Fix message receiving in MQTT

fbchat/_mqtt.py

@@ -4,6 +4,24 @@ import paho.mqtt.client
 from . import _util, _graphql
 
 
+def fetch_sequence_id(state):
+    """Fetch sequence ID."""
+    params = {
+        "limit": 1,
+        "tags": ["INBOX"],
+        "before": None,
+        "includeDeliveryReceipts": False,
+        "includeSeqID": True,
+    }
+    # Same request as in `Client.fetchThreadList`
+    (j,) = state._graphql_requests(_graphql.from_doc_id("1349387578499440", params))
+    try:
+        return int(j["viewer"]["message_threads"]["sync_sequence_id"])
+    except (KeyError, ValueError):
+        # TODO: Proper exceptions
+        raise
+
+
 @attr.s(slots=True)
 class Mqtt:
     _state = attr.ib()
@@ -21,6 +39,17 @@ class Mqtt:
 
         # Generate a random session ID between 1 and 9007199254740991
         session_id = random.randint(1, 2 ** 53)
+        last_seq_id = fetch_sequence_id(state)
+
+        messenger_sync_create_queue_payload = {
+            "sync_api_version": 10,
+            "max_deltas_able_to_process": 1000,
+            "delta_batch_size": 500,
+            "encoding": "JSON",
+            "entity_fbid": state.user_id,
+            "initial_titan_sequence_id": str(last_seq_id),
+            "device_params": None,
+        }
 
         username = {
             # The user ID
@@ -62,7 +91,20 @@ class Mqtt:
                 "/sr_res",
             ],
             # MQTT extension by FB, allows making a PUBLISH while CONNECTing
-            "pm": [],
+            "pm": [
+                # This is required to actually receive messages
+                {
+                    "topic": "/messenger_sync_create_queue",
+                    "payload": _util.json_minimal(messenger_sync_create_queue_payload),
+                    "qos": 1,
+                    "messageId": 65536,
+                }
+                # The above is more efficient, but the same effect could have been
+                # acheived with:
+                #     def on_connect(*args):
+                #         mqtt.publish("/messenger_sync_create_queue", ..., qos=1)
+                #     mqtt.on_connect = on_connect
+            ],
             # Unknown parameters
             "cp": 3,
             "ecp": 10,