Varnish - 7.x-2.x battle plan

So we finally have a stable D6 release, so now it's time to get something out for Drupal 7. I have a lot of thoughts about how this can be accomplished and here are some of them:

Create a cache plugin for varnish

The cache plugins are improved in Drupal 7, so instead of trying to do the same thing that core does ourselves for purging the cache, we could just implement a cache plugin that the site uses. This makes the varnish cache implementation work just as all other cache plugins does, instead of it being stand-alone as it is right now. This will result in quite a bit less code.

Replace the current procedural code for connecting with a class

Instead of having procedural code for connecting to a varnish terminal and issue commands, we could have a class that represents a connection. This class should have a method for each command that you can execute in the varnish terminal.
This means that:

* Each connection can be made easily by creating an instance of a VarnishConnection class.
* Everything you would want to do with the terminal is easily accessible and abstracted.

It might be a good idea to have these connections as ctools plugins, so that you could extend it and provide your own connection classes that handle stuff differently and provide more functionality. For this to be accessible, we will need an interface that describes what should be possible with a varnish connection.

By doing this, the varnish module will become easier to extend and use as an API module for dealing with Varnish.