Cope with cache connection errors

Ensure requests don't get rate limited and don't throw errors when a
memcached instance is unavailable.

.travis.yml

@@ -12,6 +12,9 @@ python:
  - "3.4"
  - "pypy"
 install:
+ - if [[ $TRAVIS_PYTHON_VERSION == 2* ]]; then pip install -q python-memcached>=1.57; fi
+ - if [[ $TRAVIS_PYTHON_VERSION == 3* ]]; then pip install -q python3-memcached>=1.51; fi
+ - if [[ $TRAVIS_PYTHON_VERSION == pypy ]]; then pip install -q python-memcached>=1.57; fi
  - pip install -q "Django>=${DJANGO_VERSION},<${DJANGO_VERSION}.99" flake8
 script:
  - ./run.sh test

ratelimit/tests.py

@@ -280,6 +280,16 @@ def view(request):
         with self.assertRaises(InvalidCacheBackendError):
             view(req)
 
+    @override_settings(RATELIMIT_USE_CACHE='connection-errors')
+    def test_cache_connection_error(self):
+
+        @ratelimit(key='ip', rate='1/m')
+        def view(request):
+            return request
+
+        req = rf.post('/')
+        assert view(req)
+
     def test_user_or_ip(self):
         """Allow custom functions to set cache keys."""
 
@@ -389,6 +399,33 @@ def do_increment(request):
         assert do_increment(req), 'Request should be rate limited.'
         assert not_increment(req), 'Request should be rate limited.'
 
+    @override_settings(RATELIMIT_USE_CACHE='connection-errors')
+    def test_is_ratelimited_cache_connection_error_without_increment(self):
+        def get_key(group, request):
+            return 'test_is_ratelimited_key'
+
+        def not_increment(request):
+            return is_ratelimited(request, increment=False,
+                                  method=is_ratelimited.ALL, key=get_key,
+                                  rate='1/m', group='a')
+
+        req = rf.get('/')
+        assert not not_increment(req)
+
+    @override_settings(RATELIMIT_USE_CACHE='connection-errors')
+    def test_is_ratelimited_cache_connection_error_with_increment(self):
+        def get_key(group, request):
+            return 'test_is_ratelimited_key'
+
+        def do_increment(request):
+            return is_ratelimited(request, increment=True,
+                                  method=is_ratelimited.ALL, key=get_key,
+                                  rate='1/m', group='a')
+
+        req = rf.get('/')
+        assert not do_increment(req)
+        assert req.limited is False
+
 
 class RatelimitCBVTests(TestCase):
 

ratelimit/utils.py

@@ -153,9 +153,12 @@ def is_ratelimited(request, group=None, fn=None, key=None, rate=None,
         count = initial_value
     else:
         if increment:
-            count = cache.incr(cache_key)
+            try:
+                count = cache.incr(cache_key)
+            except ValueError:
+                count = 0
         else:
-            count = cache.get(cache_key)
+            count = cache.get(cache_key) or 0
     limited = count > limit
     if increment:
         request.limited = old_limited or limited

test_settings.py

@@ -11,6 +11,10 @@
         'BACKEND': 'django.core.cache.backends.locmem.LocMemCache',
         'LOCATION': 'ratelimit-tests',
     },
+    'connection-errors': {
+        'BACKEND': 'django.core.cache.backends.memcached.MemcachedCache',
+        'LOCATION': 'test-connection-errors',
+    },
 }
 
 DATABASES = {

tox.ini

@@ -5,70 +5,102 @@ commands = ./run.sh test
 
 [testenv:py34-1.8]
 basepython = python3.4
-deps = Django>=1.8,<1.8.99
+deps =
+    Django>=1.8,<1.8.99
+    python3-memcached>=1.51
 
 [testenv:py34-1.7]
 basepython = python3.4
-deps = Django>=1.7,<1.7.99
+deps =
+    Django>=1.7,<1.7.99
+    python3-memcached>=1.51
 
 [testenv:py34-1.6]
 basepython = python3.4
-deps = Django>=1.6,<1.6.99
+deps =
+    Django>=1.6,<1.6.99
+    python3-memcached>=1.51
 
 [testenv:py34-1.5]
 basepython = python3.4
-deps = Django>=1.5,<1.5.99
+deps =
+    Django>=1.5,<1.5.99
+    python3-memcached>=1.51
 
 # python 3.3
 
 [testenv:py33-1.8]
 basepython = python3.3
-deps = Django>=1.8,<1.8.99
+deps =
+    Django>=1.8,<1.8.99
+    python3-memcached>=1.51
 
 [testenv:py33-1.7]
 basepython = python3.3
-deps = Django>=1.7,<1.7.99
+deps =
+    Django>=1.7,<1.7.99
+    python3-memcached>=1.51
 
 [testenv:py33-1.6]
 basepython = python3.3
-deps = Django>=1.6,<1.6.99
+deps =
+    Django>=1.6,<1.6.99
+    python3-memcached>=1.51
 
 [testenv:py33-1.5]
 basepython = python3.3
-deps = Django>=1.5,<1.5.99
+deps =
+    Django>=1.5,<1.5.99
+    python3-memcached>=1.51
 
 # python 2.7
 
 [testenv:py27-1.8]
 basepython = python2.7
-deps = Django>=1.7,<1.7.99
+deps =
+    Django>=1.7,<1.7.99
+    python-memcached>=1.57
 
 [testenv:py27-1.7]
 basepython = python2.7
-deps = Django>=1.7,<1.7.99
+deps =
+    Django>=1.7,<1.7.99
+    python-memcached>=1.57
 
 [testenv:py27-1.6]
 basepython = python2.7
-deps = Django>=1.6,<1.6.99
+deps =
+    Django>=1.6,<1.6.99
+    python-memcached>=1.57
 
 [testenv:py27-1.5]
 basepython = python2.7
-deps = Django>=1.5,<1.5.99
+deps =
+    Django>=1.5,<1.5.99
+    python-memcached>=1.57
 
 [testenv:py27-1.4]
 basepython = python2.7
-deps = Django>=1.4,<1.4.99
+deps =
+    Django>=1.4,<1.4.99
+    python-memcached>=1.57
 
 # python 2.6
 
 [testenv:py26-1.6]
 basepython = python2.6
-deps = Django>=1.6,<1.6.99
+deps =
+    Django>=1.6,<1.6.99
+    python-memcached>=1.57
 
 [testenv:py26-1.5]
 basepython = python2.6
-deps = Django>=1.5,<1.5.99
+deps =
+    Django>=1.5,<1.5.99
+    python-memcached>=1.57
 
 [testenv:py26-1.4]
 basepython = python2.6
-deps = Django>=1.4,<1.4.99
+deps =
+    Django>=1.4,<1.4.99
+    python-memcached>=1.57