Docserver: Add support for viewing docs with a codereview patch applied

chrome/common/extensions/docs/server2/patched_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.
+
+from file_system import FileSystem
+from future import Future
+import logging
+
+class _AsyncFetchFuture(object):
+  def __init__(self, paths, binary, patched_files, svn_file_system,
+      patch_file_system):
+    patched_paths = []
+    unpatched_paths = []
+    for path in paths:
+      if path in patched_files:
+        patched_paths.append(path)
+      else:
+        unpatched_paths.append(path)

[not at google - send to devlin, 2013/04/26 23:53:53]

you may want to use set()s everywhere for these patched paths rather than lists.
It will make this kind of logic much simpler. See set.difference etc.

[方觉(Fang Jue), 2013/04/27 01:02:48]

Done. Python is awesome!

+    logging.info(patched_paths)
+    logging.info(unpatched_paths)
+    self._svn_future = svn_file_system.Read(unpatched_paths, binary)
+    self._patched_future = patch_file_system.Read(patched_paths, binary)

[not at google - send to devlin, 2013/04/26 23:53:53]

Just pass these futures directly in through the constructor.

[方觉(Fang Jue), 2013/04/27 01:02:48]

Done.

+
+  def Get(self):
+    value = self._svn_future.Get()
+    value.update(self._patched_future.Get())
+    return value
+
+class PatchedFileSystem(FileSystem):
+  """ Class to fetch resources with a patch applied.
+  """
+  def __init__(self, patched_files, svn_file_system, patch_file_system):
+    self._patched_files = patched_files
+    self._svn_file_system = svn_file_system
+    self._patch_file_system = patch_file_system
+
+  def Read(self, paths, binary=False):
+    return Future(delegate=_AsyncFetchFuture(
+        paths,
+        binary,
+        self._patched_files,
+        self._svn_file_system,
+        self._patch_file_system))
+
+  # We assume that a patchset, once created, will never change.
+  def Stat(self, path):
+    return self._svn_file_system.Stat(path)