Add shim for MediaStreamTrack

Adding listeners for MediaStreamTrack objects and dispatching events has
no effect in Firefox, although it is supported in Chromium. Due to this
a shim that implements events in MediaStreamTrack is added.

Note that the implementation is a simplified one adjusted only to what
will be needed and it does not take into account advanced parameters of
event listeners like "options" or "useCapture".

Signed-off-by: Daniel Calviño Sánchez <[email protected]>

src/utils/webrtc/shims/MediaStreamTrack.js

@@ -0,0 +1,79 @@
+/**
+ *
+ * @copyright Copyright (c) 2020, Daniel Calviño Sánchez ([email protected])
+ *
+ * @license GNU AGPL version 3 or any later version
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+if (window.MediaStreamTrack) {
+	// Event implementations do not support advanced parameters like "options"
+	// or "useCapture".
+	const originalMediaStreamTrackDispatchEvent = window.MediaStreamTrack.prototype.dispatchEvent
+	const originalMediaStreamTrackAddEventListener = window.MediaStreamTrack.prototype.addEventListener
+	const originalMediaStreamTrackRemoveEventListener = window.MediaStreamTrack.prototype.removeEventListener
+
+	window.MediaStreamTrack.prototype.dispatchEvent = function(event) {
+		if (this._listeners && this._listeners[event.type]) {
+			this._listeners[event.type].forEach(listener => {
+				listener.apply(this, [event])
+			})
+		}
+
+		return originalMediaStreamTrackDispatchEvent.apply(this, arguments)
+	}
+
+	let isMediaStreamTrackDispatchEventSupported
+
+	window.MediaStreamTrack.prototype.addEventListener = function(type, listener) {
+		if (isMediaStreamTrackDispatchEventSupported === undefined) {
+			isMediaStreamTrackDispatchEventSupported = false
+			const testDispatchEventSupportHandler = () => {
+				isMediaStreamTrackDispatchEventSupported = true
+			}
+			originalMediaStreamTrackAddEventListener.apply(this, ['test-dispatch-event-support', testDispatchEventSupportHandler])
+			originalMediaStreamTrackDispatchEvent.apply(this, [new Event('test-dispatch-event-support')])
+			originalMediaStreamTrackRemoveEventListener(this, ['test-dispatch-event-support', testDispatchEventSupportHandler])
+
+			console.debug('Is MediaStreamTrack.dispatchEvent() supported?: ', isMediaStreamTrackDispatchEventSupported)
+		}
+
+		if (!isMediaStreamTrackDispatchEventSupported) {
+			if (!this._listeners) {
+				this._listeners = []
+			}
+
+			if (!this._listeners.hasOwnProperty(type)) {
+				this._listeners[type] = [listener]
+			} else if (!this._listeners[type].includes(listener)) {
+				this._listeners[type].push(listener)
+			}
+		}
+
+		return originalMediaStreamTrackAddEventListener.apply(this, arguments)
+	}
+
+	window.MediaStreamTrack.prototype.removeEventListener = function(type, listener) {
+		if (this._listeners && this._listeners[type]) {
+			const index = this._listeners[type].indexOf(listener)
+			if (index >= 0) {
+				this._listeners[type].splice(index, 1)
+			}
+		}
+
+		return originalMediaStreamTrackRemoveEventListener.apply(this, arguments)
+	}
+}