Nginx: choose alias depending on a query string parameter

Question

I want my Nginx server to give away files depending on a query string parameter. I have directories for debug files and release files and want to distribute them according to a parameter value:

location /files/ {
    if ( $arg_isDebug = "true" )
    {
        alias "C:/DebugFiles/";
    }
    if ( $!arg_isDebug != "true" )
    {
        alias "C:/ReleaseFiles/Release/";
    }
}

But it gives me an error

"alias" directive is not allowed here ...

Why can't I write it inside an 'if' statement and is there a workaround for this?

Answer 1

Why can't I write it inside an 'if' statement

The documentation states that alias can only be used in a location context.

is there a workaround for this?

Use a map directive.

For example:

map $arg_isDebug $alias {
default   "C:/ReleaseFiles/Release/";
true      "C:/DebugFiles/";
}

server {
    ...
    location ^~ /files/ {
        alias $alias;
    }
}

The map block is declared outside of the server block. Both the location value and alias value should end with / or neither end with /. You may want to use the ^~ operator to avoid a potential conflict with any regular expression locations within the same server block.