code: func (c *Connection) open(config Config) error {
  	if err := c.send(&protocolHeader{}); err != nil {
  		return err
  	}
  
  	return c.openStart(config)
  }
docs: //    Connection          = open-Connection *use-Connection close-Connection
  //    open-Connection     = C:protocol-header
  //                          S:START C:START-OK
  //                          *challenge
  //                          S:TUNE C:TUNE-OK
  //                          C:OPEN S:OPEN-OK
  //    challenge           = S:SECURE C:SECURE-OK
  //    use-Connection      = *channel
  //    close-Connection    = C:CLOSE S:CLOSE-OK
  //                        / S:CLOSE C:CLOSE-OK