Rails run code before every request before application.rb - ruby-on-rails

Question

I want to run a piece of code in rails app before every request. Also, it should run before even reaching application_controller.rb.
I know that we can put such stuff in config/initializers or application.rb. But, I want to run this before every request.

Answer 1

Sounds like a job for Rack middleware. You can checkout the Rails on Rack Guide and the RailsCast for details.
So put something like the following in lib:
#lib/my_app_middleware.rb
class MyAppMiddleware
def initialize(app)
#app = app
end
def call(env)
# place the code that you want executed on every request here
end
end
And the following in config/application.rb to enable the middleware
config.middleware.use MyAppMiddleware
Check that its inserted ok:
rake middleware
Thats it!

Answer 2

You'll want to write some Rack Middleware. It's easy to do, here's a simple example which gets the subdomain for the purpose of multi tenant scoping:
class ClientSetup
def initialize(app)
#app = app
end
def call(env)
#request = Rack::Request.new(env)
Multitenant.current_tenant = Tenant.find_by_subdomain!(get_subdomain)
#app.call(env)
end
private
def get_subdomain
host = #request.host
return nil unless !(host.nil? || /\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}$/.match(host))
subdomain = host.split('.')[0..-3].first
return subdomain unless subdomain == "www"
return host.split('.')[0..-3][1]
end
end
There's loads more examples around. You then need to add this class to your middleware stack with:
config.middleware.use 'ClientSetup'
in your application.rb.

Answer 3

It's usually a subclass of ApplicationController that gets called when routing dispatches to one of your actions. That being said, if you really want to execute code before the controller is even called (before the before_filters ... etc) then you can modify the chain of middlewares in Rails like so:
config.middleware.insert_after(Rails::Rack::Logger, MyCustomMiddlewareClass)
You can read here for more info: http://guides.rubyonrails.org/rails_on_rack.html#action-dispatcher-middleware-stack.
The example above may change depending on what you are trying to do.