cmd/tailscale/cli: add support for tailscale {up,set} --exit-node=auto:any

If the specified exit node string starts with "auto:" (i.e., can be parsed as an ipn.ExitNodeExpression),
we update ipn.Prefs.AutoExitNode instead of ipn.Prefs.ExitNodeID.

Fixes #16459

Signed-off-by: Nick Khyl <nickk@tailscale.com>

cmd/tailscale/cli/cli_test.go

@@ -972,8 +972,7 @@ func TestPrefFlagMapping(t *testing.T) {
 			// No CLI flag for this.
 			continue
 		case "AutoExitNode":
-			// TODO(nickkhyl): should be handled by tailscale {set,up} --exit-node.
+			// Handled by tailscale {set,up} --exit-node=auto:any.
-			// See tailscale/tailscale#16459.
 			continue
 		}
 		t.Errorf("unexpected new ipn.Pref field %q is not handled by up.go (see addPrefFlagMapping and checkForAccidentalSettingReverts)", prefName)
@@ -1338,6 +1337,27 @@ func TestUpdatePrefs(t *testing.T) {
 				}
 			},
 		},
+		{
+			name:  "auto_exit_node",
+			flags: []string{"--exit-node=auto:any"},
+			curPrefs: &ipn.Prefs{
+				ControlURL:    ipn.DefaultControlURL,
+				CorpDNS:       true,                 // enabled by [ipn.NewPrefs] by default
+				NetfilterMode: preftype.NetfilterOn, // enabled by [ipn.NewPrefs] by default
+			},
+			wantJustEditMP: &ipn.MaskedPrefs{
+				WantRunningSet:  true, // enabled by default for tailscale up
+				AutoExitNodeSet: true,
+				ExitNodeIDSet:   true, // we want ExitNodeID cleared
+				ExitNodeIPSet:   true, // same for ExitNodeIP
+			},
+			env: upCheckEnv{backendState: "Running"},
+			checkUpdatePrefsMutations: func(t *testing.T, newPrefs *ipn.Prefs) {
+				if newPrefs.AutoExitNode != ipn.AnyExitNode {
+					t.Errorf("AutoExitNode: got %q; want %q", newPrefs.AutoExitNode, ipn.AnyExitNode)
+				}
+			},
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {

cmd/tailscale/cli/set.go

@@ -73,7 +73,7 @@ func newSetFlagSet(goos string, setArgs *setArgsT) *flag.FlagSet {
 	setf.StringVar(&setArgs.profileName, "nickname", "", "nickname for the current account")
 	setf.BoolVar(&setArgs.acceptRoutes, "accept-routes", acceptRouteDefault(goos), "accept routes advertised by other Tailscale nodes")
 	setf.BoolVar(&setArgs.acceptDNS, "accept-dns", true, "accept DNS configuration from the admin panel")
-	setf.StringVar(&setArgs.exitNodeIP, "exit-node", "", "Tailscale exit node (IP or base name) for internet traffic, or empty string to not use an exit node")
+	setf.StringVar(&setArgs.exitNodeIP, "exit-node", "", "Tailscale exit node (IP, base name, or auto:any) for internet traffic, or empty string to not use an exit node")
 	setf.BoolVar(&setArgs.exitNodeAllowLANAccess, "exit-node-allow-lan-access", false, "Allow direct access to the local network when routing traffic via an exit node")
 	setf.BoolVar(&setArgs.shieldsUp, "shields-up", false, "don't allow incoming connections")
 	setf.BoolVar(&setArgs.runSSH, "ssh", false, "run an SSH server, permitting access per tailnet admin's declared policy")
@@ -173,7 +173,10 @@ func runSet(ctx context.Context, args []string) (retErr error) {
 	}
 
 	if setArgs.exitNodeIP != "" {
-		if err := maskedPrefs.Prefs.SetExitNodeIP(setArgs.exitNodeIP, st); err != nil {
+		if expr, useAutoExitNode := ipn.ParseAutoExitNodeString(setArgs.exitNodeIP); useAutoExitNode {
+			maskedPrefs.AutoExitNode = expr
+			maskedPrefs.AutoExitNodeSet = true
+		} else if err := maskedPrefs.Prefs.SetExitNodeIP(setArgs.exitNodeIP, st); err != nil {
 			var e ipn.ExitNodeLocalIPError
 			if errors.As(err, &e) {
 				return fmt.Errorf("%w; did you mean --advertise-exit-node?", err)

cmd/tailscale/cli/up.go

@@ -100,7 +100,7 @@ func newUpFlagSet(goos string, upArgs *upArgsT, cmd string) *flag.FlagSet {
 	upf.BoolVar(&upArgs.acceptRoutes, "accept-routes", acceptRouteDefault(goos), "accept routes advertised by other Tailscale nodes")
 	upf.BoolVar(&upArgs.acceptDNS, "accept-dns", true, "accept DNS configuration from the admin panel")
 	upf.Var(notFalseVar{}, "host-routes", hidden+"install host routes to other Tailscale nodes (must be true as of Tailscale 1.67+)")
-	upf.StringVar(&upArgs.exitNodeIP, "exit-node", "", "Tailscale exit node (IP or base name) for internet traffic, or empty string to not use an exit node")
+	upf.StringVar(&upArgs.exitNodeIP, "exit-node", "", "Tailscale exit node (IP, base name, or auto:any) for internet traffic, or empty string to not use an exit node")
 	upf.BoolVar(&upArgs.exitNodeAllowLANAccess, "exit-node-allow-lan-access", false, "Allow direct access to the local network when routing traffic via an exit node")
 	upf.BoolVar(&upArgs.shieldsUp, "shields-up", false, "don't allow incoming connections")
 	upf.BoolVar(&upArgs.runSSH, "ssh", false, "run an SSH server, permitting access per tailnet admin's declared policy")
@@ -278,7 +278,9 @@ func prefsFromUpArgs(upArgs upArgsT, warnf logger.Logf, st *ipnstate.Status, goo
 		prefs.NetfilterMode = preftype.NetfilterOff
 	}
 	if upArgs.exitNodeIP != "" {
-		if err := prefs.SetExitNodeIP(upArgs.exitNodeIP, st); err != nil {
+		if expr, useAutoExitNode := ipn.ParseAutoExitNodeString(upArgs.exitNodeIP); useAutoExitNode {
+			prefs.AutoExitNode = expr
+		} else if err := prefs.SetExitNodeIP(upArgs.exitNodeIP, st); err != nil {
 			var e ipn.ExitNodeLocalIPError
 			if errors.As(err, &e) {
 				return nil, fmt.Errorf("%w; did you mean --advertise-exit-node?", err)
@@ -408,6 +410,9 @@ func updatePrefs(prefs, curPrefs *ipn.Prefs, env upCheckEnv) (simpleUp bool, jus
 		if env.upArgs.reset {
 			visitFlags = env.flagSet.VisitAll
 		}
+		if prefs.AutoExitNode.IsSet() {
+			justEditMP.AutoExitNodeSet = true
+		}
 		visitFlags(func(f *flag.Flag) {
 			updateMaskedPrefsFromUpOrSetFlag(justEditMP, f.Name)
 		})