Secure Chat Room with Presence

Problem/Feature Description

A healthcare messaging application requires strict access control on all channels. The app uses PubNub's Access Manager to ensure only authorized users can read and write messages. Each consultation room has a channel (e.g., consult-{roomId}), and the application needs to show doctors and patients who is currently in the room.

The application must handle unreliable network conditions gracefully -- medical staff move between areas with poor connectivity, so the client needs robust reconnection logic that keeps the presence state accurate after a network drop. The heartbeat configuration needs to be tuned for a real-time chat scenario where quick detection of disconnected users matters.

Build the server-side access grant logic and the client-side presence module for this application.

Output Specification

Produce two files:

1. server-grants.js -- A Node.js script that demonstrates how to grant the necessary permissions for a user to join a consultation room channel with full presence capabilities.

2. client-presence.js -- The client-side JavaScript module that:

   • Initializes the PubNub client with appropriate configuration for real-time chat
   • Subscribes to the consultation channel with presence
   • Handles network connectivity changes robustly so users see accurate room status even after drops
   • Loads the current room occupancy when appropriate
   • Sets up a presence listener for the channel
   • Configures heartbeat and timeout values appropriate for real-time chat