def grow(self, len):
        """Grow up the content of the input buffer, the old data are
          preserved This routine handle the I18N transcoding to
          internal UTF-8 This routine is used when operating the
          parser in normal (pull) mode  TODO: one should be able to
          remove one extra copy by copying directly onto in->buffer
           or in->raw """
        ret = libxml2mod.xmlParserInputBufferGrow(self._o, len)
        return ret