code: func NewDataFileReader(filename string, datumReader DatumReader) (*DataFileReader, error) {
  	buf, err := ioutil.ReadFile(filename)
  	if err != nil {
  		return nil, err
  	}
  
  	return newDataFileReaderBytes(buf, datumReader)
  }
docs: // NewDataFileReader creates a new DataFileReader for a given file and using the given DatumReader to read the data from that file.
  // May return an error if the file contains invalid data or is just missing.