Simple.

feed.rb

require 'net/http'
require 'xmlsimple'

module SomeSite
  class Feed
    attr_accessor :url, :cache_key, :storage, :xml, :http_adapter

    # Class responsible to search the uri and save in the store
    # The store need to implement the #write and #read method.
    #
    def initialize(url = 'http://www.somesite.com.br/plantao/rss2.xml', store = Rails.cache, http_adapter = Net::HTTP)
      @url          = url
      @storage      = store
      @cache_key    = 'feed_content'
      @http_adapter = http_adapter
    end

    # Iterates each entry evaluating a block with SomeSite::Feed::Entry as instance.
    #
    def each(&block)
      entries['channel'][0]['item'].each do |entry|
        block.call(entry)
      end
    end

    # Make a request to the url and return the same object to chain methods.
    #
    def get
      @xml = http_adapter.get(URI.parse(@url))
      self 
    end

    # Find in the storage for the default cache_key
    #
    def find
      @xml = storage.read(@cache_key)
    end

    # Make the xml parse and return all nodes from feed content
    #
    def entries
      XmlSimple.xml_in(find)
    end

    # Save the xml attribute in the datastore
    #
    def save
      get.storage.write(@cache_key, @xml)
    end
  end
end