Docserver: Persist stat cache for versioned file systems

chrome/common/extensions/docs/server2/gitiles_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 base64 import b64decode
 from itertools import izip
 import json
 import logging
 import posixpath
@@ skipping 31 matching lines @@
 
 def _CreateStatInfo(json_data):
   '''Returns a StatInfo object comprised of the tree ID for |json_data|,
   as well as the tree IDs for the entries in |json_data|.
   '''
   tree = _ParseGitilesJson(json_data)
   return StatInfo(tree['id'],
                   dict((e['name'], e['id']) for e in tree['entries']))
 
 
+def _CreateIdentityFromCommit(commit):
+  return '%s/%s/%s' % (GITILES_BASE, GITILES_SRC_ROOT, commit)
+
+
 class GitilesFileSystem(FileSystem):
   '''Class to fetch filesystem data from the Chromium project's gitiles
   service.
   '''
   _logged_tokens = set()
 
   @classmethod
   def Create(cls, branch='master', commit=None):
     token, _ = app_identity.get_access_token(GITILES_OAUTH2_SCOPE)
 
@@ skipping 163 matching lines @@
       if IsDirectory(path):
         return stat_info
       if filename not in stat_info.child_versions:
         raise FileNotFoundError(
             '%s from %s was not in child versions for Stat' % (filename, path))
       return StatInfo(stat_info.child_versions[filename])
 
     fetch_future = self._FetchAsync(ToDirectory(dir_) + _JSON_FORMAT)
     return self._ResolveFetchContent(path, fetch_future).Then(stat)
 
-  def GetIdentity(self):
-    # NOTE: Do not use commit information to create the string identity.
-    # Doing so will mess up caching.
-    if self._commit is None and self._branch != 'master':
+  def GetStableIdentity(self):
+    '''The stable identity is always the same for GitilesFileSystems designated
+    to master, even if they are pinned to a specific commit'''
+    if self._branch == 'master':
+      str_id = '%s/%s/master' % (GITILES_BASE, GITILES_SRC_ROOT)
+    elif self._commit is not None:
+      str_id = _CreateIdentityFromCommit(self._commit)
+    else:
       str_id = '%s/%s/%s/%s' % (
           GITILES_BASE, GITILES_SRC_ROOT, GITILES_BRANCHES_PATH, self._branch)
-    else:
-      str_id = '%s/%s' % (GITILES_BASE, GITILES_SRC_ROOT)
     return '@'.join((self.__class__.__name__, StringIdentity(str_id)))
+
+  def GetUnstableIdentity(self):
+    '''The unstable identity always tracks the commit ID if set.'''
+    if self._commit is not None:
+      return '@'.join((self.__class__.__name__, StringIdentity(
+          _CreateIdentityFromCommit(self._commit))))
+    return self.GetStableIdentity()