Why does the server send a ping packet from version 3?

[evgencode]

Why does the server send a ping packet from version 3?
In the second version, the ping packet was sent by the client.
I think it would be more correct to send a ping from the client

[darrachequesne]

Please check the reasoning here: https://socket.io/blog/engine-io-4-release/#heartbeat-mechanism-reversal

After analysis, it seems to be caused by delayed timers on the client-side. Those timers are used in the ping-pong mechanism which helps to ensure the connection between the server and the client is still healthy. A delay on the client-side meant the client sent the ping packet too late, and the server considered that the connection was closed.

That's why the ping packets will now be sent by the server, and the client will respond with a pong packet.