PHP file download

public function downloadFile(){
        $M = M($this->tableName);
        $map['id'] = I('fileId');
        $info = $M->where($map)->find();
        $filepath = '.'.$info['path'];
        if( !file_exists($filepath) ){
            echo '文件不存在！';
            exit;
        }
 
        //$M->where($map)->setInc('download');
        $file = fopen($filepath,"r"); // 打开文件
        // 输入文件标签
        Header("Content-type: application/octet-stream");
        Header("Accept-Ranges: bytes");
        Header("Accept-Length: ".filesize($filepath));
        Header("Content-Disposition: attachment; filename=" . $info['savename']);
        // 输出文件内容
        echo fread($file,filesize($filepath));
        fclose($file);
        exit;
}