I want to "fake" 404 pages in Rails. In PHP, I only send headers with error codes as follows:

header("HTTP/1.0 404 Not Found");

How does Rails do this?

#1 building

The selected answer does not work in Rails 3.1 + because the error handler has been moved to middleware (see github issue ).

This is a solution that I am very satisfied with.

In ApplicationController:

  unless Rails.application.config.consider_all_requests_local
    rescue_from Exception, with: :handle_exception
  end

  def not_found
    raise ActionController::RoutingError.new('Not Found')
  end

  def handle_exception(exception=nil)
    if exception
      logger = Logger.new(STDOUT)
      logger.debug "Exception Message: #{exception.message} \n"
      logger.debug "Exception Class: #{exception.class} \n"
      logger.debug "Exception Backtrace: \n"
      logger.debug exception.backtrace.join("\n")
      if [ActionController::RoutingError, ActionController::UnknownController, ActionController::UnknownAction].include?(exception.class)
        return render_404
      else
        return render_500
      end
    end
  end

  def render_404
    respond_to do |format|
      format.html { render template: 'errors/not_found', layout: 'layouts/application', status: 404 }
      format.all { render nothing: true, status: 404 }
    end
  end

  def render_500
    respond_to do |format|
      format.html { render template: 'errors/internal_server_error', layout: 'layouts/application', status: 500 }
      format.all { render nothing: true, status: 500}
    end
  end

And in application.rb:

config.after_initialize do |app|
  app.routes.append{ match '*a', :to => 'application#not_found' } unless config.consider_all_requests_local
end

In my resources (show, edit, update, delete):

@resource = Resource.find(params[:id]) or not_found

Of course, this can be improved, but at least without covering the core functions of Rails, I have different views on not found and internal error.

#2 building

These will help you

Application controller

class ApplicationController < ActionController::Base
  protect_from_forgery
  unless Rails.application.config.consider_all_requests_local             
    rescue_from ActionController::RoutingError, ActionController::UnknownController, ::AbstractController::ActionNotFound, ActiveRecord::RecordNotFound, with: lambda { |exception| render_error 404, exception }
  end

  private
    def render_error(status, exception)
      Rails.logger.error status.to_s + " " + exception.message.to_s
      Rails.logger.error exception.backtrace.join("\n") 
      respond_to do |format|
        format.html { render template: "errors/error_#{status}",status: status }
        format.all { render nothing: true, status: status }
      end
    end
end

Error controller

class ErrorsController < ApplicationController
  def error_404
    @not_found_path = params[:not_found]
  end
end

views / errors / error_404.html.haml

.site
  .services-page 
    .error-template
      %h1
        Oops!
      %h2
        404 Not Found
      .error-details
        Sorry, an error has occured, Requested page not found!
        You tried to access '#{@not_found_path}', which is not a valid page.
      .error-actions
        %a.button_simple_orange.btn.btn-primary.btn-lg{href: root_path}
          %span.glyphicon.glyphicon-home
          Take Me Home

#3 building

To test error handling, you can do the following:

feature ErrorHandling do
  before do
    Rails.application.config.consider_all_requests_local = false
    Rails.application.config.action_dispatch.show_exceptions = true
  end

  scenario 'renders not_found template' do
    visit '/blah'
    expect(page).to have_content "The page you were looking for doesn't exist."
  end
end

#4 building

HTTP 404 status

To return the 404 header, simply use the: status option on the render method.

def action
  # here the code

  render :status => 404
end

If you want to render a standard 404 page, you can use the method extraction feature.

def render_404
  respond_to do |format|
    format.html { render :file => "#{Rails.root}/public/404", :layout => false, :status => :not_found }
    format.xml  { head :not_found }
    format.any  { head :not_found }
  end
end

And call it in action

def action
  # here the code

  render_404
end

If you want the operation to render an error page and stop, just use the return statement.

def action
  render_404 and return if params[:something].blank?

  # here the code that will never be executed
end

ActiveRecord and HTTP 404

Also remember that Rails saves some ActiveRecord errors, such as ActiveRecord::RecordNotFound, which displays the 404 error page.

This means you don't have to save the action yourself

def show
  user = User.find(params[:id])
end

When the user does not exist, User.find raises ActiveRecord::RecordNotFound. This is a very powerful feature. Look at the code below

def show
  user = User.find_by_email(params[:email]) or raise("not found")
  # ...
end

You can simplify this by delegating checks to Rails. Just use the exploded version.

def show
  user = User.find_by_email!(params[:email])
  # ...
end

#5 building

You can also use render files:

render file: "#{Rails.root}/public/404.html", layout: false, status: 404

You can choose whether to use the location of the layout.

Another option is to use exception to control it:

raise ActiveRecord::RecordNotFound, "Record not found."