safe_key() now hashes the prefix/version as well, just in case

these are configured to be too long in the settings.

common/djangoapps/util/memcache.py

@@ -41,11 +41,9 @@ def safe_key(key, key_prefix, version):
     # Attempt to combine the prefix, version, and key
     combined = ":".join([key_prefix, version, key])
 
-    # If the total length is too long for memcache, hash the key
-    # and combine the parts again
+    # If the total length is too long for memcache, hash it
     if len(combined) > 250:
-        key = fasthash(key)
-        combined = ":".join([key_prefix, version, key])
+        combined = fasthash(combined)
 
     # Return the result
     return combined

common/djangoapps/util/tests/test_memcache.py

@@ -4,6 +4,7 @@ Tests for memcache in util app
 
 from django.test import TestCase
 from django.core.cache import get_cache
+from django.conf import settings
 from util.memcache import safe_key
 
 
@@ -51,8 +52,17 @@ class MemcacheTest(TestCase):
 
     def test_long_key_prefix_version(self):
 
+        # Long key
         key = safe_key('a' * 300, 'prefix', 'version')
-        self.assertEqual(key[0:15], 'prefix:version:')
+        self.assertTrue(self._is_valid_key(key))
+
+        # Long prefix
+        key = safe_key('key', 'a' * 300, 'version')
+        self.assertTrue(self._is_valid_key(key))
+
+        # Long version
+        key = safe_key('key', 'prefix', 'a' * 300)
+        self.assertTrue(self._is_valid_key(key))
 
     def test_safe_key_unicode(self):