From e0479b16e5f4596346cf5a3e21e9dccf184a124d Mon Sep 17 00:00:00 2001
From: thilo jeremias <thilo@nispuk.com>
Date: Sat, 9 May 2026 19:08:57 +0200
Subject: [PATCH] Fix error in handling of remaining filed

The actual field points to the data length in this message
The logic in the file only works if it contains at max one message
if the tcp packet contains multiple mqtt packets the calculation fails

Workaround: remove extra bytes and loop call until all is handled

Not the best way to fix...
---
 mqtt_message.py | 26 +++++++++++++++++++++-----
 1 file changed, 21 insertions(+), 5 deletions(-)

diff --git a/mqtt_message.py b/mqtt_message.py
index f8b3d4e..e80d6d9 100644
--- a/mqtt_message.py
+++ b/mqtt_message.py
@@ -54,6 +54,7 @@ class MQTTControlPacket:
         UNSUBACK,
     ]
 
+    unparsed = ''
     def __init__(self, packet):
         self._packet = packet
         # Fixed header
@@ -62,6 +63,13 @@ def __init__(self, packet):
         self.packet_type_human = self.Names[self.packet_type]
         self.dup, self.qos, self.retain = self._parse_flags()
         self.remaining_length, self.total_length = self._parse_remaining_length()
+# The remaining_length only gives the data,
+# it is possible that one tcp packet contains multiple mqtt packets
+# capture the unparsed stuff
+        if self.total_length < len(packet):
+            self.unparsed = packet[self.total_length:]
+            self._packet  = packet[:self.total_length]
+
         if self.total_length > len(packet):
             # Partial packet, raise BlockingIOError (the Python error than best corresponds to errno EAGAIN)
             raise BlockingIOError(f'Incomplete MQTT control packet: only {len(packet)} bytes remaining, but header expected {self.total_length}', len(packet))
@@ -263,8 +271,12 @@ def _parse_packet_identifier(self):
 def tcp_message(flow: tcp.TCPFlow | http.HTTPFlow):
     message = flow.messages[-1]
 
-    mqtt_packet = MQTTControlPacket(message.content)
-    dump(mqtt_packet)
+    data = message.content
+    while data:
+        mqtt_packet = MQTTControlPacket(data)
+        dump(mqtt_packet)
+        data = mqtt_packet.unparsed
+
 
 
 def dump(mqtt_packet: MQTTControlPacket):
@@ -306,12 +318,16 @@ def websocket_message(flow: http.HTTPFlow):
     ws_buffer[fid] += flow.websocket.messages[-1].content
     while ws_buffer[fid]:
         try:
-            mqtt_packet = MQTTControlPacket(ws_buffer[fid])
+            data = ws_buffer[fid]
+            while data:
+                mqtt_packet = MQTTControlPacket(data)
+                dump(mqtt_packet)
+                data = mqtt_packet.unparsed
+
         except BlockingIOError as exc:
             ctx.log.debug("Awaiting more bytes for complete MQTT control packet")
             break
         else:
-            dump(mqtt_packet)
-            b = ws_buffer[fid] = mqtt_packet._extra
+            b = ws_buffer[fid] = mqtt_packet._extra # Not 100% about the logic here -- check
             if b:
                 ctx.log.debug(f'Saving remaining {len(b)} bytes after MQTT control packet')