cmd/tailscale: let --exit-node= take a machine name in addition to IP

If you're online, let tailscale up --exit-node=NAME map NAME to its IP.

We don't store the exit node name server-side in prefs, avoiding
the concern raised earlier.

Fixes #3062

Change-Id: Ieea5ceec1a30befc67e9d6b8a530b3cb047b6b40
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

cmd/tailscale/cli/cli_test.go

@@ -18,6 +18,7 @@ import (
 	"tailscale.com/ipn"
 	"tailscale.com/ipn/ipnstate"
 	"tailscale.com/tstest"
+	"tailscale.com/types/key"
 	"tailscale.com/types/persist"
 	"tailscale.com/types/preftype"
 	"tailscale.com/version/distro"
@@ -567,7 +568,7 @@ func TestPrefsFromUpArgs(t *testing.T) {
 			args: upArgsT{
 				exitNodeIP: "foo",
 			},
-			wantErr: `invalid IP address "foo" for --exit-node: ParseIP("foo"): unable to parse IP`,
+			wantErr: `invalid value "foo" for --exit-node; must be IP or unique node name`,
 		},
 		{
 			name: "error_exit_node_allow_lan_without_exit_node",
@@ -841,3 +842,78 @@ func TestUpdatePrefs(t *testing.T) {
 		})
 	}
 }
+
+func TestExitNodeIPOfArg(t *testing.T) {
+	mustIP := netaddr.MustParseIP
+	tests := []struct {
+		name    string
+		arg     string
+		st      *ipnstate.Status
+		want    netaddr.IP
+		wantErr string
+	}{
+		{
+			name: "ip",
+			arg:  "1.2.3.4",
+			want: mustIP("1.2.3.4"),
+		},
+		{
+			name:    "no_match",
+			arg:     "unknown",
+			st:      &ipnstate.Status{MagicDNSSuffix: ".foo"},
+			wantErr: `invalid value "unknown" for --exit-node; must be IP or unique node name`,
+		},
+		{
+			name: "name",
+			arg:  "skippy",
+			st: &ipnstate.Status{
+				MagicDNSSuffix: ".foo",
+				Peer: map[key.NodePublic]*ipnstate.PeerStatus{
+					key.NewNode().Public(): {
+						DNSName:      "skippy.foo.",
+						TailscaleIPs: []netaddr.IP{mustIP("1.0.0.2")},
+					},
+				},
+			},
+			want: mustIP("1.0.0.2"),
+		},
+		{
+			name: "ambiguous",
+			arg:  "skippy",
+			st: &ipnstate.Status{
+				MagicDNSSuffix: ".foo",
+				Peer: map[key.NodePublic]*ipnstate.PeerStatus{
+					key.NewNode().Public(): {
+						DNSName:      "skippy.foo.",
+						TailscaleIPs: []netaddr.IP{mustIP("1.0.0.2")},
+					},
+					key.NewNode().Public(): {
+						DNSName:      "SKIPPY.foo.",
+						TailscaleIPs: []netaddr.IP{mustIP("1.0.0.2")},
+					},
+				},
+			},
+			wantErr: `ambiguous exit node name "skippy"`,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := exitNodeIPOfArg(tt.arg, tt.st)
+			if err != nil {
+				if err.Error() == tt.wantErr {
+					return
+				}
+				if tt.wantErr == "" {
+					t.Fatal(err)
+				}
+				t.Fatalf("error = %#q; want %#q", err, tt.wantErr)
+			}
+			if tt.wantErr != "" {
+				t.Fatalf("got %v; want error %#q", got, tt.wantErr)
+			}
+			if got != tt.want {
+				t.Fatalf("got %v; want %v", got, tt.want)
+			}
+		})
+	}
+}

cmd/tailscale/cli/up.go

@@ -28,6 +28,7 @@ import (
 	"tailscale.com/tailcfg"
 	"tailscale.com/types/logger"
 	"tailscale.com/types/preftype"
+	"tailscale.com/util/dnsname"
 	"tailscale.com/version/distro"
 )
 
@@ -73,7 +74,7 @@ func newUpFlagSet(goos string, upArgs *upArgsT) *flag.FlagSet {
 	upf.BoolVar(&upArgs.acceptRoutes, "accept-routes", false, "accept routes advertised by other Tailscale nodes")
 	upf.BoolVar(&upArgs.acceptDNS, "accept-dns", true, "accept DNS configuration from the admin panel")
 	upf.BoolVar(&upArgs.singleRoutes, "host-routes", true, "install host routes to other Tailscale nodes")
-	upf.StringVar(&upArgs.exitNodeIP, "exit-node", "", "Tailscale IP of the exit node for internet traffic, or empty string to not use an exit node")
+	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.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.StringVar(&upArgs.advertiseTags, "advertise-tags", "", "comma-separated ACL tags to request; each must start with \"tag:\" (e.g. \"tag:eng,tag:montreal,tag:ssh\")")
@@ -190,6 +191,36 @@ func calcAdvertiseRoutes(advertiseRoutes string, advertiseDefaultRoute bool) ([]
 	return routes, nil
 }
 
+func exitNodeIPOfArg(arg string, st *ipnstate.Status) (ip netaddr.IP, err error) {
+	if arg == "" {
+		return ip, errors.New("invalid use of exitNodeIPOfArg with empty string")
+	}
+	ip, err = netaddr.ParseIP(arg)
+	if err == nil {
+		return ip, err
+	}
+	match := 0
+	for _, ps := range st.Peer {
+		baseName := dnsname.TrimSuffix(ps.DNSName, st.MagicDNSSuffix)
+		if !strings.EqualFold(arg, baseName) {
+			continue
+		}
+		match++
+		if len(ps.TailscaleIPs) == 0 {
+			return ip, fmt.Errorf("node %q has no Tailscale IP?", arg)
+		}
+		ip = ps.TailscaleIPs[0]
+	}
+	switch match {
+	case 0:
+		return ip, fmt.Errorf("invalid value %q for --exit-node; must be IP or unique node name", arg)
+	case 1:
+		return ip, nil
+	default:
+		return ip, fmt.Errorf("ambiguous exit node name %q", arg)
+	}
+}
+
 // prefsFromUpArgs returns the ipn.Prefs for the provided args.
 //
 // Note that the parameters upArgs and warnf are named intentionally
@@ -205,9 +236,9 @@ func prefsFromUpArgs(upArgs upArgsT, warnf logger.Logf, st *ipnstate.Status, goo
 	var exitNodeIP netaddr.IP
 	if upArgs.exitNodeIP != "" {
 		var err error
-		exitNodeIP, err = netaddr.ParseIP(upArgs.exitNodeIP)
+		exitNodeIP, err = exitNodeIPOfArg(upArgs.exitNodeIP, st)
 		if err != nil {
-			return nil, fmt.Errorf("invalid IP address %q for --exit-node: %v", upArgs.exitNodeIP, err)
+			return nil, err
 		}
 	} else if upArgs.exitNodeAllowLANAccess {
 		return nil, fmt.Errorf("--exit-node-allow-lan-access can only be used with --exit-node")