Custom error pages in rails applications

Ruby on rails is shipped with html-based error pages, but with some easy steps you can create your own erb-based pages. So, let’s do it.

Firstly you need to create controller, views and routes for your pages.

$ rails g controller errors not_found unprocessable unacceptable internal_server_error

This generator will create at least following files - app/controllers/errors_controller.rb, app/views/errors directory and add routes to your config/routes.rb

errors_controller.rb:

class ErrorsController < ApplicationController
  layout false

  def not_found
    render status: :not_found
  end

  def unprocessable
    render status: :unprocessable_entity
  end

  def unacceptable
    render status: :not_acceptable
  end

  def internal_server_error
    render status: :internal_server_error
  end
end

config/routes.rb:

  ### Errors
  match "/404", to: "errors#not_found", via: :all
  match "/406", to: "errors#unacceptable", via: :all
  match "/422", to: "errors#unprocessable", via: :all
  match "/500", to: "errors#internal_server_error", via: :all

Now, you need to disable default rails error handler. To do that you need to add following line to your config/application.rb

  class Application < Rails::Application

    # use custom error pages
    config.exceptions_app = routes

  end

If you want to test error pages locally, you need to set following option in your config/environments/development.rb

  # Show full error reports.
  config.consider_all_requests_local = false

Almost perfect, but I’d like to propose you some improvements. Let’s look back to config/environments/development.rb and to some changes

  # Show full error reports.
  config.consider_all_requests_local = !Rails.root.join("tmp/errors-dev.txt").exist?

When you start your application, it will check for file tmp/errors-dev.txt and enable or disable custom error pages. Then, let’s create file lib/tasks/dev.rake with following code

namespace :dev do
  desc "Use custom error pages"
  task :errors do
    if File.exist?("tmp/errors-dev.txt")
      puts "Now you'll use default (development) error pages" if FileUtils.rm("tmp/errors-dev.txt")
    elsif FileUtils.touch("tmp/errors-dev.txt")
      puts "Now you'll use custom error pages"
    end
  end
end

Every time you need to enable custom error pages locally, just run in console

$ rake dev:errors

then restart your server, and you’ll switch error pages from default to custom and back.