rebase: update k8s.io packages to v0.29.0

Signed-off-by: Niels de Vos <ndevos@ibm.com>

vendor/k8s.io/apimachinery/pkg/util/proxy/dial.go

@@ -0,0 +1,122 @@
+/*
+Copyright 2015 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package proxy
+
+import (
+	"context"
+	"crypto/tls"
+	"fmt"
+	"net"
+	"net/http"
+	"net/url"
+
+	utilnet "k8s.io/apimachinery/pkg/util/net"
+	"k8s.io/apimachinery/third_party/forked/golang/netutil"
+	"k8s.io/klog/v2"
+)
+
+// DialURL will dial the specified URL using the underlying dialer held by the passed
+// RoundTripper. The primary use of this method is to support proxying upgradable connections.
+// For this reason this method will prefer to negotiate http/1.1 if the URL scheme is https.
+// If you wish to ensure ALPN negotiates http2 then set NextProto=[]string{"http2"} in the
+// TLSConfig of the http.Transport
+func DialURL(ctx context.Context, url *url.URL, transport http.RoundTripper) (net.Conn, error) {
+	dialAddr := netutil.CanonicalAddr(url)
+
+	dialer, err := utilnet.DialerFor(transport)
+	if err != nil {
+		klog.V(5).Infof("Unable to unwrap transport %T to get dialer: %v", transport, err)
+	}
+
+	switch url.Scheme {
+	case "http":
+		if dialer != nil {
+			return dialer(ctx, "tcp", dialAddr)
+		}
+		var d net.Dialer
+		return d.DialContext(ctx, "tcp", dialAddr)
+	case "https":
+		// Get the tls config from the transport if we recognize it
+		tlsConfig, err := utilnet.TLSClientConfig(transport)
+		if err != nil {
+			klog.V(5).Infof("Unable to unwrap transport %T to get at TLS config: %v", transport, err)
+		}
+
+		if dialer != nil {
+			// We have a dialer; use it to open the connection, then
+			// create a tls client using the connection.
+			netConn, err := dialer(ctx, "tcp", dialAddr)
+			if err != nil {
+				return nil, err
+			}
+			if tlsConfig == nil {
+				// tls.Client requires non-nil config
+				klog.Warning("using custom dialer with no TLSClientConfig. Defaulting to InsecureSkipVerify")
+				// tls.Handshake() requires ServerName or InsecureSkipVerify
+				tlsConfig = &tls.Config{
+					InsecureSkipVerify: true,
+				}
+			} else if len(tlsConfig.ServerName) == 0 && !tlsConfig.InsecureSkipVerify {
+				// tls.HandshakeContext() requires ServerName or InsecureSkipVerify
+				// infer the ServerName from the hostname we're connecting to.
+				inferredHost := dialAddr
+				if host, _, err := net.SplitHostPort(dialAddr); err == nil {
+					inferredHost = host
+				}
+				// Make a copy to avoid polluting the provided config
+				tlsConfigCopy := tlsConfig.Clone()
+				tlsConfigCopy.ServerName = inferredHost
+				tlsConfig = tlsConfigCopy
+			}
+
+			// Since this method is primarily used within a "Connection: Upgrade" call we assume the caller is
+			// going to write HTTP/1.1 request to the wire. http2 should not be allowed in the TLSConfig.NextProtos,
+			// so we explicitly set that here. We only do this check if the TLSConfig support http/1.1.
+			if supportsHTTP11(tlsConfig.NextProtos) {
+				tlsConfig = tlsConfig.Clone()
+				tlsConfig.NextProtos = []string{"http/1.1"}
+			}
+
+			tlsConn := tls.Client(netConn, tlsConfig)
+			if err := tlsConn.HandshakeContext(ctx); err != nil {
+				netConn.Close()
+				return nil, err
+			}
+			return tlsConn, nil
+		} else {
+			// Dial.
+			tlsDialer := tls.Dialer{
+				Config: tlsConfig,
+			}
+			return tlsDialer.DialContext(ctx, "tcp", dialAddr)
+		}
+	default:
+		return nil, fmt.Errorf("unknown scheme: %s", url.Scheme)
+	}
+}
+
+func supportsHTTP11(nextProtos []string) bool {
+	if len(nextProtos) == 0 {
+		return true
+	}
+	for _, proto := range nextProtos {
+		if proto == "http/1.1" {
+			return true
+		}
+	}
+	return false
+}

vendor/k8s.io/apimachinery/pkg/util/proxy/doc.go

@@ -0,0 +1,18 @@
+/*
+Copyright 2014 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// Package proxy provides transport and upgrade support for proxies.
+package proxy // import "k8s.io/apimachinery/pkg/util/proxy"

vendor/k8s.io/apimachinery/pkg/util/proxy/transport.go

@@ -0,0 +1,272 @@
+/*
+Copyright 2014 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package proxy
+
+import (
+	"bytes"
+	"compress/flate"
+	"compress/gzip"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"path"
+	"strings"
+
+	"golang.org/x/net/html"
+	"golang.org/x/net/html/atom"
+	"k8s.io/klog/v2"
+
+	"k8s.io/apimachinery/pkg/api/errors"
+	"k8s.io/apimachinery/pkg/util/net"
+	"k8s.io/apimachinery/pkg/util/sets"
+)
+
+// atomsToAttrs states which attributes of which tags require URL substitution.
+// Sources: http://www.w3.org/TR/REC-html40/index/attributes.html
+//
+//	http://www.w3.org/html/wg/drafts/html/master/index.html#attributes-1
+var atomsToAttrs = map[atom.Atom]sets.String{
+	atom.A:          sets.NewString("href"),
+	atom.Applet:     sets.NewString("codebase"),
+	atom.Area:       sets.NewString("href"),
+	atom.Audio:      sets.NewString("src"),
+	atom.Base:       sets.NewString("href"),
+	atom.Blockquote: sets.NewString("cite"),
+	atom.Body:       sets.NewString("background"),
+	atom.Button:     sets.NewString("formaction"),
+	atom.Command:    sets.NewString("icon"),
+	atom.Del:        sets.NewString("cite"),
+	atom.Embed:      sets.NewString("src"),
+	atom.Form:       sets.NewString("action"),
+	atom.Frame:      sets.NewString("longdesc", "src"),
+	atom.Head:       sets.NewString("profile"),
+	atom.Html:       sets.NewString("manifest"),
+	atom.Iframe:     sets.NewString("longdesc", "src"),
+	atom.Img:        sets.NewString("longdesc", "src", "usemap"),
+	atom.Input:      sets.NewString("src", "usemap", "formaction"),
+	atom.Ins:        sets.NewString("cite"),
+	atom.Link:       sets.NewString("href"),
+	atom.Object:     sets.NewString("classid", "codebase", "data", "usemap"),
+	atom.Q:          sets.NewString("cite"),
+	atom.Script:     sets.NewString("src"),
+	atom.Source:     sets.NewString("src"),
+	atom.Video:      sets.NewString("poster", "src"),
+
+	// TODO: css URLs hidden in style elements.
+}
+
+// Transport is a transport for text/html content that replaces URLs in html
+// content with the prefix of the proxy server
+type Transport struct {
+	Scheme      string
+	Host        string
+	PathPrepend string
+
+	http.RoundTripper
+}
+
+// RoundTrip implements the http.RoundTripper interface
+func (t *Transport) RoundTrip(req *http.Request) (*http.Response, error) {
+	// Add reverse proxy headers.
+	forwardedURI := path.Join(t.PathPrepend, req.URL.EscapedPath())
+	if strings.HasSuffix(req.URL.Path, "/") {
+		forwardedURI = forwardedURI + "/"
+	}
+	req.Header.Set("X-Forwarded-Uri", forwardedURI)
+	if len(t.Host) > 0 {
+		req.Header.Set("X-Forwarded-Host", t.Host)
+	}
+	if len(t.Scheme) > 0 {
+		req.Header.Set("X-Forwarded-Proto", t.Scheme)
+	}
+
+	rt := t.RoundTripper
+	if rt == nil {
+		rt = http.DefaultTransport
+	}
+	resp, err := rt.RoundTrip(req)
+
+	if err != nil {
+		return nil, errors.NewServiceUnavailable(fmt.Sprintf("error trying to reach service: %v", err))
+	}
+
+	if redirect := resp.Header.Get("Location"); redirect != "" {
+		targetURL, err := url.Parse(redirect)
+		if err != nil {
+			return nil, errors.NewInternalError(fmt.Errorf("error trying to parse Location header: %v", err))
+		}
+		resp.Header.Set("Location", t.rewriteURL(targetURL, req.URL, req.Host))
+		return resp, nil
+	}
+
+	cType := resp.Header.Get("Content-Type")
+	cType = strings.TrimSpace(strings.SplitN(cType, ";", 2)[0])
+	if cType != "text/html" {
+		// Do nothing, simply pass through
+		return resp, nil
+	}
+
+	return t.rewriteResponse(req, resp)
+}
+
+var _ = net.RoundTripperWrapper(&Transport{})
+
+func (rt *Transport) WrappedRoundTripper() http.RoundTripper {
+	return rt.RoundTripper
+}
+
+// rewriteURL rewrites a single URL to go through the proxy, if the URL refers
+// to the same host as sourceURL, which is the page on which the target URL
+// occurred, or if the URL matches the sourceRequestHost.
+func (t *Transport) rewriteURL(url *url.URL, sourceURL *url.URL, sourceRequestHost string) string {
+	// Example:
+	//      When API server processes a proxy request to a service (e.g. /api/v1/namespace/foo/service/bar/proxy/),
+	//      the sourceURL.Host (i.e. req.URL.Host) is the endpoint IP address of the service. The
+	//      sourceRequestHost (i.e. req.Host) is the Host header that specifies the host on which the
+	//      URL is sought, which can be different from sourceURL.Host. For example, if user sends the
+	//      request through "kubectl proxy" locally (i.e. localhost:8001/api/v1/namespace/foo/service/bar/proxy/),
+	//      sourceRequestHost is "localhost:8001".
+	//
+	//      If the service's response URL contains non-empty host, and url.Host is equal to either sourceURL.Host
+	//      or sourceRequestHost, we should not consider the returned URL to be a completely different host.
+	//      It's the API server's responsibility to rewrite a same-host-and-absolute-path URL and append the
+	//      necessary URL prefix (i.e. /api/v1/namespace/foo/service/bar/proxy/).
+	isDifferentHost := url.Host != "" && url.Host != sourceURL.Host && url.Host != sourceRequestHost
+	isRelative := !strings.HasPrefix(url.Path, "/")
+	if isDifferentHost || isRelative {
+		return url.String()
+	}
+
+	// Do not rewrite scheme and host if the Transport has empty scheme and host
+	// when targetURL already contains the sourceRequestHost
+	if !(url.Host == sourceRequestHost && t.Scheme == "" && t.Host == "") {
+		url.Scheme = t.Scheme
+		url.Host = t.Host
+	}
+
+	origPath := url.Path
+	// Do not rewrite URL if the sourceURL already contains the necessary prefix.
+	if strings.HasPrefix(url.Path, t.PathPrepend) {
+		return url.String()
+	}
+	url.Path = path.Join(t.PathPrepend, url.Path)
+	if strings.HasSuffix(origPath, "/") {
+		// Add back the trailing slash, which was stripped by path.Join().
+		url.Path += "/"
+	}
+
+	return url.String()
+}
+
+// rewriteHTML scans the HTML for tags with url-valued attributes, and updates
+// those values with the urlRewriter function. The updated HTML is output to the
+// writer.
+func rewriteHTML(reader io.Reader, writer io.Writer, urlRewriter func(*url.URL) string) error {
+	// Note: This assumes the content is UTF-8.
+	tokenizer := html.NewTokenizer(reader)
+
+	var err error
+	for err == nil {
+		tokenType := tokenizer.Next()
+		switch tokenType {
+		case html.ErrorToken:
+			err = tokenizer.Err()
+		case html.StartTagToken, html.SelfClosingTagToken:
+			token := tokenizer.Token()
+			if urlAttrs, ok := atomsToAttrs[token.DataAtom]; ok {
+				for i, attr := range token.Attr {
+					if urlAttrs.Has(attr.Key) {
+						url, err := url.Parse(attr.Val)
+						if err != nil {
+							// Do not rewrite the URL if it isn't valid.  It is intended not
+							// to error here to prevent the inability to understand the
+							// content of the body to cause a fatal error.
+							continue
+						}
+						token.Attr[i].Val = urlRewriter(url)
+					}
+				}
+			}
+			_, err = writer.Write([]byte(token.String()))
+		default:
+			_, err = writer.Write(tokenizer.Raw())
+		}
+	}
+	if err != io.EOF {
+		return err
+	}
+	return nil
+}
+
+// rewriteResponse modifies an HTML response by updating absolute links referring
+// to the original host to instead refer to the proxy transport.
+func (t *Transport) rewriteResponse(req *http.Request, resp *http.Response) (*http.Response, error) {
+	origBody := resp.Body
+	defer origBody.Close()
+
+	newContent := &bytes.Buffer{}
+	var reader io.Reader = origBody
+	var writer io.Writer = newContent
+	encoding := resp.Header.Get("Content-Encoding")
+	switch encoding {
+	case "gzip":
+		var err error
+		reader, err = gzip.NewReader(reader)
+		if err != nil {
+			return nil, fmt.Errorf("errorf making gzip reader: %v", err)
+		}
+		gzw := gzip.NewWriter(writer)
+		defer gzw.Close()
+		writer = gzw
+	case "deflate":
+		var err error
+		reader = flate.NewReader(reader)
+		flw, err := flate.NewWriter(writer, flate.BestCompression)
+		if err != nil {
+			return nil, fmt.Errorf("errorf making flate writer: %v", err)
+		}
+		defer func() {
+			flw.Close()
+			flw.Flush()
+		}()
+		writer = flw
+	case "":
+		// This is fine
+	default:
+		// Some encoding we don't understand-- don't try to parse this
+		klog.Errorf("Proxy encountered encoding %v for text/html; can't understand this so not fixing links.", encoding)
+		return resp, nil
+	}
+
+	urlRewriter := func(targetUrl *url.URL) string {
+		return t.rewriteURL(targetUrl, req.URL, req.Host)
+	}
+	err := rewriteHTML(reader, writer, urlRewriter)
+	if err != nil {
+		klog.Errorf("Failed to rewrite URLs: %v", err)
+		return resp, err
+	}
+
+	resp.Body = io.NopCloser(newContent)
+	// Update header node with new content-length
+	// TODO: Remove any hash/signature headers here?
+	resp.Header.Del("Content-Length")
+	resp.ContentLength = int64(newContent.Len())
+
+	return resp, err
+}

vendor/k8s.io/apimachinery/pkg/util/proxy/upgradeaware.go

@@ -0,0 +1,556 @@
+/*
+Copyright 2017 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package proxy
+
+import (
+	"bufio"
+	"bytes"
+	"fmt"
+	"io"
+	"log"
+	"net"
+	"net/http"
+	"net/http/httputil"
+	"net/url"
+	"os"
+	"strings"
+	"time"
+
+	"k8s.io/apimachinery/pkg/api/errors"
+	"k8s.io/apimachinery/pkg/util/httpstream"
+	utilnet "k8s.io/apimachinery/pkg/util/net"
+	utilruntime "k8s.io/apimachinery/pkg/util/runtime"
+
+	"github.com/mxk/go-flowrate/flowrate"
+	"k8s.io/klog/v2"
+)
+
+// UpgradeRequestRoundTripper provides an additional method to decorate a request
+// with any authentication or other protocol level information prior to performing
+// an upgrade on the server. Any response will be handled by the intercepting
+// proxy.
+type UpgradeRequestRoundTripper interface {
+	http.RoundTripper
+	// WrapRequest takes a valid HTTP request and returns a suitably altered version
+	// of request with any HTTP level values required to complete the request half of
+	// an upgrade on the server. It does not get a chance to see the response and
+	// should bypass any request side logic that expects to see the response.
+	WrapRequest(*http.Request) (*http.Request, error)
+}
+
+// UpgradeAwareHandler is a handler for proxy requests that may require an upgrade
+type UpgradeAwareHandler struct {
+	// UpgradeRequired will reject non-upgrade connections if true.
+	UpgradeRequired bool
+	// Location is the location of the upstream proxy. It is used as the location to Dial on the upstream server
+	// for upgrade requests unless UseRequestLocationOnUpgrade is true.
+	Location *url.URL
+	// AppendLocationPath determines if the original path of the Location should be appended to the upstream proxy request path
+	AppendLocationPath bool
+	// Transport provides an optional round tripper to use to proxy. If nil, the default proxy transport is used
+	Transport http.RoundTripper
+	// UpgradeTransport, if specified, will be used as the backend transport when upgrade requests are provided.
+	// This allows clients to disable HTTP/2.
+	UpgradeTransport UpgradeRequestRoundTripper
+	// WrapTransport indicates whether the provided Transport should be wrapped with default proxy transport behavior (URL rewriting, X-Forwarded-* header setting)
+	WrapTransport bool
+	// UseRequestLocation will use the incoming request URL when talking to the backend server.
+	UseRequestLocation bool
+	// UseLocationHost overrides the HTTP host header in requests to the backend server to use the Host from Location.
+	// This will override the req.Host field of a request, while UseRequestLocation will override the req.URL field
+	// of a request. The req.URL.Host specifies the server to connect to, while the req.Host field
+	// specifies the Host header value to send in the HTTP request. If this is false, the incoming req.Host header will
+	// just be forwarded to the backend server.
+	UseLocationHost bool
+	// FlushInterval controls how often the standard HTTP proxy will flush content from the upstream.
+	FlushInterval time.Duration
+	// MaxBytesPerSec controls the maximum rate for an upstream connection. No rate is imposed if the value is zero.
+	MaxBytesPerSec int64
+	// Responder is passed errors that occur while setting up proxying.
+	Responder ErrorResponder
+	// Reject to forward redirect response
+	RejectForwardingRedirects bool
+}
+
+const defaultFlushInterval = 200 * time.Millisecond
+
+// ErrorResponder abstracts error reporting to the proxy handler to remove the need to hardcode a particular
+// error format.
+type ErrorResponder interface {
+	Error(w http.ResponseWriter, req *http.Request, err error)
+}
+
+// SimpleErrorResponder is the legacy implementation of ErrorResponder for callers that only
+// service a single request/response per proxy.
+type SimpleErrorResponder interface {
+	Error(err error)
+}
+
+func NewErrorResponder(r SimpleErrorResponder) ErrorResponder {
+	return simpleResponder{r}
+}
+
+type simpleResponder struct {
+	responder SimpleErrorResponder
+}
+
+func (r simpleResponder) Error(w http.ResponseWriter, req *http.Request, err error) {
+	r.responder.Error(err)
+}
+
+// upgradeRequestRoundTripper implements proxy.UpgradeRequestRoundTripper.
+type upgradeRequestRoundTripper struct {
+	http.RoundTripper
+	upgrader http.RoundTripper
+}
+
+var (
+	_ UpgradeRequestRoundTripper  = &upgradeRequestRoundTripper{}
+	_ utilnet.RoundTripperWrapper = &upgradeRequestRoundTripper{}
+)
+
+// WrappedRoundTripper returns the round tripper that a caller would use.
+func (rt *upgradeRequestRoundTripper) WrappedRoundTripper() http.RoundTripper {
+	return rt.RoundTripper
+}
+
+// WriteToRequest calls the nested upgrader and then copies the returned request
+// fields onto the passed request.
+func (rt *upgradeRequestRoundTripper) WrapRequest(req *http.Request) (*http.Request, error) {
+	resp, err := rt.upgrader.RoundTrip(req)
+	if err != nil {
+		return nil, err
+	}
+	return resp.Request, nil
+}
+
+// onewayRoundTripper captures the provided request - which is assumed to have
+// been modified by other round trippers - and then returns a fake response.
+type onewayRoundTripper struct{}
+
+// RoundTrip returns a simple 200 OK response that captures the provided request.
+func (onewayRoundTripper) RoundTrip(req *http.Request) (*http.Response, error) {
+	return &http.Response{
+		Status:     "200 OK",
+		StatusCode: http.StatusOK,
+		Body:       io.NopCloser(&bytes.Buffer{}),
+		Request:    req,
+	}, nil
+}
+
+// MirrorRequest is a round tripper that can be called to get back the calling request as
+// the core round tripper in a chain.
+var MirrorRequest http.RoundTripper = onewayRoundTripper{}
+
+// NewUpgradeRequestRoundTripper takes two round trippers - one for the underlying TCP connection, and
+// one that is able to write headers to an HTTP request. The request rt is used to set the request headers
+// and that is written to the underlying connection rt.
+func NewUpgradeRequestRoundTripper(connection, request http.RoundTripper) UpgradeRequestRoundTripper {
+	return &upgradeRequestRoundTripper{
+		RoundTripper: connection,
+		upgrader:     request,
+	}
+}
+
+// normalizeLocation returns the result of parsing the full URL, with scheme set to http if missing
+func normalizeLocation(location *url.URL) *url.URL {
+	normalized, _ := url.Parse(location.String())
+	if len(normalized.Scheme) == 0 {
+		normalized.Scheme = "http"
+	}
+	return normalized
+}
+
+// NewUpgradeAwareHandler creates a new proxy handler with a default flush interval. Responder is required for returning
+// errors to the caller.
+func NewUpgradeAwareHandler(location *url.URL, transport http.RoundTripper, wrapTransport, upgradeRequired bool, responder ErrorResponder) *UpgradeAwareHandler {
+	return &UpgradeAwareHandler{
+		Location:        normalizeLocation(location),
+		Transport:       transport,
+		WrapTransport:   wrapTransport,
+		UpgradeRequired: upgradeRequired,
+		FlushInterval:   defaultFlushInterval,
+		Responder:       responder,
+	}
+}
+
+func proxyRedirectsforRootPath(path string, w http.ResponseWriter, req *http.Request) bool {
+	redirect := false
+	method := req.Method
+
+	// From pkg/genericapiserver/endpoints/handlers/proxy.go#ServeHTTP:
+	// Redirect requests with an empty path to a location that ends with a '/'
+	// This is essentially a hack for https://issue.k8s.io/4958.
+	// Note: Keep this code after tryUpgrade to not break that flow.
+	if len(path) == 0 && (method == http.MethodGet || method == http.MethodHead) {
+		var queryPart string
+		if len(req.URL.RawQuery) > 0 {
+			queryPart = "?" + req.URL.RawQuery
+		}
+		w.Header().Set("Location", req.URL.Path+"/"+queryPart)
+		w.WriteHeader(http.StatusMovedPermanently)
+		redirect = true
+	}
+	return redirect
+}
+
+// ServeHTTP handles the proxy request
+func (h *UpgradeAwareHandler) ServeHTTP(w http.ResponseWriter, req *http.Request) {
+	if h.tryUpgrade(w, req) {
+		return
+	}
+	if h.UpgradeRequired {
+		h.Responder.Error(w, req, errors.NewBadRequest("Upgrade request required"))
+		return
+	}
+
+	loc := *h.Location
+	loc.RawQuery = req.URL.RawQuery
+
+	// If original request URL ended in '/', append a '/' at the end of the
+	// of the proxy URL
+	if !strings.HasSuffix(loc.Path, "/") && strings.HasSuffix(req.URL.Path, "/") {
+		loc.Path += "/"
+	}
+
+	proxyRedirect := proxyRedirectsforRootPath(loc.Path, w, req)
+	if proxyRedirect {
+		return
+	}
+
+	if h.Transport == nil || h.WrapTransport {
+		h.Transport = h.defaultProxyTransport(req.URL, h.Transport)
+	}
+
+	// WithContext creates a shallow clone of the request with the same context.
+	newReq := req.WithContext(req.Context())
+	newReq.Header = utilnet.CloneHeader(req.Header)
+	if !h.UseRequestLocation {
+		newReq.URL = &loc
+	}
+	if h.UseLocationHost {
+		// exchanging req.Host with the backend location is necessary for backends that act on the HTTP host header (e.g. API gateways),
+		// because req.Host has preference over req.URL.Host in filling this header field
+		newReq.Host = h.Location.Host
+	}
+
+	// create the target location to use for the reverse proxy
+	reverseProxyLocation := &url.URL{Scheme: h.Location.Scheme, Host: h.Location.Host}
+	if h.AppendLocationPath {
+		reverseProxyLocation.Path = h.Location.Path
+	}
+
+	proxy := httputil.NewSingleHostReverseProxy(reverseProxyLocation)
+	proxy.Transport = h.Transport
+	proxy.FlushInterval = h.FlushInterval
+	proxy.ErrorLog = log.New(noSuppressPanicError{}, "", log.LstdFlags)
+	if h.RejectForwardingRedirects {
+		oldModifyResponse := proxy.ModifyResponse
+		proxy.ModifyResponse = func(response *http.Response) error {
+			code := response.StatusCode
+			if code >= 300 && code <= 399 && len(response.Header.Get("Location")) > 0 {
+				// close the original response
+				response.Body.Close()
+				msg := "the backend attempted to redirect this request, which is not permitted"
+				// replace the response
+				*response = http.Response{
+					StatusCode:    http.StatusBadGateway,
+					Status:        fmt.Sprintf("%d %s", response.StatusCode, http.StatusText(response.StatusCode)),
+					Body:          io.NopCloser(strings.NewReader(msg)),
+					ContentLength: int64(len(msg)),
+				}
+			} else {
+				if oldModifyResponse != nil {
+					if err := oldModifyResponse(response); err != nil {
+						return err
+					}
+				}
+			}
+			return nil
+		}
+	}
+	if h.Responder != nil {
+		// if an optional error interceptor/responder was provided wire it
+		// the custom responder might be used for providing a unified error reporting
+		// or supporting retry mechanisms by not sending non-fatal errors to the clients
+		proxy.ErrorHandler = h.Responder.Error
+	}
+	proxy.ServeHTTP(w, newReq)
+}
+
+type noSuppressPanicError struct{}
+
+func (noSuppressPanicError) Write(p []byte) (n int, err error) {
+	// skip "suppressing panic for copyResponse error in test; copy error" error message
+	// that ends up in CI tests on each kube-apiserver termination as noise and
+	// everybody thinks this is fatal.
+	if strings.Contains(string(p), "suppressing panic") {
+		return len(p), nil
+	}
+	return os.Stderr.Write(p)
+}
+
+// tryUpgrade returns true if the request was handled.
+func (h *UpgradeAwareHandler) tryUpgrade(w http.ResponseWriter, req *http.Request) bool {
+	if !httpstream.IsUpgradeRequest(req) {
+		klog.V(6).Infof("Request was not an upgrade")
+		return false
+	}
+
+	var (
+		backendConn net.Conn
+		rawResponse []byte
+		err         error
+	)
+
+	location := *h.Location
+	if h.UseRequestLocation {
+		location = *req.URL
+		location.Scheme = h.Location.Scheme
+		location.Host = h.Location.Host
+		if h.AppendLocationPath {
+			location.Path = singleJoiningSlash(h.Location.Path, location.Path)
+		}
+	}
+
+	clone := utilnet.CloneRequest(req)
+	// Only append X-Forwarded-For in the upgrade path, since httputil.NewSingleHostReverseProxy
+	// handles this in the non-upgrade path.
+	utilnet.AppendForwardedForHeader(clone)
+	klog.V(6).Infof("Connecting to backend proxy (direct dial) %s\n  Headers: %v", &location, clone.Header)
+	if h.UseLocationHost {
+		clone.Host = h.Location.Host
+	}
+	clone.URL = &location
+	backendConn, err = h.DialForUpgrade(clone)
+	if err != nil {
+		klog.V(6).Infof("Proxy connection error: %v", err)
+		h.Responder.Error(w, req, err)
+		return true
+	}
+	defer backendConn.Close()
+
+	// determine the http response code from the backend by reading from rawResponse+backendConn
+	backendHTTPResponse, headerBytes, err := getResponse(io.MultiReader(bytes.NewReader(rawResponse), backendConn))
+	if err != nil {
+		klog.V(6).Infof("Proxy connection error: %v", err)
+		h.Responder.Error(w, req, err)
+		return true
+	}
+	if len(headerBytes) > len(rawResponse) {
+		// we read beyond the bytes stored in rawResponse, update rawResponse to the full set of bytes read from the backend
+		rawResponse = headerBytes
+	}
+
+	// If the backend did not upgrade the request, return an error to the client. If the response was
+	// an error, the error is forwarded directly after the connection is hijacked. Otherwise, just
+	// return a generic error here.
+	if backendHTTPResponse.StatusCode != http.StatusSwitchingProtocols && backendHTTPResponse.StatusCode < 400 {
+		err := fmt.Errorf("invalid upgrade response: status code %d", backendHTTPResponse.StatusCode)
+		klog.Errorf("Proxy upgrade error: %v", err)
+		h.Responder.Error(w, req, err)
+		return true
+	}
+
+	// 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)
+	if !ok {
+		klog.V(6).Infof("Unable to hijack response writer: %T", w)
+		h.Responder.Error(w, req, fmt.Errorf("request connection cannot be hijacked: %T", w))
+		return true
+	}
+	requestHijackedConn, _, err := requestHijacker.Hijack()
+	if err != nil {
+		klog.V(6).Infof("Unable to hijack response: %v", err)
+		h.Responder.Error(w, req, fmt.Errorf("error hijacking connection: %v", err))
+		return true
+	}
+	defer requestHijackedConn.Close()
+
+	if backendHTTPResponse.StatusCode != http.StatusSwitchingProtocols {
+		// If the backend did not upgrade the request, echo the response from the backend to the client and return, closing the connection.
+		klog.V(6).Infof("Proxy upgrade error, status code %d", backendHTTPResponse.StatusCode)
+		// set read/write deadlines
+		deadline := time.Now().Add(10 * time.Second)
+		backendConn.SetReadDeadline(deadline)
+		requestHijackedConn.SetWriteDeadline(deadline)
+		// write the response to the client
+		err := backendHTTPResponse.Write(requestHijackedConn)
+		if err != nil && !strings.Contains(err.Error(), "use of closed network connection") {
+			klog.Errorf("Error proxying data from backend to client: %v", err)
+		}
+		// Indicate we handled the request
+		return true
+	}
+
+	// Forward raw response bytes back to client.
+	if len(rawResponse) > 0 {
+		klog.V(6).Infof("Writing %d bytes to hijacked connection", len(rawResponse))
+		if _, err = requestHijackedConn.Write(rawResponse); err != nil {
+			utilruntime.HandleError(fmt.Errorf("Error proxying response from backend to client: %v", err))
+		}
+	}
+
+	// Proxy the connection. This is bidirectional, so we need a goroutine
+	// to copy in each direction. Once one side of the connection exits, we
+	// exit the function which performs cleanup and in the process closes
+	// the other half of the connection in the defer.
+	writerComplete := make(chan struct{})
+	readerComplete := make(chan struct{})
+
+	go func() {
+		var writer io.WriteCloser
+		if h.MaxBytesPerSec > 0 {
+			writer = flowrate.NewWriter(backendConn, h.MaxBytesPerSec)
+		} else {
+			writer = backendConn
+		}
+		_, err := io.Copy(writer, requestHijackedConn)
+		if err != nil && !strings.Contains(err.Error(), "use of closed network connection") {
+			klog.Errorf("Error proxying data from client to backend: %v", err)
+		}
+		close(writerComplete)
+	}()
+
+	go func() {
+		var reader io.ReadCloser
+		if h.MaxBytesPerSec > 0 {
+			reader = flowrate.NewReader(backendConn, h.MaxBytesPerSec)
+		} else {
+			reader = backendConn
+		}
+		_, err := io.Copy(requestHijackedConn, reader)
+		if err != nil && !strings.Contains(err.Error(), "use of closed network connection") {
+			klog.Errorf("Error proxying data from backend to client: %v", err)
+		}
+		close(readerComplete)
+	}()
+
+	// Wait for one half the connection to exit. Once it does the defer will
+	// clean up the other half of the connection.
+	select {
+	case <-writerComplete:
+	case <-readerComplete:
+	}
+	klog.V(6).Infof("Disconnecting from backend proxy %s\n  Headers: %v", &location, clone.Header)
+
+	return true
+}
+
+// FIXME: Taken from net/http/httputil/reverseproxy.go as singleJoiningSlash is not exported to be re-used.
+// See-also: https://github.com/golang/go/issues/44290
+func singleJoiningSlash(a, b string) string {
+	aslash := strings.HasSuffix(a, "/")
+	bslash := strings.HasPrefix(b, "/")
+	switch {
+	case aslash && bslash:
+		return a + b[1:]
+	case !aslash && !bslash:
+		return a + "/" + b
+	}
+	return a + b
+}
+
+func (h *UpgradeAwareHandler) DialForUpgrade(req *http.Request) (net.Conn, error) {
+	if h.UpgradeTransport == nil {
+		return dial(req, h.Transport)
+	}
+	updatedReq, err := h.UpgradeTransport.WrapRequest(req)
+	if err != nil {
+		return nil, err
+	}
+	return dial(updatedReq, h.UpgradeTransport)
+}
+
+// getResponseCode reads a http response from the given reader, returns the response,
+// the bytes read from the reader, and any error encountered
+func getResponse(r io.Reader) (*http.Response, []byte, error) {
+	rawResponse := bytes.NewBuffer(make([]byte, 0, 256))
+	// Save the bytes read while reading the response headers into the rawResponse buffer
+	resp, err := http.ReadResponse(bufio.NewReader(io.TeeReader(r, rawResponse)), nil)
+	if err != nil {
+		return nil, nil, err
+	}
+	// return the http response and the raw bytes consumed from the reader in the process
+	return resp, rawResponse.Bytes(), nil
+}
+
+// dial dials the backend at req.URL and writes req to it.
+func dial(req *http.Request, transport http.RoundTripper) (net.Conn, error) {
+	conn, err := DialURL(req.Context(), req.URL, transport)
+	if err != nil {
+		return nil, fmt.Errorf("error dialing backend: %v", err)
+	}
+
+	if err = req.Write(conn); err != nil {
+		conn.Close()
+		return nil, fmt.Errorf("error sending request: %v", err)
+	}
+
+	return conn, err
+}
+
+func (h *UpgradeAwareHandler) defaultProxyTransport(url *url.URL, internalTransport http.RoundTripper) http.RoundTripper {
+	scheme := url.Scheme
+	host := url.Host
+	suffix := h.Location.Path
+	if strings.HasSuffix(url.Path, "/") && !strings.HasSuffix(suffix, "/") {
+		suffix += "/"
+	}
+	pathPrepend := strings.TrimSuffix(url.Path, suffix)
+	rewritingTransport := &Transport{
+		Scheme:       scheme,
+		Host:         host,
+		PathPrepend:  pathPrepend,
+		RoundTripper: internalTransport,
+	}
+	return &corsRemovingTransport{
+		RoundTripper: rewritingTransport,
+	}
+}
+
+// corsRemovingTransport is a wrapper for an internal transport. It removes CORS headers
+// from the internal response.
+// Implements pkg/util/net.RoundTripperWrapper
+type corsRemovingTransport struct {
+	http.RoundTripper
+}
+
+var _ = utilnet.RoundTripperWrapper(&corsRemovingTransport{})
+
+func (rt *corsRemovingTransport) RoundTrip(req *http.Request) (*http.Response, error) {
+	resp, err := rt.RoundTripper.RoundTrip(req)
+	if err != nil {
+		return nil, err
+	}
+	removeCORSHeaders(resp)
+	return resp, nil
+}
+
+func (rt *corsRemovingTransport) WrappedRoundTripper() http.RoundTripper {
+	return rt.RoundTripper
+}
+
+// removeCORSHeaders strip CORS headers sent from the backend
+// This should be called on all responses before returning
+func removeCORSHeaders(resp *http.Response) {
+	resp.Header.Del("Access-Control-Allow-Credentials")
+	resp.Header.Del("Access-Control-Allow-Headers")
+	resp.Header.Del("Access-Control-Allow-Methods")
+	resp.Header.Del("Access-Control-Allow-Origin")
+}