text: class GQL:
      # Client -> Server message types.
      CONNECTION_INIT = "connection_init"
      START = "start"
      STOP = "stop"
      CONNECTION_TERMINATE = "connection_terminate"
  
      # Server -> Client message types.
      CONNECTION_ERROR = "connection_error"
      CONNECTION_ACK = "connection_ack"
      DATA = "data"
      ERROR = "error"
      COMPLETE = "complete"
      CONNECTION_KEEP_ALIVE = "ka"
  