new_contents: import json
  
  
  class ClientError(Exception):
      def __init__(self, code):
          super(ClientError, self).__init__(code)
          self.code = code
  
      def send_to(self, channel):
          channel.send({
              "text": json.dumps({
                  "error": self.code,
              }),
          })
  
subject: Add ClientError exception to handle sending back web socket errors to the client.