portforward: tunnel spdy through websockets

pkg/features/kube_features.go

@@ -619,6 +619,13 @@ const (
 	// Enable users to specify when a Pod is ready for scheduling.
 	PodSchedulingReadiness featuregate.Feature = "PodSchedulingReadiness"
 
+	// owner: @seans3
+	// kep: http://kep.k8s.io/4006
+	// alpha: v1.30
+	//
+	// Enables PortForward to be proxied with a websocket client
+	PortForwardWebsockets featuregate.Feature = "PortForwardWebsockets"
+
 	// owner: @jessfraz
 	// alpha: v1.12
 	//
@@ -1101,6 +1108,8 @@ var defaultKubernetesFeatureGates = map[featuregate.Feature]featuregate.FeatureS
 
 	PodSchedulingReadiness: {Default: true, PreRelease: featuregate.GA, LockToDefault: true}, // GA in 1.30; remove in 1.32
 
+	PortForwardWebsockets: {Default: false, PreRelease: featuregate.Alpha},
+
 	ProcMountType: {Default: false, PreRelease: featuregate.Alpha},
 
 	QOSReserved: {Default: false, PreRelease: featuregate.Alpha},

pkg/registry/core/pod/rest/subresources.go

@@ -242,7 +242,12 @@ func (r *PortForwardREST) Connect(ctx context.Context, name string, opts runtime
 	if err != nil {
 		return nil, err
 	}
-	return newThrottledUpgradeAwareProxyHandler(location, transport, false, true, responder), nil
+	handler := newThrottledUpgradeAwareProxyHandler(location, transport, false, true, responder)
+	if utilfeature.DefaultFeatureGate.Enabled(features.PortForwardWebsockets) {
+		tunnelingHandler := translator.NewTunnelingHandler(handler)
+		handler = translator.NewTranslatingHandler(handler, tunnelingHandler, wsstream.IsWebSocketRequestWithTunnelingProtocol)
+	}
+	return handler, nil
 }
 
 func newThrottledUpgradeAwareProxyHandler(location *url.URL, transport http.RoundTripper, wrapTransport, upgradeRequired bool, responder rest.Responder) http.Handler {

staging/src/k8s.io/apimachinery/pkg/util/httpstream/wsstream/conn.go

@@ -27,6 +27,7 @@ import (
 	"golang.org/x/net/websocket"
 
 	"k8s.io/apimachinery/pkg/util/httpstream"
+	"k8s.io/apimachinery/pkg/util/portforward"
 	"k8s.io/apimachinery/pkg/util/remotecommand"
 	"k8s.io/apimachinery/pkg/util/runtime"
 	"k8s.io/klog/v2"
@@ -106,6 +107,23 @@ func IsWebSocketRequestWithStreamCloseProtocol(req *http.Request) bool {
 	return false
 }
 
+// IsWebSocketRequestWithTunnelingProtocol returns true if the request contains headers
+// identifying that it is requesting a websocket upgrade with a tunneling protocol;
+// false otherwise.
+func IsWebSocketRequestWithTunnelingProtocol(req *http.Request) bool {
+	if !IsWebSocketRequest(req) {
+		return false
+	}
+	requestedProtocols := strings.TrimSpace(req.Header.Get(WebSocketProtocolHeader))
+	for _, requestedProtocol := range strings.Split(requestedProtocols, ",") {
+		if protocolSupportsWebsocketTunneling(strings.TrimSpace(requestedProtocol)) {
+			return true
+		}
+	}
+
+	return false
+}
+
 // IgnoreReceives reads from a WebSocket until it is closed, then returns. If timeout is set, the
 // read and write deadlines are pushed every time a new message is received.
 func IgnoreReceives(ws *websocket.Conn, timeout time.Duration) {
@@ -301,6 +319,12 @@ func protocolSupportsStreamClose(protocol string) bool {
 	return protocol == remotecommand.StreamProtocolV5Name
 }
 
+// protocolSupportsWebsocketTunneling returns true if the passed protocol
+// is a tunneled Kubernetes spdy protocol; false otherwise.
+func protocolSupportsWebsocketTunneling(protocol string) bool {
+	return strings.HasPrefix(protocol, portforward.WebsocketsSPDYTunnelingPrefix) && strings.HasSuffix(protocol, portforward.KubernetesSuffix)
+}
+
 // handle implements a websocket handler.
 func (conn *Conn) handle(ws *websocket.Conn) {
 	conn.initialize(ws)

staging/src/k8s.io/apimachinery/pkg/util/portforward/constants.go

@@ -0,0 +1,24 @@
+/*
+Copyright 2016 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 portforward
+
+const (
+	PortForwardV1Name                    = "portforward.k8s.io"
+	WebsocketsSPDYTunnelingPrefix        = "SPDY/3.1+"
+	KubernetesSuffix                     = ".k8s.io"
+	WebsocketsSPDYTunnelingPortForwardV1 = WebsocketsSPDYTunnelingPrefix + PortForwardV1Name
+)

staging/src/k8s.io/apimachinery/pkg/util/proxy/upgradeaware.go

@@ -36,6 +36,7 @@ import (
 	utilruntime "k8s.io/apimachinery/pkg/util/runtime"
 
 	"github.com/mxk/go-flowrate/flowrate"
+
 	"k8s.io/klog/v2"
 )
 
@@ -336,6 +337,7 @@ func (h *UpgradeAwareHandler) tryUpgrade(w http.ResponseWriter, req *http.Reques
 		clone.Host = h.Location.Host
 	}
 	clone.URL = &location
+	klog.V(6).Infof("UpgradeAwareProxy: dialing for SPDY upgrade with headers: %v", clone.Header)
 	backendConn, err = h.DialForUpgrade(clone)
 	if err != nil {
 		klog.V(6).Infof("Proxy connection error: %v", err)
@@ -370,13 +372,13 @@ func (h *UpgradeAwareHandler) tryUpgrade(w http.ResponseWriter, req *http.Reques
 	// 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)
+		klog.Errorf("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)
+		klog.Errorf("Unable to hijack response: %v", err)
 		h.Responder.Error(w, req, fmt.Errorf("error hijacking connection: %v", err))
 		return true
 	}
@@ -420,7 +422,7 @@ func (h *UpgradeAwareHandler) tryUpgrade(w http.ResponseWriter, req *http.Reques
 		} else {
 			writer = backendConn
 		}
-		_, err := io.Copy(writer, requestHijackedConn)
+		_, err := io.Copy(writer, &loggingReader{name: "client->backend", delegate: requestHijackedConn})
 		if err != nil && !strings.Contains(err.Error(), "use of closed network connection") {
 			klog.Errorf("Error proxying data from client to backend: %v", err)
 		}
@@ -434,7 +436,7 @@ func (h *UpgradeAwareHandler) tryUpgrade(w http.ResponseWriter, req *http.Reques
 		} else {
 			reader = backendConn
 		}
-		_, err := io.Copy(requestHijackedConn, reader)
+		_, err := io.Copy(requestHijackedConn, &loggingReader{name: "backend->client", delegate: reader})
 		if err != nil && !strings.Contains(err.Error(), "use of closed network connection") {
 			klog.Errorf("Error proxying data from backend to client: %v", err)
 		}
@@ -452,6 +454,18 @@ func (h *UpgradeAwareHandler) tryUpgrade(w http.ResponseWriter, req *http.Reques
 	return true
 }
 
+// loggingReader logs the bytes read from the "delegate" with a "name" prefix.
+type loggingReader struct {
+	name     string
+	delegate io.Reader
+}
+
+func (l *loggingReader) Read(p []byte) (int, error) {
+	n, err := l.delegate.Read(p)
+	klog.V(8).Infof("%s: %d bytes, err=%v, bytes=% X", l.name, n, err, p[:n])
+	return n, err
+}
+
 // 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 {

staging/src/k8s.io/apiserver/go.mod

@@ -16,6 +16,7 @@ require (
 	github.com/google/go-cmp v0.6.0
 	github.com/google/gofuzz v1.2.0
 	github.com/google/uuid v1.3.0
+	github.com/gorilla/websocket v1.5.0
 	github.com/grpc-ecosystem/go-grpc-prometheus v1.2.0
 	github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822
 	github.com/mxk/go-flowrate v0.0.0-20140419014527-cca7078d478f
@@ -77,7 +78,6 @@ require (
 	github.com/golang/groupcache v0.0.0-20210331224755-41bb18bfe9da // indirect
 	github.com/golang/protobuf v1.5.3 // indirect
 	github.com/google/btree v1.0.1 // indirect
-	github.com/gorilla/websocket v1.5.0 // indirect
 	github.com/grpc-ecosystem/go-grpc-middleware v1.3.0 // indirect
 	github.com/grpc-ecosystem/grpc-gateway v1.16.0 // indirect
 	github.com/grpc-ecosystem/grpc-gateway/v2 v2.16.0 // indirect

staging/src/k8s.io/apiserver/pkg/util/proxy/streamtunnel.go

@@ -0,0 +1,433 @@
+/*
+Copyright 2024 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"
+	"errors"
+	"fmt"
+	"io"
+	"net"
+	"net/http"
+	"strings"
+	"sync"
+	"time"
+
+	gwebsocket "github.com/gorilla/websocket"
+
+	"k8s.io/apimachinery/pkg/util/httpstream"
+	"k8s.io/apimachinery/pkg/util/httpstream/spdy"
+	"k8s.io/apimachinery/pkg/util/httpstream/wsstream"
+	utilnet "k8s.io/apimachinery/pkg/util/net"
+	constants "k8s.io/apimachinery/pkg/util/portforward"
+	"k8s.io/client-go/tools/portforward"
+	"k8s.io/klog/v2"
+)
+
+// TunnelingHandler is a handler which tunnels SPDY through WebSockets.
+type TunnelingHandler struct {
+	// Used to communicate between upstream SPDY and downstream tunnel.
+	upgradeHandler http.Handler
+}
+
+// NewTunnelingHandler is used to create the tunnel between an upstream
+// SPDY connection and a downstream tunneling connection through the stored
+// UpgradeAwareProxy.
+func NewTunnelingHandler(upgradeHandler http.Handler) *TunnelingHandler {
+	return &TunnelingHandler{upgradeHandler: upgradeHandler}
+}
+
+// ServeHTTP uses the upgradeHandler to tunnel between a downstream tunneling
+// connection and an upstream SPDY connection. The tunneling connection is
+// a wrapped WebSockets connection which communicates SPDY framed data.
+func (h *TunnelingHandler) ServeHTTP(w http.ResponseWriter, req *http.Request) {
+	klog.V(4).Infoln("TunnelingHandler ServeHTTP")
+
+	spdyProtocols := spdyProtocolsFromWebsocketProtocols(req)
+	if len(spdyProtocols) == 0 {
+		http.Error(w, "unable to upgrade: no tunneling spdy protocols provided", http.StatusBadRequest)
+		return
+	}
+
+	spdyRequest := createSPDYRequest(req, spdyProtocols...)
+
+	writer := &tunnelingResponseWriter{
+		w: w,
+		conn: &headerInterceptingConn{
+			initializableConn: &tunnelingWebsocketUpgraderConn{
+				w:   w,
+				req: req,
+			},
+		},
+	}
+
+	klog.V(4).Infoln("Tunnel spdy through websockets using the UpgradeAwareProxy")
+	h.upgradeHandler.ServeHTTP(writer, spdyRequest)
+}
+
+// createSPDYRequest modifies the passed request to remove
+// WebSockets headers and add SPDY upgrade information, including
+// spdy protocols acceptable to the client.
+func createSPDYRequest(req *http.Request, spdyProtocols ...string) *http.Request {
+	clone := utilnet.CloneRequest(req)
+	// Clean up the websocket headers from the http request.
+	clone.Header.Del(wsstream.WebSocketProtocolHeader)
+	clone.Header.Del("Sec-Websocket-Key")
+	clone.Header.Del("Sec-Websocket-Version")
+	clone.Header.Del(httpstream.HeaderUpgrade)
+	// Update the http request for an upstream SPDY upgrade.
+	clone.Method = "POST"
+	clone.Body = nil // Remove the request body which is unused.
+	clone.Header.Set(httpstream.HeaderUpgrade, spdy.HeaderSpdy31)
+	clone.Header.Del(httpstream.HeaderProtocolVersion)
+	for i := range spdyProtocols {
+		clone.Header.Add(httpstream.HeaderProtocolVersion, spdyProtocols[i])
+	}
+	return clone
+}
+
+// spdyProtocolsFromWebsocketProtocols returns a list of spdy protocols by filtering
+// to Kubernetes websocket subprotocols prefixed with "SPDY/3.1+", then removing the prefix
+func spdyProtocolsFromWebsocketProtocols(req *http.Request) []string {
+	var spdyProtocols []string
+	for _, protocol := range gwebsocket.Subprotocols(req) {
+		if strings.HasPrefix(protocol, constants.WebsocketsSPDYTunnelingPrefix) && strings.HasSuffix(protocol, constants.KubernetesSuffix) {
+			spdyProtocols = append(spdyProtocols, strings.TrimPrefix(protocol, constants.WebsocketsSPDYTunnelingPrefix))
+		}
+	}
+	return spdyProtocols
+}
+
+var _ http.ResponseWriter = &tunnelingResponseWriter{}
+var _ http.Hijacker = &tunnelingResponseWriter{}
+
+// tunnelingResponseWriter implements the http.ResponseWriter and http.Hijacker interfaces.
+// Only non-upgrade responses can be written using WriteHeader() and Write().
+// Once Write or WriteHeader is called, Hijack returns an error.
+// Once Hijack is called, Write, WriteHeader, and Hijack return errors.
+type tunnelingResponseWriter struct {
+	// w is used to delegate Header(), WriteHeader(), and Write() calls
+	w http.ResponseWriter
+	// conn is returned from Hijack()
+	conn net.Conn
+	// mu guards writes
+	mu sync.Mutex
+	// wrote tracks whether WriteHeader or Write has been called
+	written bool
+	// hijacked tracks whether Hijack has been called
+	hijacked bool
+}
+
+// Hijack returns a delegate "net.Conn".
+// An error is returned if Write(), WriteHeader(), or Hijack() was previously called.
+// The returned bufio.ReadWriter is always nil.
+func (w *tunnelingResponseWriter) Hijack() (net.Conn, *bufio.ReadWriter, error) {
+	w.mu.Lock()
+	defer w.mu.Unlock()
+	if w.written {
+		klog.Errorf("Hijack called after write")
+		return nil, nil, errors.New("connection has already been written to")
+	}
+	if w.hijacked {
+		klog.Errorf("Hijack called after hijack")
+		return nil, nil, errors.New("connection has already been hijacked")
+	}
+	w.hijacked = true
+	klog.V(6).Infof("Hijack returning websocket tunneling net.Conn")
+	return w.conn, nil, nil
+}
+
+// Header is delegated to the stored "http.ResponseWriter".
+func (w *tunnelingResponseWriter) Header() http.Header {
+	return w.w.Header()
+}
+
+// Write is delegated to the stored "http.ResponseWriter".
+func (w *tunnelingResponseWriter) Write(p []byte) (int, error) {
+	w.mu.Lock()
+	defer w.mu.Unlock()
+	if w.hijacked {
+		klog.Errorf("Write called after hijack")
+		return 0, http.ErrHijacked
+	}
+	w.written = true
+	return w.w.Write(p)
+}
+
+// WriteHeader is delegated to the stored "http.ResponseWriter".
+func (w *tunnelingResponseWriter) WriteHeader(statusCode int) {
+	w.mu.Lock()
+	defer w.mu.Unlock()
+	if w.written {
+		klog.Errorf("WriteHeader called after write")
+		return
+	}
+	if w.hijacked {
+		klog.Errorf("WriteHeader called after hijack")
+		return
+	}
+	w.written = true
+
+	if statusCode == http.StatusSwitchingProtocols {
+		// 101 upgrade responses must come via the hijacked connection, not WriteHeader
+		klog.Errorf("WriteHeader called with 101 upgrade")
+		http.Error(w.w, "unexpected upgrade", http.StatusInternalServerError)
+		return
+	}
+
+	// pass through non-upgrade responses we don't need to translate
+	w.w.WriteHeader(statusCode)
+}
+
+// headerInterceptingConn wraps the tunneling "net.Conn" to drain the
+// HTTP response status/headers from the upstream SPDY connection, then use
+// that to decide how to initialize the delegate connection for writes.
+type headerInterceptingConn struct {
+	// initializableConn is delegated to for all net.Conn methods.
+	// initializableConn.Write() is not called until response headers have been read
+	// and initializableConn#InitializeWrite() has been called with the result.
+	initializableConn
+
+	lock         sync.Mutex
+	headerBuffer []byte
+	initialized  bool
+}
+
+// initializableConn is a connection that will be initialized before any calls to Write are made
+type initializableConn interface {
+	net.Conn
+	InitializeWrite(backendResponse *http.Response) error
+}
+
+const maxHeaderBytes = 1 << 20
+
+// Write intercepts to initially swallow the HTTP response, then
+// delegate to the tunneling "net.Conn" once the response has been
+// seen and processed.
+func (h *headerInterceptingConn) Write(b []byte) (int, error) {
+	h.lock.Lock()
+	defer h.lock.Unlock()
+
+	if h.initialized {
+		return h.initializableConn.Write(b)
+	}
+
+	// Write into the headerBuffer, then attempt to parse the bytes
+	// as an http response.
+	if len(h.headerBuffer)+len(b) > maxHeaderBytes {
+		return 0, fmt.Errorf("header size limit exceeded")
+	}
+	h.headerBuffer = append(h.headerBuffer, b...)
+	bufferedReader := bufio.NewReader(bytes.NewReader(h.headerBuffer))
+	resp, err := http.ReadResponse(bufferedReader, nil)
+	if errors.Is(err, io.ErrUnexpectedEOF) {
+		// don't yet have a complete set of headers
+		return len(b), nil
+	}
+	if err != nil {
+		klog.Errorf("invalid headers: %v", err)
+		return len(b), err
+	}
+	resp.Body.Close() //nolint:errcheck
+
+	h.headerBuffer = nil
+	err = h.initializableConn.InitializeWrite(resp)
+	h.initialized = true
+	if err != nil {
+		return len(b), err
+	}
+
+	// Copy any remaining buffered data to the underlying conn
+	remainingBuffer, _ := io.ReadAll(bufferedReader)
+	if len(remainingBuffer) > 0 {
+		_, err = h.initializableConn.Write(remainingBuffer)
+	}
+	return len(b), err
+}
+
+type tunnelingWebsocketUpgraderConn struct {
+	// req is the websocket request, used for upgrading
+	req *http.Request
+	// w is the websocket writer, used for upgrading and writing error responses
+	w http.ResponseWriter
+
+	// lock guards conn and err
+	lock sync.RWMutex
+	// if conn is non-nil, InitializeWrite succeeded
+	conn net.Conn
+	// if err is non-nil, InitializeWrite failed or Close was called before InitializeWrite
+	err error
+}
+
+func (u *tunnelingWebsocketUpgraderConn) InitializeWrite(backendResponse *http.Response) (err error) {
+	// make sure we close a connection we open in error cases
+	var conn net.Conn
+	defer func() {
+		if err != nil && conn != nil {
+			conn.Close() //nolint:errcheck
+		}
+	}()
+
+	u.lock.Lock()
+	defer u.lock.Unlock()
+	if u.conn != nil {
+		return fmt.Errorf("InitializeWrite already called")
+	}
+	if u.err != nil {
+		return u.err
+	}
+
+	if backendResponse.StatusCode == http.StatusSwitchingProtocols {
+		connectionHeader := strings.ToLower(backendResponse.Header.Get(httpstream.HeaderConnection))
+		upgradeHeader := strings.ToLower(backendResponse.Header.Get(httpstream.HeaderUpgrade))
+		if !strings.Contains(connectionHeader, strings.ToLower(httpstream.HeaderUpgrade)) || !strings.Contains(upgradeHeader, strings.ToLower(spdy.HeaderSpdy31)) {
+			klog.Errorf("unable to upgrade: missing upgrade headers in response: %#v", backendResponse.Header)
+			u.err = fmt.Errorf("unable to upgrade: missing upgrade headers in response")
+			http.Error(u.w, u.err.Error(), http.StatusInternalServerError)
+			return u.err
+		}
+
+		// Translate the server's chosen SPDY protocol into the tunneled websocket protocol for the handshake
+		var serverWebsocketProtocols []string
+		if backendSPDYProtocol := strings.TrimSpace(backendResponse.Header.Get(httpstream.HeaderProtocolVersion)); backendSPDYProtocol != "" {
+			serverWebsocketProtocols = []string{constants.WebsocketsSPDYTunnelingPrefix + backendSPDYProtocol}
+		} else {
+			serverWebsocketProtocols = []string{}
+		}
+
+		// Try to upgrade the websocket connection.
+		// Beyond this point, we don't need to write errors to the response.
+		var upgrader = gwebsocket.Upgrader{
+			CheckOrigin:  func(r *http.Request) bool { return true },
+			Subprotocols: serverWebsocketProtocols,
+		}
+		conn, err := upgrader.Upgrade(u.w, u.req, nil)
+		if err != nil {
+			klog.Errorf("error upgrading websocket connection: %v", err)
+			u.err = err
+			return u.err
+		}
+
+		klog.V(4).Infof("websocket connection created: %s", conn.Subprotocol())
+		u.conn = portforward.NewTunnelingConnection("server", conn)
+		return nil
+	}
+
+	// anything other than an upgrade should pass through the backend response
+
+	// try to hijack
+	conn, _, err = u.w.(http.Hijacker).Hijack()
+	if err != nil {
+		klog.Errorf("Unable to hijack response: %v", err)
+		u.err = err
+		return u.err
+	}
+	// replay the backend response to the hijacked conn
+	conn.SetWriteDeadline(time.Now().Add(10 * time.Second)) //nolint:errcheck
+	err = backendResponse.Write(conn)
+	if err != nil {
+		u.err = err
+		return u.err
+	}
+	u.conn = conn
+	return nil
+}
+
+func (u *tunnelingWebsocketUpgraderConn) Read(b []byte) (n int, err error) {
+	u.lock.RLock()
+	defer u.lock.RUnlock()
+	if u.conn != nil {
+		return u.conn.Read(b)
+	}
+	if u.err != nil {
+		return 0, u.err
+	}
+	// return empty read without blocking until we are initialized
+	return 0, nil
+}
+func (u *tunnelingWebsocketUpgraderConn) Write(b []byte) (n int, err error) {
+	u.lock.RLock()
+	defer u.lock.RUnlock()
+	if u.conn != nil {
+		return u.conn.Write(b)
+	}
+	if u.err != nil {
+		return 0, u.err
+	}
+	return 0, fmt.Errorf("Write called before Initialize")
+}
+func (u *tunnelingWebsocketUpgraderConn) Close() error {
+	u.lock.Lock()
+	defer u.lock.Unlock()
+	if u.conn != nil {
+		return u.conn.Close()
+	}
+	if u.err != nil {
+		return u.err
+	}
+	// record that we closed so we don't write again or try to initialize
+	u.err = fmt.Errorf("connection closed")
+	// write a response
+	http.Error(u.w, u.err.Error(), http.StatusInternalServerError)
+	return nil
+}
+func (u *tunnelingWebsocketUpgraderConn) LocalAddr() net.Addr {
+	u.lock.RLock()
+	defer u.lock.RUnlock()
+	if u.conn != nil {
+		return u.conn.LocalAddr()
+	}
+	return noopAddr{}
+}
+func (u *tunnelingWebsocketUpgraderConn) RemoteAddr() net.Addr {
+	u.lock.RLock()
+	defer u.lock.RUnlock()
+	if u.conn != nil {
+		return u.conn.RemoteAddr()
+	}
+	return noopAddr{}
+}
+func (u *tunnelingWebsocketUpgraderConn) SetDeadline(t time.Time) error {
+	u.lock.RLock()
+	defer u.lock.RUnlock()
+	if u.conn != nil {
+		return u.conn.SetDeadline(t)
+	}
+	return nil
+}
+func (u *tunnelingWebsocketUpgraderConn) SetReadDeadline(t time.Time) error {
+	u.lock.RLock()
+	defer u.lock.RUnlock()
+	if u.conn != nil {
+		return u.conn.SetReadDeadline(t)
+	}
+	return nil
+}
+func (u *tunnelingWebsocketUpgraderConn) SetWriteDeadline(t time.Time) error {
+	u.lock.RLock()
+	defer u.lock.RUnlock()
+	if u.conn != nil {
+		return u.conn.SetWriteDeadline(t)
+	}
+	return nil
+}
+
+type noopAddr struct{}
+
+func (n noopAddr) Network() string { return "" }
+func (n noopAddr) String() string  { return "" }

staging/src/k8s.io/apiserver/pkg/util/proxy/streamtunnel_test.go

@@ -0,0 +1,197 @@
+/*
+Copyright 2024 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"
+	"crypto/rand"
+	"io"
+	"net"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"k8s.io/apimachinery/pkg/runtime"
+	"k8s.io/apimachinery/pkg/util/httpstream"
+	"k8s.io/apimachinery/pkg/util/httpstream/spdy"
+	constants "k8s.io/apimachinery/pkg/util/portforward"
+	"k8s.io/apimachinery/pkg/util/proxy"
+	"k8s.io/apimachinery/pkg/util/wait"
+	"k8s.io/apiserver/pkg/registry/rest"
+	restconfig "k8s.io/client-go/rest"
+	"k8s.io/client-go/tools/portforward"
+)
+
+func TestTunnelingHandler_UpgradeStreamingAndTunneling(t *testing.T) {
+	// Create fake upstream SPDY server, with channel receiving SPDY streams.
+	streamChan := make(chan httpstream.Stream)
+	defer close(streamChan)
+	stopServerChan := make(chan struct{})
+	defer close(stopServerChan)
+	// Create fake upstream SPDY server.
+	spdyServer := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
+		_, err := httpstream.Handshake(req, w, []string{constants.PortForwardV1Name})
+		require.NoError(t, err)
+		upgrader := spdy.NewResponseUpgrader()
+		conn := upgrader.UpgradeResponse(w, req, justQueueStream(streamChan))
+		require.NotNil(t, conn)
+		defer conn.Close() //nolint:errcheck
+		<-stopServerChan
+	}))
+	defer spdyServer.Close()
+	// Create UpgradeAwareProxy handler, with url/transport pointing to upstream SPDY. Then
+	// create TunnelingHandler by injecting upgrade handler. Create TunnelingServer.
+	url, err := url.Parse(spdyServer.URL)
+	require.NoError(t, err)
+	transport, err := fakeTransport()
+	require.NoError(t, err)
+	upgradeHandler := proxy.NewUpgradeAwareHandler(url, transport, false, true, proxy.NewErrorResponder(&fakeResponder{}))
+	tunnelingHandler := NewTunnelingHandler(upgradeHandler)
+	tunnelingServer := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
+		tunnelingHandler.ServeHTTP(w, req)
+	}))
+	defer tunnelingServer.Close()
+	// Create SPDY client connection containing a TunnelingConnection by upgrading
+	// a request to TunnelingHandler using new portforward version 2.
+	tunnelingURL, err := url.Parse(tunnelingServer.URL)
+	require.NoError(t, err)
+	dialer, err := portforward.NewSPDYOverWebsocketDialer(tunnelingURL, &restconfig.Config{Host: tunnelingURL.Host})
+	require.NoError(t, err)
+	spdyClient, protocol, err := dialer.Dial(constants.PortForwardV1Name)
+	require.NoError(t, err)
+	assert.Equal(t, constants.PortForwardV1Name, protocol)
+	defer spdyClient.Close() //nolint:errcheck
+	// Create a SPDY client stream, which will queue a SPDY server stream
+	// on the stream creation channel. Send random data on the client stream
+	// reading off the SPDY server stream, and validating it was tunneled.
+	randomSize := 1024 * 1024
+	randomData := make([]byte, randomSize)
+	_, err = rand.Read(randomData)
+	require.NoError(t, err)
+	var actual []byte
+	go func() {
+		clientStream, err := spdyClient.CreateStream(http.Header{})
+		require.NoError(t, err)
+		_, err = io.Copy(clientStream, bytes.NewReader(randomData))
+		require.NoError(t, err)
+		clientStream.Close() //nolint:errcheck
+	}()
+	select {
+	case serverStream := <-streamChan:
+		actual, err = io.ReadAll(serverStream)
+		require.NoError(t, err)
+		defer serverStream.Close() //nolint:errcheck
+	case <-time.After(wait.ForeverTestTimeout):
+		t.Fatalf("timeout waiting for spdy stream to arrive on channel.")
+	}
+	assert.Equal(t, randomData, actual, "error validating tunneled random data")
+}
+
+const responseStr = `HTTP/1.1 101 Switching Protocols
+Date: Sun, 25 Feb 2024 08:09:25 GMT
+X-App-Protocol: portforward.k8s.io
+
+`
+
+const responseWithExtraStr = `HTTP/1.1 101 Switching Protocols
+Date: Sun, 25 Feb 2024 08:09:25 GMT
+X-App-Protocol: portforward.k8s.io
+
+This is extra data.
+`
+
+const invalidResponseStr = `INVALID/1.1 101 Switching Protocols
+Date: Sun, 25 Feb 2024 08:09:25 GMT
+X-App-Protocol: portforward.k8s.io
+
+`
+
+func TestTunnelingHandler_HeaderInterceptingConn(t *testing.T) {
+	// Basic http response is intercepted correctly; no extra data sent to net.Conn.
+	testConnConstructor := &mockConnInitializer{mockConn: &mockConn{}}
+	hic := &headerInterceptingConn{initializableConn: testConnConstructor}
+	_, err := hic.Write([]byte(responseStr))
+	require.NoError(t, err)
+	assert.True(t, hic.initialized, "successfully parsed http response headers")
+	assert.Equal(t, "101 Switching Protocols", testConnConstructor.resp.Status)
+	assert.Equal(t, "portforward.k8s.io", testConnConstructor.resp.Header.Get("X-App-Protocol"))
+	assert.Equal(t, 0, len(testConnConstructor.mockConn.written), "no extra data written to net.Conn")
+	// Extra data after response headers should be sent to net.Conn.
+	hic = &headerInterceptingConn{initializableConn: testConnConstructor}
+	_, err = hic.Write([]byte(responseWithExtraStr))
+	require.NoError(t, err)
+	assert.True(t, hic.initialized)
+	assert.Equal(t, "101 Switching Protocols", testConnConstructor.resp.Status)
+	assert.Equal(t, "This is extra data.\n", string(testConnConstructor.mockConn.written), "extra data written to net.Conn")
+	// Invalid response returns error.
+	hic = &headerInterceptingConn{initializableConn: testConnConstructor}
+	_, err = hic.Write([]byte(invalidResponseStr))
+	assert.Error(t, err, "expected error from invalid http response")
+}
+
+type mockConnInitializer struct {
+	resp *http.Response
+	*mockConn
+}
+
+func (m *mockConnInitializer) InitializeWrite(backendResponse *http.Response) error {
+	m.resp = backendResponse
+	return nil
+}
+
+// mockConn implements "net.Conn" interface.
+var _ net.Conn = &mockConn{}
+
+type mockConn struct {
+	written []byte
+}
+
+func (mc *mockConn) Write(p []byte) (int, error) {
+	mc.written = make([]byte, len(p))
+	copy(mc.written, p)
+	return len(mc.written), nil
+}
+
+func (mc *mockConn) Read(p []byte) (int, error)         { return 0, nil }
+func (mc *mockConn) Close() error                       { return nil }
+func (mc *mockConn) LocalAddr() net.Addr                { return &net.TCPAddr{} }
+func (mc *mockConn) RemoteAddr() net.Addr               { return &net.TCPAddr{} }
+func (mc *mockConn) SetDeadline(t time.Time) error      { return nil }
+func (mc *mockConn) SetReadDeadline(t time.Time) error  { return nil }
+func (mc *mockConn) SetWriteDeadline(t time.Time) error { return nil }
+
+// fakeResponder implements "rest.Responder" interface.
+var _ rest.Responder = &fakeResponder{}
+
+type fakeResponder struct{}
+
+func (fr *fakeResponder) Object(statusCode int, obj runtime.Object) {}
+func (fr *fakeResponder) Error(err error)                           {}
+
+// justQueueStream skips the usual stream validation before
+// queueing the stream on the stream channel.
+func justQueueStream(streams chan httpstream.Stream) func(httpstream.Stream, <-chan struct{}) error {
+	return func(stream httpstream.Stream, replySent <-chan struct{}) error {
+		streams <- stream
+		return nil
+	}
+}

staging/src/k8s.io/client-go/tools/portforward/fallback_dialer.go

@@ -0,0 +1,57 @@
+/*
+Copyright 2024 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 portforward
+
+import (
+	"k8s.io/apimachinery/pkg/util/httpstream"
+	"k8s.io/klog/v2"
+)
+
+var _ httpstream.Dialer = &fallbackDialer{}
+
+// fallbackDialer encapsulates a primary and secondary dialer, including
+// the boolean function to determine if the primary dialer failed. Implements
+// the httpstream.Dialer interface.
+type fallbackDialer struct {
+	primary        httpstream.Dialer
+	secondary      httpstream.Dialer
+	shouldFallback func(error) bool
+}
+
+// NewFallbackDialer creates the fallbackDialer with the primary and secondary dialers,
+// as well as the boolean function to determine if the primary dialer failed.
+func NewFallbackDialer(primary, secondary httpstream.Dialer, shouldFallback func(error) bool) httpstream.Dialer {
+	return &fallbackDialer{
+		primary:        primary,
+		secondary:      secondary,
+		shouldFallback: shouldFallback,
+	}
+}
+
+// Dial is the single function necessary to implement the "httpstream.Dialer" interface.
+// It takes the protocol version strings to request, returning an the upgraded
+// httstream.Connection and the negotiated protocol version accepted. If the initial
+// primary dialer fails, this function attempts the secondary dialer. Returns an error
+// if one occurs.
+func (f *fallbackDialer) Dial(protocols ...string) (httpstream.Connection, string, error) {
+	conn, version, err := f.primary.Dial(protocols...)
+	if err != nil && f.shouldFallback(err) {
+		klog.V(4).Infof("fallback to secondary dialer from primary dialer err: %v", err)
+		return f.secondary.Dial(protocols...)
+	}
+	return conn, version, err
+}

staging/src/k8s.io/client-go/tools/portforward/fallback_dialer_test.go

@@ -0,0 +1,53 @@
+/*
+Copyright 2024 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 portforward
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestFallbackDialer(t *testing.T) {
+	protocol := "v6.fake.k8s.io"
+	// If "shouldFallback" is false, then only primary should be dialed.
+	primary := &fakeDialer{dialed: false}
+	primary.negotiatedProtocol = protocol
+	secondary := &fakeDialer{dialed: false}
+	fallbackDialer := NewFallbackDialer(primary, secondary, alwaysFalse)
+	_, negotiated, err := fallbackDialer.Dial(protocol)
+	assert.True(t, primary.dialed, "no fallback; primary should have dialed")
+	assert.Equal(t, protocol, negotiated, "")
+	assert.False(t, secondary.dialed, "no fallback; secondary should *not* have dialed")
+	assert.Nil(t, err, "error should be nil")
+	// If "shouldFallback" is true, then primary AND secondary should be dialed.
+	primary.dialed = false // reset dialed field
+	primary.err = fmt.Errorf("bad handshake")
+	secondary.dialed = false // reset dialed field
+	secondary.negotiatedProtocol = protocol
+	fallbackDialer = NewFallbackDialer(primary, secondary, alwaysTrue)
+	_, negotiated, err = fallbackDialer.Dial(protocol)
+	assert.True(t, primary.dialed, "fallback; primary should have dialed (first)")
+	assert.True(t, secondary.dialed, "fallback; secondary should have dialed")
+	assert.Equal(t, protocol, negotiated)
+	assert.Nil(t, err)
+}
+
+func alwaysTrue(err error) bool { return true }
+
+func alwaysFalse(err error) bool { return false }

staging/src/k8s.io/client-go/tools/portforward/portforward.go

@@ -191,11 +191,15 @@ func (pf *PortForwarder) ForwardPorts() error {
 	defer pf.Close()
 
 	var err error
-	pf.streamConn, _, err = pf.dialer.Dial(PortForwardProtocolV1Name)
+	var protocol string
+	pf.streamConn, protocol, err = pf.dialer.Dial(PortForwardProtocolV1Name)
 	if err != nil {
 		return fmt.Errorf("error upgrading connection: %s", err)
 	}
 	defer pf.streamConn.Close()
+	if protocol != PortForwardProtocolV1Name {
+		return fmt.Errorf("unable to negotiate protocol: client supports %q, server returned %q", PortForwardProtocolV1Name, protocol)
+	}
 
 	return pf.forward()
 }

staging/src/k8s.io/client-go/tools/portforward/portforward_test.go

@@ -430,7 +430,8 @@ func TestGetListener(t *testing.T) {
 
 func TestGetPortsReturnsDynamicallyAssignedLocalPort(t *testing.T) {
 	dialer := &fakeDialer{
-		conn: newFakeConnection(),
+		conn:               newFakeConnection(),
+		negotiatedProtocol: PortForwardProtocolV1Name,
 	}
 
 	stopChan := make(chan struct{})
@@ -570,7 +571,8 @@ func TestWaitForConnectionExitsOnStreamConnClosed(t *testing.T) {
 
 func TestForwardPortsReturnsErrorWhenConnectionIsLost(t *testing.T) {
 	dialer := &fakeDialer{
-		conn: newFakeConnection(),
+		conn:               newFakeConnection(),
+		negotiatedProtocol: PortForwardProtocolV1Name,
 	}
 
 	stopChan := make(chan struct{})
@@ -601,7 +603,8 @@ func TestForwardPortsReturnsErrorWhenConnectionIsLost(t *testing.T) {
 
 func TestForwardPortsReturnsNilWhenStopChanIsClosed(t *testing.T) {
 	dialer := &fakeDialer{
-		conn: newFakeConnection(),
+		conn:               newFakeConnection(),
+		negotiatedProtocol: PortForwardProtocolV1Name,
 	}
 
 	stopChan := make(chan struct{})

staging/src/k8s.io/client-go/tools/portforward/tunneling_connection.go

@@ -0,0 +1,153 @@
+/*
+Copyright 2023 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 portforward
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"net"
+	"sync"
+	"time"
+
+	gwebsocket "github.com/gorilla/websocket"
+
+	"k8s.io/klog/v2"
+)
+
+var _ net.Conn = &TunnelingConnection{}
+
+// TunnelingConnection implements the "httpstream.Connection" interface, wrapping
+// a websocket connection that tunnels SPDY.
+type TunnelingConnection struct {
+	name              string
+	conn              *gwebsocket.Conn
+	inProgressMessage io.Reader
+	closeOnce         sync.Once
+}
+
+// NewTunnelingConnection wraps the passed gorilla/websockets connection
+// with the TunnelingConnection struct (implementing net.Conn).
+func NewTunnelingConnection(name string, conn *gwebsocket.Conn) *TunnelingConnection {
+	return &TunnelingConnection{
+		name: name,
+		conn: conn,
+	}
+}
+
+// Read implements "io.Reader" interface, reading from the stored connection
+// into the passed buffer "p". Returns the number of bytes read and an error.
+// Can keep track of the "inProgress" messsage from the tunneled connection.
+func (c *TunnelingConnection) Read(p []byte) (int, error) {
+	klog.V(7).Infof("%s: tunneling connection read...", c.name)
+	defer klog.V(7).Infof("%s: tunneling connection read...complete", c.name)
+	for {
+		if c.inProgressMessage == nil {
+			klog.V(8).Infof("%s: tunneling connection read before NextReader()...", c.name)
+			messageType, nextReader, err := c.conn.NextReader()
+			if err != nil {
+				closeError := &gwebsocket.CloseError{}
+				if errors.As(err, &closeError) && closeError.Code == gwebsocket.CloseNormalClosure {
+					return 0, io.EOF
+				}
+				klog.V(4).Infof("%s:tunneling connection NextReader() error: %v", c.name, err)
+				return 0, err
+			}
+			if messageType != gwebsocket.BinaryMessage {
+				return 0, fmt.Errorf("invalid message type received")
+			}
+			c.inProgressMessage = nextReader
+		}
+		klog.V(8).Infof("%s: tunneling connection read in progress message...", c.name)
+		i, err := c.inProgressMessage.Read(p)
+		if i == 0 && err == io.EOF {
+			c.inProgressMessage = nil
+		} else {
+			klog.V(8).Infof("%s: read %d bytes, error=%v, bytes=% X", c.name, i, err, p[:i])
+			return i, err
+		}
+	}
+}
+
+// Write implements "io.Writer" interface, copying the data in the passed
+// byte array "p" into the stored tunneled connection. Returns the number
+// of bytes written and an error.
+func (c *TunnelingConnection) Write(p []byte) (n int, err error) {
+	klog.V(7).Infof("%s: write: %d bytes, bytes=% X", c.name, len(p), p)
+	defer klog.V(7).Infof("%s: tunneling connection write...complete", c.name)
+	w, err := c.conn.NextWriter(gwebsocket.BinaryMessage)
+	if err != nil {
+		return 0, err
+	}
+	defer func() {
+		// close, which flushes the message
+		closeErr := w.Close()
+		if closeErr != nil && err == nil {
+			// if closing/flushing errored and we weren't already returning an error, return the close error
+			err = closeErr
+		}
+	}()
+
+	n, err = w.Write(p)
+	return
+}
+
+// Close implements "io.Closer" interface, signaling the other tunneled connection
+// endpoint, and closing the tunneled connection only once.
+func (c *TunnelingConnection) Close() error {
+	var err error
+	c.closeOnce.Do(func() {
+		klog.V(7).Infof("%s: tunneling connection Close()...", c.name)
+		// Signal other endpoint that websocket connection is closing; ignore error.
+		normalCloseMsg := gwebsocket.FormatCloseMessage(gwebsocket.CloseNormalClosure, "")
+		c.conn.WriteControl(gwebsocket.CloseMessage, normalCloseMsg, time.Now().Add(time.Second)) //nolint:errcheck
+		err = c.conn.Close()
+	})
+	return err
+}
+
+// LocalAddr implements part of the "net.Conn" interface, returning the local
+// endpoint network address of the tunneled connection.
+func (c *TunnelingConnection) LocalAddr() net.Addr {
+	return c.conn.LocalAddr()
+}
+
+// LocalAddr implements part of the "net.Conn" interface, returning the remote
+// endpoint network address of the tunneled connection.
+func (c *TunnelingConnection) RemoteAddr() net.Addr {
+	return c.conn.RemoteAddr()
+}
+
+// SetDeadline sets the *absolute* time in the future for both
+// read and write deadlines. Returns an error if one occurs.
+func (c *TunnelingConnection) SetDeadline(t time.Time) error {
+	rerr := c.SetReadDeadline(t)
+	werr := c.SetWriteDeadline(t)
+	return errors.Join(rerr, werr)
+}
+
+// SetDeadline sets the *absolute* time in the future for the
+// read deadlines. Returns an error if one occurs.
+func (c *TunnelingConnection) SetReadDeadline(t time.Time) error {
+	return c.conn.SetReadDeadline(t)
+}
+
+// SetDeadline sets the *absolute* time in the future for the
+// write deadlines. Returns an error if one occurs.
+func (c *TunnelingConnection) SetWriteDeadline(t time.Time) error {
+	return c.conn.SetWriteDeadline(t)
+}

staging/src/k8s.io/client-go/tools/portforward/tunneling_connection_test.go

@@ -0,0 +1,190 @@
+/*
+Copyright 2024 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 portforward
+
+import (
+	"io"
+	"net"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"strings"
+	"testing"
+	"time"
+
+	gwebsocket "github.com/gorilla/websocket"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"k8s.io/apimachinery/pkg/util/httpstream"
+	"k8s.io/apimachinery/pkg/util/httpstream/spdy"
+	constants "k8s.io/apimachinery/pkg/util/portforward"
+	"k8s.io/apimachinery/pkg/util/wait"
+	"k8s.io/client-go/rest"
+	"k8s.io/client-go/transport/websocket"
+)
+
+func TestTunnelingConnection_ReadWriteClose(t *testing.T) {
+	// Stream channel that will receive streams created on upstream SPDY server.
+	streamChan := make(chan httpstream.Stream)
+	defer close(streamChan)
+	stopServerChan := make(chan struct{})
+	defer close(stopServerChan)
+	// Create tunneling connection server endpoint with fake upstream SPDY server.
+	tunnelingServer := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
+		var upgrader = gwebsocket.Upgrader{
+			CheckOrigin:  func(r *http.Request) bool { return true },
+			Subprotocols: []string{constants.WebsocketsSPDYTunnelingPortForwardV1},
+		}
+		conn, err := upgrader.Upgrade(w, req, nil)
+		require.NoError(t, err)
+		defer conn.Close() //nolint:errcheck
+		require.Equal(t, constants.WebsocketsSPDYTunnelingPortForwardV1, conn.Subprotocol())
+		tunnelingConn := NewTunnelingConnection("server", conn)
+		spdyConn, err := spdy.NewServerConnection(tunnelingConn, justQueueStream(streamChan))
+		require.NoError(t, err)
+		defer spdyConn.Close() //nolint:errcheck
+		<-stopServerChan
+	}))
+	defer tunnelingServer.Close()
+	// Dial the client tunneling connection to the tunneling server.
+	url, err := url.Parse(tunnelingServer.URL)
+	require.NoError(t, err)
+	dialer, err := NewSPDYOverWebsocketDialer(url, &rest.Config{Host: url.Host})
+	require.NoError(t, err)
+	spdyClient, protocol, err := dialer.Dial(constants.PortForwardV1Name)
+	require.NoError(t, err)
+	assert.Equal(t, constants.PortForwardV1Name, protocol)
+	defer spdyClient.Close() //nolint:errcheck
+	// Create a SPDY client stream, which will queue a SPDY server stream
+	// on the stream creation channel. Send data on the client stream
+	// reading off the SPDY server stream, and validating it was tunneled.
+	expected := "This is a test tunneling SPDY data through websockets."
+	var actual []byte
+	go func() {
+		clientStream, err := spdyClient.CreateStream(http.Header{})
+		require.NoError(t, err)
+		_, err = io.Copy(clientStream, strings.NewReader(expected))
+		require.NoError(t, err)
+		clientStream.Close() //nolint:errcheck
+	}()
+	select {
+	case serverStream := <-streamChan:
+		actual, err = io.ReadAll(serverStream)
+		require.NoError(t, err)
+		defer serverStream.Close() //nolint:errcheck
+	case <-time.After(wait.ForeverTestTimeout):
+		t.Fatalf("timeout waiting for spdy stream to arrive on channel.")
+	}
+	assert.Equal(t, expected, string(actual), "error validating tunneled string")
+}
+
+func TestTunnelingConnection_LocalRemoteAddress(t *testing.T) {
+	stopServerChan := make(chan struct{})
+	defer close(stopServerChan)
+	tunnelingServer := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
+		var upgrader = gwebsocket.Upgrader{
+			CheckOrigin:  func(r *http.Request) bool { return true },
+			Subprotocols: []string{constants.WebsocketsSPDYTunnelingPortForwardV1},
+		}
+		conn, err := upgrader.Upgrade(w, req, nil)
+		require.NoError(t, err)
+		defer conn.Close() //nolint:errcheck
+		require.Equal(t, constants.WebsocketsSPDYTunnelingPortForwardV1, conn.Subprotocol())
+		<-stopServerChan
+	}))
+	defer tunnelingServer.Close()
+	// Create the client side tunneling connection.
+	url, err := url.Parse(tunnelingServer.URL)
+	require.NoError(t, err)
+	tConn, err := dialForTunnelingConnection(url)
+	require.NoError(t, err, "error creating client tunneling connection")
+	defer tConn.Close() //nolint:errcheck
+	// Validate "LocalAddr()" and "RemoteAddr()"
+	localAddr := tConn.LocalAddr()
+	remoteAddr := tConn.RemoteAddr()
+	assert.Equal(t, "tcp", localAddr.Network(), "tunneling connection must be TCP")
+	assert.Equal(t, "tcp", remoteAddr.Network(), "tunneling connection must be TCP")
+	_, err = net.ResolveTCPAddr("tcp", localAddr.String())
+	assert.NoError(t, err, "tunneling connection local addr should parse")
+	_, err = net.ResolveTCPAddr("tcp", remoteAddr.String())
+	assert.NoError(t, err, "tunneling connection remote addr should parse")
+}
+
+func TestTunnelingConnection_ReadWriteDeadlines(t *testing.T) {
+	stopServerChan := make(chan struct{})
+	defer close(stopServerChan)
+	tunnelingServer := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
+		var upgrader = gwebsocket.Upgrader{
+			CheckOrigin:  func(r *http.Request) bool { return true },
+			Subprotocols: []string{constants.WebsocketsSPDYTunnelingPortForwardV1},
+		}
+		conn, err := upgrader.Upgrade(w, req, nil)
+		require.NoError(t, err)
+		defer conn.Close() //nolint:errcheck
+		require.Equal(t, constants.WebsocketsSPDYTunnelingPortForwardV1, conn.Subprotocol())
+		<-stopServerChan
+	}))
+	defer tunnelingServer.Close()
+	// Create the client side tunneling connection.
+	url, err := url.Parse(tunnelingServer.URL)
+	require.NoError(t, err)
+	tConn, err := dialForTunnelingConnection(url)
+	require.NoError(t, err, "error creating client tunneling connection")
+	defer tConn.Close() //nolint:errcheck
+	// Validate the read and write deadlines.
+	err = tConn.SetReadDeadline(time.Time{})
+	assert.NoError(t, err, "setting zero deadline should always succeed; turns off deadline")
+	err = tConn.SetWriteDeadline(time.Time{})
+	assert.NoError(t, err, "setting zero deadline should always succeed; turns off deadline")
+	err = tConn.SetDeadline(time.Time{})
+	assert.NoError(t, err, "setting zero deadline should always succeed; turns off deadline")
+	err = tConn.SetReadDeadline(time.Now().AddDate(10, 0, 0))
+	assert.NoError(t, err, "setting deadline 10 year from now succeeds")
+	err = tConn.SetWriteDeadline(time.Now().AddDate(10, 0, 0))
+	assert.NoError(t, err, "setting deadline 10 year from now succeeds")
+	err = tConn.SetDeadline(time.Now().AddDate(10, 0, 0))
+	assert.NoError(t, err, "setting deadline 10 year from now succeeds")
+}
+
+// dialForTunnelingConnection upgrades a request at the passed "url", creating
+// a websocket connection. Returns the TunnelingConnection injected with the
+// websocket connection or an error if one occurs.
+func dialForTunnelingConnection(url *url.URL) (*TunnelingConnection, error) {
+	req, err := http.NewRequest("GET", url.String(), nil)
+	if err != nil {
+		return nil, err
+	}
+	// Tunneling must initiate a websocket upgrade connection, using tunneling portforward protocol.
+	tunnelingProtocols := []string{constants.WebsocketsSPDYTunnelingPortForwardV1}
+	transport, holder, err := websocket.RoundTripperFor(&rest.Config{Host: url.Host})
+	if err != nil {
+		return nil, err
+	}
+	conn, err := websocket.Negotiate(transport, holder, req, tunnelingProtocols...)
+	if err != nil {
+		return nil, err
+	}
+	return NewTunnelingConnection("client", conn), nil
+}
+
+func justQueueStream(streams chan httpstream.Stream) func(httpstream.Stream, <-chan struct{}) error {
+	return func(stream httpstream.Stream, replySent <-chan struct{}) error {
+		streams <- stream
+		return nil
+	}
+}

staging/src/k8s.io/client-go/tools/portforward/tunneling_dialer.go

@@ -0,0 +1,93 @@
+/*
+Copyright 2023 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 portforward
+
+import (
+	"fmt"
+	"net/http"
+	"net/url"
+	"strings"
+	"time"
+
+	"k8s.io/apimachinery/pkg/util/httpstream"
+	"k8s.io/apimachinery/pkg/util/httpstream/spdy"
+	constants "k8s.io/apimachinery/pkg/util/portforward"
+	restclient "k8s.io/client-go/rest"
+	"k8s.io/client-go/transport/websocket"
+	"k8s.io/klog/v2"
+)
+
+const PingPeriod = 10 * time.Second
+
+// tunnelingDialer implements "httpstream.Dial" interface
+type tunnelingDialer struct {
+	url       *url.URL
+	transport http.RoundTripper
+	holder    websocket.ConnectionHolder
+}
+
+// NewTunnelingDialer creates and returns the tunnelingDialer structure which implemements the "httpstream.Dialer"
+// interface. The dialer can upgrade a websocket request, creating a websocket connection. This function
+// returns an error if one occurs.
+func NewSPDYOverWebsocketDialer(url *url.URL, config *restclient.Config) (httpstream.Dialer, error) {
+	transport, holder, err := websocket.RoundTripperFor(config)
+	if err != nil {
+		return nil, err
+	}
+	return &tunnelingDialer{
+		url:       url,
+		transport: transport,
+		holder:    holder,
+	}, nil
+}
+
+// Dial upgrades to a tunneling streaming connection, returning a SPDY connection
+// containing a WebSockets connection (which implements "net.Conn"). Also
+// returns the protocol negotiated, or an error.
+func (d *tunnelingDialer) Dial(protocols ...string) (httpstream.Connection, string, error) {
+	// There is no passed context, so skip the context when creating request for now.
+	// Websockets requires "GET" method: RFC 6455 Sec. 4.1 (page 17).
+	req, err := http.NewRequest("GET", d.url.String(), nil)
+	if err != nil {
+		return nil, "", err
+	}
+	// Add the spdy tunneling prefix to the requested protocols. The tunneling
+	// handler will know how to negotiate these protocols.
+	tunnelingProtocols := []string{}
+	for _, protocol := range protocols {
+		tunnelingProtocol := constants.WebsocketsSPDYTunnelingPrefix + protocol
+		tunnelingProtocols = append(tunnelingProtocols, tunnelingProtocol)
+	}
+	klog.V(4).Infoln("Before WebSocket Upgrade Connection...")
+	conn, err := websocket.Negotiate(d.transport, d.holder, req, tunnelingProtocols...)
+	if err != nil {
+		return nil, "", err
+	}
+	if conn == nil {
+		return nil, "", fmt.Errorf("negotiated websocket connection is nil")
+	}
+	protocol := conn.Subprotocol()
+	protocol = strings.TrimPrefix(protocol, constants.WebsocketsSPDYTunnelingPrefix)
+	klog.V(4).Infof("negotiated protocol: %s", protocol)
+
+	// Wrap the websocket connection which implements "net.Conn".
+	tConn := NewTunnelingConnection("client", conn)
+	// Create SPDY connection injecting the previously created tunneling connection.
+	spdyConn, err := spdy.NewClientConnectionWithPings(tConn, PingPeriod)
+
+	return spdyConn, protocol, err
+}

staging/src/k8s.io/kubectl/pkg/cmd/portforward/portforward.go

@@ -31,6 +31,7 @@ import (
 
 	corev1 "k8s.io/api/core/v1"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/util/httpstream"
 	"k8s.io/apimachinery/pkg/util/sets"
 	"k8s.io/cli-runtime/pkg/genericiooptions"
 	"k8s.io/client-go/kubernetes/scheme"
@@ -50,7 +51,7 @@ import (
 type PortForwardOptions struct {
 	Namespace     string
 	PodName       string
-	RESTClient    *restclient.RESTClient
+	RESTClient    restclient.Interface
 	Config        *restclient.Config
 	PodClient     corev1client.PodsGetter
 	Address       []string
@@ -99,11 +100,7 @@ const (
 )
 
 func NewCmdPortForward(f cmdutil.Factory, streams genericiooptions.IOStreams) *cobra.Command {
-	opts := &PortForwardOptions{
+	opts := NewDefaultPortForwardOptions(streams)
-		PortForwarder: &defaultPortForwarder{
-			IOStreams: streams,
-		},
-	}
 	cmd := &cobra.Command{
 		Use:                   "port-forward TYPE/NAME [options] [LOCAL_PORT:]REMOTE_PORT [...[LOCAL_PORT_N:]REMOTE_PORT_N]",
 		DisableFlagsInUseLine: true,
@@ -123,6 +120,14 @@ func NewCmdPortForward(f cmdutil.Factory, streams genericiooptions.IOStreams) *c
 	return cmd
 }
 
+func NewDefaultPortForwardOptions(streams genericiooptions.IOStreams) *PortForwardOptions {
+	return &PortForwardOptions{
+		PortForwarder: &defaultPortForwarder{
+			IOStreams: streams,
+		},
+	}
+}
+
 type portForwarder interface {
 	ForwardPorts(method string, url *url.URL, opts PortForwardOptions) error
 }
@@ -137,6 +142,14 @@ func (f *defaultPortForwarder) ForwardPorts(method string, url *url.URL, opts Po
 		return err
 	}
 	dialer := spdy.NewDialer(upgrader, &http.Client{Transport: transport}, method, url)
+	if cmdutil.PortForwardWebsockets.IsEnabled() {
+		tunnelingDialer, err := portforward.NewSPDYOverWebsocketDialer(url, opts.Config)
+		if err != nil {
+			return err
+		}
+		// First attempt tunneling (websocket) dialer, then fallback to spdy dialer.
+		dialer = portforward.NewFallbackDialer(tunnelingDialer, dialer, httpstream.IsUpgradeFailure)
+	}
 	fw, err := portforward.NewOnAddresses(dialer, opts.Address, opts.Ports, opts.StopChannel, opts.ReadyChannel, f.Out, f.ErrOut)
 	if err != nil {
 		return err
@@ -387,7 +400,14 @@ func (o PortForwardOptions) Validate() error {
 
 // RunPortForward implements all the necessary functionality for port-forward cmd.
 func (o PortForwardOptions) RunPortForward() error {
-	pod, err := o.PodClient.Pods(o.Namespace).Get(context.TODO(), o.PodName, metav1.GetOptions{})
+	return o.RunPortForwardContext(context.Background())
+}
+
+// RunPortForwardContext implements all the necessary functionality for port-forward cmd.
+// It ends portforwarding when an error is received from the backend, or an os.Interrupt
+// signal is received, or the provided context is done.
+func (o PortForwardOptions) RunPortForwardContext(ctx context.Context) error {
+	pod, err := o.PodClient.Pods(o.Namespace).Get(ctx, o.PodName, metav1.GetOptions{})
 	if err != nil {
 		return err
 	}
@@ -401,7 +421,10 @@ func (o PortForwardOptions) RunPortForward() error {
 	defer signal.Stop(signals)
 
 	go func() {
-		<-signals
+		select {
+		case <-signals:
+		case <-ctx.Done():
+		}
 		if o.StopChannel != nil {
 			close(o.StopChannel)
 		}

staging/src/k8s.io/kubectl/pkg/cmd/portforward/portforward_test.go

@@ -17,6 +17,7 @@ limitations under the License.
 package portforward
 
 import (
+	"context"
 	"fmt"
 	"net/http"
 	"net/url"
@@ -101,6 +102,8 @@ func testPortForward(t *testing.T, flags map[string]string, args []string) {
 			}
 
 			opts := &PortForwardOptions{}
+			ctx, cancel := context.WithCancel(context.Background())
+			defer cancel()
 			cmd := NewCmdPortForward(tf, genericiooptions.NewTestIOStreamsDiscard())
 			cmd.Run = func(cmd *cobra.Command, args []string) {
 				if err = opts.Complete(tf, cmd, args); err != nil {
@@ -110,7 +113,7 @@ func testPortForward(t *testing.T, flags map[string]string, args []string) {
 				if err = opts.Validate(); err != nil {
 					return
 				}
-				err = opts.RunPortForward()
+				err = opts.RunPortForwardContext(ctx)
 			}
 
 			for name, value := range flags {

staging/src/k8s.io/kubectl/pkg/cmd/util/helpers.go

@@ -430,6 +430,7 @@ const (
 	InteractiveDelete       FeatureGate = "KUBECTL_INTERACTIVE_DELETE"
 	OpenAPIV3Patch          FeatureGate = "KUBECTL_OPENAPIV3_PATCH"
 	RemoteCommandWebsockets FeatureGate = "KUBECTL_REMOTE_COMMAND_WEBSOCKETS"
+	PortForwardWebsockets   FeatureGate = "KUBECTL_PORT_FORWARD_WEBSOCKETS"
 )
 
 // IsEnabled returns true iff environment variable is set to true.

test/integration/apiserver/portforward/main_test.go

@@ -0,0 +1,27 @@
+/*
+Copyright 2024 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 portforward
+
+import (
+	"testing"
+
+	"k8s.io/kubernetes/test/integration/framework"
+)
+
+func TestMain(m *testing.M) {
+	framework.EtcdMain(m.Run)
+}

test/integration/apiserver/portforward/portforward_test.go

@@ -0,0 +1,228 @@
+/*
+Copyright 2024 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 portforward
+
+import (
+	"bufio"
+	"bytes"
+	"context"
+	"fmt"
+	"io"
+	"net"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"strconv"
+	"strings"
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+
+	corev1 "k8s.io/api/core/v1"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/types"
+	"k8s.io/apimachinery/pkg/util/remotecommand"
+	"k8s.io/apimachinery/pkg/util/wait"
+	utilfeature "k8s.io/apiserver/pkg/util/feature"
+	"k8s.io/cli-runtime/pkg/genericiooptions"
+	"k8s.io/client-go/kubernetes"
+	featuregatetesting "k8s.io/component-base/featuregate/testing"
+	"k8s.io/kubectl/pkg/cmd/portforward"
+	kubeletportforward "k8s.io/kubelet/pkg/cri/streaming/portforward"
+	kastesting "k8s.io/kubernetes/cmd/kube-apiserver/app/testing"
+	kubefeatures "k8s.io/kubernetes/pkg/features"
+
+	"k8s.io/kubernetes/test/integration/framework"
+)
+
+const remotePort = "8765"
+
+func TestPortforward(t *testing.T) {
+	defer featuregatetesting.SetFeatureGateDuringTest(t, utilfeature.DefaultFeatureGate, kubefeatures.PortForwardWebsockets, true)()
+	t.Setenv("KUBECTL_PORT_FORWARD_WEBSOCKETS", "true")
+
+	var podName string
+	var podUID types.UID
+	backendServer := httptest.NewTLSServer(http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
+		t.Logf("backend saw request: %v", req.URL.String())
+		kubeletportforward.ServePortForward(
+			w,
+			req,
+			&dummyPortForwarder{t: t},
+			podName,
+			podUID,
+			&kubeletportforward.V4Options{},
+			wait.ForeverTestTimeout, // idle timeout
+			remotecommand.DefaultStreamCreationTimeout, // stream creation timeout
+			[]string{kubeletportforward.ProtocolV1Name},
+		)
+	}))
+	defer backendServer.Close()
+	backendURL, _ := url.Parse(backendServer.URL)
+	backendHost := backendURL.Hostname()
+	backendPort, _ := strconv.Atoi(backendURL.Port())
+
+	etcd := framework.SharedEtcd()
+	server := kastesting.StartTestServerOrDie(t, nil, []string{"--disable-admission-plugins=ServiceAccount"}, etcd)
+	defer server.TearDownFn()
+
+	adminClient, err := kubernetes.NewForConfig(server.ClientConfig)
+	require.NoError(t, err)
+
+	node := &corev1.Node{
+		ObjectMeta: metav1.ObjectMeta{Name: "mynode"},
+		Status: corev1.NodeStatus{
+			DaemonEndpoints: corev1.NodeDaemonEndpoints{KubeletEndpoint: corev1.DaemonEndpoint{Port: int32(backendPort)}},
+			Addresses:       []corev1.NodeAddress{{Type: corev1.NodeInternalIP, Address: backendHost}},
+		},
+	}
+	if _, err := adminClient.CoreV1().Nodes().Create(context.Background(), node, metav1.CreateOptions{}); err != nil {
+		t.Fatal(err)
+	}
+
+	pod := &corev1.Pod{
+		ObjectMeta: metav1.ObjectMeta{Namespace: "default", Name: "mypod"},
+		Spec: corev1.PodSpec{
+			NodeName:   "mynode",
+			Containers: []corev1.Container{{Name: "test", Image: "test"}},
+		},
+	}
+	if _, err := adminClient.CoreV1().Pods("default").Create(context.Background(), pod, metav1.CreateOptions{}); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := adminClient.CoreV1().Pods("default").Patch(context.Background(), "mypod", types.MergePatchType, []byte(`{"status":{"phase":"Running"}}`), metav1.PatchOptions{}, "status"); err != nil {
+		t.Fatal(err)
+	}
+
+	// local port missing asks os to find random open port.
+	// Example: ":8000" (local = random, remote = 8000)
+	localRemotePort := fmt.Sprintf(":%s", remotePort)
+	streams, _, out, errOut := genericiooptions.NewTestIOStreams()
+	portForwardOptions := portforward.NewDefaultPortForwardOptions(streams)
+	portForwardOptions.Namespace = "default"
+	portForwardOptions.PodName = "mypod"
+	portForwardOptions.RESTClient = adminClient.CoreV1().RESTClient()
+	portForwardOptions.Config = server.ClientConfig
+	portForwardOptions.PodClient = adminClient.CoreV1()
+	portForwardOptions.Address = []string{"127.0.0.1"}
+	portForwardOptions.Ports = []string{localRemotePort}
+	portForwardOptions.StopChannel = make(chan struct{}, 1)
+	portForwardOptions.ReadyChannel = make(chan struct{})
+
+	if err := portForwardOptions.Validate(); err != nil {
+		t.Fatal(err)
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	wg := sync.WaitGroup{}
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		if err := portForwardOptions.RunPortForwardContext(ctx); err != nil {
+			t.Error(err)
+		}
+	}()
+
+	t.Log("waiting for port forward to be ready")
+	select {
+	case <-portForwardOptions.ReadyChannel:
+		t.Log("port forward was ready")
+	case <-time.After(wait.ForeverTestTimeout):
+		t.Error("port forward was never ready")
+	}
+
+	// Parse out the randomly selected local port from "out" stream.
+	localPort, err := parsePort(out.String())
+	require.NoError(t, err)
+	t.Logf("Local Port: %s", localPort)
+
+	timeoutContext, cleanupTimeoutContext := context.WithDeadline(context.Background(), time.Now().Add(5*time.Second))
+	defer cleanupTimeoutContext()
+	testReq, _ := http.NewRequest("GET", fmt.Sprintf("http://127.0.0.1:%s/test", localPort), nil)
+	testReq = testReq.WithContext(timeoutContext)
+	testResp, err := http.DefaultClient.Do(testReq)
+	if err != nil {
+		t.Error(err)
+	} else {
+		t.Log(testResp.StatusCode)
+		data, err := io.ReadAll(testResp.Body)
+		if err != nil {
+			t.Error(err)
+		} else {
+			t.Log("client saw response:", string(data))
+		}
+		if string(data) != fmt.Sprintf("request to %s was ok", remotePort) {
+			t.Errorf("unexpected data")
+		}
+		if testResp.StatusCode != 200 {
+			t.Error("expected success")
+		}
+	}
+
+	cancel()
+
+	wg.Wait()
+	t.Logf("stdout: %s", out.String())
+	t.Logf("stderr: %s", errOut.String())
+}
+
+// parsePort parses out the local port from the port-forward output string.
+// This should work for both IP4 and IP6 addresses.
+//
+//	Example: "Forwarding from 127.0.0.1:8000 -> 4000", returns "8000".
+func parsePort(forwardAddr string) (string, error) {
+	parts := strings.Split(forwardAddr, " ")
+	if len(parts) != 5 {
+		return "", fmt.Errorf("unable to parse local port from stdout: %s", forwardAddr)
+	}
+	// parts[2] = "127.0.0.1:<LOCAL_PORT>"
+	_, localPort, err := net.SplitHostPort(parts[2])
+	if err != nil {
+		return "", fmt.Errorf("unable to parse local port: %w", err)
+	}
+	return localPort, nil
+}
+
+type dummyPortForwarder struct {
+	t *testing.T
+}
+
+func (d *dummyPortForwarder) PortForward(ctx context.Context, name string, uid types.UID, port int32, stream io.ReadWriteCloser) error {
+	d.t.Logf("handling port forward request for %d", port)
+
+	req, err := http.ReadRequest(bufio.NewReader(stream))
+	if err != nil {
+		d.t.Logf("error reading request: %v", err)
+		return err
+	}
+	d.t.Log(req.URL.String())
+	defer req.Body.Close() //nolint:errcheck
+
+	resp := &http.Response{
+		StatusCode: 200,
+		Proto:      "HTTP/1.1",
+		ProtoMajor: 1,
+		ProtoMinor: 1,
+		Body:       io.NopCloser(bytes.NewBufferString(fmt.Sprintf("request to %d was ok", port))),
+	}
+	resp.Write(stream) //nolint:errcheck
+	return stream.Close()
+}