Question

Is there a way I could pass an argument to a controller action call from middleware?

This is the action in controller code

# in my_controller.rb
# 
def print_name(name)
    render :text => "Hello, #{name}!"
end

Here’s the code from my middleware that calls this action

# in middleware
#
def call(env)
  env['action_controller.instance'].class.action(:print_name).call(env)
end

This of course raises ArgumentError.

I’m unaware how can I pass an argument to action call. Here’s the source:

# in action_pack/lib/action_controller/metal.rb
#
def self.action(name, klass = ActionDispatch::Request)
      middleware_stack.build(name.to_s) do |env|
        new.dispatch(name, klass.new(env))
      end
end

As you can see, it returns a rack endpoint from provided controller action. I see no way I could pass an argument here.

I ended up changing the controller dynamically with class_eval and then calling the controller method from that proxy method.

# in middleware
#
def define_proxy_method(klass)
      klass.class_eval do
            def call_the_real_method
              print_name(request.env['fake_attribute'])
            end
      end
 end

def call(env)
  define_proxy_method(env['action_controller.instance'].class)
  env['fake_attrbute'] = "Yukihiro"
  env['action_controller.instance'].class.action(:call_the_real_method).call(env)
end

This seems dirty and I would like to know of a better way. Thanks.

Answer 1

You don’t want to put arguments on your action. Middleware should only interact with the request environment, not try to call into the controller directly.

You can pass the same value in the params hash:

# middleware
#
def call(env)
  request = Rack::Request.new(env)
  request['name'] = get_name
end

and read from the params hash in the controller:

# my_controller.rb
# 
def print_name
    render :text => "Hello, #{params['name']}!"
end