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
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
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
kevent() based servers.
Assuming ACCEPT_FILTER_HTTP has been included in the kernel config file or the
accf_http kernel option is also a
module that can be enabled at runtime via
if the INET option has been compiled into the kernel.
accf_http module has been loaded, this will enable the
http accept filter on the socket sok.
The accept filter mechanism and the accf_http filter were introduced in
This manual page and the filter were written by Alfred
struct accept_filter_arg afa;
setsockopt(sok, SOL_SOCKET, SO_ACCEPTFILTER, &afa, sizeof(afa));