Nginx serves response with 200 even after calling ngx.exit() - nginx

Question

I am trying to serve static content from S3. I am using nginx and lua script for its configuration. I am new to both nginx and lua.
The task that I want to achieve is :
Get request URL into nginx.
Authenticate query params of url.
Serve from S3 if parameters are valid.
Send error response if parameters are not valid.
My nginx.conf file is as follows :
location ~ "^/media/(.*?)/(.*?)/(.*)$" {
set $mediaUrl "$1/$2/$3";
set $key "$2/$3"
set $target http://$1.s3.amazonaws.com
rewrite_by_lua "
local uri = '/authenticate'
local res = ngx.location.capture(uri, {args = { param = '/xmedia/'.. ngx.var.mediaUrl }})
if (res.status ~= 200) then
return ngx.exit(ngx.HTTP_GONE)
end
";
rewrite .* /$key break;
proxy_pass $target;
}
location "/authenticate" {
proxy_set_header Range "";
proxy_set_header Content-Range "";
set_by_lua $param "
local params = ngx.req.get_uri_args()
return params.param
";
set $test_url http://127.0.0.1:some_port/authenticate?url=$param;
proxy_pass $test_url;
}
I my case, if authenticate returns 200, then everything works fine. But even if authenticate returns null, nginx returns correct file and does't give error report specified in if statement : return ngx.exit(ngx.HTTP_GONE).
Am I doing something wrong? How to achieve expected behavior in efficient manner?
Thanks.

Answer 1

As already mentioned on your question's comments, the HttpRewriteModule is always executed before rewrite_by_lua; therefore you have to put the logic on the rewrite_by_lua section using ngx.req.set_uri, like this:
location ~ "^/media/(.*?)/(.*?)/(.*)$" {
set $mediaUrl "$1/$2/$3";
set $key "$2/$3"
set $target http://$1.s3.amazonaws.com
rewrite_by_lua "
local uri = '/authenticate'
local res = ngx.location.capture(uri, {args = { param = '/xmedia/'.. ngx.var.mediaUrl }})
if (res.status ~= 200) then
ngx.exit(ngx.HTTP_GONE)
else
ngx.req.set_uri(string.format('/%s', ngx.var.key))
end
";
proxy_pass $target;
}
...