giscanner/cachestore.py

   1 # -*- Mode: Python -*-
   2 # GObject-Introspection - a framework for introspecting GObject libraries
   3 # Copyright (C) 2008  Johan Dahlin
   4 #
   5 # This library is free software; you can redistribute it and/or
   6 # modify it under the terms of the GNU Lesser General Public
   7 # License as published by the Free Software Foundation; either
   8 # version 2 of the License, or (at your option) any later version.
   9 #
  10 # This library is distributed in the hope that it will be useful,
  11 # but WITHOUT ANY WARRANTY; without even the implied warranty of
  12 # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13 # Lesser General Public License for more details.
  14 #
  15 # You should have received a copy of the GNU Lesser General Public
  16 # License along with this library; if not, write to the
  17 # Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  18 # Boston, MA 02111-1307, USA.
  19 #
  20
  21 import cPickle
  22 import hashlib
  23 import os
  24 import errno
  25
  26
  27 def _get_cachedir():
  28     cachedir = os.path.join(os.environ['HOME'], '.cache')
  29     if not os.path.exists(cachedir):
  30         os.mkdir(cachedir, 0755)
  31
  32     scannerdir = os.path.join(cachedir, 'g-ir-scanner')
  33     if not os.path.exists(scannerdir):
  34         os.mkdir(scannerdir, 0755)
  35     # If it exists and is a file, don't cache at all
  36     elif not os.path.isdir(scannerdir):
  37         return None
  38     return scannerdir
  39
  40
  41 class CacheStore(object):
  42
  43     def __init__(self):
  44         try:
  45             self._directory = _get_cachedir()
  46         except OSError, e:
  47             if e.errno != errno.EPERM:
  48                 raise
  49             self._directory = None
  50
  51     def _get_filename(self, filename):
  52         # If we couldn't create the directory we're probably
  53         # on a read only home directory where we just disable
  54         # the cache all together.
  55         if self._directory is None:
  56             return
  57         hexdigest = hashlib.sha1(filename).hexdigest()
  58         return os.path.join(self._directory, hexdigest)
  59
  60     def _cache_is_valid(self, store_filename, filename):
  61         return (os.stat(store_filename).st_mtime >=
  62                 os.stat(filename).st_mtime)
  63
  64     def _purge_cache(self, filename):
  65         try:
  66             os.unlink(filename)
  67         except IOError, e:
  68             # Permission denied
  69             if e.errno == errno.EACCES:
  70                 return
  71             # File does not exist
  72             elif e.errno == errno.ENOENT:
  73                 return
  74             else:
  75                 raise
  76
  77     def store(self, filename, data):
  78         store_filename = self._get_filename(filename)
  79         if store_filename is None:
  80             return
  81         if (os.path.exists(store_filename) and
  82             self._cache_is_valid(store_filename, filename)):
  83             return None
  84         fd = open(store_filename, 'w')
  85         try:
  86             cPickle.dump(data, fd)
  87         except IOError, e:
  88             # No space left on device
  89             if e.errno == e.ENOSPC:
  90                 return
  91             else:
  92                 raise
  93
  94     def load(self, filename):
  95         store_filename = self._get_filename(filename)
  96         if store_filename is None:
  97             return
  98         try:
  99             fd = open(store_filename)
 100         except IOError, e:
 101             if e.errno == errno.ENOENT:
 102                 return None
 103             else:
 104                 raise
 105         if not self._cache_is_valid(store_filename, filename):
 106             return None
 107         try:
 108             data = cPickle.load(fd)
 109         except (EOFError, ValueError, cPickle.BadPickleGet):
 110             # Broken cache entry, remove it
 111             self._purge_cache(store_filename)
 112             data = None
 113         return data