accf_dns —
buffer incoming DNS requests until the whole first
request is present
| options ACCEPT_FILTER_DNS |
|
This is a filter to be placed on a socket that will be using
accept() to receive incoming connections.
It prevents the application from receiving the connected descriptor via
accept() until a whole DNS request is available
on the socket. It does this by reading the first two bytes of the request, to
determine its size, and waiting until the required amount of data is available
to be read.
The
ACCEPT_FILTER_DNS kernel option is also a
module that can be enabled at runtime via
kldload(8) if the INET option has been compiled
into the kernel.
If the
accf_dns module is available in the kernel,
the following code will enable the DNS accept filter on a socket
sok.
struct accept_filter_arg afa;
bzero(&afa, sizeof(afa));
strcpy(afa.af_name, "dnsready");
setsockopt(sok, SOL_SOCKET, SO_ACCEPTFILTER, &afa, sizeof(afa));
setsockopt(2),
accept_filter(9),
accf_data(9),
accf_http(9)
The accept filter mechanism was introduced in
FreeBSD
4.0.
This manual page and the filter were written by
David Malone.