For 'long-lived connection' , you can use Ratchet for PHP. It's a library built based on Stream Socket functions that PHP has supported since PHP 5.
For client side, you need to use WebSocket that HTML5 supported instead of Socket.io (since you know, socket.io only works with node.js).
In case you still want to use Socket.io, you can try this way: - find & get socket.io.js for client to use - work with Ratchet to simulate the way socket.io does on server
Hope this helps!!