Fix EZP-21547: headers not sent for cached errors

[bdunogier]

Fixes https://jira.ez.no/browse/EZP-21547.

Maybe not the right way to do it, but it at least highlights what needs to be fixed.

1. Makes sure error headers are stored in cache data (in addition to the error code & message)
2. Sends those headers again when using the cached version

Testing

Without the patch, if you go to http://ez/Media/ as anonymous user, you get a 401. If you reload, you will get a 200 OK.
With the patch, you will consistently get a 401.

[gggeek]

Maybe the correct way would be not to cache error page at all?
It is true that by never sending an http 200ok we make downstream caching proxies behave better, but in the end isn't the view-cache just another internal-http-cache in the end? (thinking the way that Sf does brings lots of clarity to the process ;-) )

[bdunogier]

Well, except that we don't have Symfony here.

I haven't traced back the whole history, but the use-case seems quite clear to me: you have a members section, and point people to an entry page of this section, to show them a login screen OR a registration form. If the page is heavily requested and uncached, the load on the system might be quite high.

It isn't ideal from an HTTP cache perspective, but after all it is not HTTP cache :-)

[lolautruche]

+1

[yannickroger]

+1

[bdunogier]

I'm wondering if @dpobel isn't -1 on the heade( $headers[] = ... ) part... :-)

[patrickallaert]

+1

[dpobel]

I'm not fan of this syntax, but I can live with that anyway :)

[bdunogier]

Syntax changed, merging.

[bdunogier]

Merged to master.

[bdunogier]

Extra commit: 1f86c9a.