code: func (t *Transport) Open(addr string) error {
  	ln, err := net.Listen("tcp", addr)
  	if err != nil {
  		return err
  	}
  	if t.certFile != "" {
  		config, err := createTLSConfig(t.certFile, t.certKey)
  		if err != nil {
  			return err
  		}
  		ln = tls.NewListener(ln, config)
  	}
  
  	t.ln = ln
  	return nil
  }
docs: // Open opens the transport, binding to the supplied address.