[DocumentLatency] Use headers end (not start) for server response time

Bug: 448670042
Change-Id: I446e08be9b4aa9f33a490797a360a0f3cccbfc88
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/7004563
Reviewed-by: Paul Irish <[email protected]>
Commit-Queue: Connor Clark <[email protected]>
Auto-Submit: Connor Clark <[email protected]>

Author: Connor Clark

front_end/models/trace/handlers/NetworkRequestsHandler.ts

@@ -448,6 +448,15 @@ export async function finalize(): Promise<void> {
         Types.Timing.Micro((timing.receiveHeadersEnd - timing.sendEnd) * MILLISECONDS_TO_MICROSECONDS) :
         Types.Timing.Micro(0);
 
+    // Server Response Time
+    // =======================
+    // Time from when the send finished going to when the first byte of headers were received.
+    const serverResponseTime = timing ?
+        Types.Timing.Micro(
+            ((timing.receiveHeadersStart ?? timing.receiveHeadersEnd) - timing.sendEnd) *
+            MILLISECONDS_TO_MICROSECONDS) :
+        Types.Timing.Micro(0);
+
     // Download
     // =======================
     // Time from receipt of headers to the finish time.
@@ -513,6 +522,7 @@ export async function finalize(): Promise<void> {
                 stalled,
                 totalTime,
                 waiting,
+                serverResponseTime,
               },
               // All fields below are from TraceEventsForNetworkRequest.
               decodedBodyLength,

front_end/models/trace/insights/DocumentLatency.test.ts

@@ -43,11 +43,11 @@ describeWithEnvironment('DocumentLatency', function() {
     const mainRequestEvent = structuredClone(traceEvents[mainRequestEventIndex]);
     assert(Types.Events.isResourceReceiveResponse(mainRequestEvent));
     assert.strictEqual(mainRequestEvent.args.data.requestId, '1000C0FDC0A75327167272FC7438E999');
-    if (!mainRequestEvent.args.data.timing) {
+    if (!mainRequestEvent.args.data.timing?.receiveHeadersStart) {
       throw new Error('missing timing field');
     }
-    mainRequestEvent.args.data.timing.receiveHeadersEnd =
-        Types.Timing.Milli(mainRequestEvent.args.data.timing.receiveHeadersEnd + 1000);
+    mainRequestEvent.args.data.timing.receiveHeadersStart =
+        Types.Timing.Milli(mainRequestEvent.args.data.timing.receiveHeadersStart + 1000);
     traceEvents[mainRequestEventIndex] = mainRequestEvent;
 
     await processor.parse(traceEvents, {isCPUProfile: false, isFreshRecording: true});
@@ -148,8 +148,8 @@ describeWithEnvironment('DocumentLatency', function() {
         getInsightOrError('DocumentLatency', insights, getFirstOrError(data.Meta.navigationsByNavigationId.values()));
     assert.strictEqual(insight.data?.redirectDuration, 6059);
     assert.strictEqual(insight.data?.uncompressedResponseBytes, 111506);
-    assert.strictEqual(insight.data?.serverResponseTime, 2008);
-    assert.isFalse(insight.data?.checklist.serverResponseIsFast.value);
-    assert.deepEqual(insight.metricSavings, {FCP: 7967, LCP: 7967} as Trace.Insights.Types.MetricSavings);
+    assert.strictEqual(insight.data?.serverResponseTime, 1);
+    assert.isTrue(insight.data?.checklist.serverResponseIsFast.value);
+    assert.deepEqual(insight.metricSavings, {FCP: 6059, LCP: 6059} as Trace.Insights.Types.MetricSavings);
   });
 });

front_end/models/trace/insights/DocumentLatency.ts

@@ -110,7 +110,7 @@ function getServerResponseTime(request: Types.Events.SyntheticNetworkRequest): T
     return null;
   }
 
-  const ms = Helpers.Timing.microToMilli(request.args.data.syntheticData.waiting);
+  const ms = Helpers.Timing.microToMilli(request.args.data.syntheticData.serverResponseTime);
   return Math.round(ms) as Types.Timing.Milli;
 }
 

front_end/models/trace/types/TraceEvents.ts

@@ -363,8 +363,10 @@ interface SyntheticArgsData {
   ssl: Micro;
   stalled: Micro;
   totalTime: Micro;
-  /** Server response time (receiveHeadersEnd - sendEnd) */
+  /** receiveHeadersEnd - sendEnd */
   waiting: Micro;
+  /** receiveHeadersStart - sendEnd */
+  serverResponseTime: Micro;
 }
 
 export interface SyntheticNetworkRequest extends Complete, SyntheticBased<Phase.COMPLETE> {