Fix PUBREL remaining length of > 2 not being accepted for MQTT v5 message flows.

Closes #481. Thanks to Tao Su.

Author: ralight

ChangeLog.txt

@@ -4,6 +4,8 @@ v1.x.x - 20xx-xx-xx
 - Exceptions that occur in callbacks are no longer suppressed by default. They
   can optionally be suppressed by setting `client.suppress_exceptions = True`.
   Closes #365.
+- Fix PUBREL remaining length of > 2 not being accepted for MQTT v5 message
+  flows. Closes #481.
 
 v1.5.0 - 2019-10-30
 ===================

src/paho/mqtt/client.py

@@ -3229,7 +3229,10 @@ def _handle_publish(self):
             return MQTT_ERR_PROTOCOL
 
     def _handle_pubrel(self):
-        if self._in_packet['remaining_length'] != 2:
+        if self._protocol == MQTTv5:
+            if self._in_packet['remaining_length'] < 2:
+                return MQTT_ERR_PROTOCOL
+        elif self._in_packet['remaining_length'] != 2:
             return MQTT_ERR_PROTOCOL
 
         mid, = struct.unpack("!H", self._in_packet['packet'])