Some useful Jekyll tags for generating RSS/Atom feeds.

feed.rb

require 'nokogiri'
require 'uri'

module FeedTags

  def absolute_url(url, base='/')
    return url  if url.match /^(javascript|data):/
    root = @context.registers[:site].config['home']
    URI.join(root, base, url).to_s
  end

  def date_to_atom(dt)
    dt.iso8601
  end

  def date_to_rss(dt)
    dt.rfc2822
  end

  def portable_html(html, base='/')
    doc = Nokogiri::HTML::DocumentFragment.parse html
    doc.css('a').each {|a| a['href'] = absolute_url(a['href'], base) }
    doc.css('img').each {|img| img['src'] = absolute_url(img['src'], base) }
    doc.to_html
  end

  Liquid::Template.register_filter(FeedTags)
end