[PATCH] Upstream: prioritise Cache-Control over Expires

[Vadim Fedorenko]

Hi Yugo!

Looks like another solution with the same concept - store additional information
about several headers. The second patch you proposed looks a bit overcomplicated
inside this additional function. I don't see any reasons to store information
about "Vary" header. AFAIU, weed special information about 3 headers: "Expires",
"Cache-Control" and "X-Accel-Expires". And we can call 
"ngx_http_upstream_cache_validate_regardless_order" only when cacheable is still
enabled after parsing all other headers. That approach will simplify the logic
inside ngx_http_upstream_cache_validate_regardless_order. I will prepare an
improved version if you don't mind.

Thanks,
Vadim

On 18.04.2022 02:14, Yugo Horie wrote:
> We're also interested in this issue because the CDN provider like us is 
> concerned about the problems with the headers that determine the cache freshness.
> It is often a serious problem used in Nginx as the origin server or the 
> intermediate cache server that has such problems.
> In those days, we also proposed a patch to resolve it.
> https://mailman.nginx.org/archives/list/nginx-devel@nginx.org/thread/ZQVPGEXAAHVL23TBBNMXLP4KDGDJCVTW/ 
> <https://mailman.nginx.org/archives/list/nginx-devel@nginx.org/thread/ZQVPGEXAAHVL23TBBNMXLP4KDGDJCVTW/>
> 
> But it seems to have declined. We sincerely wish to resolve it and intend to do 
> anything.
> 
> Thanks,
> Yugo Horie
> 
> 2022年4月18日(月) 4:51 Vadim Fedorenko via nginx-devel <nginx-devel at nginx.org 
> <mailto:nginx-devel at nginx.org>>:
> 
>     Hi Maxim!
> 
>     On 17.04.2022 02:55, Maxim Dounin wrote:
>      > Hello!
>      >
>      >
>      > [...]
>      >
>      > Thanks for the patch.
>      >
>      > I'm quite sceptical about attempts to fix this by introducing
>      > various flags and reverting cacheable status back to 1.  This is
>      > not how it should be fixed.
>      >
>     Yeah, the solution might be a bit complicated, but I couldn't find
>     another way without breaking concept of independent header parsing.
>     Could you please suggest something if you think that current approach
>     is wrong? The ticket that this patch tries to fix is 6 years old and
>     still has discussions going on without any solution.
> 
>     Thanks,
>     Vadim
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