code: public static Path sourcePathFromParityPath(Path parityPath, FileSystem fs) 
          throws IOException {
      String parityPathStr = parityPath.toUri().getPath();
      for (Codec codec : Codec.getCodecs()) {
        String prefix = codec.getParityPrefix();
        if (parityPathStr.startsWith(prefix)) {
          // Remove the prefix to get the source file.
          String src = parityPathStr.replaceFirst(prefix, Path.SEPARATOR);
          Path srcPath = new Path(src);
          if (fs.exists(srcPath)) {
            return srcPath;
          }
        }
      }
      return null;
    }
docs: returns the source file corresponding to a parity file
  @throws IOException