code: def app_class():
      
      try:
          pkg_resources.get_distribution('invenio-files-rest')
          from invenio_files_rest.app import Flask as FlaskBase
      except pkg_resources.DistributionNotFound:
          from flask import Flask as FlaskBase
  
      # Add Host header validation via APP_ALLOWED_HOSTS configuration variable.
      class Request(TrustedHostsMixin, FlaskBase.request_class):
          pass
  
      class Flask(FlaskBase):
          request_class = Request
  
      return Flask
docs: Create Flask application class.
  
      Invenio-Files-REST needs to patch the Werkzeug form parsing in order to
      support streaming large file uploads. This is done by subclassing the Flask
      application class.