cmd/tailscale/cli: allow empty text ("") serveshayne/serve_empty_text_handler

Current behavior is broken. `tailscale serve text / ""` returns no error
and shows up in `tailscale serve status` but requests return a 500
"empty handler".

The commit changes the handler field `Text` to type of `*string`.

Closes #6405

Signed-off-by: Shayne Sweeney <shayne@tailscale.com>

4 files changed, 12 insertions, 8 deletions

diff --git a/cmd/tailscale/cli/cli.go b/cmd/tailscale/cli/cli.go
index 6845cbd93..cbe937588 100644
--- a/cmd/tailscale/cli/cli.go
+++ b/cmd/tailscale/cli/cli.go
@@ -53,6 +53,12 @@ func outln(a ...any) {
 	fmt.Fprintln(Stdout, a...)
 }
 
+// ptrTo returns a pointer to the provided value.
+// It's a convenience function to avoid having to write &value,
+// or where the language doesn't allow it.
+// Used primarily in tests.
+func ptrTo[T any](v T) *T { return &v }
+
 // ActLikeCLI reports whether a GUI application should act like the
 // CLI based on os.Args, GOOS, the context the process is running in
 // (pty, parent PID), etc.
diff --git a/cmd/tailscale/cli/serve.go b/cmd/tailscale/cli/serve.go
index 402b64da5..cc455c90c 100644
--- a/cmd/tailscale/cli/serve.go
+++ b/cmd/tailscale/cli/serve.go
@@ -285,7 +285,7 @@ func (e *serveEnv) runServe(ctx context.Context, args []string) error {
 		}
 		h.Proxy = t
 	case "text":
-		h.Text = args[2]
+		h.Text = ptrTo(args[2])
 	default:
 		fmt.Fprintf(os.Stderr, "error: unknown serve type %q\n\n", args[1])
 		return flag.ErrHelp
@@ -547,8 +547,8 @@ func printWebStatusTree(sc *ipn.ServeConfig, hp ipn.HostPort) {
 			return "path", h.Path
 		case h.Proxy != "":
 			return "proxy", h.Proxy
-		case h.Text != "":
-			return "text", "\"" + elipticallyTruncate(h.Text, 20) + "\""
+		case h.Text != nil:
+			return "text", "\"" + elipticallyTruncate(*h.Text, 20) + "\""
 		}
 		return "", ""
 	}
diff --git a/cmd/tailscale/cli/serve_test.go b/cmd/tailscale/cli/serve_test.go
index e3269b674..e526a54e8 100644
--- a/cmd/tailscale/cli/serve_test.go
+++ b/cmd/tailscale/cli/serve_test.go
@@ -151,7 +151,7 @@ func TestServeConfigMutations(t *testing.T) {
 					"/abc": {Proxy: "http://127.0.0.1:3001"},
 				}},
 				"foo.test.ts.net:10000": {Handlers: map[string]*ipn.HTTPHandler{
-					"/": {Text: "hi"},
+					"/": {Text: ptrTo("hi")},
 				}},
 			},
 		},
@@ -314,7 +314,7 @@ func TestServeConfigMutations(t *testing.T) {
 			TCP: map[uint16]*ipn.TCPPortHandler{443: {HTTPS: true}},
 			Web: map[ipn.HostPort]*ipn.WebServerConfig{
 				"foo.test.ts.net:443": {Handlers: map[string]*ipn.HTTPHandler{
-					"/": {Text: "hello"},
+					"/": {Text: ptrTo("hello")},
 				}},
 			},
 		},
@@ -547,7 +547,7 @@ func TestServeConfigMutations(t *testing.T) {
 			TCP: map[uint16]*ipn.TCPPortHandler{443: {HTTPS: true}},
 			Web: map[ipn.HostPort]*ipn.WebServerConfig{
 				"foo.test.ts.net:443": {Handlers: map[string]*ipn.HTTPHandler{
-					"/tcp": {Text: "foo"},
+					"/tcp": {Text: ptrTo("foo")},
 				}},
 			},
 		},
diff --git a/cmd/tailscale/cli/set_test.go b/cmd/tailscale/cli/set_test.go
index 013896a4a..e7a7c45f1 100644
--- a/cmd/tailscale/cli/set_test.go
+++ b/cmd/tailscale/cli/set_test.go
@@ -13,8 +13,6 @@ import (
 	"tailscale.com/net/tsaddr"
 )
 
-func ptrTo[T any](v T) *T { return &v }
-
 func TestCalcAdvertiseRoutesForSet(t *testing.T) {
 	pfx := netip.MustParsePrefix
 	tests := []struct {