Explain the related content of PHP file download class that supports breakpoint resume transfer

php supports breakpoint resumption, mainly relying on the header HTTP_RANGE in the HTTP protocol.
HTTP breakpoint resume download principle
Http header Range, Content-Range()
Range and Content are generally used in HTTP headers only for breakpoint downloads -Range entity header,
In the Range user request header, specify the position of the first byte and the position of the last byte, such as (Range: 200-300)
Content-Range is used for response headers
Request to download the entire file:
GET /test.rar HTTP/1.1
Connection: close
Host: 116.1.219.219
Range: bytes=0-801 //General requests to download the entire file are bytes =0- or do not use this header
Generally normal response
HTTP/1.1 200 OK
Content-Length: 801
Content-Type: application/octet-stream
Content-Range: bytes 0 -800/801 //801: Total file size
FileDownload.class.php

<?php
/** php下载类,支持断点续传
*   Date:   2013-06-30
*   Author: fdipzone
*   Ver:    1.0
*
*   Func:
*   download: 下载文件
*   setSpeed: 设置下载速度
*   getRange: 获取header中Range
*/
class FileDownload{ // class start
    private $_speed = 512;   // 下载速度
    /** 下载
    * @param String  $file   要下载的文件路径
    * @param String  $name   文件名称,为空则与下载的文件名称一样
    * @param boolean $reload 是否开启断点续传
    */
    public function download($file, $name=&#39;&#39;, $reload=false){
        if(file_exists($file)){
            if($name==&#39;&#39;){
                $name = basename($file);
            }
            $fp = fopen($file, &#39;rb&#39;);
            $file_size = filesize($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($this->_speed*1024,0));
                ob_flush();
                //sleep(1); // 用于测试,减慢下载速度
            }
            ($fp!=null) && fclose($fp);
        }else{
            return '';
        }
    }
    /** 设置下载速度
    * @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(&#39;start&#39;,&#39;end&#39;), $range);
            if(empty($range[&#39;start&#39;])){
                $range[&#39;start&#39;] = 0;
            }
            if(empty($range[&#39;end&#39;])){
                $range[&#39;end&#39;] = $file_size;
            }
            return $range;
        }
        return null;
    }
} // class end
?>

demo

<?php
require(&#39;FileDownload.class.php&#39;);
$file = &#39;book.zip&#39;;
$name = time().&#39;.zip&#39;;
$obj = new FileDownload();
$flag = $obj->download($file, $name);
//$flag = $obj->download($file, $name, true); // 断点续传
if(!$flag){
    echo 'file not exists';
}
?>

Breakpoint resume test method:
Use the linux wget command to test the download, wget -c -O file http://xxx
1. Turn off breakpoint resumption first
$flag = $obj->download($file, $name);

fdipzone@ubuntu:~/Downloads$ wget -O test.rar http://demo.fdipzone.com/demo.php
--2013-06-30 16:52:44--  http://demo.fdipzone.com/demo.php
正在解析主机 demo.fdipzone.com... 127.0.0.1
正在连接 demo.fdipzone.com|127.0.0.1|:80... 已连接。
已发出 HTTP 请求，正在等待回应... 200 OK
长度： 10445120 (10.0M) [application/octet-stream]
正在保存至: “test.rar”
30% [============================>                                                                     ] 3,146,580    513K/s  估时 14s
^C
fdipzone@ubuntu:~/Downloads$ wget -c -O test.rar http://demo.fdipzone.com/demo.php
--2013-06-30 16:52:57--  http://demo.fdipzone.com/demo.php
正在解析主机 demo.fdipzone.com... 127.0.0.1
正在连接 demo.fdipzone.com|127.0.0.1|:80... 已连接。
已发出 HTTP 请求，正在等待回应... 200 OK
长度： 10445120 (10.0M) [application/octet-stream]
正在保存至: “test.rar”
30% [============================>                                                                     ] 3,146,580    515K/s  估时 14s
^C
可以看到,wget -c不能断点续传

2. Enable breakpoint resume download
$flag = $obj->download($file, $name, true );

fdipzone@ubuntu:~/Downloads$ wget -O test.rar http://demo.fdipzone.com/demo.php
--2013-06-30 16:53:19--  http://demo.fdipzone.com/demo.php
正在解析主机 demo.fdipzone.com... 127.0.0.1
正在连接 demo.fdipzone.com|127.0.0.1|:80... 已连接。
已发出 HTTP 请求，正在等待回应... 200 OK
长度： 10445120 (10.0M) [application/octet-stream]
正在保存至: “test.rar”
20% [==================>                                                                               ] 2,097,720    516K/s  估时 16s
^C
fdipzone@ubuntu:~/Downloads$ wget -c -O test.rar http://demo.fdipzone.com/demo.php
--2013-06-30 16:53:31--  http://demo.fdipzone.com/demo.php
正在解析主机 demo.fdipzone.com... 127.0.0.1
正在连接 demo.fdipzone.com|127.0.0.1|:80... 已连接。
已发出 HTTP 请求，正在等待回应... 206 Partial Content
长度： 10445121 (10.0M)，7822971 (7.5M) 字节剩余 [application/octet-stream]
正在保存至: “test.rar”
100%[++++++++++++++++++++++++=========================================================================>] 10,445,121   543K/s   花时 14s   
2013-06-30 16:53:45 (543 KB/s) - 已保存 “test.rar” [10445121/10445121])
可以看到会从断点的位置(%20)开始下载。

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