1 files changed, 121 insertions, 0 deletions
diff --git a/browser/actors/EncryptedMediaChild.sys.mjs b/browser/actors/EncryptedMediaChild.sys.mjs
new file mode 100644
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+++ b/browser/actors/EncryptedMediaChild.sys.mjs
@@ -0,0 +1,121 @@
+/* vim: set ts=2 sw=2 sts=2 et tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ * GlobalCaptureListener is a class that listens for changes to the global
+ * capture state of windows and screens. It uses this information to notify
+ * observers if it's possible that media is being shared by these captures.
+ * You probably only want one instance of this class per content process.
+ */
+class GlobalCaptureListener {
+  constructor() {
+    Services.cpmm.sharedData.addEventListener("change", this);
+    // Tracks if screen capture is taking place based on shared data. Default
+    // to true for safety.
+    this._isScreenCaptured = true;
+    // Tracks if any windows are being captured. Default to true for safety.
+    this._isAnyWindowCaptured = true;
+  }
+
+  /**
+   * Updates the capture state and forces that the state is notified to
+   * observers even if it hasn't changed since the last update.
+   */
+  requestUpdateAndNotify() {
+    this._updateCaptureState({ forceNotify: true });
+  }
+
+  /**
+   * Handle changes in shared data that may alter the capture state.
+   * @param event a notification that sharedData has changed. If this includes
+   * changes to screen or window sharing state then we'll update the capture
+   * state.
+   */
+  handleEvent(event) {
+    if (
+      event.changedKeys.includes("webrtcUI:isSharingScreen") ||
+      event.changedKeys.includes("webrtcUI:sharedTopInnerWindowIds")
+    ) {
+      this._updateCaptureState();
+    }
+  }
+
+  /**
+   * Updates the capture state and notifies the state to observers if the
+   * state has changed since last update, or if forced.
+   * @param forceNotify if true then the capture state will be sent to
+   * observers even if it didn't change since the last update.
+   */
+  _updateCaptureState({ forceNotify = false } = {}) {
+    const previousCaptureState =
+      this._isScreenCaptured || this._isAnyWindowCaptured;
+
+    this._isScreenCaptured = Boolean(
+      Services.cpmm.sharedData.get("webrtcUI:isSharingScreen")
+    );
+
+    const capturedTopInnerWindowIds = Services.cpmm.sharedData.get(
+      "webrtcUI:sharedTopInnerWindowIds"
+    );
+    if (capturedTopInnerWindowIds && capturedTopInnerWindowIds.size > 0) {
+      this._isAnyWindowCaptured = true;
+    } else {
+      this._isAnyWindowCaptured = false;
+    }
+    const newCaptureState = this._isScreenCaptured || this._isAnyWindowCaptured;
+
+    const captureStateChanged = previousCaptureState != newCaptureState;
+
+    if (forceNotify || captureStateChanged) {
+      // Notify the state if the caller forces it, or if the state changed.
+      this._notifyCaptureState();
+    }
+  }
+
+  /**
+   * Notifies observers of the current capture state. Notifies observers
+   * with a null subject, "mediakeys-response" topic, and data that is either
+   * "capture-possible" or "capture-not-possible", depending on if capture is
+   * possible or not.
+   */
+  _notifyCaptureState() {
+    const isCapturePossible =
+      this._isScreenCaptured || this._isAnyWindowCaptured;
+    const isCapturePossibleString = isCapturePossible
+      ? "capture-possible"
+      : "capture-not-possible";
+    Services.obs.notifyObservers(
+      null,
+      "mediakeys-response",
+      isCapturePossibleString
+    );
+  }
+}
+
+const gGlobalCaptureListener = new GlobalCaptureListener();
+
+export class EncryptedMediaChild extends JSWindowActorChild {
+  // Expected to observe 'mediakeys-request' as notified from MediaKeySystemAccess.
+  // @param aSubject the nsPIDOMWindowInner associated with the notifying MediaKeySystemAccess.
+  // @param aTopic should be "mediakeys-request".
+  // @param aData json containing a `status` and a `keysystem`.
+  observe(aSubject, aTopic, aData) {
+    let parsedData;
+    try {
+      parsedData = JSON.parse(aData);
+    } catch (ex) {
+      console.error("Malformed EME video message with data: ", aData);
+      return;
+    }
+    const { status } = parsedData;
+    if (status == "is-capture-possible") {
+      // We handle this status in process -- don't send a message to the parent.
+      gGlobalCaptureListener.requestUpdateAndNotify();
+      return;
+    }
+
+    this.sendAsyncMessage("EMEVideo:ContentMediaKeysRequest", aData);
+  }
+}