/** writes safely (to temp file, then rename) */
public static byte[] saveBinaryFile(String fileName, byte[] contents) ctex {
  File file = new File(fileName);
  File parentFile = file.getParentFile();
  if (parentFile != null)
    parentFile.mkdirs();
  String tempFileName = fileName + "_temp";
  try (FileOutputStream fileOutputStream = newFileOutputStream(tempFileName)) {
    fileOutputStream.write(contents);
  }
  if (file.exists() && !file.delete())
    throw new IOException("Can't delete " + fileName);

  if (!new File(tempFileName).renameTo(file))
    throw new IOException("Can't rename " + tempFileName + " to " + fileName);
    
  ifndef LeanMode
  vmBus_send('wroteFile, file);
  endifndef
  ret contents;
}

static byte[] saveBinaryFile(File fileName, byte[] contents) {
  ret saveBinaryFile(fileName.getPath(), contents);
}