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ACCF_HTTP(9)               Kernel Developer's Manual              ACCF_HTTP(9)

     accf_http - buffer incoming connections until a certain complete HTTP
     requests arrive

     options INET
     pseudo-device accf_http

     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

     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

     If the accf_data accept filter is present in the kernel configuration,
     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.  They were ported to NetBSD by Coyote Point Systems and
     appeared in NetBSD 5.0.

     This manual page and the filter were written by Alfred Perlstein.

NetBSD 10.99                   September 4, 2008                  NetBSD 10.99