Ticket #12399: memcached-timeout-fixes-with-tests-r12394.diff

django/core/cache/backends/memcached.py

@@ -1 +1 @@
 "Memcached cache backend"
 
+import time
+
 from django.core.cache.backends.base import BaseCache, InvalidCacheBackendError
 from django.utils.encoding import smart_unicode, smart_str
 
@@ -16 +18 @@
         BaseCache.__init__(self, params)
         self._cache = memcache.Client(server.split(';'))
 
+    def _get_memcache_timeout(self, timeout):
+        """
+        Memcached deals with long (> 30 days) timeouts in a special
+        way. Call this function to obtain a safe value for your timeout.
+        """
+        timeout = timeout or self.default_timeout
+        if timeout > 2592000: # 60*60*24*30, 30 days
+            # See http://code.google.com/p/memcached/wiki/FAQ
+            # "You can set expire times up to 30 days in the future. After that
+            # memcached interprets it as a date, and will expire the item after
+            # said date. This is a simple (but obscure) mechanic."
+            #
+            # This means that we have to switch to absolute timestamps.
+            timeout += int(time.time())
+        return timeout
+
     def add(self, key, value, timeout=0):
         if isinstance(value, unicode):
             value = value.encode('utf-8')
-        return self._cache.add(smart_str(key), value, timeout or self.default_timeout)
+        return self._cache.add(smart_str(key), value, self._get_memcache_timeout(timeout))
 
     def get(self, key, default=None):
         val = self._cache.get(smart_str(key))
@@ -34 +52 @@
     def set(self, key, value, timeout=0):
         if isinstance(value, unicode):
             value = value.encode('utf-8')
-        self._cache.set(smart_str(key), value, timeout or self.default_timeout)
+        self._cache.set(smart_str(key), value, self._get_memcache_timeout(timeout))
 
     def delete(self, key):
         self._cache.delete(smart_str(key))

tests/regressiontests/cache/tests.py

@@ -347 +347 @@
         def setUp(self):
             self.cache = get_cache(settings.CACHE_BACKEND)
 
+        def test_long_timeout(self):
+            '''
+            Using a timeout greater than 30 days makes memcached think
+            it is an absolute expiration timestamp instead of a relative
+            offset. Test that we honour this convention. Refs #12399.
+            '''
+            self.cache.set('key1', 'eggs', 60*60*24*30 + 1) #30 days + 1 second
+            self.assert_('key1' in self.cache)
+            
 class FileBasedCacheTests(unittest.TestCase, BaseCacheTests):
     """
     Specific test cases for the file-based cache.