code: public function send(Response $response)
      {
          $body = $response->getBody();
          if ($body instanceof Body) {
              $renderer = $body->getRenderer();
              $value    = $body->getValue();
              $result   = $renderer->render($value);
              $response->setHeader(new Raw("Content-Length", strlen($result)));
          } else {
              $result   = null;
          }
          
          foreach ($response->getHeaderList() as $header) {
              if ($header instanceof Status) {
                  $code         = $header->getCode();
                  $reasonPhrase = $header->getReasonPhrase();
                  header("HTTP/1.1 {$code} {$reasonPhrase}");
                  continue;
              }
              $name  = $header->getName();
              $value = $header->format();
              $this->printHeader($name, $value);
          }
          if (strlen($result)) {
              echo $result;
          }
      }
docs: 指定された Response オブジェクトを header() や echo()
  などを使ってクライアントに送信します.
  
  @param Response $response 送信対象の Response オブジェクト