304：未修改和前端缓存 [英] 304: Not modified and front end caching

问题描述

我正在使用PHP脚本来提供文件。
我希望能够在我的http响应中发送一个 304 未修改的标头，如果该文件自客户端上次下载以来没有更改。这似乎是Apache（以及大多数其他Web服务器）的一个功能，但我不知道如何通过PHP实现这一功能。

I am using a PHP script to serve files. I would like to be able to send back a 304 not modified header in my http response if the file has not changed since the client last downloaded it. This seems to be a feature in Apache (and most other web servers), but I have no clue how this can be implemented through PHP.

我听说过使用 $ _ SERVER ['HTTP_IF_MODIFIED_SINCE'] ，但此变量似乎没有出现在我的 $ _ SERVER 超级数组中。

I have heard of using $_SERVER['HTTP_IF_MODIFIED_SINCE'], but this variable does not seem to appear in my $_SERVER super array.

我的问题不是如何返回 304 标题，而是如何知道应该返回一个。

My question is not how to return a 304 header, but how to know that one should be returned.

编辑：问题是我的 $ _ SERVER ['HTTP_IF_MODIFIED_SINCE'] 未设置。这是我的 .htaccess 文件的内容：

The problem is that my $_SERVER['HTTP_IF_MODIFIED_SINCE'] is not set. This is the content of my .htaccess file:

ExpiresActive On 
ExpiresByType image/jpeg "modification plus 1 month"
ExpiresByType image/png "modification plus 1 month"
ExpiresByType image/gif "modification plus 1 month"
Header append Cache-Control: "must-revalidate" 


<IfModule mod_rewrite.c>
   RewriteEngine On
   RewriteCond $1 !^(controller\.php)
   RewriteRule (.*\.jpg|.*\.png|.*\.gif) controller.php/$1
</IfModule>

HTTP_IF_MODIFIED_SINCE 仍未出现在 $ _ SERVER 超级数组。

HTTP_IF_MODIFIED_SINCE still does not appear in the $_SERVER super array.

推荐答案

HTTP_IF_MODIFIED_SINCE 是正确的方法。如果你没有得到它，请检查Apache是​​否有 mod_expires 和 mod_headers 启用并正常运行。借用对PHP.net的评论：

HTTP_IF_MODIFIED_SINCE is the right way to do it. If you aren't getting it, check that Apache has mod_expires and mod_headers enabled and working properly. Borrowed from a comment on PHP.net:

$last_modified_time = filemtime($file); 
$etag = md5_file($file);
// always send headers
header("Last-Modified: ".gmdate("D, d M Y H:i:s", $last_modified_time)." GMT"); 
header("Etag: $etag"); 
// exit if not modified
if (@strtotime($_SERVER['HTTP_IF_MODIFIED_SINCE']) == $last_modified_time || 
    @trim($_SERVER['HTTP_IF_NONE_MATCH']) == $etag) { 
    header("HTTP/1.1 304 Not Modified"); 
    exit; 
}

// output data

这篇关于304：未修改和前端缓存的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！