Broken precompiled assets in Rails 3.1 when deploying to a sub-URI

Question

I'm in the process of updating a Rails 3 app to use Rails 3.1 and as part of that, am making use of the new asset pipeline. So far, I've got everything working apart from one rather annoying problem I can't solve.

The application and all its assets works fine in development, but in production it is deployed to a sub-URI using Passenger (http://the-host/sub-uri/). The problem with this is that the assets are pre-compiled during deployment and one of my CSS (well, it's a .css.scss file) files is making use of the image-url helper from the sass-rails gem. Since during the pre-compilation process, the paths are hard-coded into the precompiled CSS file, the sub-uri is not taken account of:

In my .css.scss file:

body { background-image: image-url("bg.png"); }

The result in the compiled application-<md5-hash-here>.css file:

body { background-image: url(/assets/bg.png); }

What it should be to make it work correctly:

body { background-image: url(/sub-uri/assets/bg.png); }

Is this scenario just asking too much? If so, I'll have to switch back to the old non-asset-pipelined way and just serve my images and CSS from public. However it seems like something which should have been thought about and solved...? Am I missing the solution?

---

Edit 1: I should note that using the erb solution instead yields the same result, as one would expect.

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Edit 2: in response to Benoit Garret's comment

No, the problem isn't related to the config.assets.prefix. I tried setting that (to /sub-uri/assets rather than the default of /assets) but it turned out that was the wrong thing to do - it seems like this setting is already in relation to the root of the Rails app, not the server. Removing that (and thus returning to the default) has fixed all the weird issues that caused (and there were many, all the assets ended up in /sub-uri/sub-uri/assets - it was all very strange). The only problem is that the image-url helper and friends do not pick up the sub-URI when they are pre-compiled. Needless to say, this is logical since when it is pre-compiled, it couldn't possibly know that when it's running under Passenger, it'll be configured in this way. My question is how to inform it of this and thus end up with the correct paths in the precompiled result. If indeed it can be done.

My current workaround is to reference the iamge in the CSS like this: url(../images/bg.png) and place it in the non-pipelined public/images location. Hardly ideal since it doesn't benefit from the fingerprinting and everything which the pipeline provides.

Answer 1

Finally I've worked out a couple of workarounds/solutions.

1) From https://github.com/rails/sass-rails/issues/17 it looks like this could get fixed in sass-rails. I've monkey-patched helpers.rb myself along the lines of the proposed patch in the link above. I simply set the required environment variable in the asset precompile line in deploy.rb.

I do all my monkey patching in a single file config/initializers/gem_patches.rb. In this file I patched this method as:

module Sass
  module Rails
    module Helpers
      protected
      def public_path(asset, kind)
        path = options[:custom][:resolver].public_path(asset, kind.pluralize)
        path = ENV['PRODUCTION_URI'] + path if ENV['PRODUCTION_URI']
        path
      end
    end
  end
end

2) Alternatively if you are ok to embed images in the CSS, changing the stylesheet to have a .erb extension, and replacing the image-url("bg.png") with url(<%= asset_data_uri "bg.png" %>) will work without any need to change sass-rails. asset-data-uri doesn't exist as a pure Sass function so you have to use the Rails helper asset_data_uri.

Answer 2

In the latest Rails 3.1.3 you need to monkey patch a different module now, for it to work

This is what I did

module Sprockets
  module Helpers
    module RailsHelper

      def asset_path(source, options = {})
        source = source.logical_path if source.respond_to?(:logical_path)
        path = asset_paths.compute_public_path(source, asset_prefix, options.merge(:body => true))
        path = options[:body] ? "#{path}?body=1" : path
        if !asset_paths.send(:has_request?)
          path = ENV['RAILS_RELATIVE_URL_ROOT'] + path if ENV['RAILS_RELATIVE_URL_ROOT']
        end
        path
      end

    end 
  end
end

And in my deploy.rb I have:

desc "precompile the assets"
namespace :assets do
  task :precompile_assets do
    run "cd #{release_path} && rm -rf public/assets/* && RAILS_ENV=production bundle exec rake assets:precompile RAILS_RELATIVE_URL_ROOT='/my_sub_uri'"
  end
end
before "deploy:symlink", "assets:precompile_assets"

Answer 3

I'm using Rails 3.1.3 and deploying to a sub-URI successfully. I have NOT monkey-patched anything.

The key problems with this setup have been better discussed here. As you can see, the solution was applied to Rails 3.2 and never backPorted to 3.1.4.

But, I have came to a solution using Rails 3.1.3 that works for my setup.

Try this: (I'm no expert, just trying to contribute to solve a problem that hassled me for hours...)

environment.rb:

#at top:
ENV['RAILS_RELATIVE_URL_ROOT'] = '/rais'

production.rb:

config.assets.prefix = ENV['RAILS_RELATIVE_URL_ROOT'] ? ENV['RAILS_RELATIVE_URL_ROOT'] + '/assets' : '/assets'

routes.rb:

  Rais::Application.routes.draw do
       scope ENV['RAILS_RELATIVE_URL_ROOT'] || '/' do    #see config/environment.rb
             <<resources here>>
       end
  end

As you can see, I've put assets.prefix inside production.rb, not in application.rb After that you do:

rake assets:clear
rake assets:precompile

and than, test with the console:

RAILS_ENV=production rails console

Results:

foo = ActionView::Base.new
foo.stylesheet_link_tag 'application'
 => "<link href=\"/rais/assets/layout.css?body=1\" media=\"screen\" rel=\"stylesheet\" type=\"text/css\" />\n<link href=\"/rais/assets/application.css?body=1\" media=\"screen\" rel=\"stylesheet\" type=\"text/css\" />" 
foo.image_tag('arrow-up.png')
 => "<img alt=\"Arrow-up\" src=\"/rais/assets/arrow-up-ca314ad9b991768ad2b9dcbeeb8760de.png\" />" 

Answer 4

After a bit of digging around, I have found the issue. The issue is in Rails, specifically Sprockets::Helpers::RailsHelper::AssetPaths#compute_public_path. Sprockets::Helpers::RailsHelper::AssetPaths inherits from ActionView::AssetPaths and overrides a number of methods. When compute_public_path is called through the Sass::Rails::Resolver#public_path method is sass-rails, the rails sprocket helper picks up the task of resolving the asset. Sprockets::Helpers::RailsHelper::AssetPaths#compute_public_path defers to super which is ActionView::AssetPaths#compute_public_path. In this method there is a condition of has_request? on rewrite_relative_url_root as seen below:

def compute_public_path(source, dir, ext = nil, include_host = true, protocol = nil)
  ...
  source = rewrite_relative_url_root(source, relative_url_root) if has_request?
  ...
end

def relative_url_root
  config = controller.config if controller.respond_to?(:config)
  config ||= config.action_controller if config.action_controller.present?
  config ||= config
  config.relative_url_root
end

If you look at the internals of rewrite_relative_url_root it relies on a request to be present and the ability to derive it from the controller variable in order to resolve the relative url root. The issue is that when sprockets resolves these assets for sass it does not have a controller present and therefore no request.

The solution above didn't work in development mode for me. Here is the solution that I am using to make it work for now:

module Sass
  module Rails
    module Helpers
      protected
      def public_path(asset, kind)
        resolver = options[:custom][:resolver]
        asset_paths = resolver.context.asset_paths
        path = resolver.public_path(asset, kind.pluralize)
        if !asset_paths.send(:has_request?) && ENV['RAILS_RELATIVE_URL_ROOT']
          path = ENV['RAILS_RELATIVE_URL_ROOT'] + path
        end
        path
      end
    end
  end
end