ssl.SSLError: [SSL: BAD_LENGTH] bad length (_ssl.c:2423)

[joan-mido-qa]

Environment

• gevent version: From PIP
• Python version: 3.10
• Operating System: Ubuntu 23.04

Description:

We use Locust and Paho-MQTT to spawn multiple clients to load-test an IoT application. It works as expected for ~60Kb payloads, but we had problems sending heavier messages. The error rises at ~6000 requests.

• We could not reproduce the error using the Client without gevent
• We could not reproduce the error using a non-TLS connection

Do you know what's going on? Thanks in advance!

Exception in thread Thread-1 (_thread_main):
Traceback (most recent call last):
  File "/usr/lib/python3.11/threading.py", line 1038, in _bootstrap_inner
    self.run()
  File "/usr/lib/python3.11/threading.py", line 975, in run
    self._target(*self._args, **self._kwargs)
  File "venv/lib/python3.11/site-packages/paho/mqtt/client.py", line 3591, in _thread_main
    self.loop_forever(retry_first_connection=True)
  File "venv/lib/python3.11/site-packages/paho/mqtt/client.py", line 1756, in loop_forever
    rc = self._loop(timeout)
         ^^^^^^^^^^^^^^^^^^^
  File "venv/lib/python3.11/site-packages/paho/mqtt/client.py", line 1181, in _loop
    rc = self.loop_write()
         ^^^^^^^^^^^^^^^^^
  File "venv/lib/python3.11/site-packages/paho/mqtt/client.py", line 1577, in loop_write
    rc = self._packet_write()
         ^^^^^^^^^^^^^^^^^^^^
  File "venv/lib/python3.11/site-packages/paho/mqtt/client.py", line 2464, in _packet_write
    write_length = self._sock_send(
                   ^^^^^^^^^^^^^^^^
  File "venv/lib/python3.11/site-packages/paho/mqtt/client.py", line 649, in _sock_send
    return self._sock.send(buf)
           ^^^^^^^^^^^^^^^^^^^^
  File "venv/lib/python3.11/site-packages/gevent/ssl.py", line 508, in send
    return self._sslobj.write(data)
           ^^^^^^^^^^^^^^^^^^^^^^^^
ssl.SSLError: [SSL: BAD_LENGTH] bad length (_ssl.c:2423)

What I've run:

Reproducible example using mosquitto test broker: https://test.mosquitto.org

from gevent import monkey, sleep

monkey.patch_all()

import json
import ssl
import paho.mqtt.client as mqtt

mqttc = mqtt.Client()

tls_context = ssl.SSLContext(ssl.PROTOCOL_TLS_CLIENT)
tls_context.load_cert_chain("client.crt", "client.key")
tls_context.load_verify_locations("mosquitto.org.crt")

mqttc.tls_set_context(tls_context)

mqttc.connect("test.mosquitto.org", 8884, 60)

mqttc.loop_start()

for i in range(0, 1000000):
    info = mqttc.publish("test", json.dumps({"message": "1" * 200000}).encode(), qos=0)
    sleep(0.01)