code: func (c *Connection) ConnectionState() tls.ConnectionState {
  	if conn, ok := c.conn.(interface {
  		ConnectionState() tls.ConnectionState
  	}); ok {
  		return conn.ConnectionState()
  	}
  	return tls.ConnectionState{}
  }
docs: // ConnectionState returns basic TLS details of the underlying transport.
  // Returns a zero value when the underlying connection does not implement
  // ConnectionState() tls.ConnectionState.