Source Code for Module googleapiclient.discovery_cache.file_cache

  1  # Copyright 2014 Google Inc. All Rights Reserved. 
  2  # 
  3  # Licensed under the Apache License, Version 2.0 (the "License"); 
  4  # you may not use this file except in compliance with the License. 
  5  # You may obtain a copy of the License at 
  6  # 
  7  #      http://www.apache.org/licenses/LICENSE-2.0 
  8  # 
  9  # Unless required by applicable law or agreed to in writing, software 
 10  # distributed under the License is distributed on an "AS IS" BASIS, 
 11  # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 
 12  # See the License for the specific language governing permissions and 
 13  # limitations under the License. 
 14   
 15  """File based cache for the discovery document. 
 16   
 17  The cache is stored in a single file so that multiple processes can 
 18  share the same cache. It locks the file whenever accesing to the 
 19  file. When the cache content is corrupted, it will be initialized with 
 20  an empty cache. 
 21  """ 
 22   
 23  from __future__ import division 
 24   
 25  import datetime 
 26  import json 
 27  import logging 
 28  import os 
 29  import tempfile 
 30  import threading 
 31   
 32  try: 
 33    from oauth2client.contrib.locked_file import LockedFile 
 34  except ImportError: 
 35    # oauth2client < 2.0.0 
 36    try: 
 37      from oauth2client.locked_file import LockedFile 
 38    except ImportError: 
 39      # oauth2client > 4.0.0 
 40      raise ImportError( 
 41        'file_cache is unavailable when using oauth2client >= 4.0.0') 
 42   
 43  from . import base 
 44  from ..discovery_cache import DISCOVERY_DOC_MAX_AGE 
 45   
 46  LOGGER = logging.getLogger(__name__) 
 47   
 48  FILENAME = 'google-api-python-client-discovery-doc.cache' 
 49  EPOCH = datetime.datetime.utcfromtimestamp(0) 
 50   
 51   
 52 -def _to_timestamp(date): 
 53    try: 
 54      return (date - EPOCH).total_seconds() 
 55    except AttributeError: 
 56      # The following is the equivalent of total_seconds() in Python2.6. 
 57      # See also: https://docs.python.org/2/library/datetime.html 
 58      delta = date - EPOCH 
 59      return ((delta.microseconds + (delta.seconds + delta.days * 24 * 3600) 
 60               * 10**6) / 10**6) 
 61   
 62   
 63 -def _read_or_initialize_cache(f): 
 64    f.file_handle().seek(0) 
 65    try: 
 66      cache = json.load(f.file_handle()) 
 67    except Exception: 
 68      # This means it opens the file for the first time, or the cache is 
 69      # corrupted, so initializing the file with an empty dict. 
 70      cache = {} 
 71      f.file_handle().truncate(0) 
 72      f.file_handle().seek(0) 
 73      json.dump(cache, f.file_handle()) 
 74    return cache 
 75   
 76   
 77 -class Cache(base.Cache): 
 78    """A file based cache for the discovery documents.""" 
 79   
 80 -  def __init__(self, max_age): 
 81        """Constructor. 
 82   
 83        Args: 
 84          max_age: Cache expiration in seconds. 
 85        """ 
 86        self._max_age = max_age 
 87        self._file = os.path.join(tempfile.gettempdir(), FILENAME) 
 88        f = LockedFile(self._file, 'a+', 'r') 
 89        try: 
 90          f.open_and_lock() 
 91          if f.is_locked(): 
 92            _read_or_initialize_cache(f) 
 93          # If we can not obtain the lock, other process or thread must 
 94          # have initialized the file. 
 95        except Exception as e: 
 96          LOGGER.warning(e, exc_info=True) 
 97        finally: 
 98          f.unlock_and_close() 
 99   
100 -  def get(self, url): 
101      f = LockedFile(self._file, 'r+', 'r') 
102      try: 
103        f.open_and_lock() 
104        if f.is_locked(): 
105          cache = _read_or_initialize_cache(f) 
106          if url in cache: 
107            content, t = cache.get(url, (None, 0)) 
108            if _to_timestamp(datetime.datetime.now()) < t + self._max_age: 
109              return content 
110          return None 
111        else: 
112          LOGGER.debug('Could not obtain a lock for the cache file.') 
113          return None 
114      except Exception as e: 
115        LOGGER.warning(e, exc_info=True) 
116      finally: 
117        f.unlock_and_close() 
118   
119 -  def set(self, url, content): 
120      f = LockedFile(self._file, 'r+', 'r') 
121      try: 
122        f.open_and_lock() 
123        if f.is_locked(): 
124          cache = _read_or_initialize_cache(f) 
125          cache[url] = (content, _to_timestamp(datetime.datetime.now())) 
126          # Remove stale cache. 
127          for k, (_, timestamp) in list(cache.items()): 
128            if _to_timestamp(datetime.datetime.now()) >= timestamp + self._max_age: 
129              del cache[k] 
130          f.file_handle().truncate(0) 
131          f.file_handle().seek(0) 
132          json.dump(cache, f.file_handle()) 
133        else: 
134          LOGGER.debug('Could not obtain a lock for the cache file.') 
135      except Exception as e: 
136        LOGGER.warning(e, exc_info=True) 
137      finally: 
138        f.unlock_and_close() 
139   
140   
141  cache = Cache(max_age=DISCOVERY_DOC_MAX_AGE) 
142