Added Ruby helper; added README

README.md

@@ -0,0 +1,51 @@
+CDN asset URL helpers
+=====================
+
+This library contains a Rubygem and Django custom templatetag library to do the following:
+
+turn an asset path like
+
+    /images/thing.png
+
+into a CDN-pointed URL like
+
+    http://cdn.name.com/images/thing.png/{sha1}.png
+
+Rails
+-----
+
+Add `cdn_helpers` to your `Gemfile`:
+
+    gem 'cdn_helpers', :git => 'git@github.com:alphagov/cdn_helpers.git'
+
+In your `environments/production.rb`:
+
+    require 'cdn_helpers'
+    config.action_controller.asset_host = "http://cdn.url.gov.uk"
+    config.action_controller.asset_path = CdnHelpers::AssetPath
+
+Django
+------
+
+Add `cdn_helpers` to your `requirements.txt`:
+
+    -e git+ssh://git@github.com/alphagov/cdn_helpers.git#egg=cdn_helpers
+
+in `settings.py` add cdn_helpers to your list of installed apps:
+
+    INSTALLED_APPS = (
+        'django.contrib.auth',
+        ...
+        'cdn_helpers'
+    )
+
+in the appropriate `local_settings.py`:
+
+    APP_DEPLOYMENT_ENV = 'dev'   # (or staging, production)
+    CDN_HOSTS = ['cdn1', 'cdn2'] # (as appropriate for the environment)
+
+
+in templates use the `asset_url` helper:
+
+    <img src="{% asset_url "/images/thing.png" %}">
+    <img src="{% asset_url thing.image.src %}">

cdn_helpers.gemspec

@@ -15,7 +15,7 @@ Gem::Specification.new do |s|
   s.rubyforge_project = "cdn_helpers"
 
   s.files         = Dir[
-    'lib/**/*',
+    'rb/**/*',
     'README.md',
     'Gemfile',
     'Rakefile'

rb/cdn_helpers.rb

@@ -1,3 +1,18 @@
+require 'digest/sha1'
 module CdnHelpers
-  # Your code goes here...
+  module AssetPath
+    def self.asset_cache
+      @@asset_cache ||= {}
+    end
+
+    def self.call(path)
+      unless asset_cache.has_key?(path)
+        file_path = Rails.root.join('public', path.sub(/^\//, '')).to_s
+        sha1 = Digest::SHA1.file(file_path).hexdigest
+        extension = File.extname(path)
+        return asset_cache[path] = path + "/#{sha1[0..7]}#{extension}" 
+      end
+      asset_cache[path]
+    end
+  end
 end