Create helper for :subdomain in Rails 3

url_helper.rb

# -*- encoding : utf-8 -*-
module UrlHelper
  def with_subdomain(subdomain)
    subdomain = (subdomain || "")
    subdomain += "." unless subdomain.empty?
    domain_woport = request.domain.gsub(/:{1}\d*/, '')
    [subdomain, request.domain].join #request.port_string
  end

  def url_for(options = nil)
    if options.kind_of?(Hash) && options.has_key?(:subdomain)
      options[:host] = with_subdomain(options.delete(:subdomain))
      options[:only_path] = false
    end
    super
  end

end