Catch ASN Parse error more gracefully

apps/greencheck/domain_check.py

@@ -23,7 +23,7 @@
 import tld
 from django.utils import timezone
 from ipwhois.asn import IPASN
-from ipwhois.exceptions import IPDefinedError
+from ipwhois.exceptions import IPDefinedError, ASNParseError
 from ipwhois.net import Net
 
 from .choices import GreenlistChoice
@@ -309,7 +309,10 @@ def check_for_matching_asn(self, ip_address):
 
         try:
             asn_result = self.asn_from_ip(ip_address)
-        except IPDefinedError:
+        except (ASNParseError, IPDefinedError) as ex:
+            logger.warning(
+                f"Unable to parse ASN for IP: {ip_address} - error type: {type(ex).__name__} {ex}"
+            )
             return False
         except Exception as err:
             logger.exception(err)

apps/greencheck/tests/test_domain_checker.py

@@ -104,6 +104,20 @@ def test_with_green_domain_by_asn_double(self, green_asn, checker):
         assert isinstance(res, legacy_workers.SiteCheck)
         assert res.hosting_provider_id == green_asn.hostingprovider.id
 
+    def test_asn_from_ip_fails_gracefully_with_bad_asn_lookup(self, checker, caplog):
+        """
+        Sometimes calling lookup() on an IP address raises a ASNParseError.
+        Do we catch this exception and log it?
+        """
+
+        checker.asn_from_ip = mock.MagicMock(side_effect=domain_check.ASNParseError)
+        with caplog.at_level(logging.WARNING):
+            res = checker.check_for_matching_asn("23.32.24.203")
+
+        assert res is False
+        logged_error = caplog.text
+        assert "ASNParseError" in logged_error
+
     def test_with_green_domain_by_non_resolving_asn(self, green_asn, checker):
         """
         Sometimes the service we use for resolving ASNs returns
@@ -210,7 +224,6 @@ class TestDomainCheckByCarbonTxt:
     def test_lookup_green_domain(
         self, green_domain_factory, green_ip_factory, mocker, checker
     ):
-
         # mock our network lookup, so we get a consistent response when
         # looking up our domains
         green_ip = green_ip_factory.create()