[Presentation API] Additional plumbing for PresentationServiceImpl.

content/common/presentation/presentation_service.mojom

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 module presentation;
 
 import "presentation_session.mojom";
 
 struct PresentationSessionInfo {
-    PresentationSession session;

[whywhat, 2015/03/10 17:05:05]

Why removing this?

[imcheng, 2015/03/10 18:31:16]

I don't think we should include an service interface as a field in the struct.
Instead shouldn't we define the PresentationSession methods to take a
PresentationSessionInfo struct?

[whywhat, 2015/03/10 23:20:23]

Which PresentationSession do you mean? The JS interface?

[imcheng, 2015/03/12 20:03:41]

I mean the (currently empty) mojo interface defined in
presentation_session.mojom.
I guess in the PresentationSession interface you can define methods that take a
PresentationSessionInfo object, like PostMessage(PresentationSessionInfo
session, string message) .... Maybe a renaming of these objects/interfaces are
in order? (PresentationSession -> PresentationSessionService,
PresentationSessionInfo -> PresentationSession)

Besides, I'm not sure if there's any benefit to putting a PresentationSession
interface in here. It also prevents me from converting from the
content/public/browser equivalent object to this object since there's no field
that corresponds to "session" here.

[whywhat, 2015/03/13 17:44:34]

Hm, the PresentationDispatcher would keep the PresentationSessionPtr as a form
of unique id to the session. Just a URL and ID is not enough if the frame starts
two sessions with the same URL and ID. This pointer to the remote interface
would be unique though. Otherwise I think we need to add some extra session_id
to the info so that PresentationService could distinguish between the sessions.
Then the PresentationSession methods could go into PresentationService and take
the session id as an extra argument (e.g. session.postMessage() would translate
into presentation_service_->PostMessage(session_id, message).

[imcheng, 2015/03/13 23:36:45]

I want to understand this a little better. Who is responsible for mapping a
PresentationSession web object to a PresentationSessionPtr? Does Blink or
PresentationDispatcher maintain such a mapping?

Note that having PresentationSession web object map to a PresentationSessionPtr
means that mojo channels are created on a per-session basis rather than per
frame. I wonder if we can make the APIs for PresentationSession similar to
PresentationService, i.e. a per-frame service that can operate on a given handle
that identifies a PresentationSession object. That does mean we will have to
introduce a unique session id and make sure we can map a PresentationSession web
object to session id somewhere in the renderer.

     string url;
     string id;
 };
 
 enum PresentationErrorType {
     NO_AVAILABLE_SCREENS,
     SESSION_REQUEST_CANCELLED,
     NO_PRESENTATION_FOUND,
     UNKNOWN,
 };
 
 struct PresentationError {
-    PresentationErrorType errorType;
+    PresentationErrorType error_type;
     string message;
 };
 
 interface PresentationService {
     // Returns the last screen availability state if it’s changed since the last
     // time the method was called. The client has to call this method again when
     // handling the result (provided via Mojo callback) to get the next update
     // about the availability status.
     // May start discovery of the presentation screens. The implementation might
     // stop discovery once there are no active calls to GetScreenAvailability.
     // |presentation_url| can be specified to help the implementation to filter
     // out incompatible screens.
     GetScreenAvailability(string? presentation_url) => (bool available);
 
     // Called when the frame no longer listens to the
     // |availablechange| event.
     OnScreenAvailabilityListenerRemoved();
 
+    // Sets the default presentation URL for the frame.
+    // If parameter is an empty string, clears the default presentation URL.
+    SetDefaultPresentationUrl(string default_presentation_url);
+
     // Called when startSession() is called by the frame. The result callback
     // will return a non-null and valid PresentationSessionInfo if starting the
     // session succeeded, or null with a PresentationError if starting the
     // session failed.
     // The presentation id is always returned along with the initialized
     // session on success.
     // If the UA identifies a matching session (same presentation url and id),
     // the user may choose this existing session and the page will join it
     // rather than get a new one. An empty presentation id means that the
     // UA will generate the presentation id.
     StartSession(string presentation_url, string? presentation_id)
          => (PresentationSessionInfo? sessionInfo, PresentationError? error);
 
     // Called when joinSession() is called by the frame. The result callback
     // works the same as for the method above. JoinSession will join a known
     // session (i.e. when the page navigates or the user opens another tab)
     // silently and without user action.
     JoinSession(string presentation_url, string? presentation_id)
         => (PresentationSessionInfo? sessionInfo, PresentationError? error);
-};
+};