code: def receive_request(self, transaction):
          
  
          transaction.cached_element = self.cache.search_response(transaction.request)
          if transaction.cached_element is None:
              transaction.cacheHit = False
          else:
              transaction.response = transaction.cached_element.cached_response
              transaction.response.mid = transaction.request.mid
              transaction.cacheHit = True
  
              age = transaction.cached_element.creation_time + transaction.cached_element.max_age - time.time()
              if transaction.cached_element.freshness is True:
                  if age <= 0:
                      logger.debug("resource not fresh")
                      """
                      if the resource is not fresh, its Etag must be added to the request so that the server might validate it instead of sending a new one
                      """
                      transaction.cached_element.freshness = False
                      """
                      ensuring that the request goes to the server
                      """
                      transaction.cacheHit = False
                      logger.debug("requesting etag %s", transaction.response.etag)
                      transaction.request.etag = transaction.response.etag
                  else:
                      transaction.response.max_age = age
              else:
                  transaction.cacheHit = False
          return transaction
docs: checks the cache for a response to the request
  
          :param transaction:
          :return: