# all files / lighthouse-core/audits/ user-timings.js

97.56% Statements 40/41
93.94% Branches 31/33
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     /**
     * @license
     * Copyright 2016 Google Inc. All rights reserved.
     *
     * Licensed under the Apache License, Version 2.0 (the "License");
     * you may not use this file except in compliance with the License.
     * You may obtain a copy of the License at
     *
     *     http://www.apache.org/licenses/LICENSE-2.0
     *
     * Unless required by applicable law or agreed to in writing, software
     * distributed under the License is distributed on an "AS IS" BASIS,
     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     * See the License for the specific language governing permissions and
     * limitations under the License.
     */

    'use strict';

    const Audit = require('./audit');
    const Formatter = require('../formatters/formatter');
    const TimelineModel = require('../lib/traces/devtools-timeline-model');

    const FAILURE_MESSAGE = 'Trace data not found.';

    /**
     * @param {!Array<!Object>} traceData
     * @return {!Array<!UserTimingsExtendedInfo>}
     */
    function filterTrace(traceData) {
      const userTimings = [];
      const measuresStartTimes = {};
      let traceStartFound = false;
      let navigationStartTime;

      // Fetch blink.user_timing events from the tracing data
      const timelineModel = new TimelineModel(traceData);
      const modeledTraceData = timelineModel.timelineModel();

      // Get all blink.user_timing events
      // The event phases we are interested in are mark and instant events (R, i, I)
      // and duration events which correspond to measures (B, b, E, e).
      // @see https://docs.google.com/document/d/1CvAClvFfyA5R-PhYUmn5OOQtYMH4h6I0nSsKchNAySU/preview#
      modeledTraceData.mainThreadEvents()
      .filter(ut => {
        if (ut.name === 'TracingStartedInPage' || ut.name === 'navigationStart') {
          return true;
        }

        Eif (ut.hasCategory('blink.user_timing')) {
          // reject these "userTiming" events that aren't really UserTiming, by nuking ones with frame data (or requestStart)
          // https://cs.chromium.org/search/?q=trace_event.*?user_timing&sq=package:chromium&type=cs
          return !(ut.name === 'requestStart' || ut.args.frame !== undefined);
        }

        return false;
      })
      .forEach(ut => {
        // Mark events fall under phases R and I (or i)
        if (ut.phase === 'R' || ut.phase.toUpperCase() === 'I') {
          // We only care about trace events that have to do with the page
          // Sometimes other frames can show up in the frame beforehand
          if (ut.name === 'TracingStartedInPage' && !traceStartFound) {
            traceStartFound = true;
            return;
          }

          // Once TraceingStartedInPage has begun, the next navigationStart event
          // marks the start of navigation
          // Make sure to not record such events hereafter
          if (ut.name === 'navigationStart' && traceStartFound && !navigationStartTime) {
            navigationStartTime = ut.startTime;
          }

          // Add user timings event to array
          if (ut.name !== 'navigationStart') {
            userTimings.push({
              name: ut.name,
              isMark: true,        // defines type of performance metric
              args: ut.args,
              startTime: ut.startTime
            });
          }
        } else if (ut.phase.toLowerCase() === 'b') {
          // Beginning of measure event, keep track of this events start time
          measuresStartTimes[ut.name] = ut.startTime;
        } else Eif (ut.phase.toLowerCase() === 'e') {
          // End of measure event
          // Add to the array of events
          userTimings.push({
            name: ut.name,
            isMark: false,
            args: ut.args,
            startTime: measuresStartTimes[ut.name],
            duration: ut.startTime - measuresStartTimes[ut.name],
            endTime: ut.startTime
          });
        }
      });

      userTimings.forEach(ut => {
        ut.startTime -= navigationStartTime;
        if (!ut.isMark) {
          ut.endTime -= navigationStartTime;
          ut.duration = ut.duration;
        }
      });

      return userTimings;
    }

    class UserTimings extends Audit {
      /**
       * @return {!AuditMeta}
       */
      static get meta() {
        return {
          category: 'Performance',
          name: 'user-timings',
          description: 'User Timing marks and measures',
          requiredArtifacts: ['traceContents']
        };
      }

      /**
       * @param {!Artifacts} artifacts
       * @return {!AuditResult}
       */
      static audit(artifacts) {
        if (!artifacts.traceContents || !Array.isArray(artifacts.traceContents)) {
          return UserTimings.generateAuditResult({
            value: -1,
            debugString: FAILURE_MESSAGE
          });
        }

        const userTimings = filterTrace(artifacts.traceContents);

        return UserTimings.generateAuditResult({
          value: userTimings.length,
          extendedInfo: {
            formatter: Formatter.SUPPORTED_FORMATS.USER_TIMINGS,
            value: userTimings
          }
        });
      }
    }

    module.exports = UserTimings;