text: # 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.
  
  from ecl.object_store import object_store_service
  from ecl import resource
  
  
  class BaseResource(resource.Resource):
      service = object_store_service.ObjectStoreService()
  
      #: Metadata stored for this resource. *Type: dict*
      metadata = dict()
  
      _custom_metadata_prefix = None
      _system_metadata = dict()
  
      def _calculate_headers(self, metadata):
          headers = dict()
          for key in metadata:
              if key in self._system_metadata:
                  header = self._system_metadata[key]
              else:
                  header = self._custom_metadata_prefix + key
              headers[header] = metadata[key]
          return headers
  
      def set_metadata(self, session, metadata):
          url = self._get_url(self, self.id)
          session.post(url, endpoint_filter=self.service,
                       headers=self._calculate_headers(metadata))
  
      def delete_metadata(self, session, keys):
          url = self._get_url(self, self.id)
          headers = {key: '' for key in keys}
          session.post(url, endpoint_filter=self.service,
                       headers=self._calculate_headers(headers))
  
      def _set_metadata(self):
          self.metadata = dict()
          headers = self.get_headers()
  
          for header in headers:
              if header.startswith(self._custom_metadata_prefix):
                  key = header[len(self._custom_metadata_prefix):].lower()
                  self.metadata[key] = headers[header]
  
      def get(self, session, include_headers=False, args=None):
          super(BaseResource, self).get(session, include_headers, args)
          self._set_metadata()
          return self
  
      def head(self, session):
          super(BaseResource, self).head(session)
          self._set_metadata()
          return self
  
      @classmethod
      def update_by_id(cls, session, resource_id, attrs, path_args=None):
          """Update a Resource with the given attributes.
  
          :param session: The session to use for making this request.
          :type session: :class:`~ecl.session.Session`
          :param resource_id: This resource's identifier, if needed by
                              the request. The default is ``None``.
          :param dict attrs: The attributes to be sent in the body
                             of the request.
          :param dict path_args: This parameter is sent by the base
                                 class but is ignored for this method.
  
          :return: A ``dict`` representing the response headers.
          """
          url = cls._get_url(None, resource_id)
          headers = attrs.get(resource.HEADERS, dict())
          headers['Accept'] = ''
          return session.post(url, endpoint_filter=cls.service,
                              headers=headers).headers
  