Improve HTTPS DNS transport

dns/transport/https_transport.go

@@ -0,0 +1,80 @@
+package transport
+
+import (
+	"context"
+	"errors"
+	"net"
+	"net/http"
+	"sync/atomic"
+
+	"github.com/sagernet/sing-box/common/tls"
+	E "github.com/sagernet/sing/common/exceptions"
+	M "github.com/sagernet/sing/common/metadata"
+
+	"golang.org/x/net/http2"
+)
+
+var errFallback = E.New("fallback to HTTP/1.1")
+
+type HTTPSTransportWrapper struct {
+	http2Transport *http2.Transport
+	httpTransport  *http.Transport
+	fallback       *atomic.Bool
+}
+
+func NewHTTPSTransportWrapper(dialer tls.Dialer, serverAddr M.Socksaddr) *HTTPSTransportWrapper {
+	var fallback atomic.Bool
+	return &HTTPSTransportWrapper{
+		http2Transport: &http2.Transport{
+			DialTLSContext: func(ctx context.Context, _, _ string, _ *tls.STDConfig) (net.Conn, error) {
+				tlsConn, err := dialer.DialTLSContext(ctx, serverAddr)
+				if err != nil {
+					return nil, err
+				}
+				state := tlsConn.ConnectionState()
+				if state.NegotiatedProtocol == http2.NextProtoTLS {
+					return tlsConn, nil
+				}
+				tlsConn.Close()
+				fallback.Store(true)
+				return nil, errFallback
+			},
+		},
+		httpTransport: &http.Transport{
+			DialTLSContext: func(ctx context.Context, _, _ string) (net.Conn, error) {
+				return dialer.DialTLSContext(ctx, serverAddr)
+			},
+		},
+		fallback: &fallback,
+	}
+}
+
+func (h *HTTPSTransportWrapper) RoundTrip(request *http.Request) (*http.Response, error) {
+	if h.fallback.Load() {
+		return h.httpTransport.RoundTrip(request)
+	} else {
+		response, err := h.http2Transport.RoundTrip(request)
+		if err != nil {
+			if errors.Is(err, errFallback) {
+				return h.httpTransport.RoundTrip(request)
+			}
+			return nil, err
+		}
+		return response, nil
+	}
+}
+
+func (h *HTTPSTransportWrapper) CloseIdleConnections() {
+	h.http2Transport.CloseIdleConnections()
+	h.httpTransport.CloseIdleConnections()
+}
+
+func (h *HTTPSTransportWrapper) Clone() *HTTPSTransportWrapper {
+	return &HTTPSTransportWrapper{
+		httpTransport: h.httpTransport,
+		http2Transport: &http2.Transport{
+			DialTLSContext: h.http2Transport.DialTLSContext,
+		},
+		fallback: h.fallback,
+	}
+}