[PATCH] Upstream: Cache stale responses if they may be revalidated.

[Thorvaldur Thorvaldsson]

Hi,

Thanks again for your time, Maxim. And you're right,
I was assuming max-age=0 in all its forms to be equivalent
to no such header at all. I have a simple fix which I'll
post in a moment and then go ahead with adding a
relevant test case. Just let me know if I'm completely
on a wrong track here.

Best regards,
Thorvaldur

On Wed, Dec 16, 2015 at 4:52 PM, Maxim Dounin <mdounin at mdounin.ru> wrote:
> Hello!
>
> On Wed, Dec 16, 2015 at 03:37:27PM +0100, Thorvaldur Thorvaldsson wrote:
>
>> # HG changeset patch
>> # User Thorvaldur Thorvaldsson <thorvaldur.thorvaldsson at gmail.com>
>> # Date 1450190015 -3600
>> #      Tue Dec 15 15:33:35 2015 +0100
>> # Node ID 2c1f00c7f857c12587f0ac47323f04c6a881843a
>> # Parent  def9c9c9ae05cfa7467b0ec96e76afa180c23dfb
>> Upstream: Cache stale responses if they may be revalidated.
>>
>> Previously, the proxy cache would never store stale responses, e.g.,
>> when the "Cache-Control" header contained "max-age=0", even if the
>> "proxy_cache_revalidate" directive was "on" and the response included
>> both an "ETag" and a "Last-Modified" header. This came as a surprise.
>>
>> Now, a header like "Cache-Control: max-age=0, must-revalidate" can be
>> used along with an ETag/Last-Modified header to make nginx cache
>> responses that always require revalidation, e.g., when authorization is
>> required (and cheap).
>
> [...]
>
>> diff -r def9c9c9ae05 -r 2c1f00c7f857 src/http/ngx_http_upstream.c
>> --- a/src/http/ngx_http_upstream.c Sat Dec 12 10:32:58 2015 +0300
>> +++ b/src/http/ngx_http_upstream.c Tue Dec 15 15:33:35 2015 +0100
>> @@ -2815,11 +2815,16 @@
>>              valid = ngx_http_file_cache_valid(u->conf->cache_valid,
>>                                                u->headers_in.status_n);
>>              if (valid) {
>> -                r->cache->valid_sec = now + valid;
>> +                valid += now;
>> +                r->cache->valid_sec = valid;
>>              }
>>          }
>>
>> -        if (valid) {
>> +        if (valid > now
>> +            || (r->upstream->conf->cache_revalidate
>> +                && (u->headers_in.etag
>> +                    || u->headers_in.last_modified_time != -1)))
>> +        {
>>              r->cache->date = now;
>>              r->cache->body_start = (u_short) (u->buffer.pos - u->buffer.start);
>
> As far as I see, this still allows caching of all
> responses, even ones without Cache-Control/Expires/X-Accel-Expires
> and proxy_cache_valid configured.  This is not something that
> should happen because of revalidation enabled.
>
> You may want to rethink how the patch is expected to work.
>
> [...]
>
> --
> Maxim Dounin
> http://nginx.org/
>
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