Question about Cache Middleware

[llaville]

Hello Oscar,

I've used the cache middleware of release 3.19, and I've a question about multi-device usage !

The cache key is specified there https://github.com/oscarotero/psr7-middlewares/blob/master/src/Middleware/Cache.php#L121

That means the cache in PSR-6 pool is shared between all clients (desktop / mobile / tablet)

But the 304 is sent back to client device to tell it to use its device cache version. If a desktop client create a cache in PSR-6 pool (server side) it then use it by mobile client (that sould not probably have a cache version, if it's first call)

Perharps an issue ? Or did I'm wrong and missed something !

Thanks in advance for your answer. Laurent

[oscarotero]

Hi. The cache validation is done here: https://github.com/micheh/psr7-cache/blob/master/src/CacheUtil.php#L260

As you can see, the validation is done using the headers Last-Modified (from response) and If-Modified-Since (from request). If a device has not a cached version of a page it doesn't send the If-Modified-Since header, the cache validation is not passed and no 304 response will be sent.

Regards.

[llaville]

Hello again,

I think there is an issue in multi users environment. Let's me explains. Suppose we have at least two users with two browsers that send the same UserAgent header !

In such case, first user will generate a normal response and save it in cache (pool). Then after, the second user call the same URI but the response is already in cache pool (generated by first user). So as both users have the same UserArgent (headers sent), we reply a 304 to second user that does not have yet a cache copy in his browser.

Hope my explains are enough clear ?

If i'm right we should fix this situation : either with IP (ClientIp Middleware required) or with differenct cache key hash !

Tell me what you think about that !

Laurent

[oscarotero]

I think you're misunderstanding this middleware:

• User agent does not identify users, identify browser versions. And we are not using the user agent header at all.
• The cache does not save the response, just the headers of the response, that are used to validate the life time of the response.
• The behaviour of this middleware is simple:
  • Client A makes a request
  • Server return a response and say that the response is valid during 2 hours. In addition, save the headers of the response in the cache pool
  • Client B makes a request
  • Server return a response and say that the response is valid during 2 hours.
  • Client A makes the same request again. Because it has the response cached, send a If-Modified-Since to inform to the server that only need the response if it was modified since the last request.
  • Because the response is valid during 2 hours, if the last request was less than 2 hours ago, return a 304 (Not modified). If the last time was more than 2 hours ago, return a full response and update the the cache pool with the latest version.