Rails: Dynamic 404s, authlogic, Cucumber, and rescue_from

I'm using Rails, Cucumber, and authlogic. I want my 404 pages to be rendered dynamically; that way, I can use my application-wide layout, which is a lot friendlier for lost users. I want ActiveRecord::RecordNotFound exceptions to be handled by the dynamic 404 page. I want Cucumber tests to verify that everything is working correctly.

Getting everything working together at the same time turned out to be extremely challenging. Cucumber made it hard for me to test my ActiveRecord::RecordNotFound handling. authlogic made it impossible for me to catch ActionController::RoutingError exceptions. Defining ApplicationController#render_optional_error_file as described here conflicted with authlogic and/or Cucumber. After several hours, I finally got it all working. Here's how:

First, I added the following to ApplicationController:

# Note, I can't use rescue_from to catch ActionController::RoutingError,
# otherwise authlogic breaks.  Hence, I set a default route instead.
rescue_from ActiveRecord::RecordNotFound, :with => :render_404
...
# I'm handling 404s manually so that I can use the application-wide layout.
def render_404
  render :template => "errors/error_404", :status => "404 Not Found"
end

Note, render_404 must be a public method.

At the bottom of routes.rb, I have:

# If all else fails, render a 404.
map.connect '*path', :controller => :application, :action => :render_404

In app/views/errors/error_404.html.erb, I have:

Sorry, the page you were looking for does not exist.

That takes care of rendering 404s if no routes match or if there is an ActiveRecord::RecordNotFound exception.

My Cucumber tests look something like:

Scenario: there should be a custom 404 page for routing errors
  Given I am on the homepage
  And I am simulating a remote request
  When I am on an invalid URL
  Then I should get a "404 Not Found" response
  And I should see "Sorry, the page you were looking for does not exist."
  And I should see "Log In"

Scenario: there should be a custom 404 page for record not found errors
  Given I am logged in as admin
  And I am simulating a remote request
  When I am on an invalid user
  Then I should get a "404 Not Found" response
  And I should see "Sorry, the page you were looking for does not exist.

In features/step_definitions/helper_steps.rb, I have:

def assert_response_status(http_status, message)
  response.status.should == "#{http_status} #{message}"
end

Then /^I should get a "(\d+) ([^"]+)" response$/ do |http_status, message|
  assert_response_status(http_status, message)
end

Given /^I am simulating a remote request$/ do
  header "REMOTE-ADDR", "10.0.1.1"
end

Note, the REMOTE-ADDR header is necessary or else Rails will render a normal exception page when you're trying to test the 404 page.

In features/support/env.rb b/features/support/env.rb I have:

# Comment out the next line if you want Rails' own error handling
# (e.g. rescue_action_in_public / rescue_responses / rescue_from)
#
# I'm commenting it out in order to test that my 404 handling (using
# rescue_from) works properly.
# Cucumber::Rails.bypass_rescue

Update: Please see the comments on bypass_rescue and @allow-rescue below.

Figuring that out took the longest. Cucumber was monkey patching Rails behind my back. I spent a few hours trying to figure out why my Rails rescue_from clause wasn't running when it turned out that Cucumber was to blame.

In features/support/paths.rb, I have these paths defined:

when /an invalid URL/
  "/totally_bogus_dude"
when /an invalid user/
  user_path(-1)

Finally, I added the following to public/404.html:

<!--
  In theory, this file should no longer be necessary since I'm handling 404s
  dynamically.  I'm going to leave it here in case something breaks behind my
  back.
-->

Whew! That was rough!