PHP服务器端防止用户重复提交数据

<? php
session_start ();
/* *
     * 检查表单是否被重复提交
     * 相同内容的表单在设定时间内只能提交1次
     * @param int $iTimeOffset
     * @return bool
      */
function  checkFormSubmit( $iTimeOffset = 60 ){
     //  取得表单的标识
     $idForm   =   md5 ( serialize ( $_POST ));
     //  是否需要表单提交检察
     $iFormCheck   =   true ;
     if  ( isset ( $_SESSION [ ' formSubmitCheck ' ])){
         //  删除过期的表单标识
         foreach  ( array_keys ( $_SESSION [ ' formSubmitCheck ' ])  as   $val ){
             if  ( time ()  >   $val ){
                 unset ( $_SESSION [ ' formSubmitCheck ' ][ $val ]);
            }
        }
    } else  {
         $_SESSION [ ' formSubmitCheck ' ]  =   array ();
         $iFormCheck   =   false ;
    }
     if  ( $iFormCheck   ==   true ){
         //  检查是否有重复标识的提交记录
         foreach  ( $_SESSION [ ' formSubmitCheck ' ]  as   $val ){
             if  ( $val   ==   $idForm ){
                 return   false ;
            }
        }
    }
     //  保存表单标识
     $_SESSION [ ' formSubmitCheck ' ][( time () + $iTimeOffset )]  =   $idForm ;
     return   true ;
}

if  ( count ( $_POST )  >   0 ){
     if  (checkFormSubmit() === true ){
         echo   ' 表单提交成功 ' ;
    } else  {
         echo   ' 表单重复提交 ' ;
    }
}
?>

< form method = " POST " >
     < input type = " text "  name = " a " >
     < input type = " text "  name = " b " >
     < textarea name = " c " ></ textarea >
     < input type = " submit "  name = " btnSubmit "  value = " 确认 " >
</ form >
<? php
var_dump ( $_POST );
var_dump ( $_SESSION );
?>