code: func (c *Client) prefix() (string, error) {
  	if err := c.prefixOnce.Do(c.initPrefix); err != nil {
  		return "", err
  	}
  	return c.prefixv, nil
  }
docs: // prefix returns the URL prefix before "/camli/", or before
  // the blobref hash in case of a share URL.
  // Examples: http://foo.com:3179/bs or http://foo.com:3179/share