http2

var DefaultClient = http.Client{
	Transport: &http2.Transport{
		DialTLSContext: func(ctx context.Context, network, addr string, cfg *tls.Config) (net.Conn, 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 tlsConn *tls.Conn
			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 = defaultDialer.DialContext(ctx, network, net.JoinHostPort(a, port))
				if err != nil {
					continue
				}
				tlsConn = tls.Client(terasu.NewConn(conn), cfg)

				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()
				}
				err = tlsConn.HandshakeContext(ctx)
				if err == nil {
					break
				}
				_ = tlsConn.Close()
				tlsConn = nil
				conn, err = defaultDialer.DialContext(ctx, network, net.JoinHostPort(a, port))
				if err != nil {
					continue
				}
				tlsConn = tls.Client(terasu.NewConn(conn), cfg)
				err = tlsConn.HandshakeContext(ctx)
				if err == nil {
					break
				}
				_ = tlsConn.Close()
				tlsConn = nil
			}
			return tlsConn, err
		},
	},
}

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