umqtt.simple not working with mosquitto 2.0.12

Hi!

umqtt.simple fails to connect to mosquito 2.0.12. It throws back MQTTException: 2.
Meanwhile mosquitto log says: 'Bad socket read/write on client <client_id>. Invalid arguments provided.'

This is reproducible with micropython 16 and 17 both in an application and in REPL.

This is not a problem with mosquitto 2.0.11.

All other mqtt clients are working correctly with 2.0.12 (openhab, zwave2mqtt, zigbee2mqtt, etc.). So I assume this is a problem with this library. I rolled back to 2.0.11.

Thank you in advance:

Zsolt Zimmermann

The changelog of mosquitto:

2.0.12 - 2021-08-31
===================

Security:
- An MQTT v5 client connecting with a large number of user-property properties
  could cause excessive CPU usage, leading to a loss of performance and
  possible denial of service. This has been fixed.
- Fix `max_keepalive` not applying to MQTT v3.1.1 and v3.1 connections.
  These clients are now rejected if their keepalive value exceeds
  max_keepalive. This option allows CVE-2020-13849, which is for the MQTT
  v3.1.1 protocol itself rather than an implementation, to be addressed.
- Using certain listener related configuration options e.g. `cafile`, that
  apply to the default listener without defining any listener would cause a
  remotely accessible listener to be opened that was not confined to the local
  machine but did have anonymous access enabled, contrary to the
  documentation. This has been fixed. Closes #2283.
- CVE-2021-34434: If a plugin had granted ACL subscription access to a
  durable/non-clean-session client, then removed that access, the client would
  keep its existing subscription. This has been fixed.
- Incoming QoS 2 messages that had not completed the QoS flow were not being
  checked for ACL access when a clean session=False client was reconnecting.
  This has been fixed.

Broker:
- Fix possible out of bounds memory reads when reading a corrupt/crafted
  configuration file. Unless your configuration file is writable by untrusted
  users this is not a risk. Closes #567213.
- Fix `max_connections` option not being correctly counted.
- Fix TLS certificates and TLS-PSK not being able to be configured at the same
  time.
- Disable TLS v1.3 when using TLS-PSK, because it isn't correctly configured.
- Fix `max_keepalive` not applying to MQTT v3.1.1 and v3.1 connections.
  These clients are now rejected if their keepalive value exceeds
  max_keepalive. This option allows CVE-2020-13849, which is for the MQTT
  v3.1.1 protocol itself rather than an implementation, to be addressed.
- Fix broker not quiting if e.g. the `password_file` is specified as a
  directory. Closes #2241.
- Fix listener mount_point not being removed on outgoing messages.
  Closes #2244.
- Strict protocol compliance fixes, plus test suite.
- Fix $share subscriptions not being recovered for durable clients that
  reconnect.
- Update plugin configuration documentation. Closes #2286.

Client library:
- If a client uses TLS-PSK then force the default cipher list to use "PSK"
  ciphers only. This means that a client connecting to a broker configured
  with x509 certificates only will now fail. Prior to this, the client would
  connect successfully without verifying certificates, because they were not
  configured.
- Disable TLS v1.3 when using TLS-PSK, because it isn't correctly configured.
- Threaded mode is deconfigured when the mosquitto_loop_start() thread ends,
  which allows mosquitto_loop_start() to be called again. Closes #2242.
- Fix MOSQ_OPT_SSL_CTX not being able to be set to NULL. Closes #2289.
- Fix reconnecting failing when MOSQ_OPT_TLS_USE_OS_CERTS was in use, but none
  of capath, cafile, psk, nor MOSQ_OPT_SSL_CTX were set, and
  MOSQ_OPT_SSL_CTX_WITH_DEFAULTS was set to the default value of true.
  Closes #2288.

Apps:
- Fix `mosquitto_ctrl dynsec setDefaultACLAccess` command not working.

Clients:
- mosquitto_sub and mosquitto_rr now open stdout in binary mode on Windows
  so binary payloads are not modified when printing.
- Document TLS certificate behaviour when using `-p 8883`.

Build:
- Fix installation using WITH_TLS=no. Closes #2281.
- Fix builds with libressl 3.4.0. Closes #2198.
- Remove some unnecessary code guards related to libressl.
- Fix printf format build warning on MIPS. Closes #2271.

Start with the umqtt.simple connection path and reproduce the failure from the REPL or an application against mosquitto 2.0.12, then compare it with 2.0.11. Use the MQTTException: 2 result and the broker's invalid-arguments log to narrow the compatibility issue; done when umqtt.simple connects successfully to 2.0.12.