6 files changed, 52 insertions, 8 deletions
diff --git a/django/core/cache/__init__.py b/django/core/cache/__init__.py
index 1b602908cb..680f724f94 100644
--- a/django/core/cache/__init__.py
+++ b/django/core/cache/__init__.py
@@ -18,7 +18,7 @@ See docs/cache.txt for information on the public API.
 from cgi import parse_qsl
 from django.conf import settings
 from django.core import signals
-from django.core.cache.backends.base import InvalidCacheBackendError
+from django.core.cache.backends.base import InvalidCacheBackendError, CacheKeyWarning
 from django.utils import importlib
 
 # Name for use in settings file --> name of module in "backends" directory.
diff --git a/django/core/cache/backends/base.py b/django/core/cache/backends/base.py
index e58267a2e9..83dd461804 100644
--- a/django/core/cache/backends/base.py
+++ b/django/core/cache/backends/base.py
@@ -1,10 +1,18 @@
 "Base Cache class."
 
-from django.core.exceptions import ImproperlyConfigured
+import warnings
+
+from django.core.exceptions import ImproperlyConfigured, DjangoRuntimeWarning
 
 class InvalidCacheBackendError(ImproperlyConfigured):
     pass
 
+class CacheKeyWarning(DjangoRuntimeWarning):
+    pass
+
+# Memcached does not accept keys longer than this.
+MEMCACHE_MAX_KEY_LENGTH = 250
+
 class BaseCache(object):
     def __init__(self, params):
         timeout = params.get('timeout', 300)
@@ -116,3 +124,21 @@ class BaseCache(object):
     def clear(self):
         """Remove *all* values from the cache at once."""
         raise NotImplementedError
+
+    def validate_key(self, key):
+        """
+        Warn about keys that would not be portable to the memcached
+        backend. This encourages (but does not force) writing backend-portable
+        cache code.
+
+        """
+        if len(key) > MEMCACHE_MAX_KEY_LENGTH:
+            warnings.warn('Cache key will cause errors if used with memcached: '
+                    '%s (longer than %s)' % (key, MEMCACHE_MAX_KEY_LENGTH),
+                    CacheKeyWarning)
+        for char in key:
+            if ord(char) < 33 or ord(char) == 127:
+                warnings.warn('Cache key contains characters that will cause '
+                        'errors if used with memcached: %r' % key,
+                              CacheKeyWarning)
+
diff --git a/django/core/cache/backends/db.py b/django/core/cache/backends/db.py
index 833fa749aa..c4429c80b3 100644
--- a/django/core/cache/backends/db.py
+++ b/django/core/cache/backends/db.py
@@ -46,6 +46,7 @@ class CacheClass(BaseCache):
             self._cull_frequency = 3
 
     def get(self, key, default=None):
+        self.validate_key(key)
         db = router.db_for_read(self.cache_model_class)
         table = connections[db].ops.quote_name(self._table)
         cursor = connections[db].cursor()
@@ -65,9 +66,11 @@ class CacheClass(BaseCache):
         return pickle.loads(base64.decodestring(value))
 
     def set(self, key, value, timeout=None):
+        self.validate_key(key)
         self._base_set('set', key, value, timeout)
 
     def add(self, key, value, timeout=None):
+        self.validate_key(key)
         return self._base_set('add', key, value, timeout)
 
     def _base_set(self, mode, key, value, timeout=None):
@@ -103,6 +106,7 @@ class CacheClass(BaseCache):
             return True
 
     def delete(self, key):
+        self.validate_key(key)
         db = router.db_for_write(self.cache_model_class)
         table = connections[db].ops.quote_name(self._table)
         cursor = connections[db].cursor()
@@ -111,6 +115,7 @@ class CacheClass(BaseCache):
         transaction.commit_unless_managed(using=db)
 
     def has_key(self, key):
+        self.validate_key(key)
         db = router.db_for_read(self.cache_model_class)
         table = connections[db].ops.quote_name(self._table)
         cursor = connections[db].cursor()
diff --git a/django/core/cache/backends/dummy.py b/django/core/cache/backends/dummy.py
index 4337484cb1..f73b7408bc 100644
--- a/django/core/cache/backends/dummy.py
+++ b/django/core/cache/backends/dummy.py
@@ -6,22 +6,25 @@ class CacheClass(BaseCache):
     def __init__(self, *args, **kwargs):
         pass
 
-    def add(self, *args, **kwargs):
+    def add(self, key, *args, **kwargs):
+        self.validate_key(key)
         return True
 
     def get(self, key, default=None):
+        self.validate_key(key)
         return default
 
-    def set(self, *args, **kwargs):
-        pass
+    def set(self, key, *args, **kwargs):
+        self.validate_key(key)
 
-    def delete(self, *args, **kwargs):
-        pass
+    def delete(self, key, *args, **kwargs):
+        self.validate_key(key)
 
     def get_many(self, *args, **kwargs):
         return {}
 
-    def has_key(self, *args, **kwargs):
+    def has_key(self, key, *args, **kwargs):
+        self.validate_key(key)
         return False
 
     def set_many(self, *args, **kwargs):
diff --git a/django/core/cache/backends/filebased.py b/django/core/cache/backends/filebased.py
index 6057f11ef7..46e69f3091 100644
--- a/django/core/cache/backends/filebased.py
+++ b/django/core/cache/backends/filebased.py
@@ -32,6 +32,7 @@ class CacheClass(BaseCache):
             self._createdir()
 
     def add(self, key, value, timeout=None):
+        self.validate_key(key)
         if self.has_key(key):
             return False
 
@@ -39,6 +40,7 @@ class CacheClass(BaseCache):
         return True
 
     def get(self, key, default=None):
+        self.validate_key(key)
         fname = self._key_to_file(key)
         try:
             f = open(fname, 'rb')
@@ -56,6 +58,7 @@ class CacheClass(BaseCache):
         return default
 
     def set(self, key, value, timeout=None):
+        self.validate_key(key)
         fname = self._key_to_file(key)
         dirname = os.path.dirname(fname)
 
@@ -79,6 +82,7 @@ class CacheClass(BaseCache):
             pass
 
     def delete(self, key):
+        self.validate_key(key)
         try:
             self._delete(self._key_to_file(key))
         except (IOError, OSError):
@@ -95,6 +99,7 @@ class CacheClass(BaseCache):
             pass
 
     def has_key(self, key):
+        self.validate_key(key)
         fname = self._key_to_file(key)
         try:
             f = open(fname, 'rb')
diff --git a/django/core/cache/backends/locmem.py b/django/core/cache/backends/locmem.py
index eff1201b97..fe33d33307 100644
--- a/django/core/cache/backends/locmem.py
+++ b/django/core/cache/backends/locmem.py
@@ -30,6 +30,7 @@ class CacheClass(BaseCache):
         self._lock = RWLock()
 
     def add(self, key, value, timeout=None):
+        self.validate_key(key)
         self._lock.writer_enters()
         try:
             exp = self._expire_info.get(key)
@@ -44,6 +45,7 @@ class CacheClass(BaseCache):
             self._lock.writer_leaves()
 
     def get(self, key, default=None):
+        self.validate_key(key)
         self._lock.reader_enters()
         try:
             exp = self._expire_info.get(key)
@@ -76,6 +78,7 @@ class CacheClass(BaseCache):
         self._expire_info[key] = time.time() + timeout
 
     def set(self, key, value, timeout=None):
+        self.validate_key(key)
         self._lock.writer_enters()
         # Python 2.4 doesn't allow combined try-except-finally blocks.
         try:
@@ -87,6 +90,7 @@ class CacheClass(BaseCache):
             self._lock.writer_leaves()
 
     def has_key(self, key):
+        self.validate_key(key)
         self._lock.reader_enters()
         try:
             exp = self._expire_info.get(key)
@@ -127,6 +131,7 @@ class CacheClass(BaseCache):
             pass
 
     def delete(self, key):
+        self.validate_key(key)
         self._lock.writer_enters()
         try:
             self._delete(key)