Integrate persistent cache with "var_dir" conf option

[mpd-sima.git] / sima / lib / cache.py

diff --git a/sima/lib/cache.py b/sima/lib/cache.py
new file mode 100644 (file)
index 0000000..ebed3fc
--- /dev/null
+++ b/sima/lib/cache.py
@@ -0,0 +1,95 @@
+# -*- coding: utf-8 -*-
+
+# Copyright (c) 2014 Jack Kaliko <kaliko@azylum.org>
+# Copyright (c) 2012, 2013 Eric Larson <eric@ionrock.org>
+#
+#   This program 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.
+#
+#   This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+#
+"""
+The cache object API for implementing caches. The default is just a
+dictionary, which in turns means it is not threadsafe for writing.
+"""
+
+import os
+import base64
+import codecs
+
+from hashlib import md5
+from pickle import load, dump
+from threading import Lock
+
+from ..utils.filelock import FileLock
+
+
+class BaseCache:
+
+    def get(self, key):
+        raise NotImplemented()
+
+    def set(self, key, value):
+        raise NotImplemented()
+
+    def delete(self, key):
+        raise NotImplemented()
+
+
+class DictCache(BaseCache):
+
+    def __init__(self, init_dict=None):
+        self.lock = Lock()
+        self.data = init_dict or {}
+
+    def get(self, key):
+        return self.data.get(key, None)
+
+    def set(self, key, value):
+        with self.lock:
+            self.data.update({key: value})
+
+    def delete(self, key):
+        with self.lock:
+            if key in self.data:
+                self.data.pop(key)
+
+
+class FileCache:
+
+    def __init__(self, directory, forever=False):
+        self.directory = directory
+        self.forever = forever
+
+        if not os.path.isdir(self.directory):
+            os.mkdir(self.directory)
+
+    def encode(self, x):
+        return md5(x.encode('utf-8')).hexdigest()
+
+    def _fn(self, name):
+        return os.path.join(self.directory, self.encode(name))
+
+    def get(self, key):
+        name = self._fn(key)
+        if os.path.exists(name):
+            return load(codecs.open(name, 'rb'))
+
+    def set(self, key, value):
+        name = self._fn(key)
+        with FileLock(name):
+            with codecs.open(name, 'w+b') as fh:
+                dump(value, fh)
+
+    def delete(self, key):
+        if not self.forever:
+            os.remove(self._fn(key))