Closed database connections.

eb16ed0 removed (among a lot of other
things) a call to close_old_connections(), mostly because I hadn't
understood what that was doing exactly.
Since then I've been kept awake at night with the sense of dread that
old database connections were piling up unclosed on Django's server.

So I wrote this wsgi middleware that should hopefully restore balance
in the universe, or at least close db connections.

.github/workflows/tests.yml

@@ -34,6 +34,8 @@ jobs:
         uses: actions/checkout@v4
       - name: Install requirements
         run: python -m pip install -r requirements.txt
+      - name: Install backport of unittest.mock
+        run: python -m pip install mock
       - name: Run tests
         run: python -m django test tracdjangoplugin.tests
         env:

DjangoPlugin/tracdjangoplugin/middlewares.py

@@ -0,0 +1,22 @@
+from django.core.signals import request_finished, request_started
+
+
+class DjangoDBManagementMiddleware:
+    """
+    A simple WSGI middleware that manually manages opening/closing db connections.
+
+    Django normally does that as part of its own middleware chain, but we're using Trac's middleware
+    so we must do this by hand.
+    This hopefully prevents open connections from piling up.
+    """
+
+    def __init__(self, application):
+        self.application = application
+
+    def __call__(self, environ, start_response):
+        request_started.send(sender=self.__class__)
+        try:
+            for data in self.application(environ, start_response):
+                yield data
+        finally:
+            request_finished.send(sender=self.__class__)

DjangoPlugin/tracdjangoplugin/tests.py

@@ -1,13 +1,20 @@
 from functools import partial
 
+try:
+    from unittest.mock import Mock
+except ImportError:
+    from mock import Mock
+
+from django.core.signals import request_finished, request_started
 from django.contrib.auth.forms import AuthenticationForm
 from django.contrib.auth.models import User
-from django.test import TestCase
+from django.test import SimpleTestCase, TestCase
 
 from trac.test import EnvironmentStub, MockRequest
 from trac.web.api import RequestDone
 from trac.web.main import RequestDispatcher
 
+from tracdjangoplugin.middlewares import DjangoDBManagementMiddleware
 from tracdjangoplugin.plugins import PlainLoginComponent
 
 
@@ -127,3 +134,53 @@ def test_login_invalid_username_uppercased(self):
     def test_login_invalid_inactive_user(self):
         User.objects.create_user(username="test", password="test", is_active=False)
         self.assertLoginFails(username="test", password="test")
+
+
+class DjangoDBManagementMiddlewareTestCase(SimpleTestCase):
+    @classmethod
+    def setUpClass(cls):
+        # Remove receivers from the request_started and request_finished signals,
+        # replacing them with a mock object so we can still check if they were called.
+        super(DjangoDBManagementMiddlewareTestCase, cls).setUpClass()
+        cls._original_signal_receivers = {}
+        cls.signals = {}
+        for signal in [request_started, request_finished]:
+            cls.signals[signal] = Mock()
+            cls._original_signal_receivers[signal] = signal.receivers
+            signal.receivers = []
+            signal.connect(cls.signals[signal])
+
+    @classmethod
+    def tearDownClass(cls):
+        # Restore the signals we modified in setUpClass() to what they were before
+        super(DjangoDBManagementMiddlewareTestCase, cls).tearDownClass()
+        for signal, original_receivers in cls._original_signal_receivers.items():
+            # messing about with receivers directly is not an official API, so we need to
+            # call some undocumented methods to make sure caches and such are taken care of.
+            with signal.lock:
+                signal.receivers = original_receivers
+                signal._clear_dead_receivers()
+                signal.sender_receivers_cache.clear()
+
+    def setUp(self):
+        super(DjangoDBManagementMiddlewareTestCase, self).setUp()
+        for mockobj in self.signals.values():
+            mockobj.reset_mock()
+
+    def test_request_start_fired(self):
+        app = DjangoDBManagementMiddleware(lambda environ, start_response: [b"test"])
+        output = b"".join(app(None, None))
+        self.assertEqual(output, b"test")
+        self.signals[request_started].assert_called_once()
+
+    def test_request_finished_fired(self):
+        app = DjangoDBManagementMiddleware(lambda environ, start_response: [b"test"])
+        output = b"".join(app(None, None))
+        self.assertEqual(output, b"test")
+        self.signals[request_finished].assert_called_once()
+
+    def test_request_finished_fired_even_with_error(self):
+        app = DjangoDBManagementMiddleware(lambda environ, start_response: [1 / 0])
+        with self.assertRaises(ZeroDivisionError):
+            list(app(None, None))
+        self.signals[request_finished].assert_called_once()

DjangoPlugin/tracdjangoplugin/wsgi.py

@@ -12,6 +12,11 @@
 # Python 3 would perform better here, but we are still on 2.7 for Trac, so leak fds for now.
 from tracopt.versioncontrol.git import PyGIT
 
+from .middlewares import DjangoDBManagementMiddleware
+
+
+application = DjangoDBManagementMiddleware(application)
+
 PyGIT.close_fds = False
 
 trac_dsn = os.getenv("SENTRY_DSN")