提供大文件下载的PHP超时

Question

我正在尝试使用PHP来提供文件下载。我可以让文件开始下载，但它只能下载大约280MB的1GB文件。我在共享主机上，所以这可能是问题，如果这不是我的代码的问题：

function downloadFile($file){
    if (file_exists($file)) {
        if(is_dir($file)){return false;}
        header('Content-Description: File Transfer');
        header('Content-Type: application/octet-stream');
        header('Content-Transfer-Encoding: binary');
        header('Content-Disposition: attachment; filename="'.basename($file).'"');
        header('Content-Transfer-Encoding: binary');
        header('Connection: Keep-Alive');
        header('Expires: 0');
        header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
        header('Pragma: public');
        header('Content-Length: '.sprintf("%u", filesize($file)));

        ob_clean();
        $handle = fopen($file, "rb");
        $chunksize=(sprintf("%u", (filesize($file))/1024));

        set_time_limit(0);
        while (!feof($handle)) {
            echo fgets($handle, $chunksize);
            flush();
        }
        fclose($handle);
        die;
    }else{ echo "file not found";}
    return;
}