accf_http —
buffer incoming connections until a certain
complete HTTP requests arrive
| options ACCEPT_FILTER_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 kernel.
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;
bzero(&afa, sizeof(afa));
strcpy(afa.af_name, "httpready");
setsockopt(sok, SOL_SOCKET, SO_ACCEPTFILTER, &afa, sizeof(afa));
setsockopt(2),
accept_filter(9)
The accept filter mechanism and the accf_http filter were introduced in
FreeBSD 4.0.
This manual page and the filter were written by
Alfred Perlstein.