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  from oauth2client.contrib.locked_file import LockedFile
     33
     34  from . import base
     35  from ..discovery_cache import DISCOVERY_DOC_MAX_AGE
     36
     37  logger = logging.getLogger(__name__)
     38
     39  FILENAME = 'google-api-python-client-discovery-doc.cache'
     40  EPOCH = datetime.datetime.utcfromtimestamp(0)
     41
     42
     43 -def _to_timestamp(date):
     44    try:
     45      return (date - EPOCH).total_seconds()
     46    except AttributeError:
     47      # The following is the equivalent of total_seconds() in Python2.6.
     48      # See also: https://docs.python.org/2/library/datetime.html
     49      delta = date - EPOCH
     50      return ((delta.microseconds + (delta.seconds + delta.days * 24 * 3600)
     51               * 10**6) / 10**6)
     52
     53
     54 -def _read_or_initialize_cache(f):
     55    f.file_handle().seek(0)
     56    try:
     57      cache = json.load(f.file_handle())
     58    except Exception:
     59      # This means it opens the file for the first time, or the cache is
     60      # corrupted, so initializing the file with an empty dict.
     61      cache = {}
     62      f.file_handle().truncate(0)
     63      f.file_handle().seek(0)
     64      json.dump(cache, f.file_handle())
     65    return cache
     66
     67
     68 -class Cache(base.Cache):
     69    """A file based cache for the discovery documents."""
     70
     71 -  def __init__(self, max_age):
     72        """Constructor.
     73
     74        Args:
     75          max_age: Cache expiration in seconds.
     76        """
     77        self._max_age = max_age
     78        self._file = os.path.join(tempfile.gettempdir(), FILENAME)
     79        f = LockedFile(self._file, 'a+', 'r')
     80        try:
     81          f.open_and_lock()
     82          if f.is_locked():
     83            _read_or_initialize_cache(f)
     84          # If we can not obtain the lock, other process or thread must
     85          # have initialized the file.
     86        except Exception as e:
     87          logging.warning(e, exc_info=True)
     88        finally:
     89          f.unlock_and_close()
     90
     91 -  def get(self, url):
     92      f = LockedFile(self._file, 'r+', 'r')
     93      try:
     94        f.open_and_lock()
     95        if f.is_locked():
     96          cache = _read_or_initialize_cache(f)
     97          if url in cache:
     98            content, t = cache.get(url, (None, 0))
     99            if _to_timestamp(datetime.datetime.now()) < t + self._max_age:
    100              return content
    101          return None
    102        else:
    103          logger.debug('Could not obtain a lock for the cache file.')
    104          return None
    105      except Exception as e:
    106        logger.warning(e, exc_info=True)
    107      finally:
    108        f.unlock_and_close()
    109
    110 -  def set(self, url, content):
    111      f = LockedFile(self._file, 'r+', 'r')
    112      try:
    113        f.open_and_lock()
    114        if f.is_locked():
    115          cache = _read_or_initialize_cache(f)
    116          cache[url] = (content, _to_timestamp(datetime.datetime.now()))
    117          # Remove stale cache.
    118          for k, (_, timestamp) in list(cache.items()):
    119            if _to_timestamp(datetime.datetime.now()) >= timestamp + self._max_age:
    120              del cache[k]
    121          f.file_handle().truncate(0)
    122          f.file_handle().seek(0)
    123          json.dump(cache, f.file_handle())
    124        else:
    125          logger.debug('Could not obtain a lock for the cache file.')
    126      except Exception as e:
    127        logger.warning(e, exc_info=True)
    128      finally:
    129        f.unlock_and_close()
    130
    131
    132  cache = Cache(max_age=DISCOVERY_DOC_MAX_AGE)
    133