docs: private boolean isZipFile(final File file) {
          DataInputStream in = null;
          try {
              in = new DataInputStream(new FileInputStream(file));
              final int n = in.readInt();
              return n == 0x504b0304;
          } catch (IOException ex) {
              // silently ignore read exceptions
              return false;
          } finally {
              if (in != null) {
                  try {
                      in.close();
                  } catch (IOException ex) {
                      // ignore
                  }
              }
          }
      }