MAJOR ISSUE: MQTT library blocking when Subscribe

[GeirFrimann]

When I'm running this simple code to connect to Thingsboard and subscribing to a topic,
the code doesn't run passed the call to the subscribe method (line 35):

from mqtt import MQTTClient
from network import WLAN
import machine
import time
import config

def settimeout(duration):
   pass

def sub_cb(topic, msg):
  print(msg)

wlan = WLAN(mode=WLAN.STA)
wlan.antenna(WLAN.EXT_ANT)
wlan.connect(config.WLAN_SSID, auth=(WLAN.WPA2, config.WLAN_Password), timeout=5000)

while not wlan.isconnected():  
   machine.idle()
   
print("\nConnected to WiFi")

client = MQTTClient(client_id=config.MQTT_DEVICE_ID, server=config.MQTT_BROKER_ADDRESS,user=config.MQTT_DEVICE_TOKEN, password="", port=config.MQTT_BROKER_PORT)
client.settimeout = settimeout
client.connect()
print("Connected to MQTT Broker\n")

client.set_callback(sub_cb)
client.subscribe(topic="v1/devices/me/attributes")
time.sleep(1)
client.publish(topic="v1/devices/me/telemetry", msg="{\"d\":\"OFF\"}")

while True:
   print("Sending ON")
   client.publish(topic="v1/devices/me/telemetry", msg="{\"d\":\"ON\"}")
   time.sleep(1)
   print("Sending OFF")
   client.publish(topic="v1/devices/me/telemetry", msg="{\"d\":\"OFF\"}")
   client.check_msg()
   time.sleep(1)

When triggering updates in Thingsboard, the device indeed gets the subscribed updates as shown in the terminal output:

b'{"AlwaysSendData":true}'
b'{"AlwaysSendData":false}

But the code never reach the while loop, looks like the subscribe method are blocking(!?)
When idle for a few minutes, the code exits whit the following message:

Traceback (most recent call last):
  File "/flash/main.py", line 35, in <module>
  File "/flash/lib/mqtt.py", line 142, in subscribe
  File "/flash/lib/mqtt.py", line 161, in wait_msg
OSError: -1
Pycom MicroPython 1.18.2.r3 [v1.8.6-849-a1641ca] on 2019-02-28; FiPy with ESP32
Type "help()" for more information.
>>>

If I exclude the subscribe call, the loop suns as expected and updates reaches Thingsboard.

Running similar code in Arduino IDE on a Wemos Lolin ESP32 device works just fine, so it's not an issue with Thingsboard.
ANY help would be much appreciated to fix this issue, it's a showstopper for my (commercial) project!

[Eric Ang]

Hi! Did you manage to resolve this issue? I'm facing it too and would appreciate if any kind soul can assist.

[Siridar]

Hi, did this ever get resolved? I think I'm seeing the same issue...

[Osquillar]

@Siridar Hello, did you find the solution? I'm now at the same point
Regards

[saber phung]

Hello, Did you find the solution? I faced with the same issue