Exclude the trailing dot from the hostname 253-character limit (#503)

Co-authored-by: Anuraag Agrawal <anuraaga@gmail.com>

Author: LordAizen1

protovalidate/_funcs.py

@@ -210,10 +210,12 @@ def cel_is_hostname(val: object) -> bool:
 
 def _is_hostname(val: str) -> bool:
     """Internal implementation."""
-    if len(val) > 253:
-        return False
+    string = val.removesuffix(".").lower()
 
-    string = val[0 : len(val) - 1].lower() if val.endswith(".") else val.lower()
+    # The 253-character limit excludes the optional trailing dot (RFC 3339) which
+    # we just stripped.
+    if len(string) > 253:
+        return False
 
     all_digits = False
     parts = string.lower().split(sep=".")

test/test_funcs.py

@@ -0,0 +1,29 @@
+# Copyright (c) 2023-2026 Buf Technologies, Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from __future__ import annotations
+
+from protovalidate._funcs import _is_hostname
+
+
+def test_hostname_trailing_dot_excluded_from_length() -> None:
+    name253 = ("a" * 63 + ".") * 3 + "a" * 61
+    name254 = ("a" * 63 + ".") * 3 + "a" * 62
+    assert len(name253) == 253
+    assert len(name254) == 254
+    # The 253-character limit excludes the optional trailing dot (RFC 3339).
+    assert _is_hostname(name253)
+    assert _is_hostname(name253 + ".")
+    assert not _is_hostname(name254)
+    assert not _is_hostname(name254 + ".")