From d02976156e664e99e991797d9e4ae31829d5a2e7 Mon Sep 17 00:00:00 2001
From: Roger Light <roger@atchoo.org>
Date: Fri, 20 Jan 2023 22:46:32 +0000
Subject: [PATCH] Raise error on `subscribe()` when `topic` is an empty list.

Closes #690. Thanks to peromvikgoodtech.
---
 ChangeLog.txt           | 1 +
 examples/client_sub.py  | 2 +-
 src/paho/mqtt/client.py | 2 ++
 3 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/ChangeLog.txt b/ChangeLog.txt
index 975955f..ef16bc6 100644
--- a/ChangeLog.txt
+++ b/ChangeLog.txt
@@ -3,6 +3,7 @@ v1.6.2 - 2021-xx-xx
 
 - Fix handling of MQTT v5.0 PUBREL messages with remaining length not equal to
   2. Closes #696.
+- Raise error on `subscribe()` when `topic` is an empty list. Closes #690.
 
 
 v1.6.1 - 2021-10-21
diff --git a/examples/client_sub.py b/examples/client_sub.py
index 9cd54e2..e03bb44 100755
--- a/examples/client_sub.py
+++ b/examples/client_sub.py
@@ -54,6 +54,6 @@ mqttc.on_subscribe = on_subscribe
 # Uncomment to enable debug messages
 # mqttc.on_log = on_log
 mqttc.connect("mqtt.eclipseprojects.io", 1883, 60)
-mqttc.subscribe("$SYS/#", 0)
+mqttc.subscribe([])
 
 mqttc.loop_forever()
diff --git a/src/paho/mqtt/client.py b/src/paho/mqtt/client.py
index 66129e5..1020eea 100644
--- a/src/paho/mqtt/client.py
+++ b/src/paho/mqtt/client.py
@@ -1467,6 +1467,8 @@ class Client(object):
                     raise ValueError('Invalid topic.')
                 topic_qos_list = [(topic.encode('utf-8'), qos)]
         elif isinstance(topic, list):
+            if len(topic) == 0:
+                raise ValueError('Empty topic list')
             topic_qos_list = []
             if self._protocol == MQTTv5:
                 for t, o in topic:
-- 
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