The filtering system can be separated into eight major components, each of which is responsible for a specific stage of the filtering process. These components are:
Figure 4.1 shows an example of how the filtering system components interact to process a request received from a web browser. A request is sent from a web browser and received by the Server component. The Server creates a new Handler and sends it the request for processing. The Handler contacts the Filter Manager to obtain a new set of filters for processing the HTTP transaction. Internally the Filter Manager asks each of its filter factories to create a new filter and this list of filters is given to the Handler. The Handler then passes the request through each of the filters and sends the filtered request to an Http Relay which sends the request to a web server on the Internet.
Figure 4.2 shows the next step in the filtering process which is how the components interact to process a reply received from a web server. After sending a request, the Http Relay waits to receive the corresponding reply from the web server. Once received, the reply is sent to the Handler for filtering. The reply is passed through the same list of filters obtained from the Filter Manager to filter the request and then sent to the web browser.
Each of the filtering system components will be discussed in detail in the following sections.
