Extensions Docs Server: Apps samples page

chrome/common/extensions/docs/server2/appengine_blobstore.py

+# Copyright (c) 2012 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 appengine_memcache as memcache
+from appengine_memcache import AppEngineMemcache
+from appengine_wrappers import blobstore
+from appengine_wrappers import files
+
+class AppEngineBlobstore(object):
+  """A wrapper around the blobstore API, which stores the blob keys in memcache
+  and in memory. The blob keys are stored in both places in case the blob key
+  gets flushed from memcache.
+  """

[not at google - send to devlin, 2012/08/07 01:35:38]

methods could do with some documentation, e.g. what's the "version" parameter
for?

[cduvall, 2012/08/08 19:27:25]

Done.

+  def __init__(self):
+    self._memcache = AppEngineMemcache('blobstore')
+    self._blob_keys = {}

[not at google - send to devlin, 2012/08/07 01:35:38]

If the keys are only stored in volatile memory (memory or memstore) then it
seems like we could end up losing blobs sometimes. We should probably replace
the memcache layer with a datastore layer?

[cduvall, 2012/08/08 19:27:25]

Done.

+
+  def Set(self, blob, key, version):

[not at google - send to devlin, 2012/08/07 01:35:38]

usually the key would be before the value in the parameter list.

[cduvall, 2012/08/08 19:27:25]

Done.

+    key = key + '.' + str(version)
+    filename = files.blobstore.create()
+    with files.open(filename, 'a') as f:
+      f.write(blob)
+    files.finalize(filename)
+    blob_key = files.blobstore.get_blob_key(filename)
+    self._blob_keys[key] = blob_key
+    self._memcache.Set(key, blob_key, memcache.MEMCACHE_BLOBSTORE, time=0)
+
+  def Get(self, key, version):
+    key = key + '.' + str(version)
+    if key not in self._blob_keys:
+      blob_key = self._memcache.Get(key, memcache.MEMCACHE_BLOBSTORE)
+      if blob_key is None:
+        return None
+      self._blob_keys[key] = blob_key
+    else:
+      blob_key = self._blob_keys[key]
+    blob_reader = blobstore.BlobReader(blob_key)
+    return blob_reader.read()
+
+  def Delete(self, key, version):
+    key = key + '.' + str(version)
+    if key not in self._blob_keys:
+      blob_key = self._memcache.Get(key, memcache.MEMCACHE_BLOBSTORE)
+      if blob_key is None:
+        return
+    else:
+      blob_key = self._blob_keys[key]
+      self._blob_keys.pop(key)
+    blobstore.delete(blob_key)