Create a custom proxy server app

Question

A friend of mine asked me this, and I had not much of an idea about it.
So, here I am asking you:

A custom application that works like a proxy server(not the complete version of it), ie The app allows you to specify some websites that the users of the network can visit in their client browsers.

I have some idea, that this functionality is inbuilt in a proxy server and we can use Apache as a proxy server, but I don't know how to do it.

Can I develop such an application in Java, Ruby, or .NET, coz that will allow me to use a database to maintain the list of allowed and blocked websites + I can provide an easier UI to add or modify data.

Help me, I am quite confused.

Answer 1

Any proxy server has this functionality. For example using squid, you can set it to default deny any requests and only allow specific sites. However if that's the only goal, you may want to consider denying requests to port 80 and only allow specific IP ranges in your firewall instead.

Both options work though. The firewall option is faster and cannot be bypassed by the browser, but is less dynamic (DNS resolving only happens on rule start/reload) and may allow more sites then intended if one IP hosts more then one site.

You should probably ask your friend what his/her non-technical goals are. Like "I don't want my daughter to surf porn" rather then "I need an app that blocks sites".