{
  "id": .....
  "cmd": "LIST_SUBSCRIPTION"
}

{
  "id": "{req_id}",
  "cmd": "LIST_SUBSCRIPTION",
  "success": true,
  "time": {timestamp},
  "data": ["topic1", "topic2"]
}
Retrieve a list of all topics currently subscribed to on the connection. 
{
  "id": .....
  "cmd": "LIST_SUBSCRIPTION"
}

{
  "id": "{req_id}",
  "cmd": "LIST_SUBSCRIPTION",
  "success": true,
  "time": {timestamp},
  "data": ["topic1", "topic2"]
}