nginx proxy and Date header

[Frank Liu]

I understand your argument when nginx is normally used as a frontend server
and "generation of the message" happens in nginx, but in this case, the
document
<http://nginx.org/en/docs/http/ngx_http_proxy_module.html#proxy_hide_header>
is about the nginx proxy module where nginx proxies the "message"
originated from upstream.
When nginx is used as a reverse proxy, I think nginx proxy module should
NOT remove the "Date" header from origin by default. Other reverse
proxies/caches, like Varnish, are doing the same:
http://ronwilliams.io/blog/post/rfc7231-compliant-http-date-headers


On Thu, May 23, 2019 at 2:55 AM Maxim Dounin <mdounin at mdounin.ru> wrote:

> Hello!
>
> On Wed, May 22, 2019 at 10:30:57AM -0700, Frank Liu wrote:
>
> > Is there a reason why by default nginx doesn't pass the "Date" header
> from
> > upstream?
> >
> http://nginx.org/en/docs/http/ngx_http_proxy_module.html#proxy_hide_header
> >
> > https://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html seems to
> indicate
> > Date header shouldn't be altered:
> >
> > The HTTP-date sent in a Date header SHOULD NOT represent a date and time
> > subsequent to the generation of the message. It SHOULD represent the best
> > available approximation of the date and time of message generation,
> unless
> > the implementation has no means of generating a reasonably accurate date
> > and time. In theory, the date ought to represent the moment just before
> the
> > entity is generated. In practice, the date can be generated at any time
> > during the message origination without affecting its semantic value.
> >
> > If nginx, as a proxy, changes the Date header, it may mess up the caching
> > model of HTTP in some pretty subtle ways in the downstream.
>
> And not changing the Date will mess pretty badly with various
> things as introduced in nginx, such as by the "expires"
> directive (not to mention SSI, as well as returning various
> responses from cache).
>
> Since nginx is primarily developed as a frontend server, it is
> generally considered to be an origin server in terms of RFC 2616.
> Accordingly, "generation of the message" in the quote above
> happens in nginx, and it uses the current date by default.
>
> If you want to preserve Date as returned by the upstream server,
> you can use the proxy_pass_header directive to do so.
>
> --
> Maxim Dounin
> http://mdounin.ru/
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>
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