Fixed #20536 -- rewrite of the file based cache backend
* Safer for use in multiprocess environments * Better random culling * Cache files use less disk space * Safer delete behavior Also fixed #15806, fixed #15825.
This commit is contained in:
Jaap Roes
Anssi Kääriäinen
parent
ac2d86f8d3
commit
7be638390e
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@ -1,156 +1,156 @@
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"File-based cache backend"
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import errno
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import glob
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import hashlib
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import io
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import os
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import shutil
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import random
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import tempfile
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import time
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import zlib
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from django.core.cache.backends.base import BaseCache, DEFAULT_TIMEOUT
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from django.core.files.move import file_move_safe
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from django.utils.encoding import force_bytes
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try:
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from django.utils.six.moves import cPickle as pickle
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except ImportError:
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import pickle
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from django.core.cache.backends.base import BaseCache, DEFAULT_TIMEOUT
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from django.utils.encoding import force_bytes
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class FileBasedCache(BaseCache):
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cache_suffix = '.djcache'
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def __init__(self, dir, params):
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BaseCache.__init__(self, params)
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self._dir = dir
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if not os.path.exists(self._dir):
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super(FileBasedCache, self).__init__(params)
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self._dir = os.path.abspath(dir)
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self._createdir()
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def add(self, key, value, timeout=DEFAULT_TIMEOUT, version=None):
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if self.has_key(key, version=version):
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if self.has_key(key, version):
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return False
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self.set(key, value, timeout, version=version)
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self.set(key, value, timeout, version)
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return True
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def get(self, key, default=None, version=None):
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key = self.make_key(key, version=version)
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self.validate_key(key)
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fname = self._key_to_file(key)
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fname = self._key_to_file(key, version)
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if os.path.exists(fname):
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try:
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with open(fname, 'rb') as f:
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exp = pickle.load(f)
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now = time.time()
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if exp is not None and exp < now:
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self._delete(fname)
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else:
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return pickle.load(f)
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except (IOError, OSError, EOFError, pickle.PickleError):
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pass
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with io.open(fname, 'rb') as f:
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if not self._is_expired(f):
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return pickle.loads(zlib.decompress(f.read()))
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except IOError as e:
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if e.errno == errno.ENOENT:
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pass # Cache file was removed after the exists check
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return default
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def set(self, key, value, timeout=DEFAULT_TIMEOUT, version=None):
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key = self.make_key(key, version=version)
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self.validate_key(key)
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fname = self._key_to_file(key)
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dirname = os.path.dirname(fname)
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self._cull()
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self._createdir() # Cache dir can be deleted at any time.
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fname = self._key_to_file(key, version)
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self._cull() # make some room if necessary
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fd, tmp_path = tempfile.mkstemp(dir=self._dir)
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renamed = False
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try:
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if not os.path.exists(dirname):
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os.makedirs(dirname)
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with open(fname, 'wb') as f:
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with io.open(fd, 'wb') as f:
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expiry = self.get_backend_timeout(timeout)
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pickle.dump(expiry, f, pickle.HIGHEST_PROTOCOL)
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pickle.dump(value, f, pickle.HIGHEST_PROTOCOL)
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except (IOError, OSError):
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pass
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f.write(pickle.dumps(expiry, -1))
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f.write(zlib.compress(pickle.dumps(value), -1))
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file_move_safe(tmp_path, fname, allow_overwrite=True)
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renamed = True
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finally:
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if not renamed:
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os.remove(tmp_path)
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def delete(self, key, version=None):
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key = self.make_key(key, version=version)
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self.validate_key(key)
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try:
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self._delete(self._key_to_file(key))
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except (IOError, OSError):
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pass
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self._delete(self._key_to_file(key, version))
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def _delete(self, fname):
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os.remove(fname)
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if not fname.startswith(self._dir) or not os.path.exists(fname):
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return
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try:
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# Remove the 2 subdirs if they're empty
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dirname = os.path.dirname(fname)
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os.rmdir(dirname)
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os.rmdir(os.path.dirname(dirname))
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except (IOError, OSError):
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pass
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os.remove(fname)
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except OSError as e:
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# ENOENT can happen if the cache file is removed (by another
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# process) after the os.path.exists check.
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if e.errno != errno.ENOENT:
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raise
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def has_key(self, key, version=None):
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key = self.make_key(key, version=version)
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self.validate_key(key)
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fname = self._key_to_file(key)
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try:
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with open(fname, 'rb') as f:
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exp = pickle.load(f)
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now = time.time()
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if exp < now:
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self._delete(fname)
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return False
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else:
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return True
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except (IOError, OSError, EOFError, pickle.PickleError):
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fname = self._key_to_file(key, version)
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if os.path.exists(fname):
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with io.open(fname, 'rb') as f:
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return not self._is_expired(f)
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return False
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def _cull(self):
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if int(self._num_entries) < self._max_entries:
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return
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try:
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filelist = sorted(os.listdir(self._dir))
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except (IOError, OSError):
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return
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"""
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Removes random cache entries if max_entries is reached at a ratio
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of num_entries / cull_frequency. A value of 0 for CULL_FREQUENCY means
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that the entire cache will be purged.
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"""
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filelist = self._list_cache_files()
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num_entries = len(filelist)
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if num_entries < self._max_entries:
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return # return early if no culling is required
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if self._cull_frequency == 0:
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doomed = filelist
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else:
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doomed = [os.path.join(self._dir, k) for (i, k) in enumerate(filelist) if i % self._cull_frequency == 0]
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for topdir in doomed:
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try:
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for root, _, files in os.walk(topdir):
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for f in files:
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self._delete(os.path.join(root, f))
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except (IOError, OSError):
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pass
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return self.clear() # Clear the cache when CULL_FREQUENCY = 0
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# Delete a random selection of entries
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filelist = random.sample(filelist,
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int(num_entries / self._cull_frequency))
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for fname in filelist:
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self._delete(fname)
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def _createdir(self):
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if not os.path.exists(self._dir):
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try:
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os.makedirs(self._dir)
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except OSError:
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raise EnvironmentError("Cache directory '%s' does not exist and could not be created'" % self._dir)
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os.makedirs(self._dir, 0o700)
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except OSError as e:
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if e.errno != errno.EEXIST:
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raise EnvironmentError(
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"Cache directory '%s' does not exist "
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"and could not be created'" % self._dir)
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def _key_to_file(self, key):
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def _key_to_file(self, key, version=None):
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"""
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Convert the filename into an md5 string. We'll turn the first couple
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bits of the path into directory prefixes to be nice to filesystems
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that have problems with large numbers of files in a directory.
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Thus, a cache key of "foo" gets turnned into a file named
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``{cache-dir}ac/bd/18db4cc2f85cedef654fccc4a4d8``.
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Convert a key into a cache file path. Basically this is the
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root cache path joined with the md5sum of the key and a suffix.
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"""
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path = hashlib.md5(force_bytes(key)).hexdigest()
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path = os.path.join(path[:2], path[2:4], path[4:])
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return os.path.join(self._dir, path)
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def _get_num_entries(self):
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count = 0
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for _, _, files in os.walk(self._dir):
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count += len(files)
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return count
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_num_entries = property(_get_num_entries)
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key = self.make_key(key, version=version)
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self.validate_key(key)
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return os.path.join(self._dir, ''.join(
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[hashlib.md5(force_bytes(key)).hexdigest(), self.cache_suffix]))
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def clear(self):
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try:
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shutil.rmtree(self._dir)
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except (IOError, OSError):
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pass
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"""
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Remove all the cache files.
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"""
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if not os.path.exists(self._dir):
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return
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for fname in self._list_cache_files():
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self._delete(fname)
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def _is_expired(self, f):
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"""
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Takes an open cache file and determines if it has expired,
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deletes the file if it is has passed its expiry time.
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"""
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exp = pickle.load(f)
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if exp is not None and exp < time.time():
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f.close() # On Windows a file has to be closed before deleting
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self._delete(f.name)
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return True
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return False
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def _list_cache_files(self):
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"""
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Get a list of paths to all the cache files. These are all the files
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in the root cache dir that end on the cache_suffix.
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"""
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if not os.path.exists(self._dir):
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return []
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filelist = [os.path.join(self._dir, fname) for fname
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in glob.glob1(self._dir, '*%s' % self.cache_suffix)]
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return filelist
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# For backwards compatibility
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@ -253,10 +253,11 @@ model.
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Filesystem caching
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------------------
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To store cached items on a filesystem, use
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``"django.core.cache.backends.filebased.FileBasedCache"`` for
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:setting:`BACKEND <CACHES-BACKEND>`. For example, to store cached data in
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``/var/tmp/django_cache``, use this setting::
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The file-based backend serializes and stores each cache value as a separate
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file. To use this backend set :setting:`BACKEND <CACHES-BACKEND>` to
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``"django.core.cache.backends.filebased.FileBasedCache"`` and
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:setting:`LOCATION <CACHES-LOCATION>` to a suitable directory. For example,
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to store cached data in ``/var/tmp/django_cache``, use this setting::
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CACHES = {
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'default': {
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@ -265,7 +266,6 @@ To store cached items on a filesystem, use
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}
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}
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If you're on Windows, put the drive letter at the beginning of the path,
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like this::
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@ -286,10 +286,6 @@ above example, if your server runs as the user ``apache``, make sure the
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directory ``/var/tmp/django_cache`` exists and is readable and writable by the
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user ``apache``.
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Each cache value will be stored as a separate file whose contents are the
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cache data saved in a serialized ("pickled") format, using Python's ``pickle``
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module. Each file's name is the cache key, escaped for safe filesystem use.
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Local-memory caching
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--------------------
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@ -1076,33 +1076,35 @@ class FileBasedCacheTests(unittest.TestCase, BaseCacheTests):
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def tearDown(self):
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self.cache.clear()
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def test_hashing(self):
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"""Test that keys are hashed into subdirectories correctly"""
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self.cache.set("foo", "bar")
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key = self.cache.make_key("foo")
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keyhash = hashlib.md5(key.encode()).hexdigest()
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keypath = os.path.join(self.dirname, keyhash[:2], keyhash[2:4], keyhash[4:])
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self.assertTrue(os.path.exists(keypath))
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def test_subdirectory_removal(self):
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"""
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Make sure that the created subdirectories are correctly removed when empty.
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"""
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self.cache.set("foo", "bar")
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key = self.cache.make_key("foo")
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keyhash = hashlib.md5(key.encode()).hexdigest()
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keypath = os.path.join(self.dirname, keyhash[:2], keyhash[2:4], keyhash[4:])
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self.assertTrue(os.path.exists(keypath))
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self.cache.delete("foo")
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self.assertTrue(not os.path.exists(keypath))
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self.assertTrue(not os.path.exists(os.path.dirname(keypath)))
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self.assertTrue(not os.path.exists(os.path.dirname(os.path.dirname(keypath))))
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os.rmdir(self.dirname)
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def test_cull(self):
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self.perform_cull_test(50, 29)
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def test_ignores_non_cache_files(self):
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fname = os.path.join(self.dirname, 'not-a-cache-file')
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with open(fname, 'w'):
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os.utime(fname, None)
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self.cache.clear()
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self.assertTrue(os.path.exists(fname),
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'Expected cache.clear to ignore non cache files')
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os.remove(fname)
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def test_clear_does_not_remove_cache_dir(self):
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self.cache.clear()
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self.assertTrue(os.path.exists(self.dirname),
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'Expected cache.clear to keep the cache dir')
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def test_creates_cache_dir_if_nonexistent(self):
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os.rmdir(self.dirname)
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self.cache.set('foo', 'bar')
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os.path.exists(self.dirname)
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def test_zero_cull(self):
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# Regression test for #15806
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self.cache = get_cache(self.backend_name, LOCATION=self.dirname, OPTIONS={'MAX_ENTRIES': 30, 'CULL_FREQUENCY': 0})
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self.perform_cull_test(50, 19)
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class CustomCacheKeyValidationTests(unittest.TestCase):
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"""
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