Use normal public serve for reports.

app/controllers/reports_controller.rb

@@ -13,8 +13,4 @@ class ReportsController < ApplicationController
       kick_out
     end
   end
-
-  def show
-    send_file File.read(@@report_dir.join(params[:filename]))
-  end
 end

config/routes.rb

@@ -15,9 +15,7 @@ Rails.application.routes.draw do
 
   resources :grades, only: [:new, :create, :index, :edit, :update]
 
-  get '/reports/:filename', to: 'reports#show'
   post '/reports', to: 'reports#create'
 
-
   root to: "welcome#index"
 end