An Introduction to Rack Benjamin Curtis / [email protected] / @stympy 

A minimal API for connecting web servers and web frameworks What is Rack? 

You get an environment hash, and you return an array of status code, headers hash, and response body Just how minimal? 

Or, in other words… # my_rack_app.rb
 
 require 'rack'
 
 app = Proc.new do |env|
 ['200', {'Content-Type' => 'text/html'}, ['A barebones rack app.']]
 end
 
 Rack::Handler::WEBrick.run app 

The Internet talks to your web server that talks to a Ruby web server that serves your application How does it work? 

That’s a lot of web servers! o.O 

Middleware But, Rails! Why do I care? 

It’s a Freedom Patch for the Interwebs! Middlewhat? 

The refresh button, it does nothing! Rack::Etag 

Please Hammer, don’t hurt ‘em Rack::Attack 

Bit conservation to fight global warming! Rack::Deflater 

github.com/rack/rack-contrib And many more… 

You can build an entire web app* with Rack But it’s not just middleware *For certain values of app 

Rack it up require './compressed_requests'
 require './key_checker'
 require './collector'
 
 use CompressedRequests
 use KeyChecker
 
 run Collector
 

Decompress class CompressedRequests
 ValidMethods = { 'POST' => true, 'PUT' => true }.freeze
 ValidEncodings = { 'gzip' => true, 'deflate' => true }.freeze
 
 def initialize(app)
 @app = app
 end
 
 def call(env)
 if ValidMethods[env['REQUEST_METHOD']] && ValidEncodings[env['HTTP_CONTENT_ENCODING']]
 extracted = case env['HTTP_CONTENT_ENCODING']
 when 'gzip' then Zlib::GzipReader.new(env['rack.input']).read
 when 'deflate' then Zlib::Inflate.inflate(env['rack.input'].read)
 end
 
 env.delete('HTTP_CONTENT_ENCODING')
 env['CONTENT_LENGTH'] = extracted.length
 env['rack.input'] = StringIO.new(extracted)
 end
 
 @app.call(env)
 end
 end
 

Authenticate class KeyChecker
 def initialize(app)
 @app = app
 end
 
 def call(env)
 @req = Rack::Request.new(env)
 env['hb.api_key'] = @api_key = @req.env['HTTP_X_API_KEY'] || @req.params['api_key']
 
 if @api_key.nil? || @api_key == ""
 return bail_with_message("Invalid API key")
 end
 @app.call(env)
 end
 
 def bail_with_message(message, code = 403)
 if @req.env['HTTP_ACCEPT'].to_s.match(%r{text/html})
 [ code, { 'Content-Type' => 'text/html' }, [ message ] ]
 else
 [ code, { 'Content-Type' => 'application/json' }, [ %Q{{"error":"#{message}"}} ] ]
 end
 end
 end
 

Do something class Collector
 Headers = {
 html: { "Content-Type" => "text/html" },
 json: { "Content-Type" => "application/json" },
 }.freeze
 def self.call(env)
 req = Rack::Request.new(env)
 api_key = env['hb.api_key']
 
 case req.path_info
 when “/v1/notices" id = do_some_work(api_key, req)
 render(%Q{{"id":"#{id}"}})
 end end
 
 def self.render(body, headers = Headers[:json], status = 201)
 [ status, headers, [ body ] ]
 end
 
 end 

Check out a microframework… mount a Rack endpoint in your Rails app… go wild! Now what? 

Thanks! Benjamin Curtis / [email protected] / @stympy speakerdeck.com/stympy