01_invalid_usage_em-http.rb

class ItemsController < ApplicationController
  RWS_URL = 'https://app.rakuten.co.jp'

  def index
    items = http_get({'keyword' => params['keyword']})

    render :json => items
  end

  private 
  def http_get(query)
    response = nil
    query = query.merge({'applicationId' => ENV['APPLICATION_ID'],
                         'format' => 'json'})
    http = EM::HttpRequest.new(RWSC_URL).get(
      :path => '/services/api/IchibaItem/Search/20120723',
      :query => query)
    http.callback { response = http.response }
    http.errback  { logger.error http.error }
    return response
  end
end

02_development.log

$ bundle exec rails s
=> Booting Thin
=> Rails 3.2.8 application starting in development on http://0.0.0.0:3000
=> Call with -d to detach
=> Ctrl-C to shutdown server
>> Thin web server (v1.4.1 codename Chromeo)
>> Maximum connections set to 1024
>> Listening on 0.0.0.0:3000, CTRL+C to stop


Started GET "/items?keyword=abc" for 127.0.0.1 at 2012-10-31 03:21:25 +0900
Processing by ItemsController#index as HTML
  Parameters: {"keyword"=>"abc"}
Completed 200 OK in 23ms (Views: 0.2ms)

03_correct_usage_of_em-http.rb

require 'fiber'

class ItemsController < ApplicationController
  RWS_URL = 'https://app.rakuten.co.jp'

  def index
    items = http_get({'keyword' => params['keyword']})

    render :json => items
  end

  private 
  def http_get(query)
    f = Fiber.current
    query = query.merge({'applicationId' => ENV['APPLICATION_ID'],
                         'format' => 'json'})
    http = EM::HttpRequest.new(RWSC_URL).get(
      :path => '/services/api/IchibaItem/Search/20120723',
      :query => query)
    http.callback { f.resume http.response }
    http.errback  { f.resume nil }
    return Fiber.yield
  end
end

bad_use.rb

require 'eventmachine'
require 'em-http-request'

RWS_URL = 'https://app.rakuten.co.jp'

def http_get(query)
  response = 'init'
  query = query.merge('applicationId' => ENV['APPLICATION_ID'],
                      'format' => 'json')
  http = EM::HttpRequest.new(RWS_URL).get(
          :path => '/services/api/IchibaItem/Search/20120723',
          :query => query)
  http.callback { response = http.response }
  return response
end

keyword = ARGV.shift

EM.run do
  puts http_get('keyword' => keyword)
  EM.stop
end

good_use.rb

require 'eventmachine'
require 'em-http-request'

RWS_URL = 'https://app.rakuten.co.jp'

def http_get(query, &block)
  response = 'init'
  query = query.merge('applicationId' => ENV['APPLICATION_ID'],
                      'format' => 'json')
  http = EM::HttpRequest.new(RWS_URL).get(
          :path => '/services/api/IchibaItem/Search/20120723',
          :query => query)
  call_back = proc do
    case block.arity
    when 0 then block.call
    when 1 then block.call(http.response)
    else block.call(http.response, http.error)
    end
  end
  http.callback(&call_back)
  http.errback(&call_back)
end

keyword = ARGV.shift

EM.run do
  http_get('keyword' => keyword) do |response|
    puts response
    EM.stop
  end
end

good_use_with_fiber.rb

require 'eventmachine'
require 'em-http-request'
require 'fiber'

RWS_URL = 'https://app.rakuten.co.jp'

def http_get(query, &block)
  response = 'init'
  query = query.merge('applicationId' => ENV['APPLICATION_ID'],
                      'format' => 'json')
  f = Fiber.current
  http = EM::HttpRequest.new(RWS_URL).get(
          :path => '/services/api/IchibaItem/Search/20120723',
          :query => query)
  call_back = proc do
    f.resume http.response # <= (3)
  end
  http.callback(&call_back)
  http.errback(&call_back)
  return Fiber.yield # <= (2)
end

keyword = ARGV.shift

EM.run do
  Fiber.new do
    response = http_get('keyword' => keyword)
    puts response
    EM.stop
  end.resume # <= (1)
end