DMs bug fix, don't crash if text has bot @-mention and nothing else

fixes https://console.cloud.google.com/errors/detail/CJia3JTRqujKcA;locations=global;time=P30D?project=bridgy-federated

dms.py

@@ -108,28 +108,22 @@ def receive(*, from_user, obj):
                  else obj.as1)
     logger.info(f'got DM from {from_user.key.id()} to {to_proto.LABEL}: {inner_obj.get("content")}')
 
-    soup = util.parse_html(inner_obj.get('content', ''))
-
-    content = soup.get_text().strip().lower()
-    if not content:
-        return r'¯\_(ツ)_/¯', 204
-
-    def reply(text, type=None):
-        maybe_send(from_proto=to_proto, to_user=from_user, text=text, type=type,
-                   in_reply_to=inner_obj.get('id'))
-        return 'OK', 200
-
     # parse and handle message
+    soup = util.parse_html(inner_obj.get('content', ''))
+    content = soup.get_text().strip().lower()
     tokens = content.split()
     logger.info(f'  tokens: {tokens}')
 
     # remove @-mention of bot, if any
     bot_handles = (DOMAINS + ids.BOT_ACTOR_AP_IDS
                    + tuple(h.lstrip('@') for h in ids.BOT_ACTOR_AP_HANDLES))
-    if tokens[0].lstrip('@') in bot_handles:
+    if tokens and tokens[0].lstrip('@') in bot_handles:
         logger.info(f'  first token is bot mention, removing')
         tokens = tokens[1:]
 
+    if not tokens:
+        return r'¯\_(ツ)_/¯', 204
+
     if tokens[0].lstrip('/') in COMMANDS:
         cmd = tokens[0].lstrip('/')
         arg = tokens[1] if len(tokens) > 1 else None
@@ -138,6 +132,11 @@ def receive(*, from_user, obj):
         arg = tokens[0]
 
     # handle commands
+    def reply(text, type=None):
+        maybe_send(from_proto=to_proto, to_user=from_user, text=text, type=type,
+                   in_reply_to=inner_obj.get('id'))
+        return 'OK', 200
+
     if cmd in ('?', 'help', 'commands', 'info', 'hi', 'hello'):
         extra = ''
         if to_proto.LABEL == 'atproto':

tests/test_dms.py

@@ -129,6 +129,18 @@ class DmsTest(TestCase):
         self.assertEqual([], OtherFake.sent)
         self.assertEqual([], Fake.sent)
 
+    def test_receive_empty_strip_mention_of_bot(self):
+        alice, bob = self.make_alice_bob()
+
+        obj = Object(our_as1={
+            **DM_BASE,
+            'content': '<a href="https://other.brid.gy/other.brid.gy">@other.brid.gy</a> ',
+        })
+        self.assertEqual(('¯\\_(ツ)_/¯', 204), receive(from_user=alice, obj=obj))
+        self.assert_replied(OtherFake, alice, '?', ALICE_CONFIRMATION_CONTENT)
+        self.assert_sent(ExplicitFake, bob, 'request_bridging',
+                         ALICE_REQUEST_CONTENT)
+
     def test_receive_unknown_text(self):
         self.make_user(id='other.brid.gy', cls=Web)
         alice = self.make_user('efake:alice', cls=ExplicitFake,