class downLoad{    var $file_name;    var $file_dir;    var $buffer_size = 1024;    var $err = "";    public static $MIME_type = array(                                "pdf"  =>"application/pdf",                                "exe"  =>"application/octet-stream",                                "zip"  =>"application/zip",                                "doc"  =>"application/msword",                                "xls"  =>"application/vnd.ms-excel",                                "ppt"  =>"application/vnd.ms-powerpoint",                                "gif"  =>"p_w_picpath/gif",                                "png"  =>"p_w_picpath/png",                                "jpeg" =>"jpg",                                "mp3"  =>"audio/mpeg",                                "wav"  =>"audio/x-wav",                                "mpeg" =>"mpg",                                "mpe"  =>"video/mpeg",                                "mov"  =>"video/quicktime",                                "avi"  =>"video/x-msvideo",                                         );    public function __construct($file_dir="",$file_name=""){        $this->file_dir  = $file_dir;        $this->file_name = $file_name;        $this->path = $file_dir."/".$file_name;        $this->suffix = pathinfo($file_name,PATHINFO_EXTENSION);    }          public function down(){        if(!file_exists($this->path)){            $this->err = "该文件被移除了";            return false;        }        $content_type = $this->getMIME($this->suffix);        $file_size = filesize($this->path);                  header("Content-type: ".$content_type);        header('Content-Disposition: p_w_upload; filename="'.$this->file_name.'"');                  @header("Cache-control: public");        @header("Pragma: public");        header("Content-Length: ".$file_size);        ob_end_clean();        //readfile($this->path); 一次性读出来        $fp= fopen($this->path,"r");        $buffer_size = $this->buffer_size;        $cur_pos = 0; //记录读了多少了                  while(!feof($fp) && $file_size>$buffer_size+$cur_pos){            $buffer = fread($fp,$buffer_size); //每次读1024字节            echo $buffer;            $cur_pos += $buffer_size;        }        //把剩下的读出来 因为文件的带下很有很能不是1024 的整数倍        $buffer = fread($fp,$file_size-$cur_pos);        echo $buffer;        fclose($fp);        return true;           }          public function getMIME($key=""){        if($key == "" || !isset(self::$MIME_type[$key])){            return "application/octet-stream";        }        return self::$MIME_type[$key];    }}//  $x = new downLoad($file_dir,$file_name);  $file_dir路径 比如 all     $file_name文件名 比如 a.exe  合起来就是全部的路径了all/a.exe//  $x->down();