When a Rack-based framework (Rails >= 2.3, Sinatra, etc) serves a static file, it uses the Rack mimetimes hash to map the file’s extension to the Content-Type header on the response. For example, serving text/plain for .txt, or image/jpeg for .jpg.

Cyril Rohr gives us Cacheability, a caching HTTP client which cleverly mashes together RestClient and Rack::Cache. It can cache results in memory, on the filesystem, or in memcached. Grab a copy:

Rack is one of the most important developments in the Ruby web space in the past year. I suspect it’s been slow to get attention because the benefits are a bit subtle. Witness the Rails core team being confused about Rack just a few months ago. So if you don’t get what the deal is with Rack, don’t feel bad - you’re in good company.