fix(wpt): apply devtools factors to network (#5)

Author: justinribeiro

src/chrome.js

@@ -4,56 +4,94 @@ const chromeLauncher = require('chrome-launcher');
 const puppeteer = require('puppeteer-core');
 const lighthouse = require('lighthouse');
 
-// via WebPageTest settings
-// WPO-Foundation/webpagetest/blob/master/www/settings/connectivity.ini.sample
-//
-// These are divided by 8 because we need bytes/s for Chrome
-//
+/**
+ * Adjustments needed for DevTools network throttling to simulate
+ * more realistic network conditions, per Lighthouse:
+ * https://github.com/GoogleChrome/lighthouse/blob/6e5fc878f8cc69e00620b20092bfad1da6c1e4e2/lighthouse-core/config/constants.js#L8-L15
+ *
+ * @see https://crbug.com/721112
+ * @see https://docs.google.com/document/d/10lfVdS1iDWCRKQXPfbxEn4Or99D64mvNlugP1AQuFlE/edit
+ *
+ * Cheers @patrickhulce for the heads up! :-)
+ */
+const DEVTOOLS_RTT_ADJUSTMENT_FACTOR = 3.75;
+const DEVTOOLS_THROUGHPUT_ADJUSTMENT_FACTOR = 0.9;
+
+// Per https://chromium.googlesource.com/chromium/src/+/8a4e4200086bc67a61c83d60edfb450844377e5a/third_party/WebKit/Source/devtools/front_end/network_conditions/NetworkConditionsSelector.js#222
+const CHROME_SLOW_RTT_ADJUSTMENT_FACTOR = 5;
+const CHROME_SLOW_THROUGHPUT_ADJUSTMENT_FACTOR = 0.8;
+
+/**
+ * via WebPageTest settings
+ * https://github.com/WPO-Foundation/webpagetest/blob/master/www/settings/connectivity.ini.sample
+ */
 const NETWORK = {
   edge: {
     offline: false,
     latency: 840,
-    downloadThroughput: Math.floor(240000 / 8),
-    uploadThroughput: Math.floor(240000 / 8),
+    downloadThroughput: 240000,
+    uploadThroughput: 240000,
+    rttAdjustFactor: CHROME_SLOW_RTT_ADJUSTMENT_FACTOR,
+    throughputAdjustment: CHROME_SLOW_THROUGHPUT_ADJUSTMENT_FACTOR,
   },
   twog: {
     offline: false,
     latency: 800,
-    downloadThroughput: Math.floor(280000 / 8),
-    uploadThroughput: Math.floor(256000 / 8),
+    downloadThroughput: 280000,
+    uploadThroughput: 256000,
+    rttAdjustFactor: CHROME_SLOW_RTT_ADJUSTMENT_FACTOR,
+    throughputAdjustment: CHROME_SLOW_THROUGHPUT_ADJUSTMENT_FACTOR,
   },
   threegslow: {
     offline: false,
     latency: 400,
-    downloadThroughput: Math.floor(400000 / 8),
-    uploadThroughput: Math.floor(400000 / 8),
+    downloadThroughput: 400000,
+    uploadThroughput: 400000,
+    rttAdjustFactor: CHROME_SLOW_RTT_ADJUSTMENT_FACTOR,
+    throughputAdjustment: CHROME_SLOW_THROUGHPUT_ADJUSTMENT_FACTOR,
   },
   threeg: {
     offline: false,
     latency: 300,
-    downloadThroughput: Math.floor(1600000 / 8),
-    uploadThroughput: Math.floor(768000 / 8),
+    downloadThroughput: 1600000,
+    uploadThroughput: 768000,
+    rttAdjustFactor: DEVTOOLS_RTT_ADJUSTMENT_FACTOR,
+    throughputAdjustment: DEVTOOLS_THROUGHPUT_ADJUSTMENT_FACTOR,
   },
   threegfast: {
     offline: false,
     latency: 170,
-    downloadThroughput: Math.floor(1600000 / 8),
-    uploadThroughput: Math.floor(768000 / 8),
+    downloadThroughput: 1600000,
+    uploadThroughput: 768000,
+    rttAdjustFactor: DEVTOOLS_RTT_ADJUSTMENT_FACTOR,
+    throughputAdjustment: DEVTOOLS_THROUGHPUT_ADJUSTMENT_FACTOR,
   },
   fourg: {
     offline: false,
     latency: 170,
-    downloadThroughput: Math.floor(9000000 / 8),
-    uploadThroughput: Math.floor(9000000 / 8),
+    downloadThroughput: 9000000,
+    uploadThroughput: 9000000,
+    rttAdjustFactor: DEVTOOLS_RTT_ADJUSTMENT_FACTOR,
+    throughputAdjustment: DEVTOOLS_THROUGHPUT_ADJUSTMENT_FACTOR,
   },
   lte: {
     offline: false,
     latency: 70,
-    downloadThroughput: Math.floor(12000000 / 8),
-    uploadThroughput: Math.floor(12000000 / 8),
+    downloadThroughput: 12000000,
+    uploadThroughput: 12000000,
+    rttAdjustFactor: DEVTOOLS_RTT_ADJUSTMENT_FACTOR,
+    throughputAdjustment: DEVTOOLS_THROUGHPUT_ADJUSTMENT_FACTOR,
   },
 };
 
+function withDevToolsThroughputAdjustment(bits, factor) {
+  return Math.floor((bits / 8) * factor);
+}
+
+function withDevToolsRttAdjustment(ms, factor) {
+  return ms * factor;
+}
+
 /**
  * launch Chrome via Puppeteer, use puppeteer to throttle connection, run
  * lighthouse. Not ideal; would prefer adv throttle via comcast os level util
@@ -85,10 +123,21 @@ async function launchChromeAndRunLighthouse(url, opts, config) {
           console.log(
             `CDP: network conditions set to WPT ${opts.connection} profile.`,
           );
-          return client.send(
-            'Network.emulateNetworkConditions',
-            NETWORK[opts.connection],
-          );
+          return client.send('Network.emulateNetworkConditions', {
+            offline: NETWORK[opts.connection].offline,
+            latency: withDevToolsRttAdjustment(
+              NETWORK[opts.connection].latency,
+              NETWORK[opts.connection].rttAdjustFactor,
+            ),
+            downloadThroughput: withDevToolsThroughputAdjustment(
+              NETWORK[opts.connection].downloadThroughput,
+              NETWORK[opts.connection].throughputAdjustment,
+            ),
+            uploadThroughput: withDevToolsThroughputAdjustment(
+              NETWORK[opts.connection].uploadThroughput,
+              NETWORK[opts.connection].throughputAdjustment,
+            ),
+          });
         })
         .catch(err => console.error(err));
     } else {