This is a filter to be placed on a socket that will be using
accept() to receive incoming HTTP connections.
Once installed on a listening socket, this filter is activated when a connection becomes ready to receive data (at which point
accept(2) would usually return the connected descriptor to the application). The filter prevents the descriptor from being returned immediately to the application via
accept(2). The descriptor is made available to the application via
accept(2) only when one of the following conditions is met:
1.
A complete, syntactically valid HTTP/1.0 or HTTP/1.1 HEAD or GET request has been buffered by the kernel.
2.
The data buffered by the kernel cannot be part of a complete, syntactically valid HTTP 1.0 or HTTP/1.1 HEAD or GET request.
The utility of
accf_http is 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.