一个简单php数据库备份程序

/** 备份数据库 生成.sql文件
     * @param $browseinfo  String  浏览器版本
     * return $browseinfo
     */
    function createsql(){
        //创建个日期
        $timer1 = time();
        $path = "my_sql/";
        $content =gettables();
        $filename = $path.$timer1.".sql";
  
        //先判断文件夹在不在
         if(!file_exists($path)){
        //如果不存在生成这个目录,0777表示最大的读写权限
            if(mkdir($path,0777)){
            //echo"新建立目录"; 
            }
        }

        //判断文件是否存在
        if(!file_exists($filename)){
            //如果文件不存在,则创建文件
            @fopen($filename,"w");

            //判断文件是否可写
            if(is_writable($filename)){
            //打开文件以添加方式即"a"方式打开文件流
                if(!$handle =  fopen($filename,"a")){
                    echo"文件不可打开";
                    exit();
                }

            if(!fwrite($handle,$content)){
                echo"文件不可写";
                exit();
            }

        //关闭文件流
        fclose($handle);
        echo "生成文件并保存首次内容";
       
    }else {
        echo"文件$filename不可写";
    }
        }else{
            if(is_writable($filename)){
            //以添加方式打开文件流
            if(!$handle = fopen($filename,"a")){
                echo"文件不可打开";
                exit();
            }
            fclose($handle);
            }else{
                echo "文件$filename不可写";
            }
    }
}

    /**
     * 获得数据库中的表名
     * return $str 循环生成数据库建表和插入值的sql语句
     */
    function gettables(){
        $mysqli = new mysqli("localhost","root","","bbs");
        $str = '';
        if ($result = $mysqli->query("SHOW TABLES")) {
            while($row = $result->fetch_row()){
                $str.= data2sql($row[0])."
";
            }
            $mysqli->close();
            return $str;
        }  
   
    }
   

    /**
     * 获得数据库中的表结构和值
     * return $tabledump 返回一个表中的结构和值的sql语句
     */
    function data2sql($table){ 
     $mysqli = new mysqli("localhost","root","","bbs");
        /* check connection */
        if (mysqli_connect_errno()) {
            printf("Connect failed: %sn", mysqli_connect_error());
        exit();
    }
         $tabledump = "DROP TABLE IF EXISTS $table;n";
         $result = $mysqli->query("SHOW CREATE TABLE $table");
         $create = $result->fetch_row();
         $tabledump .= $create[1].";nn";
 
         $rows = $mysqli->query("SELECT * FROM $table");
         $numfields = $rows->num_rows;

            while ($row = $rows->fetch_row()){
             $comma = "";
             $tabledump .= "INSERT INTO $table VALUES(";
              for($i = 0; $i < $numfields; $i++)
              {
                 $tabledump .= $comma."'".mysql_escape_strin
g($row[$i])."'";
                 $comma = ",";
              }
             $tabledump .= ");n";
          }
         $tabledump .= "n";
 
          return $tabledump;
      }
?>