cmd/tailscale/cli, ipn/ipnlocal: [funnel] add stream mode

Adds ability to start Funnel in the foreground and stream incoming
connections. When foreground process is stopped, Funnel is turned
back off for the port.

Exampe usage:
```
TS_DEBUG_FUNNEL_STREAM=on tailscale funnel 443 stream
```

Updates #8489

Signed-off-by: Sonia Appasamy <sonia@tailscale.com>

client/tailscale/localclient.go

@@ -946,6 +946,14 @@ func (lc *LocalClient) NetworkLockForceLocalDisable(ctx context.Context) error {
 	return nil
 }
 
+// NetworkLockDisable shuts down network-lock across the tailnet.
+func (lc *LocalClient) NetworkLockDisable(ctx context.Context, secret []byte) error {
+	if _, err := lc.send(ctx, "POST", "/localapi/v0/tka/disable", 200, bytes.NewReader(secret)); err != nil {
+		return fmt.Errorf("error: %w", err)
+	}
+	return nil
+}
+
 // SetServeConfig sets or replaces the serving settings.
 // If config is nil, settings are cleared and serving is disabled.
 func (lc *LocalClient) SetServeConfig(ctx context.Context, config *ipn.ServeConfig) error {
@@ -956,14 +964,6 @@ func (lc *LocalClient) SetServeConfig(ctx context.Context, config *ipn.ServeConf
 	return nil
 }
 
-// NetworkLockDisable shuts down network-lock across the tailnet.
-func (lc *LocalClient) NetworkLockDisable(ctx context.Context, secret []byte) error {
-	if _, err := lc.send(ctx, "POST", "/localapi/v0/tka/disable", 200, bytes.NewReader(secret)); err != nil {
-		return fmt.Errorf("error: %w", err)
-	}
-	return nil
-}
-
 // GetServeConfig return the current serve config.
 //
 // If the serve config is empty, it returns (nil, nil).
@@ -982,6 +982,30 @@ func getServeConfigFromJSON(body []byte) (sc *ipn.ServeConfig, err error) {
 	return sc, nil
 }
 
+// StreamFunnel opens funnel on the provided HostPort and keeps the
+// connection to the local backend open, streaming connections made
+// to the funnel URL.
+//
+// When the context is cancelled, the funnel is closed on HostPort.
+//
+// During the duration that the connection is open, the client's
+// ServeConfig will show that funnel is streaming for this HostPort.
+func (lc *LocalClient) StreamFunnel(ctx context.Context, hp ipn.HostPort) (io.ReadCloser, error) {
+	req, err := http.NewRequestWithContext(ctx, "POST", "http://"+apitype.LocalAPIHost+"/localapi/v0/stream-funnel", jsonBody(hp))
+	if err != nil {
+		return nil, err
+	}
+	res, err := lc.doLocalRequestNiceError(req)
+	if err != nil {
+		return nil, err
+	}
+	if res.StatusCode != 200 {
+		res.Body.Close()
+		return nil, errors.New(res.Status)
+	}
+	return res.Body, nil
+}
+
 // tailscaledConnectHint gives a little thing about why tailscaled (or
 // platform equivalent) is not answering localapi connections.
 //

cmd/tailscale/cli/funnel.go

@@ -7,6 +7,7 @@ import (
 	"context"
 	"flag"
 	"fmt"
+	"io"
 	"net"
 	"os"
 	"strconv"
@@ -66,20 +67,20 @@ func (e *serveEnv) runFunnel(ctx context.Context, args []string) error {
 		return flag.ErrHelp
 	}
 
-	var on bool
+	var stream, on bool
 	switch args[1] {
+	case "stream":
+		if s := os.Getenv("TS_DEBUG_FUNNEL_STREAM"); s == "on" {
+			stream = true
+		} else {
+			return flag.ErrHelp
+		}
 	case "on", "off":
 		on = args[1] == "on"
 	default:
 		return flag.ErrHelp
 	}
-	sc, err := e.lc.GetServeConfig(ctx)
-	if err != nil {
-		return err
-	}
-	if sc == nil {
-		sc = new(ipn.ServeConfig)
-	}
+
 	st, err := e.getLocalClientStatus(ctx)
 	if err != nil {
 		return fmt.Errorf("getting client status: %w", err)
@@ -96,6 +97,18 @@ func (e *serveEnv) runFunnel(ctx context.Context, args []string) error {
 	}
 	dnsName := strings.TrimSuffix(st.Self.DNSName, ".")
 	hp := ipn.HostPort(dnsName + ":" + strconv.Itoa(int(port)))
+
+	if stream {
+		return e.streamFunnel(ctx, hp)
+	}
+
+	sc, err := e.lc.GetServeConfig(ctx)
+	if err != nil {
+		return err
+	}
+	if sc == nil {
+		sc = new(ipn.ServeConfig)
+	}
 	if on == sc.AllowFunnel[hp] {
 		printFunnelWarning(sc)
 		// Nothing to do.
@@ -117,6 +130,33 @@ func (e *serveEnv) runFunnel(ctx context.Context, args []string) error {
 	return nil
 }
 
+func (e *serveEnv) streamFunnel(ctx context.Context, hp ipn.HostPort) error {
+	sc, err := e.lc.GetServeConfig(ctx)
+	if err != nil {
+		return err
+	}
+	if sc == nil {
+		sc = new(ipn.ServeConfig)
+	}
+	if sc.AllowFunnel[hp] {
+		return fmt.Errorf("Funnel already running on %q", hp)
+	}
+
+	mak.Set(&sc.AllowFunnel, hp, true)
+	printFunnelWarning(sc)
+
+	stream, err := e.lc.StreamFunnel(ctx, hp)
+	if err != nil {
+		return err
+	}
+	defer stream.Close()
+
+	fmt.Fprintf(os.Stderr, "Funnel started on \"https://%s\".\n", hp)
+	fmt.Fprintf(os.Stderr, "Press Ctrl-C to stop Funnel.\n\n")
+	_, err = io.Copy(os.Stdout, stream)
+	return err
+}
+
 // printFunnelWarning prints a warning if the Funnel is on but there is no serve
 // config for its host:port.
 func printFunnelWarning(sc *ipn.ServeConfig) {

cmd/tailscale/cli/serve.go

@@ -128,6 +128,7 @@ type localServeClient interface {
 	Status(context.Context) (*ipnstate.Status, error)
 	GetServeConfig(context.Context) (*ipn.ServeConfig, error)
 	SetServeConfig(context.Context, *ipn.ServeConfig) error
+	StreamFunnel(context.Context, ipn.HostPort) (io.ReadCloser, error) // TODO: testing :)
 }
 
 // serveEnv is the environment the serve command runs within. All I/O should be

cmd/tailscale/cli/serve_test.go

@@ -8,6 +8,7 @@ import (
 	"context"
 	"flag"
 	"fmt"
+	"io"
 	"os"
 	"path/filepath"
 	"reflect"
@@ -782,6 +783,11 @@ func (lc *fakeLocalServeClient) SetServeConfig(ctx context.Context, config *ipn.
 	return nil
 }
 
+func (lc *fakeLocalServeClient) StreamFunnel(ctx context.Context, hp ipn.HostPort) (io.ReadCloser, error) {
+	// TODO: testing :)
+	return nil, nil
+}
+
 // exactError returns an error checker that wants exactly the provided want error.
 // If optName is non-empty, it's used in the error message.
 func exactErr(want error, optName ...string) func(error) string {

ipn/ipnlocal/local.go

@@ -242,6 +242,7 @@ type LocalBackend struct {
 
 	serveListeners     map[netip.AddrPort]*serveListener      // addrPort => serveListener
 	serveProxyHandlers sync.Map                               // string (HTTPHandler.Proxy) => *httputil.ReverseProxy
+	funnelStreamers    map[uint16]*func(ipn.FunnelRequestLog) // serve port => stream logger
 
 	// statusLock must be held before calling statusChanged.Wait() or
 	// statusChanged.Broadcast().

ipn/ipnlocal/serve.go

@@ -257,6 +257,96 @@ func (b *LocalBackend) ServeConfig() ipn.ServeConfigView {
 	return b.serveConfig
 }
 
+// StreamFunnel turns on Funnel for the given HostPort, and keeps it on
+// for the duration that the context is open.
+//
+// When the context is done, Funnel is turned off for the port.
+//
+// During the stream, any incoming connections to the port are reported
+// out to the provided io.Writer, in the format ipn.FunnelRequestLog.
+func (b *LocalBackend) StreamFunnel(ctx context.Context, w io.Writer, hp ipn.HostPort) (err error) {
+	port, err := hp.Port()
+	if err != nil {
+		return err
+	}
+
+	// Turn on Funnel for the given HostPort.
+	sc := b.ServeConfig().AsStruct()
+	mak.Set(&sc.AllowFunnel, hp, true)
+	if err := b.SetServeConfig(sc); err != nil {
+		return err
+	}
+
+	// Defer turning off Funnel once stream ends.
+	cleanup := func() {
+		sc := b.ServeConfig().AsStruct()
+		delete(sc.AllowFunnel, hp)
+		err = errors.Join(err, b.SetServeConfig(sc))
+	}
+	defer cleanup()
+
+	f, ok := w.(http.Flusher)
+	if !ok {
+		return errors.New("writer not a flusher")
+	}
+
+	var writeErrs []error
+	writeToStream := func(log ipn.FunnelRequestLog) {
+		jsonLog, err := json.Marshal(log)
+		if err != nil {
+			writeErrs = append(writeErrs, err)
+			return
+		}
+		if _, err := fmt.Fprintf(w, "%s\n", jsonLog); err != nil {
+			writeErrs = append(writeErrs, err)
+			return
+		}
+		f.Flush()
+	}
+
+	// Hook up connections stream.
+	b.mu.Lock()
+	mak.Set(&b.funnelStreamers, port, &writeToStream)
+	b.mu.Unlock()
+
+	select {
+	case <-ctx.Done():
+	}
+
+	b.mu.Lock()
+	delete(b.funnelStreamers, port)
+	b.mu.Unlock()
+
+	return errors.Join(writeErrs...)
+}
+
+// maybeLogFunnelConnection logs out an ipn.FunnelRequestLog for the
+// connection if a streamer is currently active for the given destPort.
+func (b *LocalBackend) maybeLogFunnelConnection(destPort uint16, srcAddr netip.AddrPort) {
+	b.mu.Lock()
+	stream := b.funnelStreamers[destPort]
+	b.mu.Unlock()
+	if stream == nil {
+		return
+	}
+
+	var log ipn.FunnelRequestLog
+	log.SrcAddr = srcAddr
+	log.Time = time.Now() // TODO: use a different clock somewhere?
+
+	if node, user, ok := b.WhoIs(srcAddr); ok {
+		log.NodeName = node.ComputedName
+		if node.IsTagged() {
+			log.NodeTags = node.Tags
+		} else {
+			log.UserLoginName = user.LoginName
+			log.UserDisplayName = user.DisplayName
+		}
+	}
+
+	(*stream)(log)
+}
+
 func (b *LocalBackend) HandleIngressTCPConn(ingressPeer *tailcfg.Node, target ipn.HostPort, srcAddr netip.AddrPort, getConnOrReset func() (net.Conn, bool), sendRST func()) {
 	b.mu.Lock()
 	sc := b.serveConfig
@@ -359,6 +449,7 @@ func (b *LocalBackend) tcpHandlerForServe(dport uint16, srcAddr netip.AddrPort)
 	if backDst := tcph.TCPForward(); backDst != "" {
 		return func(conn net.Conn) error {
 			defer conn.Close()
+			b.maybeLogFunnelConnection(dport, srcAddr)
 			ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
 			backConn, err := b.dialer.SystemDial(ctx, "tcp", backDst)
 			cancel()
@@ -522,6 +613,10 @@ func (b *LocalBackend) serveWebHandler(w http.ResponseWriter, r *http.Request) {
 		http.NotFound(w, r)
 		return
 	}
+	if c, ok := getServeHTTPContext(r); ok {
+		b.maybeLogFunnelConnection(c.DestPort, c.SrcAddr)
+	}
+
 	if s := h.Text(); s != "" {
 		w.Header().Set("Content-Type", "text/plain; charset=utf-8")
 		io.WriteString(w, s)

ipn/localapi/localapi.go

@@ -95,6 +95,7 @@ var handler = map[string]localAPIHandler{
 	"set-expiry-sooner":           (*Handler).serveSetExpirySooner,
 	"start":                       (*Handler).serveStart,
 	"status":                      (*Handler).serveStatus,
+	"stream-funnel":               (*Handler).serveStreamFunnel,
 	"tka/init":                    (*Handler).serveTKAInit,
 	"tka/log":                     (*Handler).serveTKALog,
 	"tka/modify":                  (*Handler).serveTKAModify,
@@ -842,6 +843,30 @@ func (h *Handler) serveServeConfig(w http.ResponseWriter, r *http.Request) {
 	}
 }
 
+func (h *Handler) serveStreamFunnel(w http.ResponseWriter, r *http.Request) {
+	if !h.PermitWrite {
+		http.Error(w, "funnel stream denied", http.StatusForbidden)
+		return
+	}
+	if r.Method != "POST" {
+		http.Error(w, "POST required", http.StatusMethodNotAllowed)
+		return
+	}
+	hp := new(ipn.HostPort)
+	if err := json.NewDecoder(r.Body).Decode(hp); err != nil {
+		writeErrorJSON(w, fmt.Errorf("decoding HostPort: %w", err))
+		return
+	}
+
+	w.(http.Flusher).Flush()
+	w.Header().Set("Content-Type", "application/json")
+	if err := h.b.StreamFunnel(r.Context(), w, *hp); err != nil {
+		writeErrorJSON(w, fmt.Errorf("streaming funnel: %w", err))
+		return
+	}
+	w.WriteHeader(http.StatusOK)
+}
+
 func (h *Handler) serveCheckIPForwarding(w http.ResponseWriter, r *http.Request) {
 	if !h.PermitRead {
 		http.Error(w, "IP forwarding check access denied", http.StatusForbidden)

ipn/serve.go

@@ -11,6 +11,7 @@ import (
 	"net/url"
 	"strconv"
 	"strings"
+	"time"
 
 	"golang.org/x/exp/slices"
 	"tailscale.com/tailcfg"
@@ -42,6 +43,21 @@ type ServeConfig struct {
 // There is no implicit port 443. It must contain a colon.
 type HostPort string
 
+// Port extracts just the port number from hp.
+// An error is reported in the case that the hp does not
+// have a valid numeric port ending.
+func (hp HostPort) Port() (uint16, error) {
+	_, port, err := net.SplitHostPort(string(hp))
+	if err != nil {
+		return 0, err
+	}
+	port16, err := strconv.ParseUint(port, 10, 16)
+	if err != nil {
+		return 0, err
+	}
+	return uint16(port16), nil
+}
+
 // A FunnelConn wraps a net.Conn that is coming over a
 // Funnel connection. It can be used to determine further
 // information about the connection, like the source address
@@ -62,6 +78,25 @@ type FunnelConn struct {
 	Src netip.AddrPort
 }
 
+// FunnelRequestLog is the JSON type written out to io.Writers
+// watching funnel connections via ipnlocal.StreamFunnel.
+//
+// This structure is in development and subject to change.
+type FunnelRequestLog struct {
+	Time time.Time `json:",omitempty"` // time of request forwarding
+
+	// SrcAddr is the address that initiated the Funnel request.
+	SrcAddr netip.AddrPort `json:",omitempty"`
+
+	// The following fields are only populated if the connection
+	// initiated from another node on the client's tailnet.
+
+	NodeName        string   `json:",omitempty"` // src node MagicDNS name
+	NodeTags        []string `json:",omitempty"` // src node tags
+	UserLoginName   string   `json:",omitempty"` // src node's owner login (if not tagged)
+	UserDisplayName string   `json:",omitempty"` // src node's owner name (if not tagged)
+}
+
 // WebServerConfig describes a web server's configuration.
 type WebServerConfig struct {
 	Handlers map[string]*HTTPHandler // mountPoint => handler