gistfile1.rb

class ApplicationController < ActionController::Base
  
  alias_method_chain :cache_page, :subdomain
  
  private
  
  ##
  # Inserts the currently requested subdomain as a directory in front of the
  # cached file location.  Assuming you've moved the default page cache 
  # storage location to /public/cache, a request to app1.example.com would be
  # cached as:
  # 
  #     RAILS_ROOT/public/cache/app1/index.html
  #     (page_cache_directory/subdomain/request_path)
  # 
  # If the request does not have a subdomain (a request directly to
  # http://example.com), the subdomain cache directory will default to 'www'.
  # 
  def cache_page_with_subdomain(content = nil, options = nil)
    subdomain = request.subdomains.last
    path      = "/#{subdomain || 'www'}/"
    path      << case options
      when Hash
        url_for(options.merge(:only_path => true, :skip_relative_url_root => true, :format => params[:format]))
      when String
        options
      else
        request.path
    end
    cache_page_without_subdomain(content, path)
  end
  
end