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MQTT: Add a heuristic sub dissector table 

Add a heuristic sub dissector table to allow other dissectors
to register and be called if no match is found for the UAT
configured sub dissectors.

Pass the topic string to the heuristic sub dissector in the data
pointer as an aid for the heuristic.
This commit is contained in:
Graham Bloice 2021-04-10 20:17:53 +01:00
parent e35b6d4859
commit 1b1a4281b4
1 changed files with 10 additions and 0 deletions
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10
epan/dissectors/packet-mqtt.c
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@ -506,6 +506,8 @@ static gint default_protocol_version;
static dissector_handle_t mqtt_handle;
static heur_dissector_list_t mqtt_topic_subdissector;
/* Initialize the protocol and registered fields */
static int proto_mqtt = -1;
@ -753,6 +755,12 @@ static void mqtt_user_decode_message(proto_tree *tree, proto_tree *mqtt_tree, pa
call_dissector(message_decode_entry->payload_proto, msg_tvb, pinfo, tree);
}
}
else {
/* No UAT match, try the heuristic dissectors, pass the topic string as data */
heur_dtbl_entry_t *hdtbl_entry;
gchar *sub_data = wmem_strdup(wmem_packet_scope(), (const gchar*)topic_str);
dissector_try_heuristic(mqtt_topic_subdissector, msg_tvb, pinfo, tree, &hdtbl_entry, sub_data);
}
}
static guint dissect_string(tvbuff_t *tvb, proto_tree *tree, guint offset, int hf_len, int hf_value)
@ -1806,6 +1814,8 @@ void proto_register_mqtt(void)
proto_register_field_array(proto_mqtt, hf_mqtt, array_length(hf_mqtt));
proto_register_subtree_array(ett_mqtt, array_length(ett_mqtt));
mqtt_topic_subdissector = register_heur_dissector_list("mqtt.topic", proto_mqtt);
expert_mqtt = expert_register_protocol(proto_mqtt);
expert_register_field_array(expert_mqtt, ei, array_length(ei));