fix: handling of None messages from notify callback

[Mocramis]

This is especially common as BaseMessageBus._finalize calls handler(None, err) when an exception is raised.

From the surrounding code, it seems the common assumption is that msg should be None if err is set. However you might want to print msg if it is here even if there is an err, but then the logs would be awkward no ?

Did not take the time to build a test to reproduce the issue though

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: -0.19% ⚠️

Comparison is base (6f6f5f8) 82.84% compared to head (1da13ff) 82.66%.
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #236      +/-   ##
==========================================
- Coverage   82.84%   82.66%   -0.19%     
==========================================
  Files          28       28              
  Lines        3259     3259              
  Branches      674      674              
==========================================
- Hits         2700     2694       -6     
- Misses        342      346       +4     
- Partials      217      219       +2     

Files Changed	Coverage Δ
src/dbus_fast/__version__.py	0.00% <0.00%> (ø)
src/dbus_fast/message_bus.py	71.63% <0.00%> (ø)

... and 2 files with indirect coverage changes

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[bdraco]

Looks ok, but we do need a test before merging

[Mocramis]

Hello, so i have a reproducer but i cannot automate it because this is triggered through a race condition and the side-effect is a log:

import pytest

from dbus_fast import DBusError, aio, glib
from dbus_fast.service import ServiceInterface


class ExampleInterface(ServiceInterface):
    def __init__(self):
        super().__init__("test.interface")


@pytest.mark.asyncio
async def test_fast_disconnect():
    bus_name = "aio.client.test.methods"

    bus = await aio.MessageBus().connect()
    bus2 = await aio.MessageBus().connect()
    await bus.request_name(bus_name)
    service_interface = ExampleInterface()
    bus.export("/test/path", service_interface)
    introspection = await bus2.introspect(bus_name, "/test/path")
    bus2.get_proxy_object(bus_name, "/test/path", introspection)
    bus2.disconnect()
    raise Exception("Failed")

This reproduce the error if you look at the captured stderr:

------------------------------------------------------------------------------------------------- Captured log call -------------------------------------------------------------------------------------------------
ERROR    root:message_bus.py:1194 add match request failed. match="sender='org.freedesktop.DBus',interface='org.freedesktop.DBus',path='/org/freedesktop/DBus',member='NameOwnerChanged'",
WARNING  root:message_bus.py:584 a message handler threw an exception on shutdown
Traceback (most recent call last):
  File "/home/mocramis/misc/dbus-fast/src/dbus_fast/aio/message_reader.py", line 22, in _message_reader
    message = unmarshaller._unmarshall()
  File "/home/mocramis/misc/dbus-fast/src/dbus_fast/_private/unmarshaller.py", line 742, in _unmarshall
    self._read_header()
  File "/home/mocramis/misc/dbus-fast/src/dbus_fast/_private/unmarshaller.py", line 611, in _read_header
    self._read_to_pos(HEADER_SIGNATURE_SIZE)
  File "/home/mocramis/misc/dbus-fast/src/dbus_fast/_private/unmarshaller.py", line 366, in _read_to_pos
    self._read_sock_without_fds(pos)
  File "/home/mocramis/misc/dbus-fast/src/dbus_fast/_private/unmarshaller.py", line 329, in _read_sock_without_fds
    raise EOFError()
EOFError

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/mocramis/misc/dbus-fast/src/dbus_fast/message_bus.py", line 582, in _finalize
    handler(None, err)
  File "/home/mocramis/misc/dbus-fast/src/dbus_fast/message_bus.py", line 737, in _reply_notify
    callback(reply, err)
  File "/home/mocramis/misc/dbus-fast/src/dbus_fast/message_bus.py", line 1197, in add_match_notify
    if msg.message_type == MessageType.ERROR:
AttributeError: 'NoneType' object has no attribute 'message_type'

However if i try to use caplog to capture the logs, the error suddenly disapear.

Any thoughs about this ?

thanks.

[bdraco]

Even if the test doesn't fail before it's still useful in case we break something else in the future as this project is definitely lighter on coverage than I would like

[Mocramis]

Should i increase the pytest timeout apparently adding this one test makes us get over the 5s limit on py38 and py39 (and the other are not very far from it)
would 10 second be ok ?

[Mocramis]

The timeout is not the issue, i fail to understand how i broke 3.8 and 3.9, i do not reproduce the issue locally with my 3.9 python version :/

[bdraco]

Thanks @Mocramis

[bdraco]

wait to merge for https://github.com/Bluetooth-Devices/dbus-fast/actions/runs/6111618499