code: func (b *Builder) makeAddrs(pri []net.Addr, sec []*net.IPAddr, port int) []net.Addr {
  	if len(pri) == 0 && len(sec) == 0 || port <= 0 {
  		return nil
  	}
  	addrs := pri
  	if len(addrs) == 0 {
  		addrs = []net.Addr{}
  		for _, a := range sec {
  			addrs = append(addrs, a)
  		}
  	}
  	var x []net.Addr
  	for _, a := range addrs {
  		x = append(x, b.makeAddr(a, nil, port))
  	}
  	return x
  }
docs: // makeAddrs creates a list of *net.TCPAddr or *net.UnixAddr entries
  // from either the primary or secondary addresses and the given port.
  // If the port is <= 0 then the address is considered to be disabled
  // and nil is returned.