code: func (c *Conn) VerifyHostname(host string) error {
  	c.handshakeMutex.Lock()
  	defer c.handshakeMutex.Unlock()
  	if !c.isClient {
  		return errors.New("tls: VerifyHostname called on TLS server connection")
  	}
  	if !c.handshakeComplete {
  		return errors.New("tls: handshake has not yet been performed")
  	}
  	if len(c.verifiedChains) == 0 {
  		return errors.New("tls: handshake did not verify certificate chain")
  	}
  	return c.peerCertificates[0].VerifyHostname(host)
  }
docs: // VerifyHostname checks that the peer certificate chain is valid for
  // connecting to host.  If so, it returns nil; if not, it returns an error
  // describing the problem.