Server setup in the app

internal/tailscale/tailscale.go

@@ -50,6 +50,32 @@ func serve(ctx context.Context, port int, target string) (string, error) {
 	return "", fmt.Errorf("tailscale serve --https=%d exited 0 but port %d is not in serve status", port, port)
 }
 
+func Problem(ctx context.Context) string {
+	_, err := os.Stat(cli)
+	if err != nil {
+		return "Install the Tailscale app from https://tailscale.com/download/mac and sign in."
+	}
+	out, err := run(ctx, "status", "--json", "--peers=false")
+	if err != nil {
+		return "Open Tailscale and sign in (" + err.Error() + ")."
+	}
+	status := struct {
+		BackendState string
+		CertDomains  []string
+	}{}
+	err = json.Unmarshal(out, &status)
+	if err != nil {
+		return "Parse tailscale status: " + err.Error()
+	}
+	if status.BackendState != "Running" {
+		return "Open Tailscale and sign in (it is " + status.BackendState + ")."
+	}
+	if len(status.CertDomains) == 0 {
+		return "Turn on HTTPS Certificates on the DNS page of Tailscale's admin console, https://login.tailscale.com/admin/dns."
+	}
+	return ""
+}
+
 func Off(ctx context.Context, port int) error {
 	_, err := run(ctx, "serve", "--https="+strconv.Itoa(port), "off")
 	return err