Package googleapiclient :: Package discovery_cache :: Module file_cache
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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    from oauth2client.locked_file import LockedFile 
 37   
 38  from . import base 
 39  from ..discovery_cache import DISCOVERY_DOC_MAX_AGE 
 40   
 41  LOGGER = logging.getLogger(__name__) 
 42   
 43  FILENAME = 'google-api-python-client-discovery-doc.cache' 
 44  EPOCH = datetime.datetime.utcfromtimestamp(0) 
 45   
 46   
47 -def _to_timestamp(date):
48 try: 49 return (date - EPOCH).total_seconds() 50 except AttributeError: 51 # The following is the equivalent of total_seconds() in Python2.6. 52 # See also: https://docs.python.org/2/library/datetime.html 53 delta = date - EPOCH 54 return ((delta.microseconds + (delta.seconds + delta.days * 24 * 3600) 55 * 10**6) / 10**6)
56 57
58 -def _read_or_initialize_cache(f):
59 f.file_handle().seek(0) 60 try: 61 cache = json.load(f.file_handle()) 62 except Exception: 63 # This means it opens the file for the first time, or the cache is 64 # corrupted, so initializing the file with an empty dict. 65 cache = {} 66 f.file_handle().truncate(0) 67 f.file_handle().seek(0) 68 json.dump(cache, f.file_handle()) 69 return cache
70 71
72 -class Cache(base.Cache):
73 """A file based cache for the discovery documents.""" 74
75 - def __init__(self, max_age):
76 """Constructor. 77 78 Args: 79 max_age: Cache expiration in seconds. 80 """ 81 self._max_age = max_age 82 self._file = os.path.join(tempfile.gettempdir(), FILENAME) 83 f = LockedFile(self._file, 'a+', 'r') 84 try: 85 f.open_and_lock() 86 if f.is_locked(): 87 _read_or_initialize_cache(f) 88 # If we can not obtain the lock, other process or thread must 89 # have initialized the file. 90 except Exception as e: 91 LOGGER.warning(e, exc_info=True) 92 finally: 93 f.unlock_and_close()
94
95 - def get(self, url):
96 f = LockedFile(self._file, 'r+', 'r') 97 try: 98 f.open_and_lock() 99 if f.is_locked(): 100 cache = _read_or_initialize_cache(f) 101 if url in cache: 102 content, t = cache.get(url, (None, 0)) 103 if _to_timestamp(datetime.datetime.now()) < t + self._max_age: 104 return content 105 return None 106 else: 107 LOGGER.debug('Could not obtain a lock for the cache file.') 108 return None 109 except Exception as e: 110 LOGGER.warning(e, exc_info=True) 111 finally: 112 f.unlock_and_close()
113
114 - def set(self, url, content):
115 f = LockedFile(self._file, 'r+', 'r') 116 try: 117 f.open_and_lock() 118 if f.is_locked(): 119 cache = _read_or_initialize_cache(f) 120 cache[url] = (content, _to_timestamp(datetime.datetime.now())) 121 # Remove stale cache. 122 for k, (_, timestamp) in list(cache.items()): 123 if _to_timestamp(datetime.datetime.now()) >= timestamp + self._max_age: 124 del cache[k] 125 f.file_handle().truncate(0) 126 f.file_handle().seek(0) 127 json.dump(cache, f.file_handle()) 128 else: 129 LOGGER.debug('Could not obtain a lock for the cache file.') 130 except Exception as e: 131 LOGGER.warning(e, exc_info=True) 132 finally: 133 f.unlock_and_close()
134 135 136 cache = Cache(max_age=DISCOVERY_DOC_MAX_AGE) 137