Provided by: freebsd-manpages_8.2-1_all
accf_http — buffer incoming connections until a certain complete HTTP
This is a filter to be placed on a socket that will be using accept() to
receive incoming HTTP connections.
It prevents the application from receiving the connected descriptor via
accept() until either a full HTTP/1.0 or HTTP/1.1 HEAD or GET request has
been buffered by the kernel.
If something other than a HTTP/1.0 or HTTP/1.1 HEAD or GET request is
received the kernel will allow the application to receive the connection
descriptor via accept().
The utility of accf_http is such that a server will not have to context
switch several times before performing the initial parsing of the
request. This effectively reduces the amount of required CPU utilization
to handle incoming requests by keeping active processes in preforking
servers such as Apache low and reducing the size of the file descriptor
set that needs to be managed by interfaces such as select(), poll() or
kevent() based servers.
The accf_http kernel option is also a module that can be enabled at
runtime via kldload(8) if the INET option has been compiled into the
Assuming ACCEPT_FILTER_HTTP has been included in the kernel config file
or the accf_http module has been loaded, this will enable the http accept
filter on the socket sok.
struct accept_filter_arg afa;
setsockopt(sok, SOL_SOCKET, SO_ACCEPTFILTER, &afa, sizeof(afa));
The accept filter mechanism and the accf_http filter were introduced in
This manual page and the filter were written by Alfred Perlstein.