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  # Copyright 2011 OpenStack LLC.
  # All Rights Reserved.
  #
  #    Licensed under the Apache License, Version 2.0 (the "License"); you may
  #    not use this file except in compliance with the License. You may obtain
  #    a copy of the License at
  #
  #         http://www.apache.org/licenses/LICENSE-2.0
  #
  #    Unless required by applicable law or agreed to in writing, software
  #    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
  #    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
  #    License for the specific language governing permissions and limitations
  #    under the License.
  
  """
  LRU Cache for Image Data
  """
  
  import hashlib
  
  from oslo.config import cfg
  
  from glance.common import exception
  from glance.common import utils
  from glance.openstack.common import importutils
  import glance.openstack.common.log as logging
  
  LOG = logging.getLogger(__name__)
  
  image_cache_opts = [
      cfg.StrOpt('image_cache_driver', default='sqlite',
                 help=_('The driver to use for image cache management.')),
      cfg.IntOpt('image_cache_max_size', default=10 * (1024 ** 3),  # 10 GB
                 help=_('The maximum size in bytes that the cache can use.')),
      cfg.IntOpt('image_cache_stall_time', default=86400,  # 24 hours
                 help=_('The amount of time to let an image remain in the '
                        'cache without being accessed')),
      cfg.StrOpt('image_cache_dir',
                 help=_('Base directory that the Image Cache uses.')),
  ]
  
  CONF = cfg.CONF
  CONF.register_opts(image_cache_opts)
  
  
  class ImageCache(object):
  
      """Provides an LRU cache for image data."""
  
      def __init__(self):
          self.init_driver()
  
      def init_driver(self):
          """
          Create the driver for the cache
          """
          driver_name = CONF.image_cache_driver
          driver_module = (__name__ + '.drivers.' + driver_name + '.Driver')
          try:
              self.driver_class = importutils.import_class(driver_module)
              LOG.info(_("Image cache loaded driver '%s'.") %
                       driver_name)
          except ImportError as import_err:
              LOG.warn(_("Image cache driver "
                         "'%(driver_name)s' failed to load. "
                         "Got error: '%(import_err)s.") % locals())
  
              driver_module = __name__ + '.drivers.sqlite.Driver'
              LOG.info(_("Defaulting to SQLite driver."))
              self.driver_class = importutils.import_class(driver_module)
          self.configure_driver()
  
      def configure_driver(self):
          """
          Configure the driver for the cache and, if it fails to configure,
          fall back to using the SQLite driver which has no odd dependencies
          """
          try:
              self.driver = self.driver_class()
              self.driver.configure()
          except exception.BadDriverConfiguration as config_err:
              driver_module = self.driver_class.__module__
              LOG.warn(_("Image cache driver "
                         "'%(driver_module)s' failed to configure. "
                         "Got error: '%(config_err)s") % locals())
              LOG.info(_("Defaulting to SQLite driver."))
              default_module = __name__ + '.drivers.sqlite.Driver'
              self.driver_class = importutils.import_class(default_module)
              self.driver = self.driver_class()
              self.driver.configure()
  
      def is_cached(self, image_id):
          """
          Returns True if the image with the supplied ID has its image
          file cached.
  
          :param image_id: Image ID
          """
          return self.driver.is_cached(image_id)
  
      def is_queued(self, image_id):
          """
          Returns True if the image identifier is in our cache queue.
  
          :param image_id: Image ID
          """
          return self.driver.is_queued(image_id)
  
      def get_cache_size(self):
          """
          Returns the total size in bytes of the image cache.
          """
          return self.driver.get_cache_size()
  
      def get_hit_count(self, image_id):
          """
          Return the number of hits that an image has
  
          :param image_id: Opaque image identifier
          """
          return self.driver.get_hit_count(image_id)
  
      def get_cached_images(self):
          """
          Returns a list of records about cached images.
          """
          return self.driver.get_cached_images()
  
      def delete_all_cached_images(self):
          """
          Removes all cached image files and any attributes about the images
          and returns the number of cached image files that were deleted.
          """
          return self.driver.delete_all_cached_images()
  
      def delete_cached_image(self, image_id):
          """
          Removes a specific cached image file and any attributes about the image
  
          :param image_id: Image ID
          """
          self.driver.delete_cached_image(image_id)
  
      def delete_all_queued_images(self):
          """
          Removes all queued image files and any attributes about the images
          and returns the number of queued image files that were deleted.
          """
          return self.driver.delete_all_queued_images()
  
      def delete_queued_image(self, image_id):
          """
          Removes a specific queued image file and any attributes about the image
  
          :param image_id: Image ID
          """
          self.driver.delete_queued_image(image_id)
  
      def prune(self):
          """
          Removes all cached image files above the cache's maximum
          size. Returns a tuple containing the total number of cached
          files removed and the total size of all pruned image files.
          """
          max_size = CONF.image_cache_max_size
          current_size = self.driver.get_cache_size()
          if max_size > current_size:
              LOG.debug(_("Image cache has free space, skipping prune..."))
              return (0, 0)
  
          overage = current_size - max_size
          LOG.debug(_("Image cache currently %(overage)d bytes over max "
                      "size. Starting prune to max size of %(max_size)d ") %
                    locals())
  
          total_bytes_pruned = 0
          total_files_pruned = 0
          entry = self.driver.get_least_recently_accessed()
          while entry and current_size > max_size:
              image_id, size = entry
              LOG.debug(_("Pruning '%(image_id)s' to free %(size)d bytes"),
                        {'image_id': image_id, 'size': size})
              self.driver.delete_cached_image(image_id)
              total_bytes_pruned = total_bytes_pruned + size
              total_files_pruned = total_files_pruned + 1
              current_size = current_size - size
              entry = self.driver.get_least_recently_accessed()
  
          LOG.debug(_("Pruning finished pruning. "
                      "Pruned %(total_files_pruned)d and "
                      "%(total_bytes_pruned)d.") % locals())
          return total_files_pruned, total_bytes_pruned
  
      def clean(self, stall_time=None):
          """
          Cleans up any invalid or incomplete cached images. The cache driver
          decides what that means...
          """
          self.driver.clean(stall_time)
  
      def queue_image(self, image_id):
          """
          This adds a image to be cache to the queue.
  
          If the image already exists in the queue or has already been
          cached, we return False, True otherwise
  
          :param image_id: Image ID
          """
          return self.driver.queue_image(image_id)
  
      def get_caching_iter(self, image_id, image_checksum, image_iter):
          """
          Returns an iterator that caches the contents of an image
          while the image contents are read through the supplied
          iterator.
  
          :param image_id: Image ID
          :param image_checksum: checksum expected to be generated while
                                 iterating over image data
          :param image_iter: Iterator that will read image contents
          """
          if not self.driver.is_cacheable(image_id):
              return image_iter
  
          LOG.debug(_("Tee'ing image '%s' into cache"), image_id)
  
          return self.cache_tee_iter(image_id, image_iter, image_checksum)
  
      def cache_tee_iter(self, image_id, image_iter, image_checksum):
          try:
              current_checksum = hashlib.md5()
  
              with self.driver.open_for_write(image_id) as cache_file:
                  for chunk in image_iter:
                      try:
                          cache_file.write(chunk)
                      finally:
                          current_checksum.update(chunk)
                          yield chunk
                  cache_file.flush()
  
                  if (image_checksum and
                          image_checksum != current_checksum.hexdigest()):
                      msg = _("Checksum verification failed. Aborted "
                              "caching of image '%s'." % image_id)
                      raise exception.GlanceException(msg)
  
          except exception.GlanceException as e:
              # image_iter has given us bad, (size_checked_iter has found a
              # bad length), or corrupt data (checksum is wrong).
              LOG.exception(e)
              raise
          except Exception as e:
              LOG.exception(_("Exception encountered while tee'ing "
                              "image '%s' into cache: %s. Continuing "
                              "with response.") % (image_id, e))
  
              # If no checksum provided continue responding even if
              # caching failed.
              for chunk in image_iter:
                  yield chunk
  
      def cache_image_iter(self, image_id, image_iter, image_checksum=None):
          """
          Cache an image with supplied iterator.
  
          :param image_id: Image ID
          :param image_file: Iterator retrieving image chunks
          :param image_checksum: Checksum of image
  
          :retval True if image file was cached, False otherwise
          """
          if not self.driver.is_cacheable(image_id):
              return False
  
          for chunk in self.get_caching_iter(image_id, image_checksum,
                                             image_iter):
              pass
          return True
  
      def cache_image_file(self, image_id, image_file):
          """
          Cache an image file.
  
          :param image_id: Image ID
          :param image_file: Image file to cache
  
          :retval True if image file was cached, False otherwise
          """
          CHUNKSIZE = 64 * 1024 * 1024
  
          return self.cache_image_iter(image_id,
                                       utils.chunkiter(image_file, CHUNKSIZE))
  
      def open_for_read(self, image_id):
          """
          Open and yield file for reading the image file for an image
          with supplied identifier.
  
          :note Upon successful reading of the image file, the image's
                hit count will be incremented.
  
          :param image_id: Image ID
          """
          return self.driver.open_for_read(image_id)
  
      def get_image_size(self, image_id):
          """
          Return the size of the image file for an image with supplied
          identifier.
  
          :param image_id: Image ID
          """
          return self.driver.get_image_size(image_id)
  
      def get_queued_images(self):
          """
          Returns a list of image IDs that are in the queue. The
          list should be sorted by the time the image ID was inserted
          into the queue.
          """
          return self.driver.get_queued_images()
  