fopen 644的權限無法打開流文件

需求是需要下載遠程文件到本地，下面是下載的函數(shù)。在我下載圖片或文本類型時fopen可以順利執(zhí)行。當下載的資源為視頻或音頻則提示failed to open stream: Permission denied,需要將文件權限設置為755才行。應該怎么解決這個問題？

function download_remote_file($url , $ext,  $path = '/public/download/')
        {
            $ch = curl_init();
            curl_setopt($ch , CURLOPT_URL , $url);
            curl_setopt($ch , CURLOPT_RETURNTRANSFER , 1);
            curl_setopt($ch , CURLOPT_CONNECTTIMEOUT , 30);
            $file = curl_exec($ch);
            curl_close($ch);

            $fileSource = pathinfo($url);

            if (empty($fileSource['extension'])) {
                $filename = $fileSource['filename'] . '.' . $ext;
            } else {
                $filename = $fileSource['basename'];
            }

            $resource = fopen($path . $filename , 'a');

            fwrite($resource , $file);
            fclose($resource);
            return $filename;
        }