Add CachingFileSystem on top of CloudStorageFileSystem

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

 # Copyright 2014 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.
 
 from third_party.cloudstorage import cloudstorage_api
 from third_party.cloudstorage import common
 from third_party.cloudstorage import errors
 
 from docs_server_utils import StringIdentity
 from file_system import FileSystem, FileNotFoundError, StatInfo
 from future import Gettable, Future
 
 import logging
 import traceback
 
+# Name of the file containing the Git hash of the latest commit sync'ed
+# to Cloud Storage. This file is generated by the Github->GCS sync script
+LAST_COMMIT_HASH_FILENAME='.__lastcommit.txt'
+
 '''See gcs_file_system_provider.py for documentation on using Google Cloud
 Storage as a filesystem.
 '''
 def _ReadFile(filename):
   try:
     with cloudstorage_api.open(filename, 'r') as f:
       return f.read()
   except errors.Error:
     raise FileNotFoundError('Read failed for %s: %s' % (filename,
         traceback.format_exc()))
 
 def _ListDir(dir_name):
   try:
     files = cloudstorage_api.listbucket(dir_name)
     return [os_path.filename for os_path in files]
   except errors.Error:
     raise FileNotFoundError('cloudstorage.listbucket failed for %s: %s' %
                             (dir_name, traceback.format_exc()))
 
 def _CreateStatInfo(bucket, path):
   bucket = '/%s' % bucket
   full_path = '/'.join( (bucket, path.lstrip('/')) )
+  last_commit_file = '%s/%s' % (bucket, LAST_COMMIT_HASH_FILENAME)
   try:
+    last_commit = _ReadFile(last_commit_file)
     if full_path.endswith('/'):
       child_versions = dict()
-      version = 0
       # Fetching stats for all files under full_path, recursively. The
       # listbucket method uses a prefix approach to simulate hierarchy,
       # but calling it without the "delimiter" argument searches for prefix,
       # which means, for directories, everything beneath it.
       for _file in cloudstorage_api.listbucket(full_path):
-        if not _file.is_dir:
-          # GCS doesn't have metadata for dirs
-          child_stat = cloudstorage_api.stat('%s' % _file.filename).st_ctime
-          filename = _file.filename[len(bucket)+1:]
-          child_versions[filename] = child_stat
-          version = max(version, child_stat)
+        filename = _file.filename[len(full_path):]
+        child_versions[filename] = last_commit
     else:
       child_versions = None
-      version = cloudstorage_api.stat(full_path).st_ctime
-    return StatInfo(version, child_versions)
+    return StatInfo(last_commit, child_versions)
   except (TypeError, errors.Error):
     raise FileNotFoundError('cloudstorage.stat failed for %s: %s' % (path,
                             traceback.format_exc()))
 
-
 class CloudStorageFileSystem(FileSystem):
   '''FileSystem implementation which fetches resources from Google Cloud
   Storage.
   '''
   def __init__(self, bucket, debug_access_token=None, debug_bucket_prefix=None):
     self._bucket = bucket
     if debug_access_token:
       logging.debug('gcs: using debug access token: %s' % debug_access_token)
       common.set_access_token(debug_access_token)
     if debug_bucket_prefix:
@@ skipping 39 matching lines @@
   def _warnAboutAuthError(self):
     logging.warn(('Authentication error on Cloud Storage. Check if your'
                   ' appengine project has permissions to Read the GCS'
                   ' buckets. If you are running a local appengine server,'
                   ' you need to set an access_token in'
                   ' local_debug/gcs_debug.conf.'
                   ' Remember that this token expires in less than 10'
                   ' minutes, so keep it updated. See'
                   ' gcs_file_system_provider.py for instructions.'));
     logging.debug(traceback.format_exc())