build_host_url

# File actionpack/lib/action_dispatch/http/url.rb, line 65
        def build_host_url(options)
          if options[:host].blank? && options[:only_path].blank?
            raise ArgumentError, 'Missing host to link to! Please provide the :host parameter, set default_url_options[:host], or set :only_path to true'
          end

          result = ""

          unless options[:only_path]
            if match = options[:host].match(HOST_REGEXP)
              options[:protocol] ||= match[1] unless options[:protocol] == false
              options[:host]       = match[2]
              options[:port]       = match[3] unless options.key?(:port)
            end

            options[:protocol] = normalize_protocol(options)
            options[:host]     = normalize_host(options)
            options[:port]     = normalize_port(options)

            result << options[:protocol]
            result << rewrite_authentication(options)
            result << options[:host]
            result << ":#{options[:port]}" if options[:port]
          end
          result
        end