Client Reconnect with Same clientID Causes Stale Connection Timeout and Incorrect Offline Status

[ogofly]

Issue Scenario:

On a device, an MQTT client connects to the mochi-mqtt/server. Without explicitly disconnecting, the device restarts and the client reconnects to the server using the same clientID. The new connection succeeds, but approximately 10–20 seconds later, the server logs indicate a read timeout for the original (first) connection. From the server’s perspective, the client with that clientID appears offline under its Clients list.

Log：

// Log printed in hook OnSessionEstablished
time=2025-11-17T10:28:49.106+08:00 level=INFO msg="Mqtt OnConnect" clientId=864865084478230 username=864865084478230 ip=39.144.46.220:32546 now=1763346529106978

time=2025-11-17T10:31:31.019+08:00 level=INFO msg="Mqtt OnConnect" clientId=864865084478230 username=864865084478230 ip=39.144.46.97:35605 now=1763346691019882
// After the device restarts, the same clientId connects to the broker again
// Why did "taken over" not occur and the old client was not removed?

// The broker detected that the client from the first connection went offline
time=2025-11-17T10:31:49.107+08:00 level=DEBUG msg="client disconnected" error="read tcp 10.0.3.131:1883->39.144.46.220:32546: i/o timeout" client=864865084478230 remote=39.144.46.220:32546 listener=tio-tcp
time=2025-11-17T10:31:49.108+08:00 level=WARN msg="" listener=tio-tcp error="read tcp 10.0.3.131:1883->39.144.46.220:32546: i/o timeout"

// Received the disconnect event in hook OnDisconnect
// Immediately checked the broker state for this clientId (in Server Clients) and found it's Closed() is False, so the business code ignored this disconnect event
time=2025-11-17T10:31:49.108+08:00 level=INFO msg="Ignore OnDisconnect message cause client is connected, may be concurrent connect and disconnect" clientId=864865084478230 username=864865084478230

// However, when checking the broker client's state later, it as removed from Server Clients
// But this client can still publish messages through the broker

Thank you for your great work on mochi-mqtt! We really appreciate the effort and dedication you’ve put into building and maintaining this project.