Integrated sync backend

Now that we have the basic sync running with the websocket_server, we should look into how we can mirror the behaviour with a PHP-only backend.

socket.io supports long polling https://socket.io/docs/v3/how-it-works/#http-long-polling which we could make use of

• provide php endpoints for GET and POST requests
• Think about way to store/distribute and handle the messages
  • server-to-client
    • init-room
    • joined-data
    • first-in-room
    • room-user-change
    • client-broadcast
    • user-follow-room-change
    • room-user-change
    • broadcast-unfollow
  • client-to-server
    • connection init
    • join-room
    • server-broadcast
    • server-volatile-broadcast
    • user-follow
    • disconnecting
    • disconnect

We could potentially require redis with https://github.com/phpredis/phpredis?tab=readme-ov-file#publish or just use a db backend if that is not present.

Required protocols to implement
https://github.com/socketio/engine.io-protocol
https://socket.io/docs/v4/socket-io-protocol#introduction

Additional resources
https://github.com/socketIo-php
https://github.com/socketIo-php/engine.io-parser
https://github.com/socketIo-php/socket.io-parser

Start by examining the existing websocket_server sync behavior and the linked Engine.IO and Socket.IO protocol documentation. Define the PHP GET and POST endpoints, message storage or distribution approach, and handling for the listed server-to-client and client-to-server events. Done means the PHP-only backend mirrors the required sync behavior and protocol interactions.