fix: Remove synchronous operation with file system. (#879)

This patch:
- introduces `helper.promisify` - a simple polyfill for the `util.promisify`. The 
  `util.promisify` could not be used due to Node6 compatibility issues.
- migrates all sync filesystem operations to the async replicas

Fixes #884.

lib/Launcher.js

@@ -15,7 +15,7 @@
  */
 const os = require('os');
 const path = require('path');
-const removeSync = require('rimraf').sync;
+const removeFolder = require('rimraf');
 const childProcess = require('child_process');
 const Downloader = require('../utils/ChromiumDownloader');
 const {Connection} = require('./Connection');
@@ -26,6 +26,9 @@ const {helper} = require('./helper');
 // @ts-ignore
 const ChromiumRevision = require('../package.json').puppeteer.chromium_revision;
 
+const mkdtempAsync = helper.promisify(fs.mkdtemp);
+const removeFolderAsync = helper.promisify(removeFolder);
+
 const CHROME_PROFILE_PATH = path.join(os.tmpdir(), 'puppeteer_dev_profile-');
 
 const DEFAULT_ARGS = [
@@ -69,7 +72,7 @@ class Launcher {
 
     if (!options.args || !options.args.some(arg => arg.startsWith('--user-data-dir'))) {
       if (!options.userDataDir)
-        temporaryUserDataDir = fs.mkdtempSync(CHROME_PROFILE_PATH);
+        temporaryUserDataDir = await mkdtempAsync(CHROME_PROFILE_PATH);
 
       chromeArguments.push(`--user-data-dir=${options.userDataDir || temporaryUserDataDir}`);
     }
@@ -107,12 +110,16 @@ class Launcher {
       chromeProcess.stderr.pipe(process.stderr);
     }
 
-    const waitForChromeToClose = new Promise(fulfill => {
+    const waitForChromeToClose = new Promise((fulfill, reject) => {
       chromeProcess.once('close', () => {
         // Cleanup as processes exit.
-        if (temporaryUserDataDir)
+        if (temporaryUserDataDir) {
-          removeSync(temporaryUserDataDir);
+          removeFolderAsync(temporaryUserDataDir)
+              .then(() => fulfill())
+              .catch(err => console.error(err));
+        } else {
           fulfill();
+        }
       });
     });
 
@@ -153,7 +160,7 @@ class Launcher {
       if (temporaryUserDataDir) {
         // Attempt to remove temporary profile directory to avoid littering.
         try {
-          removeSync(temporaryUserDataDir);
+          removeFolder.sync(temporaryUserDataDir);
         } catch (e) { }
       }
       return waitForChromeToClose;

lib/Page.js

@@ -26,6 +26,8 @@ const {Keyboard, Mouse, Touchscreen} = require('./Input');
 const Tracing = require('./Tracing');
 const {helper, debugError} = require('./helper');
 
+const writeFileAsync = helper.promisify(fs.writeFile);
+
 class Page extends EventEmitter {
   /**
    * @param {!Puppeteer.Session} client
@@ -655,7 +657,7 @@ class Page extends EventEmitter {
 
     const buffer = new Buffer(result.data, 'base64');
     if (options.path)
-      fs.writeFileSync(options.path, buffer);
+      await writeFileAsync(options.path, buffer);
     return buffer;
   }
 
@@ -703,7 +705,7 @@ class Page extends EventEmitter {
     });
     const buffer = new Buffer(result.data, 'base64');
     if (options.path)
-      fs.writeFileSync(options.path, buffer);
+      await writeFileAsync(options.path, buffer);
     return buffer;
   }
 

lib/Tracing.js

@@ -13,8 +13,12 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-const fs = require('fs');
 const {helper} = require('./helper');
+const fs = require('fs');
+
+const openAsync = helper.promisify(fs.open);
+const writeAsync = helper.promisify(fs.write);
+const closeAsync = helper.promisify(fs.close);
 
 class Tracing {
   /**
@@ -68,14 +72,14 @@ class Tracing {
    */
   async _readStream(handle, path) {
     let eof = false;
-    const file = fs.openSync(path, 'w');
+    const file = await openAsync(path, 'w');
     while (!eof) {
       const response = await this._client.send('IO.read', {handle});
       eof = response.eof;
       if (path)
-        fs.writeSync(file, response.data);
+        await writeAsync(file, response.data);
     }
-    fs.closeSync(file);
+    await closeAsync(file);
     await this._client.send('IO.close', {handle});
   }
 }

lib/helper.js

@@ -209,6 +209,22 @@ class Helper {
   static isNumber(obj) {
     return typeof obj === 'number' || obj instanceof Number;
   }
+
+  static promisify(nodeFunction) {
+    function promisified(...args) {
+      return new Promise((resolve, reject) => {
+        function callback(err, ...result) {
+          if (err)
+            return reject(err);
+          if (result.length === 1)
+            return resolve(result[0]);
+          return resolve(result);
+        }
+        nodeFunction.call(null, ...args, callback);
+      });
+    }
+    return promisified;
+  }
 }
 
 module.exports = {