[PATCH 2 of 2] Cache: send conditional requests only for cached 200 OK responses

[Maxim Dounin]

Hello!

On Tue, Nov 25, 2014 at 05:14:48PM -0800, Piotr Sikora wrote:

> Hey Maxim,
> 
> > The question is: how many other status codes should be considered?
> > I _think_ that 200 and 206 is good enough list, but I'm not sure.
> 
> Well, even if we miss a status code or two (and I don't think that we
> do), then the worst thing that's going to happen is, to quote your
> argument from the other thread, "suboptimal operation, nothing really
> bad can happen", which is much, much better than the current
> situation.

Fair enough.

> > Here is the first problem in the upstream server: it returns an
> > error with the Last-Modified.  This is what nginx avoids for a
> > reason.
> 
> As far as I can tell, that's neither wrong nor forbidden by RFC.

Much like nginx behaviour to use it in the If-Modified-Since.  So 
nobody does anything wrong/forbidden, but there is a problem as a 
result.  And nginx already does at least two things to mitigate 
such problems on server-side, and it probably won't hurt much to 
add another client-side mitigation.

-- 
Maxim Dounin
http://nginx.org/