[Predator] Add local cache for get command output.

appengine/findit/util_scripts/local_cache.py

Index: appengine/findit/util_scripts/local_cache.py
diff --git a/appengine/findit/util_scripts/local_cache.py b/appengine/findit/util_scripts/local_cache.py
new file mode 100644
index 0000000000000000000000000000000000000000..e81b2e8d283b9b3a8b632d9e8b50709c8ed9c78b
--- /dev/null
+++ b/appengine/findit/util_scripts/local_cache.py
@@ -0,0 +1,41 @@
+# Copyright 2015 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
+
+
+class LocalCacher(Cacher):
+  """Cacher that uses local files to cache data."""
+  lock = threading.Lock()
+
+  def __init__(self, cache_dir):
+    self.cache_dir = cache_dir
+    assert os.path.exists(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 e:  # pragma: no cover.
+        logging.error('Failed loading cache: %s', e)

[stgao, 2016/11/08 22:00:43]

Could we use logging.exception instead? Same for below.

[Sharu Jiang, 2016/11/11 00:54:21]

Done.

+        return None
+
+  def Set(self, key, data):  # 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.error('Failed setting cache for key %s: %s', key, e)