使PHP页面返回＆QUOT; 304未修改＆QUOT;如果它没有被修改 [英] Make PHP page return "304 Not Modified" if it hasn't been modified

问题描述

我有一个PHP文件，将每次返回同样的事情在同一$ _GET参数 - 这是确定的。

I have a PHP file that will return the same thing with the same $_GET parameters every time -- it's deterministic.

不幸的是，效率（请求该文件很多时候），Apache的默认每次请求PHP页面200 OK响应，让用户重新下载该文件。

Unfortunately for efficiency (this file is requested very often), Apache defaults to a "200 OK" response whenever a PHP page is requested, making the user download the file again.

有没有什么办法来发送 304未修改头的当且仅当的参数是一样的吗？

Is there any way to send a 304 Not Modified header if and only if the parameters are the same?

奖金：
我可以设置它的到期时间，因此，如果缓存的页面比说，老三天以上，它发送一个200 OK的反应？

Bonus: Can I set an expiry time on it, so that if the cached page is more than, say, three days old, it sends a "200 OK" response?

推荐答案

没有缓存的网页自己（或至少其Etag的）你不能真正利用304的全功能的缓存算法有点超出范围的，但总体思路：

Without caching the page yourself (or at least its Etag) you cannot really make use of the 304. A full fledged caching algorithm is somewhat out of scope, but the general idea:

<?php 
function getUrlEtag($url){
    //some logic to get an etag, possibly stored in memcached / database / file etc.
}
function setUrlEtag($url,$etag){
    //some logic to get an etag, possibly stored in memcached / database / file etc.
}
function getPageCache($url,$etag=''){
    //[optional]some logic to get the page from cache instead, possibly not even using etag
}
function setPageCache($url,$content,$etag=''){
    //[optional]some logic to save the page to cache, possibly not even using etag
}
ob_start();
$etag = getUrlEtag($_SERVER['REQUEST_URI']);
if(isset($_SERVER['HTTP_IF_NONE_MATCH']) && trim($_SERVER['HTTP_IF_NONE_MATCH']) == $etag) { 
    header("HTTP/1.1 304 Not Modified"); 
    exit; 
}
if(($content=getPageCache($_SERVER['REQUEST_URI'],$etag))!==false){
    echo $content;
    exit;
}
?>
//the actual page
<?php
$content = ob_get_clean();
setUrlEtag($_SERVER['REQUEST_URI'],$etag=md5($url.$content));
function setPageCache($_SERVER['REQUEST_URI'],$content,$etag);
header("Etag: $etag");
echo $content;
?>

所有常见的陷阱适用：你都不可能不登录的用户，部分内容缓存可能是更理想的显示缓存页面，你是你自己负责缓存preventing陈旧的内容（可能使用在后台触发或数据库的修改，或者只是玩弄的 getUrlEtag 逻辑），等等等等。

您也可以玩弄 HTTP_IF_MODIFIED_SINCE 如果这是更容易控制。

You could also play around with HTTP_IF_MODIFIED_SINCE if that's easier to control.

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