drafts.

A print intent is associated with more complex behavior than a view
intent, so this separation of effort would seem to make sense.

-- 
Dave Raggett <dsr@w3.org> http://www.w3.org/People/Raggett
Received on Saturday, 14 January 2012 13:44:37 GMT

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