opensoul.org

Need to force all URLs in a controller or action to be absolute URLs, but don’t want to use the *_url named routes or, even worse, :only_path => false everywhere?

Background

As we were putting the finishing touches on an awesome Facebook app today (yes I said “awesome” in the same sentence as “facebook app”…you’ll see), we needed to make it so that users can add the app as a tab in their profile. Facebook makes this very easy, but there’s an interesting quirk feature. From the developer’s wiki:

• Absolute URLs on a tab take the user to your application’s canvas page.
• Relative URLs are treated as if they are relative to your home canvas page and AJAX-loads in the tab.

We needed all of the URLs on the page to be absolute so that they would take the user out of the tab and into our application. So we were faced with two options:

1. Change all of our named routes from *_path to *_url and use explicit paths instead of polymorphic urls (you know, that thing that lets you do form_for @model, or link_to h(@model.name), @model)
2. Figure out some quick hack that forced Rails to generate absolute URLs on this one page and go on about our lives

The page reused a lot of components from all over the site, so we weren’t excited about option 1. And, like all good developers, we were just adverse to that much work.

So we started looking for a good fit for option 2. We needed to force :only_path to be false on any URL generation. There’s a way to specify default_url_options, but as the name implies, those are only defaults. Using the *_path named routes forces :only_path to true.

Solution

It turns out, Rails passes all URL generation through a method on your controller called #rewrite_options. So we just overrode that method to force :only_path to false on our one action. Here’s the code we used:

class ContentController < ApplicationController
  # …

  def profile
    # profile action
  end

private
  # Force absolute URLs on the profile tab.
  def rewrite_options(options)
    super(action_name == 'profile' ? options.merge(:only_path => false) : options)
  end
end

It’s slightly evil, but it worked beautifully.

We’ve been working on a Facebook app (yeah, I know, I’m sorry) and have had all kinds of fun challenges. We wanted to test FBML tags in the view, but the problem is that FBML uses namespaced elements.

It turns out, CSS selectors don’t work with namespaced elements. There is a CSS3 namespace module, but Rails’ #assert_select and RSpec’s #have_tag (built on #assert_select) don’t support them. We were going to have to turn to XPath, but #have_tag only supports CSS selectors.

But Hpricot supports XPath. A little searching revealed the rspec_hpricot_matchers plugin, which replaces have_tag with an Hpricot-backed version. The only problem is that the new version isn’t backwards compatible. So we forked it and renamed #have_tag to #match_element.

Usage

It’s pretty straight forward. Install the rspec_hpricot_matchers plugin, and include the module in the RSpec config in spec_helper.rb.

Spec::Runner.configure do |config|
  config.include RspecHpricotMatchers
end

Our view had something similar to:

<fb:multi-friend-input prefill_ids="<%= @friends.join(', ') %>" />

And in the view spec, we use #match_element with an XPath expression.

describe "things/edit.fbml.erb" do
  it "should prefill selected friends" do
    render "things/edit.fbml.erb"
    response.should match_element("//fb:multi-friend-input[@prefill_ids='333,444,555']")
  end
end