rss_tag.rb

class RenderRSS < Liquid::Block

  def initialize(tag_name, markup, tokens)
     super
     @markup =  markup
     @attributes = {}
     markup.scan(Liquid::TagAttributes) do |key, value|
      @attributes[key] = value
     end 

     RestClient.get(@attributes['source']).force_encoding('UTF-8')    
     @parsed_rss = SimpleRSS.parse(rss_data)
  end

  def render(context)
    rss_reg = {
      "title" => @parsed_rss.title,
      "items" => @parsed_rss.items.map{|u| u.stringify_keys}
    }    
     context.stack do
          context['feed'] = rss_reg
          render_all(@nodelist, context)
      end
  end
end

Liquid::Template.register_tag('rss', RenderRSS)