Curl file download - PHP

function curlToFile($url, $filename, $download_folder) {
                if (!(file_exists($download_folder)))
                    mkdir($download_folder);
                chdir($download_folder);
                $fp = fopen($filename, "w+");
                $curl = curl_init();
                curl_setopt($curl, CURLOPT_URL, $url);
                curl_setopt($curl, CURLOPT_POST, 1);
                curl_setopt($curl, CURLOPT_FOLLOWLOCATION, 1);
                curl_setopt($curl, CURLOPT_AUTOREFERER, 1);
                curl_setopt($curl, CURLOPT_REFERER, "http://www.somedomain.com");
                curl_setopt($curl, CURLOPT_USERAGENT, "Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:1.9.1.10) Gecko/20100504 Firefox/3.5.10");
                curl_setopt($curl, CURLOPT_FILE, $fp);
                $ret = curl_exec($curl);
                if (!$ret) {
                    $this->lastError = curl_error($curl);
                }
                curl_close($curl);
                return $ret;
            }