Fix MessagesDelivered user parsing

fbchat/_delta_class.py

@@ -99,8 +99,11 @@ class MessagesDelivered(ThreadEvent):
 
     @classmethod
     def _parse(cls, session, data):
-        author = _user.User(session=session, id=data["actorFbId"])
         thread = cls._get_thread(session, data)
+        if "actorFbId" in data:
+            author = _user.User(session=session, id=data["actorFbId"])
+        else:
+            author = thread
         messages = [_message.Message(thread=thread, id=x) for x in data["messageIds"]]
         at = _util.millis_to_datetime(int(data["deliveredWatermarkTimestampMs"]))
         return cls(author=author, thread=thread, messages=messages, at=at)

tests/test_delta_class.py

@@ -133,7 +133,7 @@ def test_forced_fetch(session):
     ) == parse_delta(session, data)
 
 
-def test_delivery_receipt(session):
+def test_delivery_receipt_group(session):
     data = {
         "actorFbId": "1234",
         "deliveredWatermarkTimestampMs": "1500000000000",
@@ -156,6 +156,28 @@ def test_delivery_receipt(session):
     ) == parse_delta(session, data)
 
 
+def test_delivery_receipt_user(session):
+    data = {
+        "deliveredWatermarkTimestampMs": "1500000000000",
+        "irisSeqId": "1111111",
+        "irisTags": ["DeltaDeliveryReceipt", "is_from_iris_fanout"],
+        "messageIds": ["mid.$XYZ", "mid.$ABC"],
+        "requestContext": {"apiArgs": {}},
+        "threadKey": {"otherUserFbId": "1234"},
+        "class": "DeliveryReceipt",
+    }
+    thread = User(session=session, id="1234")
+    assert MessagesDelivered(
+        author=thread,
+        thread=thread,
+        messages=[
+            Message(thread=thread, id="mid.$XYZ"),
+            Message(thread=thread, id="mid.$ABC"),
+        ],
+        at=datetime.datetime(2017, 7, 14, 2, 40, tzinfo=datetime.timezone.utc),
+    ) == parse_delta(session, data)
+
+
 def test_read_receipt(session):
     data = {
         "actionTimestampMs": "1600000000000",