use route helper post_url

app/controllers/posts_controller.rb

@@ -1,6 +1,4 @@
 class PostsController < ApplicationController
-  helper_method :permalink_url
-
   # Archive page
   #
   # @return [Hash] posts keyed by month and year. e.g. 'June 2012'
@@ -33,12 +31,4 @@ def show
   def error
     raise "something went wrong"
   end
-
-  # Returns fully qualified url for given permalink
-  # @param [URI] permalink
-  def permalink_url(permalink)
-    uri = URI.parse(request.url)
-    uri.path = '/posts' + permalink
-    uri
-  end
 end

app/views/posts/index.xml.builder

@@ -12,7 +12,7 @@ xml.rss(:version => "2.0") {
           xml.description { xml.cdata!(post.description) }
           xml.author("Jerry Cheung")
           xml.pubDate(post.date.rfc822)
-          xml.link(permalink_url(post.permalink))
+          xml.link(post_url(post.permalink))
         end
       end
     end

test/integration/production_test.rb

@@ -65,3 +65,9 @@ class HerokuTest < ActiveSupport::TestCase
     assert_equal 'http://www.whatcodecraves.com/', res.headers['Location']
   end
 end
+
+class GitHubPagesTest < ActiveSupport::TestCase
+  include ProductionTests
+
+  self.base_url = 'http://jch.github.io/'
+end