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    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