kube-apiserver: check upgrade header to detect upgrade connections

staging/src/k8s.io/kube-aggregator/pkg/apiserver/BUILD

@@ -52,6 +52,7 @@ go_library(
         "//vendor/k8s.io/apimachinery/pkg/runtime:go_default_library",
         "//vendor/k8s.io/apimachinery/pkg/runtime/schema:go_default_library",
         "//vendor/k8s.io/apimachinery/pkg/runtime/serializer:go_default_library",
+        "//vendor/k8s.io/apimachinery/pkg/util/httpstream:go_default_library",
         "//vendor/k8s.io/apimachinery/pkg/util/httpstream/spdy:go_default_library",
         "//vendor/k8s.io/apimachinery/pkg/util/runtime:go_default_library",
         "//vendor/k8s.io/apimachinery/pkg/util/sets:go_default_library",

staging/src/k8s.io/kube-aggregator/pkg/apiserver/handler_proxy.go

@@ -22,6 +22,7 @@ import (
 	"sync/atomic"
 
 	"k8s.io/apimachinery/pkg/runtime"
+	"k8s.io/apimachinery/pkg/util/httpstream"
 	"k8s.io/apimachinery/pkg/util/httpstream/spdy"
 	"k8s.io/apiserver/pkg/endpoints/handlers/responsewriters"
 	genericapirequest "k8s.io/apiserver/pkg/endpoints/request"
@@ -144,8 +145,7 @@ func (r *proxyHandler) ServeHTTP(w http.ResponseWriter, req *http.Request) {
 
 // maybeWrapForConnectionUpgrades wraps the roundtripper for upgrades.  The bool indicates if it was wrapped
 func maybeWrapForConnectionUpgrades(restConfig *restclient.Config, rt http.RoundTripper, req *http.Request) (http.RoundTripper, bool, error) {
-	connectionHeader := req.Header.Get("Connection")
-	if len(connectionHeader) == 0 {
+	if !httpstream.IsUpgradeRequest(req) {
 		return rt, false, nil
 	}