# File lib/aws/s3/client.rb, line 52
      def sign_request request
        version = @config.s3_signature_version ?
          @config.s3_signature_version.to_sym :
          (@region =~ /cn-/ ? :v4 : :v3)
        case version
        when :v4 then v4_signer.sign_request(request)
        when :v3 then v3_signer.sign_request(request)
        else
          raise "invalid signature version #{version.inspect}"
        end
      end