lighthouse/core/gather/gatherers/trace.js

Automated auditing, performance metrics, and best practices for the web.

/**
 * @license
 * Copyright 2021 Google LLC
 * SPDX-License-Identifier: Apache-2.0
 */

/**
 * @fileoverview
 * This gatherer collects all network and page devtools protocol traffic during the timespan/navigation.
 * This protocol log can be used to recreate the network records using lib/network-recorder.js.
 */

import BaseGatherer from '../base-gatherer.js';
import {TraceProcessor} from '../../lib/tracehouse/trace-processor.js';

class Trace extends BaseGatherer {
  /** @type {LH.Trace} */
  _trace = {traceEvents: []};

  static getDefaultTraceCategories() {
    return [
      // Exclude default categories. We'll be selective to minimize trace size
      '-*',

      // Used instead of 'toplevel' in Chrome 71+
      'disabled-by-default-lighthouse',

      // Used for Cumulative Layout Shift metric
      'loading',

      // All compile/execute events are captured by parent events in devtools.timeline..
      // But the v8 category provides some nice context for only <0.5% of the trace size
      'v8',
      // Same situation here. This category is there for RunMicrotasks only, but with other teams
      // accidentally excluding microtasks, we don't want to assume a parent event will always exist
      'v8.execute',

      // For extracting UserTiming marks/measures
      'blink.user_timing',

      // Not mandatory but not used much
      'blink.console',

      // Most of the events we need are from these two categories
      'devtools.timeline',
      'disabled-by-default-devtools.timeline',

      // Up to 450 (https://goo.gl/rBfhn4) JPGs added to the trace
      'disabled-by-default-devtools.screenshot',

      // This doesn't add its own events, but adds a `stackTrace` property to devtools.timeline events
      'disabled-by-default-devtools.timeline.stack',

      // Additional categories used by devtools. Not used by Lighthouse, but included to facilitate
      // loading traces from Lighthouse into the Performance panel.
      'disabled-by-default-devtools.timeline.frame',
      'latencyInfo',

      // Enhanced traces.
      'disabled-by-default-devtools.target-rundown',
      'disabled-by-default-devtools.v8-source-rundown-sources',
      'disabled-by-default-devtools.v8-source-rundown',

      // Not used by Lighthouse (yet) but included for users that want JS samples when looking at
      // a trace collected by Lighthouse (e.g. "View Trace" workflow in DevTools)
      // TODO: Re-enable after investigating b/325659693
      // 'disabled-by-default-v8.cpu_profiler',
    ];
  }

  /**
   * @param {LH.Gatherer.ProtocolSession} session
   * @return {Promise<LH.Trace>}
   */
  static async endTraceAndCollectEvents(session) {
    /** @type {Array<LH.TraceEvent>} */
    const traceEvents = [];

    /**
     * Listener for when dataCollected events fire for each trace chunk
     * @param {LH.Crdp.Tracing.DataCollectedEvent} data
     */
    const dataListener = function(data) {
      traceEvents.push(...data.value);
    };
    session.on('Tracing.dataCollected', dataListener);

    return new Promise((resolve, reject) => {
      session.once('Tracing.tracingComplete', _ => {
        session.off('Tracing.dataCollected', dataListener);
        resolve({traceEvents});
      });

      session.sendCommand('Tracing.end').catch(reject);
    });
  }

  static symbol = Symbol('Trace');

  /** @type {LH.Gatherer.GathererMeta} */
  meta = {
    symbol: Trace.symbol,
    supportedModes: ['timespan', 'navigation'],
  };

  /**
   * @param {LH.Gatherer.Context} passContext
   */
  async startSensitiveInstrumentation({driver, gatherMode, settings}) {
    const traceCategories = Trace.getDefaultTraceCategories()
      .concat(settings.additionalTraceCategories || []);
    await driver.defaultSession.sendCommand('Page.enable');
    await driver.defaultSession.sendCommand('Tracing.start', {
      categories: traceCategories.join(','),
      options: 'sampling-frequency=10000', // 1000 is default and too slow.
    });

    if (gatherMode === 'timespan') {
      await driver.defaultSession.sendCommand('Tracing.recordClockSyncMarker',
        {syncId: TraceProcessor.TIMESPAN_MARKER_ID});
    }
  }

  /**
   * @param {LH.Gatherer.Context} passContext
   */
  async stopSensitiveInstrumentation({driver}) {
    this._trace = await Trace.endTraceAndCollectEvents(driver.defaultSession);
  }

  getDebugData() {
    return this._trace;
  }

  getArtifact() {
    return this._trace;
  }
}

export default Trace;