http3

var DefaultClient = http.Client{
	Transport: &http3.Transport{
		Dial: func(ctx context.Context, addr string, tlsCfg *tls.Config, cfg *quic.Config) (quic.EarlyConnection, error) {
			host, port, err := net.SplitHostPort(addr)
			if err != nil {
				return nil, err
			}
			addrs, err := dns.LookupHost(ctx, host)
			if err != nil {
				return nil, err
			}
			if len(addrs) == 0 {
				return nil, ErrEmptyHostAddress
			}
			var conn net.Conn
			var qConn quic.EarlyConnection
			for _, a := range addrs {
				if defaultDialer.Timeout != 0 {
					var cancel context.CancelFunc
					ctx, cancel = context.WithTimeout(context.Background(), defaultDialer.Timeout)
					defer cancel()
				} else if !defaultDialer.Deadline.IsZero() {
					var cancel context.CancelFunc
					ctx, cancel = context.WithDeadline(context.Background(), defaultDialer.Deadline)
					defer cancel()
				}
				conn, err = net.ListenUDP("udp", nil)
				if err != nil {
					continue
				}
				ucon := conn.(*net.UDPConn)
				raddr := net.UDPAddrFromAddrPort(
					netip.MustParseAddrPort(net.JoinHostPort(a, port)),
				)
				n := (mrand.Intn(128) + 128) / 7 * 14
				w := bytes.NewBuffer(make([]byte, 0, base14.EncodeLen(n)))
				e := base14.NewEncoder(w)
				_, _ = io.CopyN(e, rand.Reader, int64(n))
				_ = e.Close()
				_, _ = ucon.WriteToUDP(w.Bytes(), raddr)

				if defaultDialer.Timeout != 0 {
					var cancel context.CancelFunc
					ctx, cancel = context.WithTimeout(context.Background(), defaultDialer.Timeout)
					defer cancel()
				} else if !defaultDialer.Deadline.IsZero() {
					var cancel context.CancelFunc
					ctx, cancel = context.WithDeadline(context.Background(), defaultDialer.Deadline)
					defer cancel()
				}
				qConn, err = quic.DialEarly(ctx, ucon, raddr, tlsCfg, cfg)
				if err == nil {
					break
				}
				panic(err)
			}
			return qConn, err
		},
	},
}

var ErrEmptyHostAddress = errors.New("empty host addr")