you need to setup your middleware in your application.rb
config.middleware.insert_before "ActionDispatch::Cookies", "GeoFilterMiddleware"
and in your middleware do something like this:
def call(env)
status, headers, body = @app.call(env)
if from_uk?(env)
Rack::Utils.set_cookie_header!(headers, 'country', { :value => 'UK', :path => '/'})
end
[status, headers, body]
end