Example: mobile phone redirection.
We want to redirect all mobile phones from http://www.mysite.com to http://mobile.mysite.com

The client type is done with the HTTP User-Agent header sent by the browser. Problem: Squid will put in cache only one version of the query to http://www.mysite.com. The response from the cache will probably be the home page, not the 301 redirection.

It’s also possible to configure the HTTP server to add the Vary: User-Agent header to tell Squid to store one version by browser. With this the cache will be split (one cache per browser), lowering a lot the cache efficiency.

Here is the solution:

###################################
# we redirect mobiles to mobile.mysite.com
url_rewrite_program /etc/squid/redirect_mobile.sh

acl symbian browser Symbian
acl iphone browser iP(hone|od)
acl mobile_url dstdomain mobile.monsite.com

url_rewrite_access deny mobile_url
url_rewrite_access allow symbian
url_rewrite_access allow iphone
url_rewrite_access deny all

And the /etc/squid/redirect_mobile.sh script simply contains:

#!/bin/sh
while read line
do
        echo "301:http://mobile.mysite.com"
done

Notes:

• The mobile detection method is far from being exhaustive. If you know a simple method covering 95% of browsers, I’m interested!
• With more recent Squid versions (3, 2.HEAD), you can use a better method using internal redirectors.

Links:

• http://www.squid-cache.org/Versions/v2/2.6/cfgman/
• http://wiki.squid-cache.org/Features/Redirectors
• http://wiki.squid-cache.org/Features/InternalRedirectors
• http://wiki.squid-cache.org/ConfigExamples/PhpRedirectors
• http://www1.za.squid-cache.org/mail-archive/squid-users/200507/0247.html