This class can be used to convert a :class:`file`-like object into
an iterable. It yields `buffer_size` blocks until the file is fully
read.
You should not use this class directly but rather use the
:func:`wrap_file` function that uses the WSGI server's file wrapper
support if it's available.
.. versionadded:: 0.5
If you're using this object together with a :class:`BaseResponse` you have
to use the `direct_passthrough` mode.
:param file: a :class:`file`-like object with a :meth:`~file.read` method.
:param buffer_size: number of bytes for one iteration.