How do you test if an nginx variable is set in Lua?

ssimpson · 2014-03-08T06:18:50+00:00

Hello! On Fri, Mar 7, 2014 at 9:20 AM, Yaroslav Rodionov wrote: > How openresty and redis/0mq pubsub can be integrated best way? > What exactly do yo...

How do you test if an nginx variable is set in Lua?

ssimpson

I'm trying to check if an nginx variable is set in lua. I'm doing

if ngx.var.myvar ~= "" then
...
end

where "myvar" isn't set in the nginx.conf. I'm getting

2014/03/07 14:09:50 [warn] 2127#0: *8 using uninitialized "myvar" variable, client: 127.0.0.1, server: localhost, request: "GET /no_cookies/index.html HTTP/1.1", host: "localhost:8080

in error.log. How do I test if the nginx variable is set?

agentzh

Hello!

On Fri, Mar 7, 2014 at 2:18 PM, simpson wrote:
> I'm trying to check if an nginx variable is set in lua. I'm doing
>
> if ngx.var.myvar ~= "" then

You should take into account nil values here too, that is, use the
following line instead:

    if ngx.var.myvar and ngx.var.myvar ~= "" then

> where "myvar" isn't set in the nginx.conf. I'm getting
>
> 2014/03/07 14:09:50 [warn] 2127#0: *8 using uninitialized "myvar" variable,

This warning is generated by the standard ngx_rewrite module, not ngx_lua.

And this harmless warning can be disabled by adding the following line
to your nginx.conf:

    uninitialized_variable_warn off;

See also http://nginx.org/en/docs/http/ngx_http_rewrite_module.html#uninitialized_variable_warn

Best regards,
-agentzh

ssimpson

It seems my problem is related to variable scope. In nginx.conf I have

    location /no_cookies {
        access_by_lua_file "check_access.lua";
        proxy_pass http://$proxy_machine$uri;
       }
    location /sess_cookies {
        set $sess_block_over_time_prefix "sess_";
         access_by_lua_file "check_access.lua";
        proxy_pass http://$proxy_machine$uri;
       }

When I access a page in /no_cookies, I'm checking ngx.var.sess_block_over_time_prefix and getting the error in the error log. If I change the first nginx block to

      location /no_cookies {
        set $sess_block_over_time_prefix "";
        access_by_lua_file "check_access.lua";
        proxy_pass http://$proxy_machine$uri;
       }

then it works. I appears that if you use a variable in one block it must exist in the other blocks if you wish to test these variables in lua. Otherwise you get an error message. I don't know why this is the case.

ssimpson

OK. Sorry. Just saw your reply. I'll try that.