/r/ redirect: handle bad URLs

fixes https://console.cloud.google.com/errors/detail/CJ30oPbsoqmI7QE;time=P30D?project=bridgy-federated

redirect.py

@@ -60,7 +60,10 @@ def redir(to):
     if not util.is_web(to):
         error(f'Expected fully qualified URL; got {to}')
 
-    to_domain = urllib.parse.urlparse(to).hostname
+    try:
+        to_domain = urllib.parse.urlparse(to).hostname
+    except ValueError as e:
+        error(f'Invalid URL {to} : {e}')
 
     # check conneg
     accept_as2 = False

tests/test_redirect.py

@@ -65,6 +65,10 @@ class RedirectTest(testutil.TestCase):
         got = self.client.get(r'/r/https://v2.jacky.wtf\"')
         self.assertEqual(404, got.status_code)
 
+    def test_redirect_url_parse_value_error(self):
+        got = self.client.get(r'/r/https:/[DOMAIN]/')
+        self.assertEqual(400, got.status_code)
+
     def test_as2(self):
         self._test_as2(as2.CONTENT_TYPE)