Trick IE into reserving a connection for Comet traffic

“Comet” is a dhtml technique for sending updates from the server to a browser client. One way to do it is to place a hidden iframe in one’s page and have the server write a <script> to the response whenever there’s an update; the script executes as soon as the client receives it, and it might popout a window containing a new message or change styling in the parent doc. In order for the client to keep getting updates, the server purposely never indicates that it has finished writing the response.

A webapp that uses Comet typically needs one connection for Comet and one to send requests to the server whenever the user makes some kind of edit (aka RPC = remote procedure call).  While the second connection isn’t needed all the time, IE6 permits only two connections to be used at any time, so any other windows open in IE have to fight with your service for them, which sometimes leads IE to close one of your connections prematurely.

Although it’s not friendly to such other services, one can trick IE into reserving one of its connections for your Comet page by requesting that page from a different domain than one makes RPCs from. If the server must maintain state, the domains can even point to the same machine (although you probably need to map both domains to a switch that then uses a cookie to find the particular machine)

To simulate such a setup on a Window dev machine, add the following line to C:WINDOWSsystem32driversetchosts       fake-domain1                       fake-domain2

Print Friendly, PDF & Email