[feature] Add domain permission drafts and excludes (#3547)

* [feature] Add domain permission drafts and excludes

* fix typescript complaining

* lint

* make filenames more consistent

* test own domain excluded

web/source/settings/lib/util/formvalidators.ts

@@ -0,0 +1,48 @@
+/*
+	GoToSocial
+	Copyright (C) GoToSocial Authors admin@gotosocial.org
+	SPDX-License-Identifier: AGPL-3.0-or-later
+
+	This program is free software: you can redistribute it and/or modify
+	it under the terms of the GNU Affero General Public License as published by
+	the Free Software Foundation, either version 3 of the License, or
+	(at your option) any later version.
+
+	This program is distributed in the hope that it will be useful,
+	but WITHOUT ANY WARRANTY; without even the implied warranty of
+	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+	GNU Affero General Public License for more details.
+
+	You should have received a copy of the GNU Affero General Public License
+	along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+import isValidDomain from "is-valid-domain";
+
+/**
+ * Validate the "domain" field of a form.
+ * @param domain 
+ * @returns 
+ */
+export function formDomainValidator(domain: string): string {
+	if (domain.length === 0) {
+		return "";
+	}
+
+	if (domain[domain.length-1] === ".") {
+		return "invalid domain";
+	}
+
+	const valid = isValidDomain(domain, {
+		subdomain: true,
+		wildcard: false,
+		allowUnicode: true,
+		topLevel: false,
+	});
+
+	if (valid) {
+		return "";
+	}
+
+	return "invalid domain";
+}