'There can only be one source of request data.
Bytes are always read.'

def _body_from_file(self, fd):

    if self.args.data:
        self.error('Request    body    (from    stdin    or    a    file)    and    request    data    (key=value)    cannot    be    mixed.')
    self.args.data = getattr(fd, 'buffer', fd).read()
