An awesome caching proxy should...

caching.txt

Imagine something like:

    var http = require('http')
      , cache = require('cache')
      ;

    var options = {
      ignoreCookies: true,
      cacheStatics: 300 // 5 minutes, unless an explicit cache-control header is given
    };

    http.createServer( // bog standard node
      new cache.WriteThroughCache(function(req, res) { // wrap the usual handler in a write-through cache
        // all of the usual node things
      }, options)
    ).listen(80);

Where in reality the server function would be the http-proxy one, which we use for routing to our PHP/Rails/nginx servers.  Though it could be anything that writes HTTP responses.  This is complete pseudo-code.  I have no idea what shape this will take when I actually write it.

What would make it more awesome than Varnish and Squid?

  * Routing and caching contained to a single process = less HTTP hops
  * Being written in node.js = insane concurrency support
  * Being written in node.js = flexibility
  * Being written in node.js = potential to *eventually* do SSL unwrapping and load balancing all in one process
  * Being written in node.js = support for websockets

Assuming that by default the cache is RFC2616 compliant, what options should it support to make it useful as a really agressive cache?

  * Ability to force a resource to be cached, even if some factors would otherwise prevent it
    - is this just cookies in practice, or are there other things?
    - perhaps list headers to ignore if Cache-Control says to cache?
    - allow a callback function to be supplied to do this work?
  * Is caching on disk slow?
    - use memory if possible? multiple "storage" implementations with a defined interface?
    - use a mix of memory/disk?
      * what stays in memory for longer?  recently accessed?  most frequently accessed? smallest file sizes?
  * Should responses for static file types that don't provide a Cache-Control header be cached for some period of time anyway?

What types of things do we fine tune in Squid/Varnish that one might overlook, if they were just following RFC2616 to the letter?