[TYPO3-mvc] Strange caching behaviour

[Helmut Hummel]

Hi Jan!

On 20.04.14 12:38, Jan Kornblum wrote:

> Now calling (1) again after this, the page displays the plugins output
> of (3), the show action instead of the list action!? The result of (3)
> seems to have been cached for (1), because a cHash was missing when
> calling (3).
>
> Is this a bug?

It works as desinged at least.

TYPO3 caches a page on first hit.
If different parameters cause a different page output, then the version 
of the page is cached which is rendered first.

Since there is the need to have different output for one page, different 
cache entries are written for one page in the following conditions:

1) Different page type
2) Different usergroup combinations
3) Different matched TypoScript conditions
4) Different (valid) cHash value

So if you call the page first with parameters that do not cause any of 
these conditions to be true, but renders different output than without 
these parameters, then still the page will be cached and you get this 
cached result even when skipping these parameters on consecutive calls.

> I'm aware that the caching mechanism can't work correctly when the
> cHash param is missing or incorrect but i'm sure that all the links are
> built correctly from inside my plugin (containing a cHash).
>
> The problem is, that this scenario regularly happens to a live website
> and i don't know how to prevent it (as everybody in the www might just
> call (3) without any cHash param).

Of course you can't control with which parameters your website is called 
and indeed this behavior is not wanted.

> How can i prevent this behaviour?

The issue you have is that a URL is called which (in the sense of the 
caching implementation) is not valid, as it misses the cHash which makes 
the URL valid.

You have some control what should happen in such a case, but first, you 
need to tell TYPO3 which parameters require a cHash to be calculated.

You can do so by adding all these parameters to:

TYPO3_CONF_VARS[FE][cHashRequiredParameters]

e.g.:

TYPO3_CONF_VARS[FE][cHashRequiredParameters] = 
tx_news_pi1[news],tx_news_pi1[action],tx_news_pi1[controller]

When configuring that and URLs are called with these parameters set, but 
no cHash parameter is set, then you can choose between two different 
behaviors:

1) Throw a 404 - Page Not Found error
2) Disable the cache

You can control this with the following configuration:

TYPO3_CONF_VARS['FE']['pageNotFoundOnCHashError']

I would recommend to let a 404 error occur in case the cHash is invalid 
and at the same time use and configure realurl so that all query 
parameters are transformed into a path. If you do so, realurl saves the 
cHash for the URL in the database and correctly populates it if the URL 
is requested.

Then you will have two different URLs similar to these:

/pluginpage.html
/my/show/model.html

Now it is impossible to call the second URL without cHash as realurl 
will automatically populate it.

Given the recommendation above the following URL:

pluginpage.html?tx_ext[controller]=MyController&tx_ext[action]=show&tx_ext[myModel]=123

Would lead to a 404 so that search engines will quickly throw this out 
of their index (asuming that search results are the main reason why such 
URLs are called).


HTH

Kind regards,
Helmut

-- 
Helmut Hummel
Release Manager TYPO3 6.0
TYPO3 Core Developer, TYPO3 Security Team Member

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