code: func (c *Client) GetVolume(appID, id string) (*ct.Volume, error) {
  	if appID == "" {
  		return nil, errors.New("controller: missing app ID")
  	}
  	if id == "" {
  		return nil, errors.New("controller: missing id")
  	}
  	vol := &ct.Volume{}
  	return vol, c.Get(fmt.Sprintf("/apps/%s/volumes/%s", appID, id), vol)
  }
docs: // GetVolume returns a Volume for the given volume ID