Bug 1843606 - Add test api that can make use of the dev tools network throttler r=necko-reviewers,jdescottes,kershaw

To create network tests that capture various codepaths and optimizations we need to fix network particulars such as latency and bandwidth.
This module provides access to the dev tools throttler for use in browsertime pageload tests.

Differential Revision: https://phabricator.services.mozilla.com/D183618

netwerk/test/moz.build

@@ -18,6 +18,10 @@ XPCSHELL_TESTS_MANIFESTS += [
     "unit_ipc/xpcshell.ini",
 ]
 
+EXTRA_JS_MODULES["netwerk-perf"] += [
+    "perf/NetworkThrottlingUtils.sys.mjs",
+]
+
 TESTING_JS_MODULES += [
     "browser/cookie_filtering_helper.sys.mjs",
     "browser/early_hint_preload_test_helper.sys.mjs",

netwerk/test/perf/NetworkThrottlingUtils.sys.mjs

@@ -0,0 +1,106 @@
+/* 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, {
+  NetworkObserver:
+    "resource://devtools/shared/network-observer/NetworkObserver.sys.mjs",
+});
+
+/**
+ * The NetworkThrottler uses the dev tools NetworkObserver to provide api to throttle all network activity.
+ *
+ * This can be used to fix network conditions in browsertime pageload tests, e.g.
+ *
+ * const script = `
+ *             var {NetworkThrottler} = ChromeUtils.importESModule("resource://gre/modules/netwerk-perf/NetworkThrottlingUtils.sys.mjs");
+ *
+ *             let networkThrottler = new NetworkThrottler();
+ *
+ *             let throttleData = {
+ *               latencyMean: 200,
+ *               latencyMax: 200,
+ *               downloadBPSMean: 125000,
+ *               downloadBPSMax: 125000,
+ *               uploadBPSMean: 125000,
+ *               uploadBPSMax: 125000
+ *             };
+ *             networkThrottler.start(throttleData);
+ *
+ *             ... run throttled tests ...
+ *
+ *             networkThrottler.stop();
+ *   `;
+ *   commands.js.runPrivileged(script);
+ *
+ */
+
+// A minimal struct for onNetworkEvent handling
+class NetworkEventRecord {
+  addRequestPostData() {}
+  addResponseStart() {}
+  addSecurityInfo() {}
+  addEventTimings() {}
+  addResponseCache() {}
+  addResponseContent() {}
+  addServerTimings() {}
+}
+
+export class NetworkThrottler {
+  #devtoolsNetworkObserver;
+  #throttling;
+
+  constructor() {
+    this.#throttling = false;
+  }
+
+  destroy() {
+    this.stop();
+  }
+
+  start(throttleData) {
+    if (this.#throttling) {
+      console.error("NetworkThrottler already started");
+      return;
+    }
+
+    this.#devtoolsNetworkObserver = new lazy.NetworkObserver({
+      ignoreChannelFunction: this.#ignoreChannelFunction,
+      onNetworkEvent: this.#onNetworkEvent,
+    });
+
+    this.#devtoolsNetworkObserver.setThrottleData(throttleData);
+
+    this.#throttling = true;
+  }
+
+  stop() {
+    if (!this.#throttling) {
+      return;
+    }
+
+    this.#devtoolsNetworkObserver.destroy();
+    this.#devtoolsNetworkObserver = null;
+
+    this.#throttling = false;
+  }
+
+  #ignoreChannelFunction = channel => {
+    // Ignore chrome-privileged or DevTools-initiated requests
+    if (
+      channel.loadInfo?.loadingDocument === null &&
+      (channel.loadInfo.loadingPrincipal ===
+        Services.scriptSecurityManager.getSystemPrincipal() ||
+        channel.loadInfo.isInDevToolsContext)
+    ) {
+      return true;
+    }
+    return false;
+  };
+
+  #onNetworkEvent = (networkEvent, channel) => {
+    return new NetworkEventRecord(networkEvent, channel, this);
+  };
+}

tools/esmify/map.json

@@ -852,6 +852,7 @@
   "resource://gre/modules/narrate/Narrator.jsm": "toolkit/components/narrate/Narrator.jsm",
   "resource://gre/modules/narrate/VoiceSelect.jsm": "toolkit/components/narrate/VoiceSelect.jsm",
   "resource://gre/modules/netwerk-dns/PublicSuffixList.jsm": "netwerk/dns/PublicSuffixList.jsm",
+  "resource://gre/modules/netwerk-perf/NetworkThrottlingUtils.jsm": "netwerk/test/perf/NetworkThrottlingUtils.jsm",
   "resource://gre/modules/nsAsyncShutdown.jsm": "toolkit/components/asyncshutdown/nsAsyncShutdown.jsm",
   "resource://gre/modules/nsCrashMonitor.jsm": "toolkit/components/crashmonitor/nsCrashMonitor.jsm",
   "resource://gre/modules/nsFormAutoCompleteResult.jsm": "toolkit/components/satchel/nsFormAutoCompleteResult.jsm",