[paho-dev] Offline buffering in Python3 Paho MQTT client

[Lars Noodén <lars.nooden@xxxxxxxxx>]

Hello, paho-dev list members,	

The Eclipse web site mentions this list as the place to discuss Paho
clients.  Though I see in the archives little about python specifically.
 If there is a more appropriate venue for this kind of usage question,
please point it out.

I am trying to have a Python3-based Paho MQTT client do offline
buffering during longer intervals when there is no network connectivity.
 Can someone please point me to the right documentation and/or a code
snippet showing the right way to do that?  Short intervals work but not
longer ones.

The examples I've found so far seem to have offline buffering disabled.
The documentation [1] suggests that enabling it might only be a matter
of setting clean_session to 'False', but that alone appears to be
insufficient for longer connectivity outages.

I have a test script [2] otherwise working.  It sends data to the MQTT
broker just fine while there is network connectivity and resumes sending
once the connectivity is restored after a short period of disconnection.
 However, the messages which would have been sent during a longer period
without connectivity seem to disappear completely.  I would have
expected the client to have kept a queue which gets sent in bulk once
the connection is re-established.

What should I modify in the script below and/or what should I read in
the documentation?

Regards,
Lars

PS.  Thank you in advance for not top-posting.

--

[1] 	https://pypi.org/project/paho-mqtt/#client
	https://www.eclipse.org/paho/index.php?page=clients/python/docs/index.php#network-loop


[2]

#!/usr/bin/python3

import time
import paho.mqtt.client as mqtt
import ssl

def on_connect(client, userdata, flags, rc):
    print("Connection returned result: "+connack_string(rc))

def on_disconnect(client, userdata, rc):
    if rc != 0:
        print("Unexpected disconnection.")
    else:
        print("MQTT disconnected")

mqtthost = "server.example.com"
mqttport = 8883
mqttclient = mqtt.Client(client_id="test1and2",
                         clean_session=False,
                         transport="tcp")

mqttclient.username_pw_set("foo", password="bar")
mqttclient.reconnect_delay_set(min_delay=1, max_delay=120)
mqttclient.tls_set(
    ca_certs='/etc/mosquitto/certs/mqtt-server.crt',
    certfile='/etc/mosquitto/certs/pub-client.crt',
    keyfile ='/etc/mosquitto/certs/pub-client.key',
    tls_version=ssl.PROTOCOL_TLSv1_2
)

mqttclient.on_connect    = on_connect
mqttclient.on_disconnect = on_disconnect
mqttclient.connect(mqtthost, mqttport)
mqttclient.loop_start()

while True:
    epoch = int(time.clock_gettime(0))
    msg = str(epoch)+"\t9\t"+str(time.strftime("%H:%M"))
    try:
        mqttclient.publish("temperatures", payload=msg)
        print("temperatures", msg)
    except:
        mqttclient.reconnect()
        print("Reconnect")

    time.sleep(5)