def stream_to_handler(self, request_handler):
        """Write the contents of this file to a
        :class:`tornado.web.RequestHandler`. This method calls
        :meth:`~tornado.web.RequestHandler.flush` on
        the RequestHandler, so ensure all headers have already been set.
        For a more complete example see the implementation of
        :class:`~motor.web.GridFSHandler`.

        .. code-block:: python

            class FileHandler(tornado.web.RequestHandler):
                @tornado.web.asynchronous
                @gen.coroutine
                def get(self, filename):
                    db = self.settings['db']
                    fs = yield motor.MotorGridFSBucket(db())
                    try:
                        gridout = yield fs.open_download_stream_by_name(filename)
                    except gridfs.NoFile:
                        raise tornado.web.HTTPError(404)

                    self.set_header("Content-Type", gridout.content_type)
                    self.set_header("Content-Length", gridout.length)
                    yield gridout.stream_to_handler(self)
                    self.finish()

        .. seealso:: Tornado `RequestHandler <http://tornadoweb.org/en/stable/web.html#request-handlers>`_
        """
        written = 0
        while written < self.length:
            # Reading chunk_size at a time minimizes buffering.
            f = self._framework.yieldable(self.read(self.chunk_size))
            yield f
            chunk = f.result()

            # write() simply appends the output to a list; flush() sends it
            # over the network and minimizes buffering in the handler.
            request_handler.write(chunk)
            request_handler.flush()
            written += len(chunk)