code: func (c *Client) StorageGeneration() (string, error) {
  	if err := c.condDiscovery(); err != nil {
  		return "", err
  	}
  	if c.storageGen == "" {
  		return "", ErrNoStorageGeneration
  	}
  	return c.storageGen, nil
  }
docs: // StorageGeneration returns the server's unique ID for its storage
  // generation, reset whenever storage is reset, moved, or partially
  // lost.
  //
  // This is a value that can be used in client cache keys to add
  // certainty that they're talking to the same instance as previously.
  //
  // If the server doesn't return such a value, the error will be
  // ErrNoStorageGeneration.