I'm trying to have openresty to reverse proxy TCP dynamicaly using lua.

For the start, I have :

    stream {
        server {
            listen     9291;
            set_by_lua_block $proxy '
                ngx.var.proxy = "10.128.128.3:8291"
            ';
            proxy_pass $proxy;
        }
    }

But openresty -t says:

nginx: [emerg] "set_by_lua_block" directive is not allowed here in /usr/local/openresty/nginx/conf/nginx.conf:129

I found many docs on dynamic proxy_pass, but all for 'http'.