'This forces ``environ[\'wsgi.input\']`` to be seekable.
That means that, the content is copied into a BytesIO or temporary
file and flagged as seekable, so that it will not be unnecessarily
copied again.
After calling this method the .body_file is always seeked to the
start of file and .content_length is not None.
The choice to copy to BytesIO is made from
``self.request_body_tempfile_limit``'

def make_body_seekable(self):

    if self.is_body_seekable:
        self.body_file_raw.seek(0)
    else:
        self.copy_body()
