Rack apps and middleware

What is Rack?

• Number 2 most downloaded gem on rubygems.org
• A spec for code that responds to HTTP:
  1. Object that responds to call
  2. Takes one argument (env)
  3. Returns [status, headers, body] where body responds to each

Why Rack?

• Universal adapter
  • Original design
  • Only useful for framework/webserver designers

Without Rack

With Rack

Other uses

• Good model for HTTP requests
• Middleware

Basic Rack app

• Class or proc based.
• env is a big hash of stuff from the request. See app the outputs its env and list of keys in such an env

Middleware

• Sits between the user and the app
• Can intercept requests/responses and modify them
• Can be chained together

Example middleware (logs time):

• App
• Logger middleware
• Runner

Rack::Builder

• Shortcut to all the nesting
• use for Middleware (classes)
• run for apps (instance)
• run via the command-line with rackup

Example middleware (logs time):

• App
• Logger middleware
• Rackup file

Rails on Rack

• Rails apps are rack apps (see config.ru)
• Rails has middleware (see rake middleware)
• Cookies, sessions, and params are handled by middleware
• Routes can point to any Rack app (or stack)

In the wild

• Rack::Attack (rate limiting)
• Rack::Honeypot (spam trap)