PHP实现下载断点续传的方法

<?php
/*
?* PHP下载断点续传
?*/
function dl_file_resume($file){
?
??? //检测文件是否存在
??? if (!is_file($file)) { die("<b>404 File not found!</b>"); }
?????
??? $len = filesize($file);//获取文件大小
??? $filename = basename($file);//获取文件名字
??? $file_extension = strtolower(substr(strrchr($filename,"."),1));//获取文件扩展名
?????
??? //根据扩展名 指出输出浏览器格式
??? switch( $file_extension ) {
??????? case "exe": $ctype="application/octet-stream"; break;
??????? case "zip": $ctype="application/zip"; break;
??????? case "mp3": $ctype="audio/mpeg"; break;
??????? case "mpg":$ctype="video/mpeg"; break;
??????? case "avi": $ctype="video/x-msvideo"; break;
??????? default: $ctype="application/force-download";
??? }
?????
??? //Begin writing headers
??? header("Cache-Control:");
??? header("Cache-Control: public");
?????
??? //设置输出浏览器格式
??? header("Content-Type: $ctype");
??? if (strstr($_SERVER['HTTP_USER_AGENT'],"MSIE")) {//如果是IE浏览器
??????? # workaround for IE filename bug with multiple periods / multiple dots in filename
??????? # that adds square brackets to filename - eg. setup.abc.exe becomes setup[1].abc.exe
??????? $iefilename = preg_replace('/./','%2e',$filename,substr_count($filename,'.') - 1);
??????? header("Content-Disposition: attachment; filename="$iefilename"");
??? } else {
??????? header("Content-Disposition: attachment; filename="$filename"");
??? }
??? header("Accept-Ranges: bytes");
?????
??? $size=filesize($file);
??? //如果有$_SERVER['HTTP_RANGE']参数
??? if(isset($_SERVER['HTTP_RANGE'])) {
/*?? ---------------------------
?? Range头域 　　Range头域可以哀求实体的一个或者多个子范围.例如,　　表示头500个字节：bytes=0-499 　　表示第二个500字节：bytes=500-999 　　表示最后500个字节：bytes=-500 　　表示500字节以后的范围：bytes=500- 　　第一个和最后一个字节：bytes=0-0,-1 　　同时指定几个范围：bytes=500-600,601-999 　　但是服务器可以忽略此哀求头,如果无条件GET包含Range哀求头,响应会以状态码206(PartialContent)返回而不是以200 (OK).
?? ---------------------------*/
???
// 断点后再次连接 $_SERVER['HTTP_RANGE'] 的值 bytes=4390912-
???
??????? list($a,$range)=explode("=",$_SERVER['HTTP_RANGE']);
?? //if yes,download missing part
??????? str_replace($range,"-",$range);//这句干什么的呢....
?? $size2=$size-1;//文件总字节数
??????? $new_length=$size2-$range;//获取下次下载的长度
??????? header("HTTP/1.1 206 Partial Content");
??????? header("Content-Length: $new_length");//输入总长
??????? header("Content-Range: bytes $range$size2/$size");//Content-Range: bytes 4908618-4988927/4988928?? 95%的时候
??? } else {//第一次连接
??????? $size2=$size-1;
??????? header("Content-Range: bytes 0-$size2/$size"); //Content-Range: bytes 0-4988927/4988928
??????? header("Content-Length: ".$size);//输出总长
??? }
??? //打开文件
??? $fp=fopen("$file","rb");
??? //设置指针位置
??? fseek($fp,$range);
??? //虚幻输出
??? while(!feof($fp)){
??????? //设置文件最长执行时间
??????? set_time_limit(0);
??????? print(fread($fp,1024*8));//输出文件
??????? flush();//输出缓冲
??????? ob_flush();
??? }
??? fclose($fp);
??? exit;
}
?
dl_file_resume("1.zip");//同级目录的1.zip 文件
?
//---------------------------------------
?
//不支持断点续传的文件下载.
?
//---------------------------------------
?
downFile("1.zip");
?
function downFile($sFilePath)
{
?? if(file_exists($sFilePath)){
?????? $aFilePath=explode("/",str_replace("","/",$sFilePath),$sFilePath);
?????? $sFileName=$aFilePath[count($aFilePath)-1];
?????? $nFileSize=filesize ($sFilePath);
?????? header ("Content-Disposition: attachment; filename=" . $sFileName);
?????? header ("Content-Length: " . $nFileSize);
?????? header ("Content-type: application/octet-stream");
?????? readfile($sFilePath);
?? }
?? else
?? {
?????? echo("文件不存在!");
?? }
}
?>