nginx not returning updated headers from origin server on conditional GET

[B.R.]

>From what I understand, 304 answers should not try to modify headers, as
the cache having made the conditional request to check the correctness of
its entry will not necessarily update it:
https://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10.3.5.
The last sentence sums it all: '*If* a cache uses a received 304 response
to update a cache entry, [...]'
---
*B. R.*

On Sun, Sep 11, 2016 at 12:56 PM, jchannon <nginx-forum at forum.nginx.org>
wrote:

> I have nginx and its cache working as expected apart from one minor issue.
> When a request is made for the first time it hits the origin server,
> returns
> a 200 and nginx caches that response. If I make another request I can see
> from the X-Cache-Status header that the cache has been hit. When I wait a
> while knowing the cache will have expired I can see nginx hit my origin
> server doing a conditional GET because I have proxy_cache_revalidate on;
> defined.
>
> When I check if the resource has changed in my app on the origin server I
> see it hasn't and return a 304 with a new Expires header. Some may argue
> why
> are you returning a new Expires header if the origin server says nothing
> has
> changed and you are returning 304. The answer is, the HTTP RFC says that
> this can be done https://tools.ietf.org/html/rfc7234#section-4.3.4
>
> One thing I have noticed, no matter what headers are I add or modify, when
> the origin server returns 304 nginx will give a response with the first set
> of response headers it saw for that resource.
>
> Also if I change the Cache-Control:max-age header value from the first
> request when I return the 304 response it appears nginx obeys the new value
> as my resource is cached for that time however the response header value is
> that of what was given on the first request not the value that I modified
> on
> the 304 response.   This applies to all subsequent requests if the origin
> server issues a 304.
>
> I am running nginx version: nginx/1.10.1
>
> Posted at Nginx Forum: https://forum.nginx.org/read.
> php?2,269457,269457#msg-269457
>
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