Refactor the devserver to make it easier to control caching

chrome/common/extensions/docs/server2/caching_file_system.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.
 
 from file_system import FileSystem, StatInfo, FileNotFoundError
 from future import Future
-import object_store
+from object_store_creator import ObjectStoreCreator
 
 class _AsyncUncachedFuture(object):
   def __init__(self,
                uncached,
                current_result,
                file_system,
-               object_store,
-               namespace):
+               object_store):
     self._uncached = uncached
     self._current_result = current_result
     self._file_system = file_system
     self._object_store = object_store
-    self._namespace = namespace
 
   def Get(self):
     mapping = {}
     new_items = self._uncached.Get()
     for item in new_items:
       version = self._file_system.Stat(item).version
       mapping[item] = (new_items[item], version)
       self._current_result[item] = new_items[item]
-    self._object_store.SetMulti(mapping, self._namespace, time=0)
+    self._object_store.SetMulti(mapping, time=0)
     return self._current_result
 
-class MemcacheFileSystem(FileSystem):
-  """FileSystem implementation which memcaches the results of Read.
+class CachingFileSystem(FileSystem):
+  """FileSystem implementation which caches its results in an object store.
   """
-  def __init__(self, file_system, object_store):
+  def __init__(self, file_system):
     self._file_system = file_system
-    self._object_store = object_store
+    object_store_creator = ObjectStoreCreator(CachingFileSystem)
+    self._stat_object_store = object_store_creator.Create(
+        category='stat')
+    self._read_object_store = object_store_creator.Create(
+        category='read')
+    self._read_binary_object_store = object_store_creator.Create(
+        category='read-binary')
 
   def Stat(self, path, stats=None):
     """Stats the directory given, or if a file is given, stats the files parent
     directory to get info about the file.
     """
     # TODO(kalman): store the whole stat info, not just the version.
-    version = self._object_store.Get(path, object_store.FILE_SYSTEM_STAT).Get()
+    version = self._stat_object_store.Get(path).Get()
     if version is not None:
       return StatInfo(version)
 
     # Always stat the parent directory, since it will have the stat of the child
     # anyway, and this gives us an entire directory's stat info at once.
     if path.endswith('/'):
       dir_path = path
     else:
       dir_path = path.rsplit('/', 1)[0] + '/'
 
     dir_stat = self._file_system.Stat(dir_path)
     if path == dir_path:
       version = dir_stat.version
     else:
       version = dir_stat.child_versions.get(path.split('/')[-1], None)
       if version is None:
         raise FileNotFoundError(path)
     mapping = { path: version }
 
     for child_path, child_version in dir_stat.child_versions.iteritems():
       child_path = dir_path + child_path
       mapping[child_path] = child_version
-    self._object_store.SetMulti(mapping, object_store.FILE_SYSTEM_STAT)
+    self._stat_object_store.SetMulti(mapping)
     return StatInfo(version)
 
   def Read(self, paths, binary=False):
     """Reads a list of files. If a file is in memcache and it is not out of
     date, it is returned. Otherwise, the file is retrieved from the file system.
     """
     result = {}
     uncached = []
-    namespace = object_store.FILE_SYSTEM_READ
-    if binary:
-      namespace = '%s.binary' % namespace
-    results = self._object_store.GetMulti(paths, namespace, time=0).Get()
+    read_object_store = (self._read_binary_object_store if binary else
+                         self._read_object_store)
+    results = read_object_store.GetMulti(paths).Get()
     result_values = [x[1] for x in sorted(results.iteritems())]
-    stats = self._object_store.GetMulti(paths,
-                                        object_store.FILE_SYSTEM_STAT).Get()
+    stats = self._stat_object_store.GetMulti(paths).Get()
     stat_values = [x[1] for x in sorted(stats.iteritems())]
     for path, cached_result, stat in zip(sorted(paths),
                                          result_values,
                                          stat_values):
       if cached_result is None:
         uncached.append(path)
         continue
       data, version = cached_result
       # TODO(cduvall): Make this use a multi stat.
       if stat is None:
         stat = self.Stat(path).version
       if stat != version:
         uncached.append(path)
         continue
       result[path] = data
 
     if not uncached:
       return Future(value=result)
     return Future(delegate=_AsyncUncachedFuture(
         self._file_system.Read(uncached, binary=binary),
         result,
         self,
-        self._object_store,
-        namespace))
+        read_object_store))