Extensions Docs Server: Uniform handling of file not found errors

chrome/common/extensions/docs/server2/server_instance.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 fnmatch import fnmatch
 import mimetypes
 import os
 
+from file_system import FileNotFoundError
+
 STATIC_DIR_PREFIX = 'docs/server2'
 DOCS_PATH = 'docs'
 
 class ServerInstance(object):
   """This class is used to hold a data source and fetcher for an instance of a
   server. Each new branch will get its own ServerInstance.
   """
   def __init__(self,
                template_data_source_factory,
                example_zipper,
                cache_builder):
     self._template_data_source_factory = template_data_source_factory
     self._example_zipper = example_zipper
     self._cache = cache_builder.build(lambda x: x)
     mimetypes.init()
 
   def _FetchStaticResource(self, path, response):
     """Fetch a resource in the 'static' directory.
     """
     try:
       result = self._cache.GetFromFile(STATIC_DIR_PREFIX + '/' + path)
       base, ext = os.path.splitext(path)
       response.headers['content-type'] = mimetypes.types_map[ext]
       return result
-    except Exception:
-      return ''
+    except FileNotFoundError:
+      return None
 
   def Get(self, path, request, response):
     templates = self._template_data_source_factory.Create(request)
 
     if fnmatch(path, 'extensions/examples/*.zip'):
       content = self._example_zipper.Create(
           path[len('extensions/'):-len('.zip')])
       response.headers['content-type'] = mimetypes.types_map['.zip']
     elif path.startswith('extensions/examples/'):
       content = self._cache.GetFromFile(
           DOCS_PATH + '/' + path[len('extensions/'):])
       response.headers['content-type'] = 'text/plain'
     elif path.startswith('static/'):
       content = self._FetchStaticResource(path, response)
     else:
       content = templates.Render(path)
 
     if content:
       response.out.write(content)
     else:
       response.set_status(404);
       response.out.write(templates.Render('404'))