platform: MicroPython v1.21.0 on 2023-10-06; Generic ESP32 module
broker: mosquitto
description:
got OSError: -1 after sending 65535 packets

Result:

pkcnt 65000
Traceback (most recent call last):
File "<stdin>", line 47, in <module>
File "<stdin>", line 40, in publish_test
File "umqtt/simple.py", line 144, in publish
File "umqtt/simple.py", line 184, in wait_msg
OSError: -1

code:

from umqtt.simple import MQTTClient
import time
import ujson as json
from machine import unique_id
import sys, os

def str_current_time():
    tm_ns = time.time_ns()
    tm_rem_ms = (tm_ns % 1_000_000_000) // 1_000_000
    tm = time.localtime(tm_ns//1_000_000_000)
    str_tm = str(tm[3])+':'+str(tm[4])+':'+str(tm[5])+'.'+ str(tm_rem_ms)
    return str_tm
   

id = unique_id() #machine.unique_id()
id_str = '{:02x}{:02x}{:02x}{:02x}'.format(id[0], id[1], id[2], id[3])

mq_id = id_str
mq_machine = os.uname().machine.split()[0]
mq_server = '192.168.12.25'
mq_user='esp32-srv'
mq_pass='123456'
mq_topic= b'esp/test'
mq_message = {'id':mq_id, 'machine': mq_machine, 'time': str_current_time(), 'hello': 'hello'}
mqClient = MQTTClient(mq_id, mq_server, port=1883, user=mq_user, password=mq_pass, keepalive=60*60*12)
mqClient.connect(clean_session=True) # only support clean_sesson=True
mqClient.publish(b'esp/hello', json.dumps(mq_message), qos=1)

pkcnt = 0x00_00_00_01
pkcnt_max = 999_999

def publish_test():
    global pkcnt, pkcnt_max
    pkcnt += 1
    if pkcnt >= pkcnt_max :
        pkcnt = 1
    tm = time.time()
    message = {'id':mq_id, 'machine': mq_machine, 'time': tm, 'current': 1, 'ctrl': 1, 'pkcnt':pkcnt}
    mq_message = json.dumps(message)
    mqClient.publish(mq_topic, mq_message, qos=1)
    if pkcnt % 1000 == 0:
        print('pkcnt',pkcnt, 'time', tm)

if __name__ == '__main__' :
    print('test start')
    while True :
        publish_test()