[Predator] Add local cache for get command output.

appengine/findit/util_scripts/local_cache.py

+# Copyright 2016 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+import logging
+import os
+import pickle
+import threading
+import zlib
+
+from lib.cache_decorator import Cacher
+
+CACHE_DIR = os.path.join(os.path.expanduser('~'), '.predator', 'cache')
+
+
+class LocalCacher(Cacher):
+  """Cacher that uses local files to cache data."""
+  lock = threading.Lock()
+
+  def __init__(self, cache_dir=CACHE_DIR):
+    self.cache_dir = cache_dir
+    with LocalCacher.lock:
+      if not os.path.exists(cache_dir): # pragma: no cover.
+        os.makedirs(cache_dir)
+
+  def Get(self, key):
+    with LocalCacher.lock:
+      path = os.path.join(self.cache_dir, key)
+      if not os.path.exists(path):
+        return None
+
+      try:
+        with open(path) as f:
+          return pickle.loads(zlib.decompress(f.read()))
+      except Exception as error:  # pragma: no cover.
+        logging.exception('Failed loading cache: %s', error)
+        return None
+
+  def Set(self, key, data, expire_time=0):  # pylint: disable=W
+    with LocalCacher.lock:
+      try:
+        with open(os.path.join(self.cache_dir, key), 'wb') as f:
+          f.write(zlib.compress(pickle.dumps(data)))
+      except Exception as e:  # pragma: no cover.
+        logging.exception('Failed setting cache for key %s: %s', key, e)