1 files changed, 63 insertions, 0 deletions
diff --git a/devtools/server/actors/resources/tracing-state.js b/devtools/server/actors/resources/tracing-state.js
new file mode 100644
index 0000000000..7a11a85ff8
--- /dev/null
+++ b/devtools/server/actors/resources/tracing-state.js
@@ -0,0 +1,63 @@
+/* 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/. */
+
+"use strict";
+
+const {
+  TYPES: { TRACING_STATE },
+} = require("resource://devtools/server/actors/resources/index.js");
+
+// Bug 1827382, as this module can be used from the worker thread,
+// the following JSM may be loaded by the worker loader until
+// we have proper support for ESM from workers.
+const {
+  addTracingListener,
+  removeTracingListener,
+} = require("resource://devtools/server/tracer/tracer.jsm");
+
+class TracingStateWatcher {
+  /**
+   * Start watching for tracing state changes for a given target actor.
+   *
+   * @param TargetActor targetActor
+   *        The target actor from which we should observe
+   * @param Object options
+   *        Dictionary object with following attributes:
+   *        - onAvailable: mandatory function
+   *          This will be called for each resource.
+   */
+  async watch(targetActor, { onAvailable }) {
+    this.targetActor = targetActor;
+    this.onAvailable = onAvailable;
+
+    this.tracingListener = {
+      onTracingToggled: this.onTracingToggled.bind(this),
+    };
+    addTracingListener(this.tracingListener);
+  }
+
+  /**
+   * Stop watching for tracing state
+   */
+  destroy() {
+    removeTracingListener(this.tracingListener);
+  }
+
+  // Emit a TRACING_STATE resource with:
+  //   enabled = true|false
+  // When Javascript tracing is enabled or disabled.
+  onTracingToggled(enabled) {
+    const tracerActor = this.targetActor.getTargetScopedActor("tracer");
+    const logMethod = tracerActor?.getLogMethod() | "stdout";
+    this.onAvailable([
+      {
+        resourceType: TRACING_STATE,
+        enabled,
+        logMethod,
+      },
+    ]);
+  }
+}
+
+module.exports = TracingStateWatcher;