From: Michael Tremer <michael.tremer@ipfire.org>
Date: Sat, 6 Dec 2025 15:47:49 +0000 (+0000)
Subject: util: Add a helper function to check if something is a valid FQDN
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=e31b0b06904ad61749b8d1f499a9b5b94dad4050;p=dbl.git

util: Add a helper function to check if something is a valid FQDN

Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>
---

diff --git a/src/dnsbl/util.py b/src/dnsbl/util.py
index a35aa3c..bd8e8cd 100644
--- a/src/dnsbl/util.py
+++ b/src/dnsbl/util.py
@@ -18,6 +18,7 @@
 #                                                                             #
 ###############################################################################
 
+import idna
 import re
 import unicodedata
 
@@ -43,3 +44,37 @@ def slugify(text, iteration=None):
 	text = re.sub(r"-+", "-", text)
 
 	return text
+
+def is_fqdn(s):
+	"""
+		Checks if a string is a valid FQDN.
+	"""
+	# Decode any internationalized domains names
+	try:
+		s = idna.encode(s).decode("ascii")
+	except idna.IDNAError:
+		return False
+
+	if len(s) > 253:
+		return False
+
+	# Remove final dot, allowed in DNS but not in DB checks
+	if s.endswith("."):
+		s = s[:-1]
+
+	labels = s.split(".")
+
+	# FQDN must have at least two labels (e.g., example.com)
+	if len(labels) < 2:
+		return False
+
+	for label in labels:
+		if not 1 <= len(label) <= 63:
+			return False
+		if not label[0].isalnum() or not label[-1].isalnum():
+			return False
+		for ch in label:
+			if not (ch.isalnum() or ch == "-"):
+				return False
+
+	return True