C Prototypes for Filter Methods

The C prototypes for the filter methods are:

int insert(FilterLayer *layer, pblock *pb);
void remove(FilterLayer *layer);
int flush(FilterLayer *layer);
int read(FilterLayer *layer, void *buf, int amount, int timeout);
int write(FilterLayer *layer, const void *buf, int amount);
int writev(FilterLayer *layer, const struct iovec *iov, int iov_size);
int sendfile(FilterLayer *layer, sendfiledata *sfd);

The layer parameter is a pointer to a FilterLayer data structure, which contains variables related to a particular instance of a filter.

The most important fields in the FilterLayer data structure are:

• context->sn: Contains information relating to a single TCP/IP session (the same sn pointer that’s passed to SAFs).

• context->rq: Contains information relating to the current request (the same rq pointer that’s passed to SAFs).

• context->data: Pointer to filter-specific data.

• lower: A platform-independent socket descriptor used to communicate with the next filter in the stack.

The meaning of the context->data field is defined by the filter developer. Filters that must maintain state information across filter method calls can use context->data to store that information.

For more information about FilterLayer, see FilterLayer Data Structure.