code: func (c *Client) BlobRoot() (string, error) {
  	prefix, err := c.prefix()
  	if err != nil {
  		return "", err
  	}
  	return prefix + "/", nil
  }
docs: // BlobRoot returns the server's blobroot URL prefix.
  // If the client was constructed with an explicit path,
  // that path is used. Otherwise the server's
  // default advertised blobRoot is used.