generate_canonical_link.rb

require 'uri'

def generate_canonical_link
  query_elements = []
  query_elements << "page=#{params[:page]}"   unless params[:page].to_i <= 1 # page=0 should be valid?
  query_elements << "query=#{params[:query]}" if params[:query]

  # use URI::Generic.build2 to automatically escape the query params
  # you can actually get away with simple string manipulation here, but you get the idea
  uri = URI::Generic.build( :scheme => request.env['rack.url_scheme'],
                            :host   => SERVICE_DOMAIN,
                            :path   => request.env['REQUEST_PATH'],
                            :query  => query_elements.join('&amp;'))
  
  # chop off trailing '?' and return link
  %(<link rel="canonical" href="#{uri.to_s.chomp '?'}" />)
end