Re: Proposal related to bug 22270 "Adding tracks to MediaStream should only be possible for constructed streams"

This might be overly constraining.  It's not necessary for the
platform-constructed objects to have a constructor.  But it would be
nice if applications could do the following:

var mediaStream = new MediaStream(...)
plaformMediaStream instanceof MediaStream // === true

have you considered the possibility of having addTrack/removeTrack
throw on platform-constructed streams, i.e.:

// [NoInterfaceObject]
function PlatformMediaStream() {
    MediaStream.apply(this, [].concat.apply(arguments));
}
PlatformMediaStream.prototype = new MediaStream();
function notAllowed() {
   throw new Error('operation not permitted');
   // or use DOMError as appropriate, I'm no longer able to follow that thread
}
PlatformMediaStream.prototype.addStream = notAllowed;
PlatformMediaStream.prototype.removeStream = notAllowed;

On 24 October 2013 04:19, Stefan Håkansson LK
<stefan.lk.hakansson@ericsson.com> wrote:
> Hi, this relates to bug 22270,
> https://www.w3.org/Bugs/Public/show_bug.cgi?id=22270, that proposes to
> allow adding/removing tracks from a (by the app) constructed MediaStream
> only. Platform generated MediaStreams (those coming from getUserMedia,
> and on the remote side of a PeerConnection) should not have those methods.
>
> We could spec that by having completely independent IDLs for
> "Constructed" and "Platform" MediaStream's, but since there is such a
> large overlap between them it seems more efficient to use a base
> description that they both extend.
>
> I've sketched on two alternatives. The second one (Alternative B)is
> inspired by Web Worker's (and its AbstractWorker) with an
> AbstractMediaStream which is "implemented" by Platform/Constructed
> MediaStreams. The first one (alternative A) uses inheritance instead of
> "implements".
>
> I'm far from a WEBIdl expert, but to me Alternative A seems better in
> that we can specify consumers be able to consume the "BaseMediaStream"
> only, and would not have to worry about updating them if we would ever
> add another type of MediaStream (that inherits from BaseMS). If we go
> with alternative B we would have to spec that every consumer can handle
> two types of MediaStream's for now (PlatfromMediaStream and
> ConstructedMediaStream), and would have to update them if we add another
> type in the future.
>
> Are there any comments or opinions? (And yes, the names are horrible.)
>
> Stefan
>
>
>
>
> Alternative A
> =============
> interface BaseMediaStream : EventTarget {
>              readonly    attribute DOMString    id;
>              sequence<MediaStreamTrack> getAudioTracks ();
>              sequence<MediaStreamTrack> getVideoTracks ();
>              MediaStreamTrack?          getTrackById (DOMString trackId);
>              readonly    attribute boolean      active;
>                          attribute EventHandler oninactive;
> };
>
>
> interface PlatformMediaStream : BaseMediaStream {
>                          attribute EventHandler onaddtrack;
>                          attribute EventHandler onremovetrack;
> };
>
>
>
> [Constructor,
>                  Constructor (BaseMediaStream stream),
>                  Constructor (MediaStreamTrackSequence tracks)]
> interface ConstructedMediaStream : BaseMediaStream  {
>              void                       addTrack (MediaStreamTrack track);
>              void                       removeTrack (MediaStreamTrack
> track);
> };
>
>
> Alternative B
> =============
> [NoInterfaceObject]
> interface AbstractMediaStream {
>             readonly    attribute DOMString    id;
>             sequence<MediaStreamTrack> getAudioTracks ();
>             sequence<MediaStreamTrack> getVideoTracks ();
>             MediaStreamTrack?          getTrackById (DOMString trackId);
>             readonly    attribute boolean      active;
>                         attribute EventHandler oninactive;
> };
>
>
> interface PlatformMediaStream : EventTarget {
>                         attribute EventHandler onaddtrack;
>                         attribute EventHandler onremovetrack;
> };
> PlatformMediaStream implements AbstractMediaStream;
>
>
> [Constructor,
>                 Constructor (ConstructedMediaStream stream),
>                 Constructor (PlatformMediaStream stream),
>                 Constructor (MediaStreamTrackSequence tracks)]
> interface ConstructedMediaStream  : EventTarget {
>             void                       addTrack (MediaStreamTrack track);
>             void                       removeTrack (MediaStreamTrack track);
> };
> ConstructedMediaStream implements AbstractMediaStream;
>

Received on Thursday, 24 October 2013 18:57:19 UTC