Docserver: Persist stat cache for versioned file systems

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

 # Copyright 2013 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 posixpath
 
 from file_system import FileSystem, FileNotFoundError
 from future import Future
 from test_file_system import _List, _StatTracker, TestFileSystem
 from path_util import IsDirectory
 
 
 class MockFileSystem(FileSystem):
   '''Wraps FileSystems to add a selection of mock behaviour:
   - asserting how often Stat/Read calls are being made to it.
   - primitive changes/versioning via applying object "diffs", mapping paths to
     new content (similar to how TestFileSystem works).
   '''
   def __init__(self, file_system):
     self._file_system = file_system
     # Updates are stored as TestFileSystems because it already implements a
     # bunch of logic to intepret paths into dictionaries.
     self._updates = []
     self._stat_tracker = _StatTracker()
     self._read_count = 0
     self._read_resolve_count = 0
     self._stat_count = 0
+    self._version = None
 
   @staticmethod
   def Create(file_system, updates):
     mock_file_system = MockFileSystem(file_system)
     for update in updates:
       mock_file_system.Update(update)
     return mock_file_system
 
   #
   # FileSystem implementation.
@@ skipping 41 matching lines @@
     stat.version = stradd(stat.version, self._stat_tracker.GetVersion(path))
     if stat.child_versions:
       for child_path, child_version in stat.child_versions.iteritems():
         stat.child_versions[child_path] = stradd(
             stat.child_versions[child_path],
             self._stat_tracker.GetVersion(posixpath.join(path, child_path)))
 
     return stat
 
   def GetCommitID(self):
-    return Future(value=self._stat_tracker.GetVersion(''))
+    return Future(value=str(self._stat_tracker.GetVersion('')))
 
   def GetPreviousCommitID(self):
-    return Future(value=self._stat_tracker.GetVersion('') - 1)
+    return Future(value=str(self._stat_tracker.GetVersion('') - 1))
 
   def GetIdentity(self):
     return self._file_system.GetIdentity()
 
+  def GetVersion(self):
+    return self._version
+
   def __str__(self):
     return repr(self)
 
   def __repr__(self):
     return 'MockFileSystem(read_count=%s, stat_count=%s, updates=%s)' % (
         self._read_count, self._stat_count, len(self._updates))
 
   #
   # Testing methods.
   #
@@ skipping 22 matching lines @@
     self._read_resolve_count = 0
     self._stat_count = 0
 
   def Update(self, update):
     self._updates.append(TestFileSystem(update))
     for path in _List(update).iterkeys():
       # Any files (not directories) which changed are now at the version
       # derived from |_updates|.
       if not IsDirectory(path):
         self._stat_tracker.SetVersion(path, len(self._updates))
+
+  def SetVersion(self, version):
+    '''Override the reported FileSystem version (default None) for testing.'''
+    self._version = version