Hello!

On Thu, Dec 12, 2013 at 11:36:21PM +0000, Paul Taylor wrote:

> Hi Maxim,
> Thanks for your response. You’re right! Using the map did work
> (I thought I’d tried that, but must have been tired!).
> So, now I have one other challenge, the value of $foo that you
> define below is needed to identify whether to cache the response
> of not. The only issue is that I have a number of other
> directives that I also need to add into the mix - therefore I
> use the set_by_lua code to nest/combine OR within an if
> statement…code below (I’ve kept the variable name as foo, so
> it’s clear which I’m referring to):
> map $upstream_http_x_no_cache $foo {
> "" 0;
> default 1;
> }
> set_by_lua $bypass_cache '
> local no_cache_dirs = tonumber(ngx.var.no_cache_dirs) or 0
> local logged_in = tonumber(ngx.var.logged_in) or 0
> local no_cache_header = tonumber(ngx.var.foo) or 0
>
> if((no_cache_dirs == 1) or (no_cache_header == 1) or
> (logged_in == 1)) then
> return 1;
> end
>
> return 0;
> ';
> Now when I make the Lua local variable declaration in order to
> use it, the value of $upstream_http_x_no_cache is reset to 0,
> even when it was set as 1 originally. If I comment out the line
> declaring the local variable within the Lua call, it returns to
> being a value of 1 again.
> Am I getting the sequencing of events wrong again? Is there any
> way that I can get the value of $upstream_http_x_no_cache into
> this Lua block, or would I need to do it another way?

Are you going to use the result in proxy_no_cache? If yes, you
can just use multiple variables there, something like this should
work:

proxy_no_cache $upstream_http_x_no_cache
$no_cache_dirs
$logged_in;

See here for details:

http://nginx.org/r/proxy_no_cache

> Thanks very much for your help so far Maxim.
> Paul
> __________________________________________________________________
> Hello!
>
> On Thu, Dec 12, 2013 at 07:19:56PM +0000, Paul Taylor wrote:
>
> > I’m in the process of making some amends to an environment,
> > where my upstream servers are sending a custom header
> > (X-No-Cache), which I need to detect and alter caching rules
> > within the configuration.
> >
> > The custom header is visible within the output, and I can
> > re-output it as another header through configuration (i.e.
> > add_header X-Sent-No-Cache $sent_http_x_no_cache; ).
> >
> > However, as soon as I perform any type of testing of this custom
> > header, it disappears.
> >
> > For example, if I was to perform a map on the custom header, try
> > to set an Nginx variable to the value of the header, or test
> > within an IF statement, any future call to this header is no
> > longer possible. Additionally any setting or testing of the
> > header fails.
>
> Both "set" and "if" directives you mentioned are executed _before_
> a request is sent to upstream, and at this point there is no
> X-No-Cache header in the response. Due to this, using the
> $sent_http_x_no_cache variable in "set" or "if" will result in an
> empty value, and this value will be cached for later use.
>
> It's not clear what you are trying to do so I can't advise any
> further, but certainly using the $sent_http_x_no_cache variable in
> "if" or "set" directives isn't going to work, and this is what
> causes behaviour you see.
>
> Just a map{} should work fine though - as long as you don't try to
> call the map before the X-No-Cache header is actually available.
> E.g., something like this should work fine:
>
> map $sent_http_x_no_cache $foo {
> "" empty;
> default foo;
> }
>
> add_header X-Foo $foo;
>
> It might be also a goo idea to use $upstream_http_x_no_cache
> variable instead, see here:
>
> http://nginx.org/en/docs/http/ngx_http_upstream_module.html#variables
>
> --
> Maxim Dounin
> http://nginx.org/
>

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> http://mailman.nginx.org/mailman/listinfo/nginx


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

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