diff --git a/web/lib/validhostname.php b/web/lib/validhostname.php
new file mode 100644
index 0000000..3d215d8
--- /dev/null
+++ b/web/lib/validhostname.php
@@ -0,0 +1,18 @@
+<?php
+function validhostname($hostname,$pattmods='') {
+	preg_replace('/./u','.',$hostname,-1,$c);
+	(strlen($hostname)>$c) ? $multibyte=true : $multibyte=false;
+	if ($multibyte) $hostname=idn_to_ascii($hostname,IDNA_DEFAULT,INTL_IDNA_VARIANT_UTS46);
+	if (strlen($hostname)>253)
+		return false;
+	$labs=explode('.',$hostname);
+	foreach ($labs as $lab) {
+		$len=strlen($lab);
+		if ($len==0 || $len>63)
+			return false;
+		if (preg_match('#^[a-z0-9]([a-z0-9-]*[a-z0-9])?$#i'.$pattmods,$lab)!==1)
+			return false;
+	}
+	return true;
+}
+?>