The Texis ISAPI software acts as a pass-through. IIS is configured to give requests to Texis ISAPI, which in turn passes it along to Webinator. Texis ISAPI receives Webinator's response, and passes that response back to the web browser.
There are two types of ISAPI programs: filters and extensions. Texis
ISAPI contains both a filter and an extension in
ProxyModule.dll, although you will only use one or the other
(which one depends on which version of IIS you're running). Both the
Texis ISAPI filter and Texis ISAPI extension offer the same features
and functionality, they only differ in how they are implemented in and
communicate with IIS (the installer is able to set up either for you
SF_NOTIFY_READ_RAW_DATA. It is invoked for every request, but takes no action unless the request begins with
/texis. If the request does, Texis ISAPI takes control of the request and processes it appropriately.
SF_NOTIFY_READ_RAW_DATAfor filters is explicitly denied, so Texis ISAPI uses an ISAPI Extension mapped as a Wildcard Application Mapping. The installer accesses the default site and creates a new virtual directory,
texis. It creates custom Application Settings for that virtual directory, and adds Texis ISAPI's DLL file as a Wildcard Application Map. This means that any request that comes to that virtual directory (i.e.
/texis/...) will not map to a real file location, but will instead be handed off to Texis ISAPI. The installer also adds Texis ISAPI as an "allowed" extension to the IIS Web Service Extensions Restriction List.
Wildcard Application Maps are not available prior to IIS 6, so the filter is still used for earlier versions.