# File lib/nanoc/extra/link_collector.rb, line 39
    def hrefs_in_file(filename)
      hrefs_in_file = Set.new
      doc = Nokogiri::HTML(::File.read(filename))
      doc.css('a').each { |e| hrefs_in_file << e[:href] unless e[:href].nil? }
      doc.css('img').each { |e| hrefs_in_file << e[:src]  }

      # Convert protocol-relative urls
      # e.g. //example.com => http://example.com
      hrefs_in_file.map! { |href| href.gsub /^\/\//, 'http://' }

      # Strip fragment
      hrefs_in_file.map! { |href| href.gsub(/#.*$/, '') }

      hrefs_in_file.select(&@filter)
    end