I'm using the PassthruAPP method to hook into HTTP/HTTPS requests made by IE.

It's working well for the most part, however I noticed a problem. Only one download thread is active at a time. I can see two IInternetProtocol objects getting created, but IE uses only one at a time. This is happening with IE7.

The odd thing is that the problem occurs when overriding the existing default HTTP/HTTPS handler, even if the handler is not the one being used to make the request. E.g. Registering a handler for the HTTPS protocol will cause HTTP requests to be made sequentially, even though HTTP requests are not hooked.

I installed Google Gears and it has the same problem.

This always happens for the first few items on the page, but it seems that after the document complete is issued, concurrent downloads can occur again. For example Javascript code that is executed after the page has finished loading can load images concurrently just fine.

One option is to try to IAT patch the 'IInternetProtocol' registered for HTTP requests, but Google Gears does this already and it has the same problem.

I know installing a HTTP Proxy is another option, but I don't want to monkey with the users' HTTP Proxy settings if there another option.