.\"
.\" Copyright (c) 2000 Alfred Perlstein
.\"
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR
.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT,
.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
.\" $FreeBSD: src/share/man/man9/accf_http.9,v 1.1.2.6 2002/07/02 01:03:59 brian Exp $
.\" $DragonFly: src/share/man/man9/accf_http.9,v 1.2 2003/06/17 04:37:01 dillon Exp $
.\" "
.Dd November 15, 2000
.Os
.Dt ACCF_HTTP 9
.Sh NAME
.Nm accf_http
.Nd "buffer incoming connections until a certain complete HTTP requests arrive"
.Sh SYNOPSIS
.Nm options INET
.Nm options ACCEPT_FILTER_HTTP
.Nm kldload accf_http
.Sh DESCRIPTION
This is a filter to be placed on a socket that will be using
.Fn accept
to receive incoming HTTP connections.
.Pp
It prevents the application from receiving the connected descriptor via
.Fn accept
until either a full HTTP/1.0 or HTTP/1.1 HEAD or GET request has
been buffered by the kernel.
.Pp
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
.Fn accept .
.Pp
The utility of
.Xr accf_http 9
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 filedescriptor set that needs
to be managed by interfaces such as
.Fn select ,
.Fn poll
or
.Fn kevent
based servers.
.Pp
The
.Xr accf_http 9
kernel option is also a module that can be enabled at runtime via
.Xr kldload 8
if the INET option has been compiled into the kernel.
.Sh EXAMPLE
Assuming ACCEPT_FILTER_HTTP has been included in the kernel config
file or the module
.Xr accf_http 9
has been loaded, this will enable the http accept filter
on the socket
.Fa sok .
.Bd -literal -offset 0i
	struct accept_filter_arg afa;

	bzero(&afa, sizeof(afa));
	strcpy(afa.af_name, "httpready");
	setsockopt(sok, SOL_SOCKET, SO_ACCEPTFILTER, &afa, sizeof(afa));
.Ed
.Sh SEE ALSO
.Xr setsockopt 2 ,
.Xr accept_filter 9
.Sh HISTORY
The accept filter mechanism and the
accf_http filter were introduced in
.Fx 4.0 .
.Sh AUTHORS
This manual page and the filter were written by
.An Alfred Perlstein .