Doesn't pretty much every browser now support Connection: Keep-Alive?

Yes, but the browser usually closes the socket when it's done rendering a page, IIRC.

Ah, that may well be the case. I thought that the browser kept it open until the site was left or the window closed but I can certainly see how it might make sense to close it when done rendering. Oh well.

Hrm. If the browser does indeed close the connection after rendering the page, what about opening your own connection manually via javascript? Are javascript sockets automatically closed when the page is closed / unloaded? I would think they would be, so that means you could perhaps simply open a connection to a "keep alive" server, stick it in a globally scoped variable, and then just forget about it. I haven't done enough with javascript sockets to know if this is feasible. Alternatively, you could perhaps use a hidden frame that never finishes rendering to accomplish the same effect.

bbfu
Black flowers blossom
Fearless on my breath

With the growing ubiquity of the XMLHttpRequest object in browsers now, you could have the app ping the server with requests every so often and have the server watch for this heartbeat to die.