discourse/lib/middleware/discourse_public_exceptions.rb

# since all the rescue from clauses are not caught by the application controller for matches
# we need to handle certain exceptions here
module Middleware
  class DiscoursePublicExceptions < ::ActionDispatch::PublicExceptions

    def initialize(path)
      super
    end

    def call(env)
      # this is so so gnarly
      # sometimes we leak out exceptions prior to creating a controller instance
      # this can happen if we have an exception in a route constraint in some cases
      # this code re-dispatches the exception to our application controller so we can
      # properly translate the exception to a page
      exception = env["action_dispatch.exception"]
      response = ActionDispatch::Response.new

      if exception
        fake_controller = ApplicationController.new
        fake_controller.response = response

        if ApplicationController.rescue_with_handler(exception, object: fake_controller)
          return [response.status, response.headers, response.body]
        end
      end
      super
    end

  end
end