Hello!

On Fri, Feb 01, 2013 at 08:59:38AM -0500, shrikeh wrote:

> Hi,
>
> I'm currently using OpenResty, and one of the things I am trying to do is
> have the backend send a specific header, and if that header is present, run
> a body_filter_by_lua call on the output. However, while I can use the
> $upstream_http_* vars for populating (i.e. I can go add_header SomeHeader
> $upstream_http_foo, and if Foo has been sent see SomeHeader: FooVar in the
> output. However, all tests for them seem to break.
>
> Example:
>
> location @backend {
> expires off;
> proxy_pass http://_varnish;
> set $test $upstream_http_csrf; # definitely exists, I can
> see it in the response headers

The "set" directive is rewrite module directive, and it is
executed during the rewrite request processing phase, which
happens before a request is passed to the upstream.

Unless the request was previusly processed using an upstream
server, the $test variable will be empty.

> add_header SomeHeader $upstream_http_csrf; # And I can read
> it, but....

This will work.

> if ($upstream_http_csrf = 1) { # doesn't matter if it's 1,
> "one" ~* "one", anything....
> # this block never gets called
> }

This won't, for the same reasons as outlined above - the "if"
directive can't see upstream response headers as it's executed
before a response is available.

> add_header someOtherHeader $test; # Not present in output as
> empty

See above.

> set_by_lua $use_token
> '
> if not ngx.var.sent_http_csrf == "" then
> return ngx.var.upstream_http_csrf
> end
> return "baz"
> '; # Always return 'baz'
> add_header WIllThisWork $use_token; # Again, empty

I'm not familiar with lua module, but likely the explanation is
the same - set_by_lua is executed before a response is available.

--
Maxim Dounin
http://nginx.com/support.html

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