ISAPI extensions communicate with IIS through the EXTENSION_CONTROL_BLOCK. Once the main entry point for an ISAPI extension, HttpExtensionProc, takes a pointer to the EXTENSION_CONTROL_BLOCK, the ISAPI extension can also use callback functions to communicate with IIS.
The following callback functions are made available to ISAPI extensions by IIS:
In addition, if you are going to be performing certain types of asynchronous I/O operations, you will need to provide a callback function of your own:
All function declarations and data structures are available in the ISAPI extension header file httpext.h.