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Building Web Services (HTTP APIs) with Ruby (and Sinatra)

Agenda

  • What's Sinatra?
  • Let a Thousand Sinatra Clones Bloom
  • Why Sinatra? Goodies
  • Example Web Service (HTTP API) - Routes
  • Sinatra in Action - get '/beer/:key'
  • What's JSON?
  • What's JSONP?
  • Serializers - From Ruby Objects to JavaScript Objects
  • Appendix: Sinatra Styles - Classic or Modern (Modular)
  • Appendix: Database Connection Management
  • Appendix: Sinatra Books
  • Appendix: What's Rack?

What's Sinatra?

Simple (yet powerful and flexible) micro webframework.

require 'sinatra'

get '/' do
  'Hallo Wien!'
end

Sinatra itself less than 2000 lines of code.

Installation. Type in your terminal (shell):

$ gem install sinatra

What's Sinatra? (Continued)

Example - hallo.rb:

require 'sinatra'

get '/' do
  'Hallo Wien!'
end

Run script (server):

$ ruby hallo.rb

>> Sinatra has taken the stage...
>> Listening on 0.0.0.0:4567, CTRL+C to stop

Open browser:

Let a Thousand Sinatra Clones Bloom

Micro Frameworks Inspired by Sinatra

Express.js (in Server-Side JavaScript w/ Node.js):

var express = require( 'express' );
var app = express();

app.get( '/', function( req, res ) {
  res.send( 'Hallo Wien!' );
});

app.listen( 4567 );

Scotty (in Haskell):

import Web.Scotty

main :: IO ()
main = scotty 4567 $ do
    get "/" $ text "Hallo Wien!"

Dancer (Perl), Fitzgerald (PHP), Ratpack (Groovy), Zappa (CoffeeScript), Mercury (Lua), Frank (F#), Nancy (C#/.NET), Bogart (C), Flask (Python), and many more.

Why Sinatra? Goodies

  1. Single file scripts

  2. Easy to package up into a gem. Example:

    $ gem install beerdb # Yes, the beerdb includes a Sinatra app.

  3. Lets you build command line tools. Example:

    $ beerdb serve # Startup web service (HTTP API).

  4. Lets you mount app inside app (including Rails). Example:

    mount BeerDb::Server, :at => '/api/v1'

Example Web Service (HTTP API) - Routes

Lets build a beer and brewery API.

Get beer by key /beer/:key. Examples:

  • /beer/guinness
  • /beer/murphysred
  • /beer/brooklynlager
  • /beer/ottakringerhelles

Get brewery by key /brewery/:key. Examples:

  • /brewery/guinness
  • /brewery/fullers
  • /brewery/brooklyn
  • /brewery/ottakringer

Bonus:

Get random beer /beer/rand and random brewery /brewery/rand.

Sinatra in Action - get '/beer/:key'

beerdb/server.rb:

get '/beer/:key' do |key|

  beer = Beer.find_by_key!( key )
  json_or_jsonp( beer.as_json )

end

get '/brewery/:key' do |key|

  brewery = Brewery.find_by_key!( key )
  json_or_jsonp( brewery.as_json )

end

That's it.

Bonus:

get '/beer/:key' do |key|

  if ['r', 'rnd', 'rand', 'random'].include?( key )
    beer = Beer.rnd.first
  else
    beer = Beer.find_by_key!( key )
  end

  json_or_jsonp( beer.as_json )
end

get '/brewery/:key' do |key|

  if ['r', 'rnd', 'rand', 'random'].include?( key )
    brewery = Brewery.rnd.first
  else
    brewery = Brewery.find_by_key!( key )
  end

  json_or_jsonp( brewery.as_json )
end

What's JSON?

JSON = JavaScript Object Notation

Example - GET /beer/ottakringerhelles:

{
  key: "ottakringerhelles",
  title: "Ottakringer Helles",
  synonyms: "16er Blech|16er Hüs'n",
  abv: "5.2",
  og: "11.8",
  tags: [ "lager" ],
  brewery: {
    key: "ottakringer",
    title: "Ottakringer Brauerei"
  },
  country: {
   key: "at",
   title: "Austria"
  }
}

What's JSONP?

JSONP = JSON with Padding. Why?

Call Home Restriction. Cross-Domain Browser Requests Get Blocked.

Hack: Wrap JSON into a JavaScript function/callback e.g. functionCallback( <json_data_here> ) and serve as plain old JavaScript.

Example - Content-Type: application/json:

{
  key: "ottakringerhelles",
  title: "Ottakringer Helles",
  synonyms: "16er Blech|16er Hüs'n",
  abv: "5.2",
  ...
}

becomes Content-Type: application/javascript:

functionCallback(
  {
    key: "ottakringerhelles",
    title: "Ottakringer Helles",
    synonyms: "16er Blech|16er Hüs'n",
    abv: "5.2",
    ...
  }
);

Bonus: Little Sinatra helper for JSON or JSONP response (depending on callback parameter).

def json_or_jsonp( json )
  callback = params.delete('callback')

  if callback
    content_type :js
    response = "#{callback}(#{json})"
  else
    content_type :json
    response = json
  end
end

Serializers - From Ruby Objects (in Memory) to JavaScript Object (in Text)

JSON built into Ruby 2.0 as a standard library. Example:

require 'json'

hash =
{
  key:   "ottakringerhelles",
  title: "Ottakringer Helles"
}

1) JSON.generate

puts JSON.generate( hash )

>> {"key":"ottakringerhelles","title":"Ottakringer Helles"}

2) #to_json

puts hash.to_json

>>  {"key":"ottakringerhelles","title":"Ottakringer Helles"}

Serializers - From Ruby Objects (in Memory) to JavaScript Object (in Text) Continued

Serializers for your Models. Example:

class BeerSerializer

  def initialize( beer )
    @beer = beer
  end

  attr_reader :beer

  def as_json
    data = { key:      beer.key,
             title:    beer.title,
             synonyms: beer.synonyms,
             abv:      beer.abv,
             ...
           }
    data.to_json
  end

end # class BeerSerializer

And add as_json to your Model. Example:

class Beer < ActiveRecord::Base

  def as_json_v2( opts={} )
    BeerSerializer.new( self ).as_json
  end

end # class Beer

That's it. Thanks.

Questions? Comments?

Learn more about Sinatra @ sinatrarb.com

Learn more about the open beer 'n' brewery database (beer.db) @ github.com/openbeer

Appendix: Sinatra Styles - Classic or Modern (Modular)

require 'sinatra'

get '/' do
  'Hallo Wien!'
end

vs.

require 'sinatra/base'

class Server < Sinatra::Base

  get '/' do
    'Hallo Wien!'
  end

end

Appendix: Tip - Database Connection Management

Sinatra will NOT auto-magically close your database connection after every request. It's up to you.

  1. Use the ConnectionManagement middleware. Example:
Server.use ActiveRecord::ConnectionAdapters::ConnectionManagement
  1. Or do it yourself. Example:
Server.after do
  ActiveRecord::Base.connection.close
end

Appendix: Sinatra Books

Sinatra: Up and Running by Alan Harris, Konstantin Haase; November 2011, O'Reilly, 122 Pages

Jump Start Sinatra by Darren Jones; January 2013, SitePoint, 150 Pages

Appendix: What's Rack?

Lets you mix 'n' match servers and apps.

Lets you stack apps inside apps inside apps inside apps inside apps.

Good News: A Sinatra app is a Rack app.

Learn more about Rack @ rack.github.io.