I'm looking into ways to develop an extension for IE6+ that will allow handling of custom MIME types.
As an example, I need to be able to take a document with a custom MIME type that is returned by the server, perform some processing on it, and then change the MIME type back to something that IE can natively handle, such as text/html or image/jpeg.
I am familiar with the urlmon MIME filters, but they have a huge weakness; they are only invoked for the top level document, and not for any of the additional page content such as images and the like.
The one way that I can think of that will work is to hook the HTTP/S protocol handlers using vtable/iat patches, similar to the way Google Gears works, to be able to intercept the response headers, and modify the headers and response body when a document with the specified MIME type is received.
I'm wondering if anybody else has any good ideas on how this could be accomplished in a less hacky/intrusive way.
Edit: Just thought I'd follow up on this and mention that I went with the vtable patch into the HTTP/S protocol handlers, and it worked much better than I expected. If anybody else is looking to do something like this, I highly recommend taking a look at the HttpHandlerPatch class in Google Gears for some inspiration.