Docserver: Add FileSystem.Exists method and start sanity checking path format

chrome/common/extensions/docs/server2/path_util.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
+
+
+# TODO(kalman): Write a Path class and use that everywhere rather than a
+# utility class.
+
+
+def IsDirectory(path):
+  '''Returns whether |path| should be considered a directory.
+  '''
+  # This assertion is sprinkled throughout the code base.
+  assert not path.startswith('/'), path
+  return path == '' or path.endswith('/')
+
+
+def SplitParent(path):
+  '''Returns the parent directory and base name of |path| in a tuple.
+  Any trailing slash of |path| is preserved, such that the parent of
+  '/hello/world/' is '/hello' and the base is 'world/'.
+  '''
+  parent, base = posixpath.split(path.rstrip('/'))
+  if path.endswith('/'):
+    base += '/'
+  return parent, base
+
+
+def ToDirectory(path):
+  '''Returns a string representing |path| as a directory, that is,
+  IsDirectory(result) is True (and does not fail assertions). If |path| is
+  already a directory then this is a no-op.
+  '''
+  return path if IsDirectory(path) else (path + '/')