Force http/1.1 for upgrade (Traefik v2)

pkg/server/service/smart_roundtripper.go

@@ -0,0 +1,38 @@
+package service
+
+import (
+	"net/http"
+
+	"golang.org/x/net/http/httpguts"
+	"golang.org/x/net/http2"
+)
+
+func newSmartRoundTripper(transport *http.Transport) (http.RoundTripper, error) {
+	transportHTTP1 := transport.Clone()
+
+	err := http2.ConfigureTransport(transport)
+	if err != nil {
+		return nil, err
+	}
+
+	return &smartRoundTripper{
+		http2: transport,
+		http:  transportHTTP1,
+	}, nil
+}
+
+type smartRoundTripper struct {
+	http2 *http.Transport
+	http  *http.Transport
+}
+
+// smartRoundTripper implements RoundTrip while making sure that HTTP/2 is not used
+// with protocols that start with a Connection Upgrade, such as SPDY or Websocket.
+func (m *smartRoundTripper) RoundTrip(req *http.Request) (*http.Response, error) {
+	// If we have a connection upgrade, we don't use HTTP/2
+	if httpguts.HeaderValuesContainsToken(req.Header["Connection"], "Upgrade") {
+		return m.http.RoundTrip(req)
+	}
+
+	return m.http2.RoundTrip(req)
+}