Using Callback Functions

When your extension processes a request, it needs a way of communicating with IIS. This is the purpose of the callback functions in the ECB. The four callback functions used with ISAPI extensions are:

• GetServerVariable is used to obtain server variables that contain information about the request and server. Some server variables, such as Request_Method and Content_Length are embedded in the ECB structure. You can use GetServerVariable to obtain information about the request or server that is not included in the ECB.
• ReadClient is used to read data, supplied by the client, into a buffer.
• ServerSupportFunction provides a variety of functions that the extension can use in processing a request.
• WriteClient used to send a response back to the client.

Specific examples showing how to use the callback functions are provided in Sending a Header and Reading and Writing Asynchronously.

For more information on server variables see: http://hoohoo.ncsa.uiuc.edu/cgi/env.html