patch-kube-api-1.7.3

diff --git a/staging/src/k8s.io/apiserver/pkg/registry/generic/rest/proxy.go b/staging/src/k8s.io/apiserver/pkg/registry/generic/rest/proxy.go
index e6ef8cb..dc4eead 100644
--- a/staging/src/k8s.io/apiserver/pkg/registry/generic/rest/proxy.go
+++ b/staging/src/k8s.io/apiserver/pkg/registry/generic/rest/proxy.go
@@ -17,6 +17,8 @@ limitations under the License.
 package rest
 
 import (
+	"bufio"
+	"bytes"
 	"context"
 	"fmt"
 	"io"
@@ -77,6 +79,15 @@ func NewUpgradeAwareProxyHandler(location *url.URL, transport http.RoundTripper,
 	}
 }
 
+func getResponseCode(r io.Reader) (int, []byte, error) {
+	rawResponse := bytes.NewBuffer(make([]byte, 0, 256))
+	resp, err := http.ReadResponse(bufio.NewReader(io.TeeReader(r, rawResponse)), nil)
+	if err != nil {
+		return 0, nil, err
+	}
+	return resp.StatusCode, rawResponse.Bytes(), nil
+}
+
 // ServeHTTP handles the proxy request
 func (h *UpgradeAwareProxyHandler) ServeHTTP(w http.ResponseWriter, req *http.Request) {
 	if len(h.Location.Scheme) == 0 {
@@ -156,6 +167,16 @@ func (h *UpgradeAwareProxyHandler) tryUpgrade(w http.ResponseWriter, req *http.R
 	}
 	defer backendConn.Close()
 
+	rawResponseCode, headerBytes, err := getResponseCode(io.MultiReader(bytes.NewReader(rawResponse), backendConn))
+	if err == nil {
+		glog.V(6).Infof("Proxy connection error: %v", err)
+		h.Responder.Error(fmt.Errorf("Proxy connection Error: %T", w))
+		return true
+	}
+
+	if len(headerBytes) > len(rawResponse) {
+		rawResponse = headerBytes
+	}
 	// Once the connection is hijacked, the ErrorResponder will no longer work, so
 	// hijacking should be the last step in the upgrade.
 	requestHijacker, ok := w.(http.Hijacker)
@@ -177,6 +198,15 @@ func (h *UpgradeAwareProxyHandler) tryUpgrade(w http.ResponseWriter, req *http.R
 		}
 	}
 
+	if rawResponseCode != http.StatusSwitchingProtocols {
+		glog.V(6).Infof("Proxy upgrade error, status code %d", rawResponseCode)
+		_, err := io.Copy(requestHijackedConn, backendConn)
+		if err != nil && !strings.Contains(err.Error(), "use of closed network connection") {
+			glog.Errorf("Error proxying data from backend to client: %v", err)
+		}
+		return true
+	}
+
 	// Proxy the connection.
 	wg := &sync.WaitGroup{}
 	wg.Add(2)