public function addResponseHeaderLine($curl, $header_line)
    {
        $trimmed_header = trim($header_line, "\r\n");

        if ($trimmed_header === "") {
            $this->response_header_continue = false;
        } elseif (strtolower($trimmed_header) === 'http/1.1 100 continue') {
            $this->response_header_continue = true;
        } elseif (!$this->response_header_continue) {
            $this->response_headers[] = $trimmed_header;
        }
        
        return strlen($header_line);
    }