Use a key function that is safe for use w/ memcache

envs/dev.py

@@ -31,7 +31,8 @@ CACHES = {
     # In staging/prod envs, the sessions also live here.
     'default': {
         'BACKEND': 'django.core.cache.backends.locmem.LocMemCache',
-        'LOCATION': 'mitx_loc_mem_cache'
+        'LOCATION': 'mitx_loc_mem_cache',
+        'KEY_FUNCTION': 'util.memcache.safe_key',
     },
 
     # The general cache is what you get if you use our util.cache. It's used for
@@ -43,6 +44,7 @@ CACHES = {
         'BACKEND': 'django.core.cache.backends.dummy.DummyCache',
         'KEY_PREFIX': 'general',
         'VERSION': 4,
+        'KEY_FUNCTION': 'util.cache.memcache_safe_key',
     }
 }
 

envs/devplus.py

@@ -30,12 +30,14 @@ CACHES = {
    'default': {
        'BACKEND': 'django.core.cache.backends.memcached.MemcachedCache',
        'LOCATION': '127.0.0.1:11211',
+       'KEY_FUNCTION': 'util.memcache.safe_key',
    },
    'general': {
        'BACKEND': 'django.core.cache.backends.memcached.MemcachedCache',
        'LOCATION': '127.0.0.1:11211',
        'KEY_PREFIX' : 'general',
        'VERSION' : 5,
+       'KEY_FUNCTION': 'util.memcache.safe_key',
    }
 }
 

envs/static.py

@@ -30,7 +30,8 @@ CACHES = {
     # In staging/prod envs, the sessions also live here.
     'default': {
         'BACKEND': 'django.core.cache.backends.locmem.LocMemCache',
-        'LOCATION': 'mitx_loc_mem_cache'
+        'LOCATION': 'mitx_loc_mem_cache',
+        'KEY_FUNCTION': 'util.memcache.safe_key',
     },
 
     # The general cache is what you get if you use our util.cache. It's used for
@@ -42,6 +43,7 @@ CACHES = {
         'BACKEND': 'django.core.cache.backends.dummy.DummyCache',
         'KEY_PREFIX': 'general',
         'VERSION': 4,
+        'KEY_FUNCTION': 'util.memcache.safe_key',
     }
 }
 

envs/test.py

@@ -54,7 +54,8 @@ CACHES = {
     # In staging/prod envs, the sessions also live here.
     'default': {
         'BACKEND': 'django.core.cache.backends.locmem.LocMemCache',
-        'LOCATION': 'mitx_loc_mem_cache'
+        'LOCATION': 'mitx_loc_mem_cache',
+        'KEY_FUNCTION': 'util.memcache.safe_key',
     },
 
     # The general cache is what you get if you use our util.cache. It's used for
@@ -66,6 +67,7 @@ CACHES = {
         'BACKEND': 'django.core.cache.backends.dummy.DummyCache',
         'KEY_PREFIX': 'general',
         'VERSION': 4,
+        'KEY_FUNCTION': 'util.memcache.safe_key',
     }
 }
 

lib/util/memcache.py

+"""
+This module provides a KEY_FUNCTION suitable for use with a memcache backend
+so that we can cache any keys, not just ones that memcache would ordinarily accept
+"""
+from django.utils.hashcompat import md5_constructor
+from django.utils.encoding import smart_str
+import string
+
+def safe_key(key, key_prefix, version):
+    safe_key = smart_str(key)
+    for char in safe_key:
+        if ord(char) < 33 or ord(char) == 127:
+            safe_key = safe_key.replace(char, '_')
+
+    if len(safe_key) > 250:
+        safe_key = md5_constructor(safe_key)
+
+    return ":".join([key_prefix, str(version), safe_key])