Tracing.ts

/**
 * Copyright 2017 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.
 */
import { assert } from './assert.js';
import { helper } from './helper.js';
import { CDPSession } from './Connection.js';

/**
 * @public
 */
export interface TracingOptions {
  path?: string;
  screenshots?: boolean;
  categories?: string[];
}

/**
 * The Tracing class exposes the tracing audit interface.
 * @remarks
 * You can use `tracing.start` and `tracing.stop` to create a trace file
 * which can be opened in Chrome DevTools or {@link https://chromedevtools.github.io/timeline-viewer/ | timeline viewer}.
 *
 * @example
 * ```js
 * await page.tracing.start({path: 'trace.json'});
 * await page.goto('https://www.google.com');
 * await page.tracing.stop();
 * ```
 *
 * @public
 */
export class Tracing {
  _client: CDPSession;
  _recording = false;
  _path = '';

  /**
   * @internal
   */
  constructor(client: CDPSession) {
    this._client = client;
  }

  /**
   * Starts a trace for the current page.
   * @remarks
   * Only one trace can be active at a time per browser.
   * @param options - Optional `TracingOptions`.
   */
  async start(options: TracingOptions = {}): Promise<void> {
    assert(
      !this._recording,
      'Cannot start recording trace while already recording trace.'
    );

    const defaultCategories = [
      '-*',
      'devtools.timeline',
      'v8.execute',
      'disabled-by-default-devtools.timeline',
      'disabled-by-default-devtools.timeline.frame',
      'toplevel',
      'blink.console',
      'blink.user_timing',
      'latencyInfo',
      'disabled-by-default-devtools.timeline.stack',
      'disabled-by-default-v8.cpu_profiler',
      'disabled-by-default-v8.cpu_profiler.hires',
    ];
    const {
      path = null,
      screenshots = false,
      categories = defaultCategories,
    } = options;

    if (screenshots) categories.push('disabled-by-default-devtools.screenshot');

    this._path = path;
    this._recording = true;
    await this._client.send('Tracing.start', {
      transferMode: 'ReturnAsStream',
      categories: categories.join(','),
    });
  }

  /**
   * Stops a trace started with the `start` method.
   * @returns Promise which resolves to buffer with trace data.
   */
  async stop(): Promise<Buffer> {
    let fulfill: (value: Buffer) => void;
    let reject: (err: Error) => void;
    const contentPromise = new Promise<Buffer>((x, y) => {
      fulfill = x;
      reject = y;
    });
    this._client.once('Tracing.tracingComplete', (event) => {
      helper
        .readProtocolStream(this._client, event.stream, this._path)
        .then(fulfill, reject);
    });
    await this._client.send('Tracing.end');
    this._recording = false;
    return contentPromise;
  }
}