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A DSAPI filter allows you to customize the processing of an HTTP request when
particular events occur, such as when a user accesses a resource on the server
for the first time and you want to use special authentication processing instead of
the normal Domino Web authentication. The process uses a set of pre-defined
event types. The HTTP stack notifies the DSAPI filter of the events, then the logic
determined by the DSAPI developer decides what to do based on the event
occurrence. There are currently 13 events after the StartRequest event that can
be captured by a DSAPI filter. Depending on the design and its implementation, a
filter can support one or any number of events.
The implementation of the DSAPI interface relies on the filter to indicate
(“register”) which of the events it supports. The filter then receives notifications
from the stack connection manager only for those events it claims it supports.
Figure 7-2 shows where the DSAPI filter comes into play in the Domino HTTP
server in relation to other Web server processing:
TCPIP protocol
stack connection
management
Figure 7-2 Domino 6 Internet protocol stack process flow
DSAPI
Servlet engine
(R5 compatibility)
Internotes web engine
Overall, events occur in a specific sequence. They reflect the state of the HTTP
stack at each of its processing steps. Event notifications can be seen as an
opportunity for a filters, or filters, to override the default implementation of a given
processing step. With each event, a structure, which contains additional
information and in most cases additional callback functions, is passed to the
filter's event notification handling routine. The filter can call the callback functions
to get additional information or to have a service performed. The event
notification routine is only called for those events the filter is registered for (those
that were passed in the Filter Init Data structure when the filter was loaded and
CGI
File system
sequence
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