I live in an area where reliable DSL is not available, therefore I access the Internet at home using 3G mobile broadband and short wave radio. However, my 3G mobile broadband contract is limited to 15GB of bandwidth per month, if I exceed that limit then I start incurring additional charges which can mount up very quickly.

nullserv is a minimal webserver. It's only purpose is to serve up null content. nullserv was inspired by pixelserv which serves a 1x1 pixel transparent .gif. nullserv expands on this idea by serving up null .html, .js, .css, .php, .cgi, .pl, .asp, .aspx, .txt, .gif, .png, .jpeg and .swf files.

Using some creative firewalling (netfilter/iptables) rules or local DNS you can redirect some requests (for adverts for example) to nullserv, thus saving bandwidth :-)

nullserv is heavily based on in.www which is part of the excellent inetdextra package. The null .swf is compiled from swfdec_test_initialize.as which is part of swfdec 0.9.2.

I developed nullserv on Ubuntu Lucid 10.04 LTS and deployed it on a NSLU2 running Debian Lenny.

make
sudo make install

• inetd (or similar).

Currently, I'm using dnsmasq on a Gargoyle router to redirect ad-server IP addresses to nullserv running on an embedded Debian Squeeze box. Gargoyle is based on OpenWRT, so this technique should also work with OpenWRT.

Install git and the compiler toolchain.

sudo apt-get install build-essential git-core

Compile and install nullserv

git clone https://github.com/flexiondotorg/nullserv.git
cd nullserv
make
sudo make install

Install OpenBSD inetd.

sudo apt-get install openbsd-inetd

Add the following to /etc/inetd.conf

www  stream  tcp  nowait  nobody  /usr/sbin/tcpd  /usr/bin/nullserv

Restart inetd.conf.

sudo /etc/init.d/openbsd-inetd restart

Some ads are served via https, we can use stunnel to forward https connections to nullserv.

Install stunnel

sudo apt-get install stunnel

Create SSL certificate and a key.

sudo openssl req -new -nodes -x509 -out /etc/ssl/certs/stunnel.pem -keyout /etc/ssl/certs/stunnel.pem

Enable the [https] section in /etc/stunnel.conf, I also disable the [pop3s], [imaps] and [ssmtp] as I don't require them.

[https]
accept  = 443
connect = 80
TIMEOUTclose = 0

Enable stunnel in /etc/default/stunnel4. Find ENABLED and set it to 1.

ENABLED=1

Start stunnel.

sudo /etc/init.d/stunnel4 start

Open a web browser and request anything you like from http://192.168.2.1 or whatever the IP address is the host where nullserv is installed. If you request a file type that is not recognised by nullserv it with send back a 0 byte response of Content-Type: text/plain.

Run contrib/adaway.sh and then scp the generated adaway.txt to /etc/ on your Gargoyle/OpenWRT router.

cd contrib ./adaway.sh scp adaway.txt root@192.168.2.1:/etc/

Add the following to /etc/config/dhcp under the config dnsmasq section.

list addnhosts '/etc/adaway.txt'

Restart dnsmasq

/etc/init.d/dnsmasq restart

You should now find that ads are blocked and replaced with null content. You can do lots more with dnasmasq on Gargoyle/OpenWRT, see the Wiki:

• http://wiki.openwrt.org/doc/uci/dhcp

• Merged fixes and improvements contributed by Ben Shadwick.
• Updated documentation.

• Added optional logging.

• Initial release

• I am not a C programmer ;-)

• Document dnsmasq and in.dns configurations to compliment nullserv.

You can grab the source from Launchpad. Contributions are welcome :-)

• https://github.com/flexiondotorg/nullserv

A minimal webserver for serving up null content. Copyright (c) 2013 Flexion.Org, http://flexion.org/

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.