'Receive body frames and append them to the stack. When the body size
matches, call the finish method.
:param Body body_frame: The body frame
:raises: pika.exceptions.BodyTooLongError
:rtype: tuple(pika.frame.Method, pika.frame.Header, str)|None'

def _handle_body_frame(self, body_frame):

    self._seen_so_far += len(body_frame.fragment)
    self._body_fragments.append(body_frame.fragment)
    if (self._seen_so_far == self._header_frame.body_size):
        return self._finish()
    elif (self._seen_so_far > self._header_frame.body_size):
        raise exceptions.BodyTooLongError(self._seen_so_far, self._header_frame.body_size)
    return None
