Docserver: Override Walk in CachingFileSystem

chrome/common/extensions/docs/server2/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.
 
 import posixpath
 import traceback
 
 from future import Future
 from path_util import (
     AssertIsDirectory, AssertIsValid, IsDirectory, IsValid, SplitParent,
@@ skipping 137 matching lines @@
 
   def GetIdentity(self):
     '''The identity of the file system, exposed for caching classes to
     namespace their caches. this will usually depend on the configuration of
     that file system - e.g. a LocalFileSystem with a base path of /var is
     different to that of a SubversionFileSystem with a base path of /bar, is
     different to a LocalFileSystem with a base path of /usr.
     '''
     raise NotImplementedError(self.__class__)
 
-  def Walk(self, root, depth=-1):
+  def Walk(self, root, depth=-1, walk_delegate=None):
     '''Recursively walk the directories in a file system, starting with root.
 
     Behaviour is very similar to os.walk from the standard os module, yielding
     (base, dirs, files) recursively, where |base| is the base path of |files|,
     |dirs| relative to |root|, and |files| and |dirs| the list of files/dirs in
     |base| respectively. If |depth| is specified and greater than 0, Walk will
     only recurse |depth| times.
 
+    |walk_delegate|, if specified, should be a callback of signature

[not at google - send to devlin, 2014/08/29 19:28:31]

Neat!

How about a more descriptive name than |walk_delegate|? Something that expresses
that it reads the files and dirs out of a single level of a walk.

+
+      def my_walk_delegate(root):,
+
+    which returns a tuple (dirs, files), where |dirs| is a list of directory
+    names under |root|, and |files| is a list of file names under |root|.
+
     Note that directories will always end with a '/', files never will.
 
     If |root| cannot be found, raises a FileNotFoundError.
     For any other failure, raises a FileSystemError.
     '''
     AssertIsDirectory(root)
     basepath = root
 
     def walk(root, depth):
       if depth == 0:
         return
       AssertIsDirectory(root)
-      dirs, files = [], []
 
-      for f in self.ReadSingle(root).Get():
-        if IsDirectory(f):
-          dirs.append(f)
-        else:
-          files.append(f)
+      if walk_delegate:
+        dirs, files = walk_delegate(root)
+      else:
+        dirs, files = [], []
+        for f in self.ReadSingle(root).Get():
+          if IsDirectory(f):
+            dirs.append(f)
+          else:
+            files.append(f)
 
       yield root[len(basepath):].rstrip('/'), dirs, files
 
       for d in dirs:
         for walkinfo in walk(root + d, depth - 1):
           yield walkinfo
 
     for walkinfo in walk(root, depth):
       yield walkinfo
 
   def __eq__(self, other):
     return (isinstance(other, FileSystem) and
             self.GetIdentity() == other.GetIdentity())
 
   def __ne__(self, other):
     return not (self == other)
 
   def __repr__(self):
     return '<%s>' % type(self).__name__
 
   def __str__(self):
     return repr(self)