/* ====================================================================
 * Copyright (c) 1995-1998 The Apache Group.  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.
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 *    distribution.
 *
 * 3. All advertising materials mentioning features or use of this
 *    software must display the following acknowledgment:
 *    "This product includes software developed by the Apache Group
 *    for use in the Apache HTTP server project (http://www.apache.org/)."
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 *    apache@apache.org.
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 *
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 *
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 * on public domain software written at the National Center for
 * Supercomputing Applications, University of Illinois, Urbana-Champaign.
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 * project, please see <http://www.apache.org/>.
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 */

/* proxy_add_forward module
 *
 * This module adds a 'X-Forwarded-For' header to outgoing
 * proxy requests like Squid does.
 *
 * You can then get the client ip back on the "proxied host" by
 * setting r->connection->remote_ip from this header.
 *
 * Ask Bjoern Hansen <ask@netcetera.dk>, October 1998

 * Changes:
 * June   8 1999: Added instructions on how to compile it into the
 *                frontend apache
 *
 * April 12 1999: Changed the sample code so it doesn't confuse the
 *                C compiler, ydkhr! Thanks to Mike Whitaker for 
 *                noticing. 
 *
 * March  1 1999: Added sample code on how to use the header with
 *                mod_perl
 * 

To use the module you have to compile it into the frontend part of
your server, I usually copy the module to apache-1.3/src/modules/extra/
and use APACI like:

  ./configure --prefix=/usr/local/apache \
     --activate-module=src/modules/extra/mod_proxy_add_forward.c \
     --enable-module=proxy_add_forward [... more apaci options ...]    

You should also be able to compile and use this module as a
dynamically loaded module (DSO).
 
TMTOWTDI, but I usually make the 'backend' part of the system
something like the following:

in startup.pl:

  sub My::ProxyRemoteAddr ($) {
    my $r = shift;

	# we'll only look at the X-Forwarded-For header if the requests
	# comes from our proxy at localhost
	return OK unless ($r->connection->remote_ip eq "127.0.0.1");

	if (my ($ip) = $r->header_in('X-Forwarded-For') =~ /([^,\s]+)$/) {
	  $r->connection->remote_ip($ip);
	}
	
	return OK;
  }

And in httpd.conf:

  PerlPostReadRequestHandler My::ProxyRemoteAddr
 
 */


#include "httpd.h"
#include "http_config.h"
#include "http_core.h"

module MODULE_VAR_EXPORT proxy_add_forward_module;

static int add_forward_header(request_rec *r)
{
    if (r->proxyreq) {
	  ap_table_set(r->headers_in, "X-Forwarded-For",
				   r->connection->remote_ip);
	  return OK;
    } 
	return DECLINED;

}

module MODULE_VAR_EXPORT proxy_add_forward_module = {
    STANDARD_MODULE_STUFF,
    NULL,                       /* initializer */
    NULL,                       /* dir config creater */
    NULL,                       /* dir merger --- default is to override */
    NULL,                       /* server config */
    NULL,                       /* merge server configs */
    NULL,                       /* command table */
    NULL,                       /* handlers */
    NULL,                       /* filename translation */
    NULL,                       /* check_user_id */
    NULL,                       /* check auth */
    NULL,                       /* check access */
    NULL,                       /* type_checker */
    add_forward_header,         /* fixups */
    NULL,                       /* logger */
    NULL,                       /* header parser */
    NULL,                       /* child_init */
    NULL,                       /* child_exit */
    NULL                        /* post read-request */
};