From 9c328713e7574882c9726e40b48b411170aad6ed Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Aleksi=20Ha=CC=88kli?= <aleksi.hakli@iki.fi>
Date: Fri, 1 Feb 2019 17:51:05 +0200
Subject: [PATCH] Use Django checks for cache configuration
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Fixes #383

Signed-off-by: Aleksi Häkli <aleksi.hakli@iki.fi>
---
 axes/apps.py              | 10 -------
 axes/checks.py            | 56 +++++++++++++++++++++++++++++++++++++++
 axes/tests/test_checks.py | 42 +++++++++++++++++++++++++++++
 docs/configuration.rst    | 12 +++++++++
 4 files changed, 110 insertions(+), 10 deletions(-)
 create mode 100644 axes/checks.py
 create mode 100644 axes/tests/test_checks.py

diff --git a/axes/apps.py b/axes/apps.py
index f4b641b..8896d07 100644
--- a/axes/apps.py
+++ b/axes/apps.py
@@ -7,16 +7,6 @@ class AppConfig(apps.AppConfig):
     name = 'axes'
 
     def ready(self):
-        from django.conf import settings
-        from django.core.exceptions import ImproperlyConfigured
-
-        if settings.CACHES[getattr(settings, 'AXES_CACHE', 'default')]['BACKEND'] == \
-                'django.core.cache.backends.locmem.LocMemCache':
-            raise ImproperlyConfigured(
-                'django-axes does not work properly with LocMemCache as the default cache backend'
-                ' please add e.g. a DummyCache backend for axes and configure it with AXES_CACHE'
-            )
-
         from django.contrib.auth.views import LoginView
         from django.utils.decorators import method_decorator
 
diff --git a/axes/checks.py b/axes/checks.py
new file mode 100644
index 0000000..1215256
--- /dev/null
+++ b/axes/checks.py
@@ -0,0 +1,56 @@
+from __future__ import unicode_literals
+
+from django.core.checks import Error, Tags, register
+
+from django.conf import settings
+
+
+class Messages:
+    CACHE_MISSING = 'missing cache configuration for AXES_CACHE'
+    CACHE_INVALID = 'invalid cache configuration for settings.AXES_CACHE'
+
+
+class Hints:
+    CACHE_MISSING = (
+        'django-axes needs to have a cache configured with settings.AXES_CACHE'
+    )
+    CACHE_INVALID = (
+        'django-axes does not work properly with LocMemCache as the cache backend'
+        ' please add e.g. a DummyCache backend and configure it with settings.AXES_CACHE'
+    )
+
+
+class Codes:
+    CACHE_MISSING = 'axes.E001'
+    CACHE_INVALID = 'axes.E002'
+
+
+@register(Tags.caches)
+def axes_cache_backend_check(app_configs, **kwargs):  # pylint: disable=unused-argument
+    errors = []
+
+    axes_cache_key = getattr(settings, 'AXES_CACHE', 'default')
+    axes_cache_config = settings.CACHES.get(axes_cache_key, {})
+    axes_cache_backend = axes_cache_config.get('BACKEND', '')
+
+    axes_cache_incompatible_backends = [
+        'django.core.cache.backends.locmem.LocMemCache',
+    ]
+
+    if not axes_cache_config:
+        errors.append(Error(
+            msg=Messages.CACHE_MISSING,
+            hint=Hints.CACHE_MISSING,
+            obj=settings.CACHES,
+            id=Codes.CACHE_MISSING,
+        ))
+
+    if axes_cache_backend in axes_cache_incompatible_backends:
+        errors.append(Error(
+            msg=Messages.CACHE_INVALID,
+            hint=Hints.CACHE_INVALID,
+            obj=settings.CACHES,
+            id=Codes.CACHE_INVALID,
+        ))
+
+    return errors
diff --git a/axes/tests/test_checks.py b/axes/tests/test_checks.py
new file mode 100644
index 0000000..24a9503
--- /dev/null
+++ b/axes/tests/test_checks.py
@@ -0,0 +1,42 @@
+from __future__ import unicode_literals
+
+from django.core.checks import run_checks, Error
+from django.conf import settings
+from django.test import TestCase, override_settings
+
+from axes.checks import Messages, Hints, Codes
+
+
+class CacheCheckTestCase(TestCase):
+    @override_settings(
+        AXES_CACHE='nonexistent',
+    )
+    def test_cache_missing_produces_check_error(self):
+        errors = run_checks()
+        error = Error(
+            msg=Messages.CACHE_MISSING,
+            hint=Hints.CACHE_MISSING,
+            obj=settings.CACHES,
+            id=Codes.CACHE_MISSING,
+        )
+
+        self.assertIn(error, errors)
+
+    @override_settings(
+        AXES_CACHE='axes',
+        CACHES={
+            'axes': {
+                'BACKEND': 'django.core.cache.backends.locmem.LocMemCache',
+            },
+        },
+    )
+    def test_cache_misconfiguration_produces_check_error(self):
+        errors = run_checks()
+        error = Error(
+            msg=Messages.CACHE_INVALID,
+            hint=Hints.CACHE_INVALID,
+            obj=settings.CACHES,
+            id=Codes.CACHE_INVALID,
+        )
+
+        self.assertIn(error, errors)
diff --git a/docs/configuration.rst b/docs/configuration.rst
index 8404142..b36d024 100644
--- a/docs/configuration.rst
+++ b/docs/configuration.rst
@@ -27,6 +27,18 @@ Add ``axes.backends.AxesModelBackend`` to the top of ``AUTHENTICATION_BACKENDS``
 
 Run ``python manage.py migrate`` to sync the database.
 
+Running checks
+--------------
+
+Use the ``python manage.py check`` command to verify the correct configuration in both
+development and production environments. It is probably best to use this step as part
+of your regular CI workflows to verify that your project is not misconfigured.
+
+django-axes uses the checks to verify your cache configuration to see that your caches
+should be functional with the configuration axes. Many people have different configurations
+for their development and production environments.
+
+
 Known configuration problems
 ----------------------------