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

   1 # Copyright 2013 The Chromium Authors. All rights reserved.
   2 # Use of this source code is governed by a BSD-style license that can be
   3 # found in the LICENSE file.
   4
   5 import logging
   6
   7 from extensions_paths import APP_YAML
   8
   9
  10 _APP_YAML_CONTAINER = '''
  11 application: chrome-apps-doc
  12 version: %s
  13 runtime: python27
  14 api_version: 1
  15 threadsafe: false
  16 '''
  17
  18
  19 class AppYamlHelper(object):
  20   '''Parses the app.yaml file, and is able to step back in the host file
  21   system's revision history to find when it changed to some given version.
  22   '''
  23   def __init__(self,
  24                object_store_creator,
  25                host_file_system_provider):
  26     self._store = object_store_creator.Create(
  27         AppYamlHelper,
  28         category=host_file_system_provider.GetTrunk().GetIdentity(),
  29         start_empty=False)
  30     self._host_file_system_provider = host_file_system_provider
  31
  32   @staticmethod
  33   def ExtractVersion(app_yaml, key='version'):
  34     '''Extracts the 'version' key from the contents of an app.yaml file.
  35     Allow overriding the key to parse e.g. the cron file ('target').
  36     '''
  37     # We could properly parse this using a yaml library but Python doesn't have
  38     # one built in so whatevs.
  39     key_colon = '%s:' % key
  40     versions = [line.strip()[len(key_colon):].strip()
  41                 for line in app_yaml.split('\n')
  42                 if line.strip().startswith(key_colon)]
  43     if not versions:
  44       raise ValueError('No versions found for %s in %s' % (
  45           key, app_yaml))
  46     if len(set(versions)) > 1:
  47       raise ValueError('Inconsistent versions found for %s in %s: %s' % (
  48           key, app_yaml, versions))
  49     return versions[0]
  50
  51   @staticmethod
  52   def IsGreater(lhs, rhs):
  53     '''Return whether the app.yaml version |lhs| > |rhs|. This is tricky
  54     because versions are typically not numbers but rather 2-0-9, 2-0-12,
  55     2-1-0, etc - and 2-1-0 > 2-0-10 > 2-0-9.
  56     '''
  57     lhs_parts = lhs.replace('-', '.').split('.')
  58     rhs_parts = rhs.replace('-', '.').split('.')
  59     while lhs_parts and rhs_parts:
  60       lhs_msb = int(lhs_parts.pop(0))
  61       rhs_msb = int(rhs_parts.pop(0))
  62       if lhs_msb != rhs_msb:
  63         return lhs_msb > rhs_msb
  64     return len(lhs) > len(rhs)
  65
  66   @staticmethod
  67   def GenerateAppYaml(version):
  68     '''Probably only useful for tests.
  69     '''
  70     return _APP_YAML_CONTAINER % version
  71
  72   def IsUpToDate(self, app_version):
  73     '''Returns True if the |app_version| is up to date with respect to the one
  74     checked into the host file system.
  75     '''
  76     checked_in_app_version = AppYamlHelper.ExtractVersion(
  77         self._host_file_system_provider.GetTrunk().ReadSingle(APP_YAML).Get())
  78     if app_version == checked_in_app_version:
  79       return True
  80     if AppYamlHelper.IsGreater(app_version, checked_in_app_version):
  81       logging.warning(
  82           'Server is too new! Checked in %s < currently running %s' % (
  83               checked_in_app_version, app_version))
  84       return True
  85     return False
  86
  87   def GetFirstRevisionGreaterThan(self, app_version):
  88     '''Finds the first revision that the version in app.yaml was greater than
  89     |app_version|.
  90
  91     WARNING: if there is no such revision (e.g. the app is up to date, or
  92     *oops* the app is even newer) then this will throw a ValueError. Use
  93     IsUpToDate to validate the input before calling this method.
  94     '''
  95     stored = self._store.Get(app_version).Get()
  96     if stored is None:
  97       stored = self._GetFirstRevisionGreaterThanImpl(app_version)
  98       assert stored is not None
  99       self._store.Set(app_version, stored)
 100     return stored
 101
 102   def _GetFirstRevisionGreaterThanImpl(self, app_version):
 103     def get_app_yaml_revision(file_system):
 104       return int(file_system.Stat(APP_YAML).version)
 105
 106     def has_greater_app_version(file_system):
 107       app_version_in_file_system = AppYamlHelper.ExtractVersion(
 108           file_system.ReadSingle(APP_YAML).Get())
 109       return AppYamlHelper.IsGreater(app_version_in_file_system, app_version)
 110
 111     found = None
 112     next_file_system = self._host_file_system_provider.GetTrunk()
 113
 114     while has_greater_app_version(next_file_system):
 115       found = get_app_yaml_revision(next_file_system)
 116       # Back up a revision then find when app.yaml was last updated before then.
 117       if found == 0:
 118         logging.warning('All revisions are greater than %s' % app_version)
 119         return 0
 120       next_file_system = self._host_file_system_provider.GetTrunk(
 121           revision=found - 1)
 122
 123     if found is None:
 124       raise ValueError('All revisions are less than %s' % app_version)
 125     return found