Liquid Filter to convert URLs to short URLs automatically

bitly_filter.rb

require 'bitly'

module Jekyll
  class BitlyFilterCache
    def initialize
      @result_cache = {}
      config = Jekyll.configuration({})
      @username = config['bitly']['username']
      @key = config['bitly']['api_key']
      Bitly.use_api_version_3
    end

    @@instance = BitlyFilterCache.new

    def self.instance
      @@instance
    end

    def shorten(input)
      input.strip!
      return @result_cache[input] if @result_cache.has_key?(input)
      puts "Shortening #{input}..."
      bitly = Bitly.new(@username, @key)
      u = bitly.shorten(input, :history => 1)
      @result_cache[input] = u.short_url
      puts "New url: #{u.short_url}"
      return u.short_url
    end
  end

  module Filters
    def bitly(input)
      BitlyFilterCache.instance.shorten(input)
    end
  end
end

sample_output

This is a link to <a href="http://xorcode.net/PZFMOb">Xorcode</a>.
You could also use a variable, http://xorcode.net/QCpD1G.

sample_tag

This is a link to [Xorcode]({{ 'http://xorcode.com/' | bitly }}).
You could also use a variable, {{ site.production_url + '/' + page.url | bitly }}.