Issue 4231 - Fix unstable FilterEngineTest.testSetRemoveFilterChangeCallback

libadblockplus-android/src/org/adblockplus/libadblockplus/FileSystemUtils.java

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2017 eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
  */
 
 package org.adblockplus.libadblockplus;
 
 import java.io.File;
-import java.io.FileNotFoundException;
+import java.io.FileInputStream;
 import java.io.FileOutputStream;
 import java.io.IOException;
-import java.util.NoSuchElementException;
-import java.util.Scanner;
+import java.io.InputStream;
 import java.util.UUID;
 
 public class FileSystemUtils
 {
+
+  private static byte[] readStream(InputStream inputStream, int length) throws IOException
+  {
+    byte[] data = new byte[length];
+    int bytesRead, totalBytesRead = 0;
+    while ((bytesRead = inputStream.read(data, totalBytesRead, length - totalBytesRead)) > 0)
+    {
+      totalBytesRead += bytesRead;
+    }
+    return data;
+  }
+
+  /**
+   * Convert java signed int to byte
+   * @param b int representation of byte
+   * @return byte representation of byte
+   */
+  public static byte byteFromInt(int b)
+  {
+    return (byte)(b & 0xFF);
+  }
+
   /**
    * Read all the file data to string
    *
    * @param file path to read data
    * @return file data
-   * @throws java.io.FileNotFoundException
+   * @throws java.io.IOException
    */
-  public static String readFile(File file) throws FileNotFoundException
+  public static byte[] readFile(File file) throws IOException
   {
-    Scanner scanner = null;
+    FileInputStream fileInputStream = new FileInputStream(file);
     try
     {
-      scanner = new Scanner(file);
-      return scanner.useDelimiter("\\A").next();

[sergei, 2017/05/22 12:09:07]

I'm not sure that it's the best way to read files in java at least I don't see
any reason to parse it here and use any delimiter. What if \a will be a valid
byte in the file? I would recommend to rather not use strings but use just bytes
when we are writing and reading from a file. BTW, C++ interface is operating
bytes for reading and writing.

[anton, 2017/05/22 13:04:38]

there are lots of ways for "reading file as string" and lot's of research for
this topic.
as for me using scanner is pretty old-school so i'll change it to more
common-spread impl with streams.

-    }
-    catch (NoSuchElementException e)
-    {
-      return "";
+      return readStream(fileInputStream, (int) file.length());
     }
     finally
     {
-      if (scanner != null)
+      try
       {
-        scanner.close();
+        fileInputStream.close();
+      }
+      catch (IOException e)
+      {
+        // ignored
       }
     }
   }
 
   /**
    * Write data to file (with rewriting)
    *
    * @param file file
    * @param data file data
    */
-  public static void writeFile(File file, String data) throws IOException
+  public static void writeFile(File file, byte[] data) throws IOException
   {
     FileOutputStream fos = null;
     try
     {
       fos = new FileOutputStream(file);
       if (data != null)
       {
-        fos.write(data.getBytes());

[sergei, 2017/05/22 12:09:07]

If we still use String then I think we should pass UTF-8 into getBytes method.

[anton, 2017/05/22 13:04:38]

Acknowledged.

+        fos.write(data);
       }
     }
     finally
     {
       if (fos != null)
       {
         try
         {
           fos.close();
         }
@@ skipping 23 matching lines @@
     sb.append(UUID.randomUUID().toString());
 
     if (suffix != null)
     {
       sb.append(suffix);
     }
 
     return sb.toString();
   }
 }