Mimicking the ‘devise_for’ Devise routes helper

Mounting a path outside your Rails Engine’s namespace

TL;DR add a method in ActionRouting::Dispatch::Mapper

Devise has this nifty helper that you can use in your config/routes.rb file to mount paths:

# config/routes.rb
devise_for :users

At Bloom we we’re building a Rails engine that helps Rails apps to become Stellar Anchors. One of the requirements in becoming part of the Stellar ecosystem is to adhere to their protocol; a part of that protocol requires services to mount a /.well-known/stellar endpoint that contains a toml file. The toml file specifies where 3rd-parties can check where they can transact/integrate with your organization using Stellar.

With that said: it would be nice if the users of that Rails engine could have that /.well-known/stellar easily in their app . Since Rails engines get mounted via mount MyEngine => "/my_engine" you can’t really supply paths outside of that isolated namespace unless you do something really funky.

It would be nice if we could mimic Devise’s devise_for

# config/initializers/my_engine.rb
# or whatever you use to require it in your app
MyEngine.setup do
  ...
end
# config/routes.rb
Rails.application.routes.draw do
  ...
  mount MyEngine => "/my_engine"
  mount_some_path_outside_my_engine
  ...
end

Opening up the Devise gem, you could see that they’ve actually added devise_for in ActionDispatch::Routing::Mapper and it calls resources and other familiar Rails route methods. It’s really educational just reading through it.

So, in our Rails engine, we could do something like:

module ActionDispatch
  module Routing
    class Mapper
      def mount_some_path_outside_my_engine
        # stellar_base/home#show is a controller inside 
        # the Rails Engine
        get(
          "/.well-known/stellar" => "stellar_base/home#show",
          :as => :stellar_toml,
          :defaults => { format: "toml" },
        )
      end
    end
  end
end

You can then write an spec/acceptance for this in your Rails engine, so people would know and expect that the helpers do mount a path outside your engine namespace.