range协议用途：一般是用在断点续传的时候，但是实际的用户很大，例如你的web server需要输出一个大文件，那么用range可以分段输出，缓解压力。同时在提供音乐视频等服务时可以缓冲下载，如果用户中途关闭，可以节约网络带宽。

<?php

// 文件名
$filename = $_GET ["filename"];

// 文件路径
$location = "media/" . $filename;

// 后缀
$extension = substr ( strrchr ( $filename, "." ), 1 );

if ($extension == "mp3") {
	$mimeType = "audio/mpeg";
} else if ($extension == "ogg") {
	$mimeType = "audio/ogg";
}

if (! file_exists ( $location )) {
	header ( "HTTP/1.1 404 Not Found" );
	return;
}

$size = filesize ( $location );
$time = date ( "r", filemtime ( $location ) );

$fm = @fopen ( $location, "rb" );
if (! $fm) {
	header ( "HTTP/1.1 505 Internal server error" );
	return;
}

$begin = 0;
$end = $size - 1;

if (isset ( $_SERVER ["HTTP_RANGE"] )) {
	if (preg_match ( "/bytes=h*(d+)-(d*)[D.*]?/i", $_SERVER ["HTTP_RANGE"], $matches )) {
		// 读取文件，起始节点
		$begin = intval ( $matches [1] );

		// 读取文件，结束节点
		if (! empty ( $matches [2] )) {
			$end = intval ( $matches [2] );
		}
	}
}

if (isset ( $_SERVER ["HTTP_RANGE"] )) {
	header ( "HTTP/1.1 206 Partial Content" );
} else {
	header ( "HTTP/1.1 200 OK" );
}

header ( "Content-Type: $mimeType" );
header ( "Cache-Control: public, must-revalidate, max-age=0" );
header ( "Pragma: no-cache" );
header ( "Accept-Ranges: bytes" );
header ( "Content-Length:" . (($end - $begin) + 1) );

if (isset ( $_SERVER ["HTTP_RANGE"] )) {
	header ( "Content-Range: bytes $begin-$end/$size" );
}

header ( "Content-Disposition: inline; filename=$filename" );
header ( "Content-Transfer-Encoding: binary" );
header ( "Last-Modified: $time" );

$cur = $begin;

// 定位指针
fseek ( $fm, $begin, 0 );

while ( ! feof ( $fm ) && $cur <= $end && (connection_status () == 0) ) {
	print fread ( $fm, min ( 1024 * 16, ($end - $cur) + 1 ) );
	$cur += 1024 * 16;
}

range协议官方文档：http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html