Accept trailing-dot FQDN hosts in domain_filter

courlan/filters.py

@@ -8,6 +8,7 @@
 
 from .hosts import _canonical_ip, _idna_encode
 from .langcodes import langcodes_score
+from .urlutils import _strip_trailing_dot
 
 LOGGER = logging.getLogger(__name__)
 
@@ -128,6 +129,8 @@ def _valid_port(tail: str) -> bool:
 
 def domain_filter(domain: str) -> bool:
     "Find invalid domain/host names."
+    # FQDN absolute form ("example.com.") is valid; extract_domain already strips it
+    domain = _strip_trailing_dot(domain)
     # no valid FQDN exceeds the DNS length limit
     if len(domain) > 253:
         return False

courlan/urlutils.py

@@ -12,8 +12,13 @@
 
 
 def _strip_trailing_dot(host: str) -> str:
-    "Drop a single trailing dot (FQDN form); multiple trailing dots stay invalid."
-    return host[:-1] if host.endswith(".") and not host.endswith("..") else host
+    "Drop a single trailing FQDN dot from host or host:port; multiple dots stay invalid."
+    if host.endswith(".") and not host.endswith(".."):
+        return host[:-1]
+    head, sep, tail = host.rpartition(":")
+    if sep and "@" not in host and head.endswith(".") and not head.endswith(".."):
+        return f"{head[:-1]}:{tail}"
+    return host
 
 
 def get_tldinfo(url: str) -> tuple[str | None, str | None]:

tests/unit_tests.py

@@ -807,6 +807,16 @@ def test_urlcheck_domain():
     # bare suffix has no registrable domain, though domain_filter alone accepts it
     assert check_url("https://a.ck/page") is None
     assert check_url("https://co.uk/page") is None
+    # trailing-dot FQDN URLs are valid; domain matches extract_domain stripping
+    assert check_url("http://example.com./page") == (
+        "http://example.com./page",
+        "example.com",
+    )
+    assert check_url("http://192.168.0.1./x") == (
+        "http://192.168.0.1./x",
+        "192.168.0.1",
+    )
+    assert check_url("http://example.com../page") is None
 
 
 def test_urlcheck_port():
@@ -874,6 +884,15 @@ def test_domain_filter():
     assert domain_filter("[::1]:99999") is False
     assert domain_filter("[not-an-ip]") is False
     assert domain_filter("[::1") is False
+    # trailing-dot FQDN (absolute DNS form) matches extract_domain, not false-reject
+    assert domain_filter("example.com.") is True
+    assert domain_filter("www.example.com.") is True
+    assert domain_filter("example.com.:8080") is True
+    assert domain_filter("192.168.0.1.") is True
+    assert domain_filter("192.168.0.1.:8080") is True
+    assert (
+        domain_filter("example.com..") is False
+    )  # multiple trailing dots stay invalid
 
     # hex-only strings that are not IPs must still be validated as domains
     assert domain_filter("abc.de") is True