private function processHead() {
        if ($this->existsInMetaData($this->uuid, 'ID') === false) {
            $this->getResponse()->setStatusCode(PhpResponse::STATUS_CODE_404);
            return;
        }

        // if file in storage does not exists
        if (!file_exists($this->directory . $this->getFilename())) {
            // allow new upload
            $this->removeFromMetaData($this->uuid);
            $this->getResponse()->setStatusCode(PhpResponse::STATUS_CODE_404);
            return;
        }

        $this->getResponse()->setStatusCode(PhpResponse::STATUS_CODE_200);

        $offset = $this->getMetaDataValue($this->uuid, 'Offset');
        $headers = $this->getResponse()->getHeaders();
        $headers->addHeaderLine('Upload-Offset', $offset);

        $length = $this->getMetaDataValue($this->uuid, 'Size');
        $headers->addHeaderLine('Upload-Length', $length);

        $headers->addHeaderLine('Cache-Control', 'no-store');
    }