我在 PHP 中执行 HTTP Conditional Get answers 是否可以?

问题描述

经过大量搜索，阅读了我找到的每个教程并在这里提出了一些问题，我终于设法正确地回答了(至少我认为)if-none-match 和 if-modified-since HTTP 请求.

After searching a lot, reading every tutorials I've found and asking some questions here, I've finally managed to answer corrctly (at least I think) to if-none-match and if-modified-since HTTP requests.

简要回顾一下，这是我对每个可缓存页面所做的:

To do a quick recap, this is what I do on every pages cacheable:

session_cache_limiter('public'); //Cache on clients and proxies
session_cache_expire(180); //3 hours
header('Content-Type: ' . $documentMimeType . '; charset=' . $charset);
header('ETag: "' . $eTag . '"'); //$eTag is a MD5 of $currentLanguage + $lastModified
if ($isXML)
    header('Vary: Accept'); //$documentMimeType can be either application/xhtml+xml or text/html for XHTML (based on $_SERVER['HTTP_ACCEPT'])
header('Last-Modified: ' . $lastModified);
header('Content-Language: ' . $currentLanguage);

此外，每个页面都有自己的 URL(适用于每种语言).例如，index.php"将在英文 URL/en/home"和法文 URL/fr/accueil"下提供.

Also, every page have it's own URL (for every languages). For example, "index.php" will be served under URL "/en/home" in English and "/fr/accueil" in French.

我的大问题是仅在需要时回答304 Not Modified"到 if-none-match 和 if-modified-since HTTP 请求.

My big problem was to answer a "304 Not Modified" to if-none-match and if-modified-since HTTP requests only when needed.

我找到的最好的文档是:http://rithiur.anthd.com/tutorials/conditionalget.php

The best doc I've found is: http://rithiur.anthd.com/tutorials/conditionalget.php

这是我对它的实现(这段代码在可以缓存的页面上被称为 ASAP):

And this is the implementation I did of it (this piece of code is called ASAP on pages that can be cached):

$ifNoneMatch = array_key_exists('HTTP_IF_NONE_MATCH', $_SERVER) ? $_SERVER['HTTP_IF_NONE_MATCH'] : false;
$ifModifiedSince = array_key_exists('HTTP_IF_MODIFIED_SINCE', $_SERVER) ? $_SERVER['HTTP_IF_MODIFIED_SINCE'] : false;

if ($ifNoneMatch !== false && $ifModifiedSince !== false)
{
    //Both if-none-match and if-modified-since were received.
    //They must match the document values in order to send a HTTP 304 answer.
    if ($ifNoneMatch == $eTag && $ifModifiedSince == $lastModified)
    {
        header('Not Modified', true, 304);
        exit();
    }
}
else
{
    //Only one header received, it it match the document value, send a HTTP 304 answer.
    if (($ifNoneMatch !== false && $ifNoneMatch == $eTag) || ($ifModifiedSince !== false && $ifModifiedSince == $lastModified))
    {
        header('Not Modified', true, 304);
        exit();
    }
}

我的问题有两个:

• 这是正确的做法吗?我的意思是当发送 if-none-match 和 if-modified-since 时，both 必须匹配才能回答 304，如果只发送两者中的一个，则只匹配这个就可以发送304?
• 在此处描述的上下文中使用时，这 2 个片段是否对公共缓存友好(我的意思是代理 和 Web 浏览器上的缓存友好)?

• Is it the correct way to do it? I mean when if-none-match and if-modified-since are sent, both must match to answer a 304, and if only one of the two is sent, only matching this one is OK to send a 304?
• When used in the context described here, is these 2 snippets are public cache friendly (I mean cache friendly on proxies and Web browsers)?

顺便说一句，我只使用 PHP 5.1.0+(我不支持低于该版本的版本).

BTW, I use PHP 5.1.0+ only (I don't support versions lower that that).

增加了赏金...我希望得到高质量的答案.如果您猜到了什么，请不要回答/投票！

Added bounty... I expect quality answer. Don't answer/vote if you are guessing something!

推荐答案

• 这不太正确.请看一下算法:alt text http://img532.imageshack.us/img532/1017/cache.png
• 该解决方案对代理友好，您可以使用 Cache-control: proxy-revalidate 来强制缓存遵循您提供的有关资源的任何新鲜信息(仅适用于共享|代理缓存)

以下是可能有帮助的功能:

Here is the function that might help:

function isModified($mtime, $etag) {
    return !( (
        isset($_SERVER['HTTP_IF_MODIFIED_SINCE'])
        && 
        strtotime($_SERVER['HTTP_IF_MODIFIED_SINCE']) >= $mtime
    ) || (
        isset($_SERVER['HTTP_IF_NONE_MATCH'])
        && 
        $_SERVER['HTTP_IF_NONE_MATCH'] == $etag
    ) ) ;
}

我建议你看看下面的文章:http://www.peej.co.uk/articles/http-caching.html

I suggest that you take a look at the following article: http://www.peej.co.uk/articles/http-caching.html

更新:

[AlexV] 甚至可以同时接收 if-none-match 和 if-modified-since 吗?

[AlexV] Is is even possible to receive if-none-match AND if-modified-since at the same time?

你绝对可以同时设置.然而:

You can definitely have both set. However:

如果没有一个实体标签匹配，那么服务器可以执行请求的方法，就好像 If-None-Match 头域不存在，但也必须忽略任何 If-Modified-Since 头域在要求.也就是说，如果没有实体标签匹配，则服务器不得返回 304(未修改)响应.

If none of the entity tags match, then the server MAY perform the requested method as if the If-None-Match header field did not exist, but MUST also ignore any If-Modified-Since header field(s) in the request. That is, if no entity tags match, then the server MUST NOT return a 304 (Not Modified) response.

RFC2616 #14.26

示例值(W 代表弱"；在 RFC2616 #13.3.3):

Example values (W stands for 'weak'; read more in RFC2616 #13.3.3):

If-None-Match: "xyzzy", "r2d2xxxx", "c3piozzzz"
If-None-Match: W/"xyzzy", W/"r2d2xxxx", W/"c3piozzzz"
If-Modified-Since: Sat, 29 Oct 1994 19:43:31 GMT
If-None-Match: *

作为一种特殊情况，值*"是匹配资源的任何当前实体.

As a special case, the value "*" matches any current entity of the resource.

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