text: # -*- coding: utf-8 -*-
  #
  # Licensed to the Apache Software Foundation (ASF) under one
  # or more contributor license agreements.  See the NOTICE file
  # distributed with this work for additional information
  # regarding copyright ownership.  The ASF licenses this file
  # to you 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 airflow import configuration
  from airflow.exceptions import AirflowException
  from airflow.utils.log.logging_mixin import LoggingMixin
  
  
  class InvalidFernetToken(Exception):
      # If Fernet isn't loaded we need a valid exception class to catch. If it is
      # loaded this will get reset to the actual class once get_fernet() is called
      pass
  
  
  class NullFernet:
      """
      A "Null" encryptor class that doesn't encrypt or decrypt but that presents
      a similar interface to Fernet.
  
      The purpose of this is to make the rest of the code not have to know the
      difference, and to only display the message once, not 20 times when
      `airflow initdb` is ran.
      """
      is_encrypted = False
  
      def decrypt(self, b):
          return b
  
      def encrypt(self, b):
          return b
  
  
  _fernet = None
  
  
  def get_fernet():
      """
      Deferred load of Fernet key.
  
      This function could fail either because Cryptography is not installed
      or because the Fernet key is invalid.
  
      :return: Fernet object
      :raises: airflow.exceptions.AirflowException if there's a problem trying to load Fernet
      """
      global _fernet
      log = LoggingMixin().log
  
      if _fernet:
          return _fernet
      try:
          from cryptography.fernet import Fernet, MultiFernet, InvalidToken
          global InvalidFernetToken
          InvalidFernetToken = InvalidToken
  
      except ImportError:
          log.warning(
              "cryptography not found - values will not be stored encrypted."
          )
          _fernet = NullFernet()
          return _fernet
  
      try:
          fernet_key = configuration.conf.get('core', 'FERNET_KEY')
          if not fernet_key:
              log.warning(
                  "empty cryptography key - values will not be stored encrypted."
              )
              _fernet = NullFernet()
          else:
              _fernet = MultiFernet([
                  Fernet(fernet_part.encode('utf-8'))
                  for fernet_part in fernet_key.split(',')
              ])
              _fernet.is_encrypted = True
      except (ValueError, TypeError) as ve:
          raise AirflowException("Could not create Fernet object: {}".format(ve))
  
      return _fernet
  