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diff --git a/src/mailman/interfaces/cache.py b/src/mailman/interfaces/cache.py
new file mode 100644
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+++ b/src/mailman/interfaces/cache.py
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+# Copyright (C) 2016 by the Free Software Foundation, Inc.
+#
+# This file is part of GNU Mailman.
+#
+# GNU Mailman is free software: you can redistribute it and/or modify it under
+# the terms of the GNU General Public License as published by the Free
+# Software Foundation, either version 3 of the License, or (at your option)
+# any later version.
+#
+# GNU Mailman is distributed in the hope that it will be useful, but WITHOUT
+# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+# FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+# more details.
+#
+# You should have received a copy of the GNU General Public License along with
+# GNU Mailman.  If not, see <http://www.gnu.org/licenses/>.
+
+"""File caches."""
+
+from mailman import public
+from zope.interface import Interface
+
+
+@public
+class ICacheManager(Interface):
+    """Manager for managing cached files."""
+
+    def add(key, contents, lifetime=None):
+        """Add the contents to the cache, indexed by the key.
+
+        If there is already some contents cached under the given key, the old
+        contents are overwritten with the new contents.
+
+        :param key: The key to use when storing the contents.
+        :type name: str
+        :param contents: The contents to store in the cache.  If this is a
+            bytes object, it will be stored on disk in binary.  If it's a str,
+            it will be stored in UTF-8.  Either way, the manager will remember
+            the type and return it when you access the file.
+        :type contents: bytes or str
+        :param lifetime: How long should the file be cached for, before it
+            expires (leading to its eventual eviction)?  If not given, the
+            system default lifetime is used.
+        :type lifetime: datetime.timedelta
+        :return: The SHA256 hash under which the file contents are stored.
+        :rtype: str
+        """
+
+    def get(key, *, expunge=False):
+        """Return the contents cached under the given key.
+
+        :param key: The key identifying the contents you want to retrieve.
+        :type key: str
+        :param expunge: A flag indicating whether the file contents should
+            also be removed from the cache.
+        :type expunge: bool
+        :return: The contents of the cached file or None if the given id isn't
+            in the cache (or it's already expired).
+        :rtype: bytes or str, depending on the original contents.
+        """
+
+    def evict():
+        """Evict all files which have expired."""
+
+    def clear():
+        """Clear the entire cache of files."""