How to create a random string in Artillery for every connection

Question

I am doing a load test for socket.io using Artillery

# my-scenario.yml
config:
  target: "http://localhost:4000"
  phases:
    - duration: 60
      arrivalRate: 10
  engines:
   socketio-v3: {transports: ['websocket']}
  socketio:
    query:
      address: "{{ $randomString() }}"

scenarios:
  - name: My sample scenario
    engine: socketio-v3

I need the address field to be a different random string of fixed length for every connection.

Currently, $randomString() only generates 1 random string which is used for all connections, and also I can't control its length.

Thanks in advance!