Reloading rails middleware without restarting the server in development

Question

I have a rails 4 app with middleware located at lib/some/middleware.rb which is currently injected into the stack though an initializer like so:

MyApp::Application.configure.do |config|
    config.middleware.use 'Some::Middleware'
end

Unfortunately, any time I change something I need to restart the server. How can I reload it on each request in development mode? I've seen similar questions about reloading lib code with either autoloading or wrapping code in a to_prepare block but I'm unsure how that could be applied in this scenario.

Thanks, - FJM

Update #1

If I try to delete the middleware and then re-add it in a to_prepare block I get an error "Can't modify frozen array".

Answer 1

I thought that at some point Rails was smart enough replacing middleware code at runtime, but I may be wrong.

Here is what I came up with, circumventing Ruby class loading craziness and leveraging Rails class reloading.

Add the middleware to the stack:

# config/environments/development.rb
[...]
config.middleware.use "SomeMiddleware", "some_additional_paramter"

Make use of auto-reloading, but make sure that the running rails instance and the already initialized middleware object keep "forgetting" about the actual code that is executed:

# app/middlewares/some_middleware.rb
class SomeMiddleware
  def initialize(*args)
    @args = args
  end

  def call(env)
    "#{self.class}::Logic".constantize.new(*@args).call(env)
  end

  class Logic
    def initialize(app, additional)
      @app        = app
      @additional = additional
    end

    def call(env)
      [magic]
      @app.call(env)
    end
  end
end

Changes in Logic should be picked up by rails auto reloading on each request.

I think that this actually might become a useful gem!