Building web framework with Rack

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Building web framework with Rack Marcin Kulik EuRuKo, 2010/05/30

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I am: Senior developer @ Lunar Logic Polska - agile Ruby on Rails development services Working with web for 10 years Using Ruby, Python, Java and others - in love with Ruby since 2006

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Open Source contributor: CodeRack.org - Rack middleware repository Open File Fast - Netbeans and JEdit plugin racksh - console for Rack apps and many more (check github.com/sickill)

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Why would you need another framework? "Because world needs yet another framework ;-)" - Tomash

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No, you probably don't need it actually :)

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Several mature frameworks Tens of custom/experimental ones "Don't reinvent the wheel", right? But...

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But it's so easy that you should at least try

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Rack provides everything you'll need, is extremely simple but extremely powerful It will help you to better understand HTTP It will make you better developer Your custom framework will be the fastest one * It's fun! A lot of fun :)

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What is Rack?

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Ruby web applications interface library

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Simplest Rack application run lambda do |env| [200, { "Content-type" => "text/plain" }, ["Hello"]] end

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Simplest Rack middleware class EurukoMiddleware def initialize(app) @app = app end def call(env) env['euruko'] = 2010 @app.call end end

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Let's transform it into framework!

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How does typical web framework look like?

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Rails Merb Pylons Django Rango

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Looks like MVC, more or less

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What features we'd like to have?

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dependencies management RESTful routing controllers (session, flash messages) views (layouts, templates, partials) ORM authentication testing console

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Available Rack middleware and tools we can use

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(1/8) Gem dependency management

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bundler "A gem to bundle gems" github.com/carlhuda/bundler

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# Gemfile source "http://gemcutter.org" gem "rack" # config.ru require "bundler" Bundler.setup Bundler.require

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(2/8) Routing

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Usher "Pure ruby general purpose router with interfaces for rails, rack, email or choose your own adventure" github.com/joshbuddy/usher

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# Gemfile gem "usher" # config.ru require APP_ROOT / "config" / "router.rb" run Foobar::Router

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# config/router.rb module Foobar Router = Usher::Interface.for(:rack) do get('/').to(HomeController.action(:welcome)).name(:root) # root add('/login').to(SessionController.action(:login)).name(:login) get('/logout').to(SessionController.action(:logout)).name(:logo ... default ExceptionsController.action(:not_found) # 404 end end

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(3/8) Controller

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Let's build our base controller every action is valid Rack endpoint value returned from action becomes body of the response

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# lib/base_controller.rb module Foobar class BaseController def call(env) @request = Rack::Request.new(env) @response = Rack::Response.new resp_text = self.send(env['x-rack.action-name']) @response.write(resp_text) @response.finish end def self.action(name) lambda do |env| env['x-rack.action-name'] = name self.new.call(env) end end end end

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# config.ru require APP_ROOT / "lib" / "base_controller.rb" Dir[APP_ROOT / "app" / "controllers" / "*.rb"].each do |f| require f end

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Now we can create UsersController

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# app/controllers/users_controller.rb class UsersController < Foobar::BaseController def index "Hello there!" end end

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Controllers also need following: session access setting flash messages setting HTTP headers redirects url generation

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rack-contrib "Contributed Rack Middleware and Utilities" github.com/rack/rack-contrib rack-flash "Simple flash hash implementation for Rack apps" nakajima.github.com/rack-flash

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# Gemfile gem "rack-flash" gem "rack-contrib", :require => 'rack/contrib' # config.ru use Rack::Flash use Rack::Session::Cookie use Rack::MethodOverride use Rack::NestedParams

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# lib/base_controller.rb module Foobar class BaseController def status=(code); @response.status = code; end def headers; @response.header; end def session; @request.env['rack.session']; end def flash; @request.env['x-rack.flash']; end def url(name, opts={}); Router.generate(name, opts); end def redirect_to(url) self.status = 302 headers["Location"] = url "You're being redirected" end end end

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Now we can use #session, #flash and #redirect_to

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# app/controllers/users_controller.rb class UsersController < Foobar::BaseController def openid if session["openid.url"] flash[:notice] = "Cool!" redirect_to "/cool" else render end end end

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(4/8) Views

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Tilt "Generic interface to multiple Ruby template engines" github.com/rtomayko/tilt

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# Gemfile gem "tilt"

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# lib/base_controller.rb module Foobar class BaseController def render(template=nil) template ||= @request.env['x-rack.action-name'] views_path = "#{APP_ROOT}/app/views" template_path = "#{views_path}/#{self.class.to_s.underscore}/" + "#{template}.html.erb" layout_path = "#{views_path}/layouts/application.html.erb" Tilt.new(layout_path).render(self) do Tilt.new(template_path).render(self) end end end end

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(5/8) ORM

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DataMapper "DataMapper is a Object Relational Mapper written in Ruby. The goal is to create an ORM which is fast, thread-safe and feature rich." datamapper.org

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# Gemfile gem "dm-core" gem "dm-..." # app/models/user.rb class User include DataMapper::Resource property :id, Serial property :login, String, :required => true property :password, String, :required => true end # config.ru Dir[APP_ROOT / "app" / "models" / "*.rb"].each do |f| require f end

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(6/8) Authentication

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Warden "General Rack Authentication Framework" github.com/hassox/warden

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# Gemfile gem "warden" # config.ru use Warden::Manager do |manager| manager.default_strategies :password manager.failure_app = ExceptionsController.action(:unauthenticated) end require "#{APP_ROOT}/lib/warden.rb"

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# lib/warden.rb Warden::Manager.serialize_into_session do |user| user.id end Warden::Manager.serialize_from_session do |key| User.get(key) end Warden::Strategies.add(:password) do def authenticate! u = User.authenticate( params["username"], params["password"] ) u.nil? ? fail!("Could not log in") : success!(u) end end

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# lib/base_controller.rb module Foobar class BaseController def authenticate! @request.env['warden'].authenticate! end def logout!(scope=nil) @request.env['warden'].logout(scope) end def current_user @request.env['warden'].user end end end

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Now we can guard our action: # app/controllers/users_controller.rb class UsersController < Foobar::BaseController def index authenticate! @users = User.all(:id.not => current_user.id) render end end

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(7/8) Testing

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rack-test "Rack::Test is a small, simple testing API for Rack apps. It can be used on its own or as a reusable starting point for Web frameworks and testing libraries to build on." github.com/brynary/rack-test

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# Gemfile gem "rack-test"

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require "rack/test" class UsersControllerTest < Test::Unit::TestCase include Rack::Test::Methods def app Foobar::Router.new end def test_redirect_from_old_dashboard get "/old_dashboard" follow_redirect! assert_equal "http://example.org/new_dashboard", last_request.url assert last_response.ok? end end

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(8/8) Console

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racksh (aka Rack::Shell) "racksh is a console for Rack based ruby web applications. It's like Rails script/console or Merb's merb -i, but for any app built on Rack" github.com/sickill/racksh

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Installation

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gem install racksh

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Example racksh session

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$ racksh Rack::Shell v0.9.7 started in development environment. >> $rack.get "/" => #"text/html", "Content-Length"=>"1812"} @status=200, ... >> User.count => 123

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Questions?

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That's it! Example code available at: github.com/sickill/example-rack- framework email: marcin.kulik at gmail.com / www: ku1ik.com / twitter: @sickill