Adding AvailabilityFinder to Doc Server

chrome/common/extensions/docs/server2/availability_finder.py

Index: chrome/common/extensions/docs/server2/availability_finder.py
diff --git a/chrome/common/extensions/docs/server2/availability_finder.py b/chrome/common/extensions/docs/server2/availability_finder.py
new file mode 100644
index 0000000000000000000000000000000000000000..083c2e5138aa525cfa6fa09631fcc9ca619ec337
--- /dev/null
+++ b/chrome/common/extensions/docs/server2/availability_finder.py
@@ -0,0 +1,247 @@
+# Copyright (c) 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 collections
+import os
+
+from branch_utility import BranchUtility
+from compiled_file_system import CompiledFileSystem
+from file_system import FileNotFoundError
+import svn_constants
+from third_party.json_schema_compiler import json_parse, model
+from third_party.json_schema_compiler.memoize import memoize
+
+_API_AVAILABILITIES = svn_constants.JSON_PATH + '/api_availabilities.json'
+_API_FEATURES = svn_constants.API_PATH + '/_api_features.json'
+_EXTENSION_API = svn_constants.API_PATH + '/extension_api.json'
+_MANIFEST_FEATURES = svn_constants.API_PATH + '/_manifest_features.json'
+_PERMISSION_FEATURES = svn_constants.API_PATH + '/_permission_features.json'
+_STABLE = 'stable'
+
+class AvailabilityInfo(object):
+  def __init__(self, channel, version):
+    self.channel = channel
+    self.version = version
+
+def _GetChannelFromFeatures(api_name, file_system, path):
+  '''Finds API channel information within _features.json files at the given
+  |path| for the given |file_system|. Returns None if channel information for
+  the API cannot be located.
+  '''
+  feature = file_system.GetFromFile(path).get(api_name)
+
+  if feature is None:
+    return None
+  if isinstance(feature, collections.Mapping):
+    # The channel information dict is nested within a list for whitelisting
+    # purposes.
+    return feature.get('channel')
+  # Features can contain a list of entries. Take the newest branch.
+  return BranchUtility.NewestChannel(entry.get('channel')
+                                     for entry in feature)
+
+def _GetChannelFromApiFeatures(api_name, file_system):
+  try:
+    return _GetChannelFromFeatures(api_name, file_system, _API_FEATURES)
+  except FileNotFoundError as e:
+    # TODO(epeterson) Remove except block once _api_features is in all channels.
+    return None
+
+def _GetChannelFromPermissionFeatures(api_name, file_system):
+  return _GetChannelFromFeatures(api_name, file_system, _PERMISSION_FEATURES)
+
+def _GetChannelFromManifestFeatures(api_name, file_system):
+  return _GetChannelFromFeatures(#_manifest_features uses unix_style API names
+                                 model.UnixName(api_name),
+                                 file_system,
+                                 _MANIFEST_FEATURES)
+
+def _ExistsInFileSystem(api_name, file_system):
+  '''Checks for existence of |api_name| within the list of files in the api/
+  directory found using the given file system.
+  '''
+  file_names = file_system.GetFromFileListing(svn_constants.API_PATH)
+  # File names switch from unix_hacker_style to camelCase at versions <= 20.
+  return model.UnixName(api_name) in file_names or api_name in file_names
+
+def _ExistsInExtensionApi(api_name, file_system):
+  '''Parses the api/extension_api.json file (available in Chrome versions
+  before 18) for an API namespace. If this is successfully found, then the API
+  is considered to have been 'stable' for the given version.
+  '''
+  try:
+    extension_api_json = file_system.GetFromFile(_EXTENSION_API)
+    api_rows = [row.get('namespace') for row in extension_api_json
+                if 'namespace' in row]
+    return True if api_name in api_rows else False
+  except FileNotFoundError as e:
+    # This should only happen on preview.py since extension_api.json is no
+    # longer present in trunk.
+    return False
+
+class AvailabilityFinder(object):
+  '''Uses API data sources generated by a ChromeVersionDataSource in order to
+  search the filesystem for the earliest existence of a specified API throughout
+  the different versions of Chrome; this constitutes an API's availability.
+  '''
+  class Factory(object):
+    def __init__(self,
+                 object_store_creator,
+                 compiled_host_fs_factory,
+                 branch_utility,
+                 # Takes a |version|, and returns a caching offline or online
+                 # subversion file system for that version.
+                 create_file_system_at_version):
+      self._object_store_creator = object_store_creator
+      self._compiled_host_fs_factory = compiled_host_fs_factory
+      self._branch_utility = branch_utility
+      self._create_file_system_at_version = create_file_system_at_version
+
+    def Create(self):
+      return AvailabilityFinder(self._object_store_creator,
+                                self._compiled_host_fs_factory,
+                                self._branch_utility,
+                                self._create_file_system_at_version)
+
+  def __init__(self,
+               object_store_creator,
+               compiled_host_fs_factory,
+               branch_utility,
+               create_file_system_at_version):
+    self._object_store_creator = object_store_creator
+    self._json_cache = compiled_host_fs_factory.Create(
+        lambda _, json: json_parse.Parse(json),
+        AvailabilityFinder,
+        'json-cache')
+    self._branch_utility = branch_utility
+    self._create_file_system_at_version = create_file_system_at_version
+    self._object_store = object_store_creator.Create(AvailabilityFinder)
+
+  @memoize
+  def _CreateFeaturesAndNamesFileSystems(self, version):
+    '''The 'features' compiled file system's populate function parses and
+    returns the contents of a _features.json file. The 'names' compiled file
+    system's populate function creates a list of file names with .json or .idl
+    extensions.
+    '''
+    fs_factory = CompiledFileSystem.Factory(
+        self._create_file_system_at_version(version),
+        self._object_store_creator)
+    features_fs = fs_factory.Create(lambda _, json: json_parse.Parse(json),
+                                    AvailabilityFinder,
+                                    category='features')
+    names_fs = fs_factory.Create(self._GetExtNames,
+                                 AvailabilityFinder,
+                                 category='names')
+    return (features_fs, names_fs)
+
+  def _GetExtNames(self, base_path, apis):
+    return [os.path.splitext(api)[0] for api in apis
+            if os.path.splitext(api)[1][1:] in ['json', 'idl']]
+
+  def _FindEarliestStableAvailability(self, api_name, version):
+    '''Searches in descending order through filesystem caches tied to specific
+    chrome version numbers and looks for the availability of an API, |api_name|,
+    on the stable channel. When a version is found where the API is no longer
+    available on stable, returns the previous version number (the last known
+    version where the API was stable).
+    '''
+    available = True
+    while available:
+      if version < 5:
+        # SVN data isn't available below version 5.
+        return version + 1
+      available = False
+      features_fs, names_fs = self._CreateFeaturesAndNamesFileSystems(version)
+      if version >= 28:
+        # The _api_features.json file first appears in version 28 and should be
+        # the most reliable for finding API availabilities, so it gets checked
+        # first. The _permission_features.json and _manifest_features.json files
+        # are present in Chrome 20 and onwards. Fall back to a check for file
+        # system existence if the API is not stable in any of the _features.json
+        # files.
+        available = _GetChannelFromApiFeatures(api_name, features_fs) == _STABLE
+      if version >= 20:
+        # Check other _features.json files/file existence if the API wasn't
+        # found in _api_features.json, or if _api_features.json wasn't present.
+        available = available or (
+            _GetChannelFromPermissionFeatures(api_name, features_fs) == _STABLE
+            or _GetChannelFromManifestFeatures(api_name, features_fs) == _STABLE
+            or _ExistsInFileSystem(api_name, names_fs))
+      elif version >= 18:
+        # These versions are a little troublesome. Version 19 has
+        # _permission_features.json, but it lacks 'channel' information.
+        # Version 18 lacks all of the _features.json files. For now, we're using
+        # a simple check for filesystem existence here.
+        available = _ExistsInFileSystem(api_name, names_fs)
+      elif version >= 5:
+        # Versions 17 and down to 5 have an extension_api.json file which
+        # contains namespaces for each API that was available at the time. We
+        # can use this file to check for API existence.
+        available = _ExistsInExtensionApi(api_name, features_fs)
+
+      if not available:
+        return version + 1
+      version -= 1
+
+  def _GetAvailableChannelForVersion(self, api_name, version):
+    '''Searches through the _features files for a given |version| and returns
+    the channel that the given API is determined to be available on.
+    '''
+    features_fs, names_fs = self._CreateFeaturesAndNamesFileSystems(version)
+    channel = (_GetChannelFromApiFeatures(api_name, features_fs)
+               or _GetChannelFromPermissionFeatures(api_name, features_fs)
+               or _GetChannelFromManifestFeatures(api_name, features_fs))
+    if channel is None and _ExistsInFileSystem(api_name, names_fs):
+      # If an API is not represented in any of the _features files, but exists
+      # in the filesystem, then assume it is available in this version.
+      # The windows API is an example of this.
+      return self._branch_utility.GetChannelForVersion(version)
+
+    return channel
+
+  def GetApiAvailability(self, api_name):
+    '''Determines the availability for an API by testing several scenarios.
+    (i.e. Is the API experimental? Only available on certain development
+    channels? If it's stable, when did it first become stable? etc.)
+    '''
+    availability = self._object_store.Get(api_name).Get()
+    if availability is not None:
+      return availability
+
+    # Check for a predetermined availability for this API.
+    api_info = self._json_cache.GetFromFile(_API_AVAILABILITIES).get(api_name)
+    if api_info is not None:
+      channel = api_info.get('channel')
+      return AvailabilityInfo(
+          channel,
+          api_info.get('version') if channel == _STABLE else None)
+
+    # Check for the API in the development channels.
+    availability = None
+    for channel_info in self._branch_utility.GetAllChannelInfo():
+      available_channel = self._GetAvailableChannelForVersion(
+          api_name,
+          channel_info.version)
+      # If the |available_channel| for the API is the same as, or older than,
+      # the channel we're checking, then the API is available on this channel.
+      if (available_channel is not None and
+          BranchUtility.NewestChannel((available_channel, channel_info.channel))
+              == channel_info.channel):
+        availability = AvailabilityInfo(channel_info.channel,
+                                        channel_info.version)
+        break
+
+    # The API should at least be available on trunk. It's a bug otherwise.
+    assert availability, 'No availability found for %s' % api_name
+
+    # If the API is in stable, find the chrome version in which it became
+    # stable.
+    if availability.channel == _STABLE:
+      availability.version = self._FindEarliestStableAvailability(
+          api_name,
+          availability.version)
+
+    self._object_store.Set(api_name, availability)
+    return availability