feat: Implement JavaScript Coverage (#1673)

This patch introduces a new `page.coverage` namespace with two methods:
- `page.coverage.startJSCoverage` to initiate JavaScript coverage
  recording
- `page.coverage.stopJSCoverage` to stop JavaScript coverage and get
  results

lib/Coverage.js

@@ -0,0 +1,178 @@
+/**
+ * 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.
+ */
+
+const {helper, debugError} = require('./helper');
+
+class Coverage {
+  /**
+   * @param {!Puppeteer.Session} client
+   */
+  constructor(client) {
+    this._jsCoverage = new JSCoverage(client);
+  }
+
+  /**
+   * @param {!Object} options
+   */
+  async startJSCoverage(options) {
+    return await this._jsCoverage.start(options);
+  }
+
+  async stopJSCoverage() {
+    return await this._jsCoverage.stop();
+  }
+}
+
+module.exports = {Coverage};
+helper.tracePublicAPI(Coverage);
+
+class JSCoverage {
+  /**
+   * @param {!Puppeteer.Session} client
+   */
+  constructor(client) {
+    this._client = client;
+    this._enabled = false;
+    this._scriptURLs = new Map();
+    this._scriptSources = new Map();
+    this._eventListeners = [];
+    this._resetOnNavigation = false;
+  }
+
+  /**
+   * @param {!Object} options
+   */
+  async start(options = {}) {
+    console.assert(!this._enabled, 'JSCoverage is already enabled');
+    this._resetOnNavigation = options.resetOnNavigation === undefined ? true : !!options.resetOnNavigation;
+    this._enabled = true;
+    this._scriptURLs.clear();
+    this._scriptSources.clear();
+    this._eventListeners = [
+      helper.addEventListener(this._client, 'Debugger.scriptParsed', this._onScriptParsed.bind(this)),
+      helper.addEventListener(this._client, 'Runtime.executionContextsCleared', this._onExecutionContextsCleared.bind(this)),
+    ];
+    await Promise.all([
+      this._client.send('Profiler.enable'),
+      this._client.send('Profiler.startPreciseCoverage', {callCount: false, detailed: true}),
+      this._client.send('Debugger.enable'),
+      this._client.send('Debugger.setSkipAllPauses', {skip: true})
+    ]);
+  }
+
+  _onExecutionContextsCleared() {
+    if (!this._resetOnNavigation)
+      return;
+    this._scriptURLs.clear();
+    this._scriptSources.clear();
+  }
+
+  /**
+   * @param {!Object} event
+   */
+  async _onScriptParsed(event) {
+    // Ignore anonymous scripts
+    if (!event.url)
+      return;
+    try {
+      const response = await this._client.send('Debugger.getScriptSource', {scriptId: event.scriptId});
+      this._scriptURLs.set(event.scriptId, event.url);
+      this._scriptSources.set(event.scriptId, response.scriptSource);
+    } catch (e) {
+      // This might happen if the page has already navigated away.
+      debugError(e);
+    }
+  }
+
+  /**
+   * @return {!Promise<!Array<!{url:string, text:string, ranges:!Array<!{start:number, end:number}>}>>}
+   */
+  async stop() {
+    console.assert(this._enabled, 'JSCoverage is not enabled');
+    this._enabled = false;
+    const [profileResponse] = await Promise.all([
+      this._client.send('Profiler.takePreciseCoverage'),
+      this._client.send('Profiler.stopPreciseCoverage'),
+      this._client.send('Profiler.disable'),
+      this._client.send('Debugger.disable'),
+    ]);
+    helper.removeEventListeners(this._eventListeners);
+
+    const coverage = [];
+    for (const entry of profileResponse.result) {
+      const url = this._scriptURLs.get(entry.scriptId);
+      const text = this._scriptSources.get(entry.scriptId);
+      if (text === undefined || url === undefined)
+        continue;
+      const flattenRanges = [];
+      for (const func of entry.functions)
+        flattenRanges.push(...func.ranges);
+      const ranges = convertToDisjointRanges(flattenRanges);
+      coverage.push({url, ranges, text});
+    }
+    return coverage;
+  }
+}
+
+/**
+ * @param {!Array<!{startOffset:number, endOffset:number, count:number}>} nestedRanges
+ * @return {!Array<!{start:number, end:number}>}
+ */
+function convertToDisjointRanges(nestedRanges) {
+  const points = [];
+  for (const range of nestedRanges) {
+    points.push({ offset: range.startOffset, type: 0, range });
+    points.push({ offset: range.endOffset, type: 1, range });
+  }
+  // Sort points to form a valid parenthesis sequence.
+  points.sort((a, b) => {
+    // Sort with increasing offsets.
+    if (a.offset !== b.offset)
+      return a.offset - b.offset;
+    // All "end" points should go before "start" points.
+    if (a.type !== b.type)
+      return b.type - a.type;
+    const aLength = a.range.endOffset - a.range.startOffset;
+    const bLength = b.range.endOffset - b.range.startOffset;
+    // For two "start" points, the one with longer range goes first.
+    if (a.type === 0)
+      return bLength - aLength;
+    // For two "end" points, the one with shorter range goes first.
+    return aLength - bLength;
+  });
+
+  const hitCountStack = [];
+  const results = [];
+  let lastOffset = 0;
+  // Run scanning line to intersect all ranges.
+  for (const point of points) {
+    if (hitCountStack.length && lastOffset < point.offset && hitCountStack[hitCountStack.length - 1] > 0) {
+      const lastResult = results.length ? results[results.length - 1] : null;
+      if (lastResult && lastResult.end === lastOffset)
+        lastResult.end = point.offset;
+      else
+        results.push({start: lastOffset, end: point.offset});
+    }
+    lastOffset = point.offset;
+    if (point.type === 0)
+      hitCountStack.push(point.range.count);
+    else
+      hitCountStack.pop();
+  }
+  // Filter out empty ranges.
+  return results.filter(range => range.end - range.start > 1);
+}
+

lib/Page.js

@@ -25,6 +25,7 @@ const {FrameManager} = require('./FrameManager');
 const {Keyboard, Mouse, Touchscreen} = require('./Input');
 const Tracing = require('./Tracing');
 const {helper, debugError} = require('./helper');
+const {Coverage} = require('./Coverage');
 
 const writeFileAsync = helper.promisify(fs.writeFile);
 
@@ -77,6 +78,7 @@ class Page extends EventEmitter {
     /** @type {!Map<string, Function>} */
     this._pageBindings = new Map();
     this._ignoreHTTPSErrors = ignoreHTTPSErrors;
+    this._coverage = new Coverage(client);
 
     this._screenshotTaskQueue = screenshotTaskQueue;
 
@@ -123,6 +125,13 @@ class Page extends EventEmitter {
     return this._touchscreen;
   }
 
+  /**
+   * @return {!Coverage}
+   */
+  get coverage() {
+    return this._coverage;
+  }
+
   /**
    * @param {string} selector
    */