support disconnect reason to `handleDisconnect` args

[yizumi1012xxx]

Is there an existing issue that is already proposing this?

• I have searched the existing issues

Is your feature request related to a problem? Please describe it

I use @nestjs/websocket.
https://docs.nestjs.com/websockets/gateways

To add disconnect event handler, OnGatewayDisconnect lifecycle hook is useful.
But this hook is not able to get disconnect reason.

Describe the solution you'd like

My code is below. (handleDisconnect can not get disconnect reason.)

export class EventsGateway implements OnGatewayConnection<Socket> {
  async handleConnection(socket: Socket) {
    // add disconnect handler manually.
    socket.on('disconnect', async reason => {
      await this._handleDisconnect(socket, reason)
    })
  }

  async _handleDisconnect(socket: Socket, reason: DisconnectReason) {
    // handle disconnect
  }
}

Expect code is below. (handleDisconnect can get disconnect reason.)

export class EventsGateway implements OnGatewayConnection<Socket>, OnGatewayDisconnect <Socket> {
  async handleConnection(socket: Socket) {
    // handle connect
  }

  async handleDisconnect(socket: Socket, reason: DisconnectReason) {
    // handle disconnect
  }
}

Teachability, documentation, adoption, migration strategy

n/a

What is the motivation / use case for changing the behavior?

n/a

[snowykte0426]

I think your suggestion is great! Being able to access the disconnect reason would definitely help with debugging and error handling.

I've implemented this feature by adding an optional reason parameter to the handleDisconnect method:

handleDisconnect(client: Socket, reason?: string) {
  console.log('Client disconnected:', client.id, 'Reason:', reason);
}

The implementation is fully backward compatible, so existing code continues to work without any changes.

Here's the PR: #15451

[kamilmysliwiec]

Let's track this here #15451

[yizumi1012xxx]

Thank you for handling this.