FileDownload.class.php

<?php
class FileDownload{ // class start
    private $_speed = 512;   // download speed
    /** download
    * @param String  $file   要download的文件路径
    * @param String  $name   文件名称,为空则与download的文件名称一样
    * @param boolean $reload 是否开启断点续传
    */
    public function download($file, $name='', $reload=false){
        if(file_exists($file)){
            if($name==''){
                $name = basename($file);
            }
            $fp = fopen($file, 'rb');
            $file_size = filesize($file);
            $ranges = $this->getRange($file_size);
            header('cache-control:public');
            header('content-type:application/octet-stream');
            header('content-disposition:attachment; filename='.$name);
            if($reload && $ranges!=null){ // 使用续传
                header('HTTP/1.1 206 Partial Content');
                header('Accept-Ranges:bytes');
                
                // 剩余长度
                header(sprintf('content-length:%u',$ranges['end']-$ranges['start']));
                
                // range信息
                header(sprintf('content-range:bytes %s-%s/%s', $ranges['start'], $ranges['end'], $file_size));
                
                // fp指针跳到断点位置
                fseek($fp, sprintf('%u', $ranges['start']));
            }else{
                header('HTTP/1.1 200 OK');
                header('content-length:'.$file_size);
            }
            while(!feof($fp)){
                echo fread($fp, round($this->_speed*1024,0));
                ob_flush();
                //sleep(1); // 用于slowly ,减慢download speed
            }
            ($fp!=null) && fclose($fp);
        }else{
            return '';
        }
    }
    /** 设置download speed
    * @param int $speed
    */
    public function setSpeed($speed){
        if(is_numeric($speed) && $speed>16 && $speed<4096){
            $this->_speed = $speed;
        }
    }
    /** 获取header range信息
    * @param  int   $file_size 文件大小
    * @return Array
    */
    private function getRange($file_size){
        if(isset($_SERVER['HTTP_RANGE']) && !empty($_SERVER['HTTP_RANGE'])){
            $range = $_SERVER['HTTP_RANGE'];
            $range = preg_replace('/[\s|,].*/', '', $range);
            $range = explode('-', substr($range, 6));
            if(count($range)<2){
                $range[1] = $file_size;
            }
            $range = array_combine(array('start','end'), $range);
            if(empty($range['start'])){
                $range['start'] = 0;
            }
            if(empty($range['end'])){
                $range['end'] = $file_size;
            }
            return $range;
        }
        return null;
    }
} // class end
?>

demo.php

<?php

require('FileDownload.class.php');
$file = 'book.zip';
$name = time().'.zip';
$obj = new FileDownload();
$flag = $obj->download($file, $name);
//$flag = $obj->download($file, $name, true); // 断点续传

if(!$flag){
    echo 'file not exists';
}

?>