1 files changed, 81 insertions, 0 deletions
diff --git a/remote/shared/messagehandler/test/browser/resources/modules/windowglobal/eventemitter.sys.mjs b/remote/shared/messagehandler/test/browser/resources/modules/windowglobal/eventemitter.sys.mjs
new file mode 100644
index 0000000000..c86954c5e0
--- /dev/null
+++ b/remote/shared/messagehandler/test/browser/resources/modules/windowglobal/eventemitter.sys.mjs
@@ -0,0 +1,81 @@
+/* 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/. */
+
+import { Module } from "chrome://remote/content/shared/messagehandler/Module.sys.mjs";
+
+class EventEmitterModule extends Module {
+  #isSubscribed;
+  #subscribedEvents;
+
+  constructor(messageHandler) {
+    super(messageHandler);
+    this.#isSubscribed = false;
+    this.#subscribedEvents = new Set();
+  }
+
+  destroy() {}
+
+  /**
+   * Commands
+   */
+
+  emitTestEvent() {
+    if (this.#isSubscribed) {
+      const text = `event from ${this.messageHandler.contextId}`;
+      this.emitEvent("eventemitter.testEvent", { text });
+    }
+
+    // Emit another event consistently for monitoring during the test.
+    this.emitEvent("eventemitter.monitoringEvent", {});
+  }
+
+  isSubscribed() {
+    return this.#isSubscribed;
+  }
+
+  _applySessionData(params) {
+    const { category } = params;
+    if (category === "event") {
+      const filteredSessionData = params.sessionData.filter(item =>
+        this.messageHandler.matchesContext(item.contextDescriptor)
+      );
+      for (const event of this.#subscribedEvents.values()) {
+        const hasSessionItem = filteredSessionData.some(
+          item => item.value === event
+        );
+        // If there are no session items for this context, we should unsubscribe from the event.
+        if (!hasSessionItem) {
+          this.#unsubscribeEvent(event);
+        }
+      }
+
+      // Subscribe to all events, which have an item in SessionData
+      for (const { value } of filteredSessionData) {
+        this.#subscribeEvent(value);
+      }
+    }
+  }
+
+  #subscribeEvent(event) {
+    if (event === "eventemitter.testEvent") {
+      if (this.#isSubscribed) {
+        throw new Error("Already subscribed to eventemitter.testEvent");
+      }
+      this.#isSubscribed = true;
+      this.#subscribedEvents.add(event);
+    }
+  }
+
+  #unsubscribeEvent(event) {
+    if (event === "eventemitter.testEvent") {
+      if (!this.#isSubscribed) {
+        throw new Error("Not subscribed to eventemitter.testEvent");
+      }
+      this.#isSubscribed = false;
+      this.#subscribedEvents.delete(event);
+    }
+  }
+}
+
+export const eventemitter = EventEmitterModule;