Reloading rails middleware without restarting the server in development

user_1198440 0
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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".

rack-middleware rack ruby-on-rails-4 ruby-on-rails
4 Answers

Building up on @phoet's answer we can actually wrap any middleware with this kind of lazy loading, which I found even more useful:

class ReloadableMiddleware
  def initialize(app, middleware_module_name, *middleware_args)
    @app = app
    @name = middleware_module_name
    @args = middleware_args
  end

  def call(env)
    # Lazily initialize the middleware item and call it immediately
    @name.constantize.new(@app, *@args).call(env)
  end
end

It can be then hooked into the Rails config with any other middleware as its first argument, given as a string:

Rails.application.config.middleware.use ReloadableMiddleware, 'YourMiddleware'

Alternatively - I packaged it into a gem called reloadable_middleware, which can be used like so:

Rails.application.config.middleware.use ReloadableMiddleware.wrap(YourMiddleware)
user_1538860

In Rails 6 with the new default Zeitwork code loader, this works for me:

# at the top of config/application.rb, after Bundler.require    

# Load the middleware. It will later be hot-reloaded in config.to_prepare
Dir["./app/middleware/*.rb"].each do |middleware|
  load middleware
end

Below it in the section that configures your class Application, add hot-reloading in config.to_prepare:

middleware = "#{Rails.root}/app/middleware"
Rails.autoloaders.main.ignore(middleware)

# Run before every request in development mode, or before the first request in production
config.to_prepare do
  Dir.glob("#{middleware}/*.rb").each do |middleware|
    load middleware
  end
end
user_36707560
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