code: protected function readString($fileHandle, $length, $offset = null)
      {
          if ($offset !== null) {
              fseek($fileHandle, $offset);
          }
  
          return $this->readBytes($fileHandle, $length);
      }
docs: Reads a string.
  @param resource $fileHandle file handle
  @param int $length of the string
  @param int $offset of the string in the file. If null, it reads from the current position.
  @return string the result