public function sendHeaders()
    {
        $codes = $this->getHttpResponseCodes();
        if (!array_key_exists($this->status, $codes)) {
            $this->status = 500;
            $string = 'HTTP/1.0 500 ' . $codes[500];
        } else {
            if ($this->isValidRedirectStatus()) {
                throw new \Exception(
                    'You cannot send a redirect using a regular response. Use $this->response->redirect(url, status);'
                );
            }
            $string = 'HTTP/1.0 ' . $this->status . ' ' . $codes[$this->status];
        }

        header($string);
        $this->outputHeaders();
    }