protected void unpackComponents() throws IOException, FileNotFoundException {
    File applicationPackage = new File(getApplication().getPackageResourcePath());
    File componentsDir = new File(sGREDir, "components");
    if (componentsDir.lastModified() == applicationPackage.lastModified()) return;

    componentsDir.mkdir();
    componentsDir.setLastModified(applicationPackage.lastModified());

    GeckoAppShell.killAnyZombies();

    ZipFile zip = new ZipFile(applicationPackage);

    byte[] buf = new byte[32768];
    try {
      if (unpackFile(zip, buf, null, "removed-files")) removeFiles();
    } catch (Exception ex) {
      // This file may not be there, so just log any errors and move on
      Log.w(LOG_FILE_NAME, "error removing files", ex);
    }

    // copy any .xpi file into an extensions/ directory
    Enumeration<? extends ZipEntry> zipEntries = zip.entries();
    while (zipEntries.hasMoreElements()) {
      ZipEntry entry = zipEntries.nextElement();
      if (entry.getName().startsWith("extensions/") && entry.getName().endsWith(".xpi")) {
        Log.i("GeckoAppJava", "installing extension : " + entry.getName());
        unpackFile(zip, buf, entry, entry.getName());
      }
    }
  }
  private boolean unpackFile(ZipFile zip, byte[] buf, ZipEntry fileEntry, String name)
      throws IOException, FileNotFoundException {
    if (fileEntry == null) fileEntry = zip.getEntry(name);
    if (fileEntry == null)
      throw new FileNotFoundException("Can't find " + name + " in " + zip.getName());

    File outFile = new File(sGREDir, name);
    if (outFile.lastModified() == fileEntry.getTime() && outFile.length() == fileEntry.getSize())
      return false;

    File dir = outFile.getParentFile();
    if (!dir.exists()) dir.mkdirs();

    InputStream fileStream;
    fileStream = zip.getInputStream(fileEntry);

    OutputStream outStream = new FileOutputStream(outFile);

    while (fileStream.available() > 0) {
      int read = fileStream.read(buf, 0, buf.length);
      outStream.write(buf, 0, read);
    }

    fileStream.close();
    outStream.close();
    outFile.setLastModified(fileEntry.getTime());
    return true;
  }
  /**
   * Read block from file.
   *
   * @param file - File to read.
   * @param off - Marker position in file to start read from if {@code -1} read last blockSz bytes.
   * @param blockSz - Maximum number of chars to read.
   * @param lastModified - File last modification time.
   * @return Read file block.
   * @throws IOException In case of error.
   */
  public static VisorFileBlock readBlock(File file, long off, int blockSz, long lastModified)
      throws IOException {
    RandomAccessFile raf = null;

    try {
      long fSz = file.length();
      long fLastModified = file.lastModified();

      long pos = off >= 0 ? off : Math.max(fSz - blockSz, 0);

      // Try read more that file length.
      if (fLastModified == lastModified && fSz != 0 && pos >= fSz)
        throw new IOException(
            "Trying to read file block with wrong offset: " + pos + " while file size: " + fSz);

      if (fSz == 0)
        return new VisorFileBlock(file.getPath(), pos, fLastModified, 0, false, EMPTY_FILE_BUF);
      else {
        int toRead = Math.min(blockSz, (int) (fSz - pos));

        byte[] buf = new byte[toRead];

        raf = new RandomAccessFile(file, "r");

        raf.seek(pos);

        int cntRead = raf.read(buf, 0, toRead);

        if (cntRead != toRead)
          throw new IOException(
              "Count of requested and actually read bytes does not match [cntRead="
                  + cntRead
                  + ", toRead="
                  + toRead
                  + ']');

        boolean zipped = buf.length > 512;

        return new VisorFileBlock(
            file.getPath(), pos, fSz, fLastModified, zipped, zipped ? zipBytes(buf) : buf);
      }
    } finally {
      U.close(raf, null);
    }
  }