One ping/pong failure will make the websocket disconnect, is that too sensitive ?

[qiulang]

Correct me if I am wrong I think that one ping/pong failure will make the websocket disconnect. Is this too sensitive, e.g. why doesn't the heartbeat mechanism add some re-try before it marks the websocket disconnect ?

I know engine.io has reconnect option like reconnectionDelay & randomizationFactor (their meanings are obvious). I assume after a ping/pong failure socket.io will use a new websocket to reconnect. But I can't find a clear document to explain this reconnect process. Can someone shed some light on this ?

[darrachequesne]

why doesn't the heartbeat mechanism add some re-try before it marks the websocket disconnect ?

That's a good question. If a ping/pong fails, then the WebSocket connection is surely in an invalid state, and thus retrying will only delay the reconnection.

I assume after a ping/pong failure socket.io will use a new websocket to reconnect

Yes, that's right. The codebase is split in two projects:

• Engine.IO: the engine.io-client package provides a WebSocket-like object, which falls back to HTTP long-polling (but no reconnection, similarly to the WebSocket API). The heartbeat mechanism happens here, and the connection gets closed if the heartbeat fails.

Source: https://github.com/socketio/engine.io-client/

• Socket.IO: the socket.io-client package provides some syntactic sugar over Engine.IO, with an API inspired from the Node.js EventEmitter (socket.on() / socket.emit()). The reconnection is handled here: if the underlying Engine.IO client gets closed, then it creates another one.

Source: https://github.com/socketio/socket.io-client/

[qiulang]

Thanks for answering my question!

One of reasons I asked my question is that through our socket.io server logs I found some client-side disconnect events were missing. I searched socket.io issues found this one #635. It was closed in 2017 but others commented they still hit the problem. I will open another discussion for that.