Refactor the devserver to make it easier to control caching

chrome/common/extensions/docs/server2/intro_data_source.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 HTMLParser import HTMLParser
 import logging
 import os
 import re
 
 from docs_server_utils import FormatKey
 from file_system import FileNotFoundError
 import compiled_file_system as compiled_fs
 from third_party.handlebar import Handlebar
 
-# Increment this version if there are changes to the table of contents dict that
-# IntroDataSource caches.
-_VERSION = 4
+# TODO(kalman): rename this HTMLDataSource or other, then have separate intro
+# article data sources created as instances of it.
+
+# Increment this if the data model changes for IntroDataSource.
+_VERSION = 5
 
 _H1_REGEX = re.compile('<h1[^>.]*?>.*?</h1>', flags=re.DOTALL)
 
 class _IntroParser(HTMLParser):
   """ An HTML parser which will parse table of contents and page title info out
   of an intro.
   """
   def __init__(self):
     HTMLParser.__init__(self)
     self.toc = []
@@ skipping 30 matching lines @@
       else:
         self.page_title += data
     elif self._recent_tag in ['h2', 'h3']:
       self._current_heading['title'] += data
 
 class IntroDataSource(object):
   """This class fetches the intros for a given API. From this intro, a table
   of contents dictionary is created, which contains the headings in the intro.
   """
   class Factory(object):
-    def __init__(self, cache_factory, ref_resolver_factory, base_paths):
-      self._cache = cache_factory.Create(self._MakeIntroDict,
-                                         compiled_fs.INTRO,
-                                         version=_VERSION)
+    def __init__(self, compiled_fs_factory, ref_resolver_factory, base_paths):
+      self._cache = compiled_fs_factory.Create(self._MakeIntroDict,
+                                               IntroDataSource,
+                                               version=_VERSION)
       self._ref_resolver = ref_resolver_factory.Create()
       self._base_paths = base_paths
 
     def _MakeIntroDict(self, intro_path, intro):
       # Guess the name of the API from the path to the intro.
       api_name = os.path.splitext(intro_path.split('/')[-1])[0]
       intro_with_links = self._ref_resolver.ResolveAllLinks(intro,
                                                             namespace=api_name)
       apps_parser = _IntroParser()
       apps_parser.feed(Handlebar(intro_with_links).render(
@@ skipping 18 matching lines @@
       }
 
     def Create(self):
       return IntroDataSource(self._cache, self._base_paths)
 
   def __init__(self, cache, base_paths):
     self._cache = cache
     self._base_paths = base_paths
 
   def get(self, key):
-    real_path = FormatKey(key)
-    error = None
+    path = FormatKey(key)
+    def get_from_base_path(base_path):
+      return self._cache.GetFromFile('%s/%s' % (base_path, path))
     for base_path in self._base_paths:
       try:
-        return self._cache.GetFromFile(base_path + '/' + real_path)
-      except FileNotFoundError as error:
-        pass
-    raise ValueError(str(error) + ': No intro found for "%s".' % key)
+        return get_from_base_path(base_path)
+      except FileNotFoundError:
+        continue
+    # Not found. Do the first operation again so that we get a stack trace - we
+    # know that it'll fail.
+    get_from_base_path(self._base_paths[0])
+    raise AssertionError()