1 files changed, 85 insertions, 0 deletions
diff --git a/remote/shared/listeners/ContextualIdentityListener.sys.mjs b/remote/shared/listeners/ContextualIdentityListener.sys.mjs
new file mode 100644
index 0000000000..d93b44ed77
--- /dev/null
+++ b/remote/shared/listeners/ContextualIdentityListener.sys.mjs
@@ -0,0 +1,85 @@
+/* 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/. */
+
+const lazy = {};
+
+ChromeUtils.defineESModuleGetters(lazy, {
+  EventEmitter: "resource://gre/modules/EventEmitter.sys.mjs",
+});
+
+const OBSERVER_TOPIC_CREATED = "contextual-identity-created";
+const OBSERVER_TOPIC_DELETED = "contextual-identity-deleted";
+
+/**
+ * The ContextualIdentityListener can be used to listen for notifications about
+ * contextual identities (containers) being created or deleted.
+ *
+ * Example:
+ * ```
+ * const listener = new ContextualIdentityListener();
+ * listener.on("created", onCreated);
+ * listener.startListening();
+ *
+ * const onCreated = (eventName, data = {}) => {
+ *   const { identity } = data;
+ *   ...
+ * };
+ * ```
+ *
+ * @fires message
+ *    The ContextualIdentityListener emits "created" and "deleted" events,
+ *    with the following object as payload:
+ *      - {object} identity
+ *            The contextual identity which was created or deleted.
+ */
+export class ContextualIdentityListener {
+  #listening;
+
+  /**
+   * Create a new BrowsingContextListener instance.
+   */
+  constructor() {
+    lazy.EventEmitter.decorate(this);
+
+    this.#listening = false;
+  }
+
+  destroy() {
+    this.stopListening();
+  }
+
+  observe(subject, topic, data) {
+    switch (topic) {
+      case OBSERVER_TOPIC_CREATED:
+        this.emit("created", { identity: subject.wrappedJSObject });
+        break;
+
+      case OBSERVER_TOPIC_DELETED:
+        this.emit("deleted", { identity: subject.wrappedJSObject });
+        break;
+    }
+  }
+
+  startListening() {
+    if (this.#listening) {
+      return;
+    }
+
+    Services.obs.addObserver(this, OBSERVER_TOPIC_CREATED);
+    Services.obs.addObserver(this, OBSERVER_TOPIC_DELETED);
+
+    this.#listening = true;
+  }
+
+  stopListening() {
+    if (!this.#listening) {
+      return;
+    }
+
+    Services.obs.removeObserver(this, OBSERVER_TOPIC_CREATED);
+    Services.obs.removeObserver(this, OBSERVER_TOPIC_DELETED);
+
+    this.#listening = false;
+  }
+}