1 files changed, 54 insertions, 0 deletions
diff --git a/lib/private/Net/HostnameClassifier.php b/lib/private/Net/HostnameClassifier.php
new file mode 100644
index 00000000000..e0f1435d6f1
--- /dev/null
+++ b/lib/private/Net/HostnameClassifier.php
@@ -0,0 +1,54 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * SPDX-FileCopyrightText: 2022 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace OC\Net;
+
+use function filter_var;
+use function in_array;
+use function strrchr;
+use function substr;
+use function substr_count;
+
+/**
+ * Classifier for network hostnames
+ *
+ * @internal
+ */
+class HostnameClassifier {
+	private const LOCAL_TOPLEVEL_DOMAINS = [
+		'local',
+		'localhost',
+		'intranet',
+		'internal',
+		'private',
+		'corp',
+		'home',
+		'lan',
+	];
+
+	/**
+	 * Check host identifier for local hostname
+	 *
+	 * IP addresses are not considered local. Use the IpAddressClassifier for those.
+	 */
+	public function isLocalHostname(string $hostname): bool {
+		// Disallow local network top-level domains from RFC 6762
+		$topLevelDomain = substr((strrchr($hostname, '.') ?: ''), 1);
+		if (in_array($topLevelDomain, self::LOCAL_TOPLEVEL_DOMAINS)) {
+			return true;
+		}
+
+		// Disallow hostname only
+		if (substr_count($hostname, '.') === 0 && !filter_var($hostname, FILTER_VALIDATE_IP, FILTER_FLAG_IPV6)) {
+			return true;
+		}
+
+		return false;
+	}
+}