sync on unload doesn't work for XHR-Polling or JSONP

[crickeys]

I can't get the disconnectSync to actually disconnect the client if they close their browser in chrome (haven't tried elsewhere yet). To reproduce:

1. Start a socket server with only XHR polling or only JSONP polling transports and debug log on
2. Open connection in chrome (You'll see the handshake and connection in the debug log
3. Close the browser tab
4. Nothing registers on the server side.

[bajtos]

You can ask the client to notify the server about disconnect by turning on the flag sync disconnect on unload:

var socket = io.connect('http://localhost', {
  'sync disconnect on unload': true
});

This solution has some shortcomings though, see this pull request for more details.

See also a related StackOverflow question & answer.

[mattcodez]

Is there a server-side solution for this issue? While the client option works on desktop browsers, I'd still prefer not to rely on the client to inform the server of a disconnect.