Register media instance with session and prepare communication with embedder

components/constellation/constellation.rs

@@ -474,6 +474,9 @@ pub struct Constellation<Message, LTF, STF> {
 
     /// Mechanism to force the compositor to process events.
     event_loop_waker: Option<Box<dyn EventLoopWaker>>,
+    
+    /// Browser ID of the active media session, if any.
+    active_media_session: Option<TopLevelBrowsingContextId>,
 }
 
 /// State needed to construct a constellation.
@@ -843,6 +846,7 @@ where
                     glplayer_threads: state.glplayer_threads,
                     player_context: state.player_context,
                     event_loop_waker: state.event_loop_waker,
+                    active_media_session: None,
                 };
 
                 constellation.run();
@@ -1774,6 +1778,9 @@ where
                     new_value,
                 );
             },
+            FromScriptMsg::MediaSessionEventMsg(browser_id, event) => {
+                // TODO
+            },
         }
     }
 

components/script/dom/htmlmediaelement.rs

@@ -15,8 +15,10 @@ use crate::dom::bindings::codegen::Bindings::HTMLMediaElementBinding::HTMLMediaE
 use crate::dom::bindings::codegen::Bindings::HTMLSourceElementBinding::HTMLSourceElementMethods;
 use crate::dom::bindings::codegen::Bindings::MediaErrorBinding::MediaErrorConstants::*;
 use crate::dom::bindings::codegen::Bindings::MediaErrorBinding::MediaErrorMethods;
+use crate::dom::bindings::codegen::Bindings::NavigatorBinding::NavigatorBinding::NavigatorMethods;
 use crate::dom::bindings::codegen::Bindings::NodeBinding::NodeBinding::NodeMethods;
 use crate::dom::bindings::codegen::Bindings::TextTrackBinding::{TextTrackKind, TextTrackMode};
+use crate::dom::bindings::codegen::Bindings::WindowBinding::WindowBinding::WindowMethods;
 use crate::dom::bindings::codegen::InheritTypes::{ElementTypeId, HTMLElementTypeId};
 use crate::dom::bindings::codegen::InheritTypes::{HTMLMediaElementTypeId, NodeTypeId};
 use crate::dom::bindings::codegen::UnionTypes::{
@@ -78,6 +80,7 @@ use net_traits::request::{Destination, Referrer};
 use net_traits::{CoreResourceMsg, FetchChannels, FetchMetadata, FetchResponseListener, Metadata};
 use net_traits::{NetworkError, ResourceFetchTiming, ResourceTimingType};
 use script_layout_interface::HTMLMediaData;
+use script_traits::MediaSessionEvent;
 use servo_config::pref;
 use servo_media::player::audio::AudioRenderer;
 use servo_media::player::video::{VideoFrame, VideoFrameRenderer};
@@ -592,7 +595,6 @@ impl HTMLMediaElement {
         match (old_ready_state, ready_state) {
             (ReadyState::HaveNothing, ReadyState::HaveMetadata) => {
                 task_source.queue_simple_event(self.upcast(), atom!("loadedmetadata"), &window);
-
                 // No other steps are applicable in this case.
                 return;
             },
@@ -1883,6 +1885,12 @@ impl HTMLMediaElement {
             self.media_element_load_algorithm();
         }
     }
+
+    fn send_media_session_event(&self, event: MediaSessionEvent) {
+        let global = self.global();
+        let media_session = global.as_window().Navigator().MediaSession();
+        media_session.send_event(event);
+    }
 }
 
 // XXX Placeholder for [https://github.com/servo/servo/issues/22293]

components/script/dom/mediasession.rs

@@ -11,12 +11,13 @@ use crate::dom::bindings::codegen::Bindings::MediaSessionBinding::MediaSessionMe
 use crate::dom::bindings::codegen::Bindings::MediaSessionBinding::MediaSessionPlaybackState;
 use crate::dom::bindings::reflector::{reflect_dom_object, DomObject, Reflector};
 use crate::dom::bindings::root::{DomRoot, MutNullableDom};
+use crate::dom::htmlmediaelement::HTMLMediaElement;
 use crate::dom::mediametadata::MediaMetadata;
 use crate::dom::window::Window;
 use crate::script_thread::ScriptThread;
 use dom_struct::dom_struct;
 use msg::constellation_msg::TopLevelBrowsingContextId;
-use script_traits::MediaSessionActionType;
+use script_traits::{MediaSessionActionType, MediaSessionEvent, ScriptMsg};
 use std::collections::HashMap;
 use std::rc::Rc;
 
@@ -30,6 +31,9 @@ pub struct MediaSession {
     /// https://w3c.github.io/mediasession/#supported-media-session-actions
     #[ignore_malloc_size_of = "Rc"]
     action_handlers: DomRefCell<HashMap<MediaSessionActionType, Rc<MediaSessionActionHandler>>>,
+    /// The media instance controlled by this media session.
+    /// For now only HTMLMediaElements are controlled by media sessions.
+    media_instance: MutNullableDom<HTMLMediaElement>,
 }
 
 impl MediaSession {
@@ -40,6 +44,7 @@ impl MediaSession {
             metadata: Default::default(),
             playback_state: DomRefCell::new(MediaSessionPlaybackState::None),
             action_handlers: DomRefCell::new(HashMap::new()),
+            media_instance: Default::default(),
         };
         ScriptThread::register_media_session(&media_session, browsing_context_id);
         media_session
@@ -63,6 +68,18 @@ impl MediaSession {
         }
         // TODO default action.
     }
+
+    pub fn send_event(&self, event: MediaSessionEvent) {
+        let global = self.global();
+        let browser_id = global
+            .as_window()
+            .window_proxy()
+            .top_level_browsing_context_id();
+        let _ = global
+            .script_to_constellation_chan()
+            .send(ScriptMsg::MediaSessionEventMsg(browser_id, event))
+            .unwrap();
+    }
 }
 
 impl MediaSessionMethods for MediaSession {

components/script/dom/navigator.rs

@@ -21,6 +21,7 @@ use crate::dom::promise::Promise;
 use crate::dom::serviceworkercontainer::ServiceWorkerContainer;
 use crate::dom::window::Window;
 use crate::dom::xr::XR;
+use crate::script_thread::ScriptThread;
 use dom_struct::dom_struct;
 use std::rc::Rc;
 
@@ -192,7 +193,24 @@ impl NavigatorMethods for Navigator {
 
     /// https://w3c.github.io/mediasession/#dom-navigator-mediasession
     fn MediaSession(&self) -> DomRoot<MediaSession> {
-        self.mediasession
-            .or_init(|| MediaSession::new(self.global().as_window()))
+        self.mediasession.or_init(|| {
+            // There is a single MediaSession instance per top level browsing context
+            // and only one active MediaSession globally.
+            //
+            // MediaSession creation can happen in two cases:
+            //
+            // - If content gets `navigator.mediaSession`
+            // - If a media instance (HTMLMediaElement so far) starts playing media.
+            //
+            // The MediaSession constructor is in charge of registering itself with
+            // the script thread.
+            let global = self.global();
+            let window = global.as_window();
+            let browsing_context_id = window.window_proxy().top_level_browsing_context_id();
+            match ScriptThread::get_media_session(browsing_context_id) {
+                Some(session) => session,
+                None => MediaSession::new(window),
+            }
+        })
     }
 }

components/script/script_thread.rs

@@ -3993,6 +3993,19 @@ impl ScriptThread {
                 .remove(&browsing_context_id);
         })
     }
+
+    pub fn get_media_session(
+        browsing_context_id: TopLevelBrowsingContextId,
+    ) -> Option<DomRoot<MediaSession>> {
+        SCRIPT_THREAD_ROOT.with(|root| {
+            let script_thread = unsafe { &*root.get().unwrap() };
+            script_thread
+                .media_sessions
+                .borrow()
+                .get(&browsing_context_id)
+                .map(|s| DomRoot::from_ref(&**s))
+        })
+    }
 }
 
 impl Drop for ScriptThread {

components/script_traits/lib.rs

@@ -1087,3 +1087,34 @@ pub enum MediaSessionActionType {
     /// The action intent is to move the playback time to a specific time.
     SeekTo,
 }
+
+/// https://w3c.github.io/mediasession/#mediametadata
+#[derive(Clone, Debug, Deserialize, Serialize)]
+pub struct MediaMetadata {
+    /// Title
+    pub title: String,
+    /// Artist
+    pub artist: Option<String>,
+    /// Album
+    pub album: Option<String>,
+}
+
+/// https://w3c.github.io/mediasession/#enumdef-mediasessionplaybackstate
+#[derive(Clone, Debug, Deserialize, Serialize)]
+pub enum MediaSessionPlaybackState {
+    /// The browsing context does not specify whether it’s playing or paused.
+    None_,
+    /// The browsing context has paused media and it can be resumed.
+    Playing,
+    /// The browsing context is currently playing media and it can be paused.
+    Paused,
+}
+
+/// Type of events sent from script to the constellation about the media session.
+#[derive(Clone, Debug, Deserialize, Serialize)]
+pub enum MediaSessionEvent {
+    /// Indicates that the media metadata is available.
+    SetMetadata(MediaMetadata),
+    /// Indicates that the playback state has changed.
+    PlaybackStateChange(MediaSessionPlaybackState),
+}

components/script_traits/script_msg.rs

@@ -8,6 +8,7 @@ use crate::DocumentState;
 use crate::IFrameLoadInfoWithData;
 use crate::LayoutControlMsg;
 use crate::LoadData;
+use crate::MediaSessionEvent;
 use crate::MessagePortMsg;
 use crate::PortMessageTask;
 use crate::StructuredSerializedData;
@@ -254,6 +255,9 @@ pub enum ScriptMsg {
     GetScreenSize(IpcSender<DeviceIntSize>),
     /// Get the available screen size (pixel)
     GetScreenAvailSize(IpcSender<DeviceIntSize>),
+    /// Notifies the constellation about media session events
+    /// (i.e. when there is metadata for the active media session, playback state changes...).
+    MediaSessionEventMsg(TopLevelBrowsingContextId, MediaSessionEvent),
 }
 
 impl fmt::Debug for ScriptMsg {
@@ -305,6 +309,7 @@ impl fmt::Debug for ScriptMsg {
             GetClientWindow(..) => "GetClientWindow",
             GetScreenSize(..) => "GetScreenSize",
             GetScreenAvailSize(..) => "GetScreenAvailSize",
+            MediaSessionEventMsg(..) => "MediaSessionEventMsg",
         };
         write!(formatter, "ScriptMsg::{}", variant)
     }

ports/glutin/browser.rs

@@ -449,6 +449,10 @@ where
                         error!("Failed to store profile: {}", e);
                     }
                 },
+                EmbedderMsg::MediaSession(_) => {
+                    debug!("MediaSession received");
+                    // TODO(ferjm)
+                },
             }
         }
     }