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From: Martin Kraemer <Martin.Kraemer@mch.sni.de>
Message-Id: <199704181000.MAA03171@deejai.mch.sni.de>
Subject: [TIP]: How to use an Apache Proxy to filter Advertisements
To: new-httpd@apache.org (Apache Mailing List),
        sni.intranet.usenet@deejai.mch.sni.de
Date: Fri, 18 Apr 1997 12:00:01 +0200 (MET DST)
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Hi,

Here's a short note about a "feature" which can easily be realized using
one of the latest apaches: the optional filtering of unwanted
ads/commercials/promotions/sponsor banners etc. In place of the
requested advertisement gif, a small "NoAds.gif" image is delivered
(which is available locally on the server).

On our proxy server, we offer a second port which delivers the filtered
services, while the primary port works transparently:

    Port   80
    # Primary server Port 80
    Listen 80
    # Anti-SPAM Port 81
    Listen 81

We configure our server as proxy and enable the rewriting module (needs
mod_rewrite and mod_proxy defined in Configuration, and mod_proxy must
be defined _prior_to_ the definition of mod_rewrite!!!):

<IfModule mod_proxy.c>
  ProxyRequests      On
  ProxyRemote        *        http://firewall.to.inter.net
</IfModule>

This virtual host on the second port is now configured to filter ads.
A <VirtualHost> directive is used for this purpose, in order not to
disturb services on the primary port. The rules can be explained as
follows:

    1) When the browser sent a "Pragma: No-Cache" header (Reload pressed),
       proceed normally and serve the request. Otherwise:

    2) if the request contains a subdirectory called /sponsor/, /ads/, /
       promotion/ and the like, (or /werbung/ for a german server),
       then:

    3) serve the NoAds.gif instead.

The rules could of course be refined to check whether the request really
tried to load a *.jpeg, *.gif or *.png graphics file. But the result is
already astonishingly successful.

<VirtualHost myproxy.mch.sni.de:81>
  ServerAdmin WebMaster+81@myproxy.mch.sni.de
  ServerName myproxy.mch.sni.de
  ##### Anti-SPAM on port 81. Filter out typical commercials, unless [Reload] pressed
  RewriteEngine On
  #RewriteLog   logs/rewrite_log
  #RewriteLogLevel 2
  RewriteCond  %{HTTP:Pragma}  !^no-cache                               [NC]
  RewriteCond  %{REQUEST_URI}  ^http://[^/]*.*/[Pp]romotions/           [OR]
  RewriteCond  %{REQUEST_URI}  ^http://[^/]*.*/[Aa]d[vs]/               [OR]
  RewriteCond  %{REQUEST_URI}  ^http://[^/]*.*/[Ss]ponsors*/            [OR]
  RewriteCond  %{REQUEST_URI}  ^http://[a-zA-Z0-9.]*.de/[Ww]erbung/
  RewriteRule  ^.*$            /var/WWW/Web/images/NoAds.gif
</VirtualHost>

Cheers,
    Martin