gistfile1.rb

##
# sync api: return values and exceptions

begin
  images = []

  results = RestClient.get('http://google.com/search?q=ruby')
  Hpricot(results).find('a').each{ |link|
    page = RestClient.get(link)
    begin
      images << Hpricot(page).find('img')
    rescue RestClient::RequestFailed
    end
  }

  images.flatten.each{ |img| p(img) }
rescue RestClient::RequestFailed
  pus 'error!'
end

##
# async api: separate callback and errback blocks

request = EM::HttpClient.get('http://google.com/search?q=ruby')
request.errback{ puts 'error!' }
request.callback{ |results|
  images = []
  link = Hpricot(results).find('a')
  num_links = links.size

  on_images_done = proc{
    images.flatten.each{ |img| p(img) }
  }

  links.each{ |link|
    page_request = EM::HttpClient.get(link)
    page_request.callback{ |page|
      images << Hpricot(page).find('img')

      num_links -= 1
      if num_links == 0 # all pages fetched
        on_images_done.call
      end
    }
    page_request.errback{
      num_links -= 1
      if num_links == 0 # all pages fetched
        on_images_done.call
      end      
    }
  }
}

##
# fibered compat layer: sync interface to async code

def RestClient.get url
  f = Fiber.current
  request = EM::HttpClient.get(url)
  request.callback{|page| f.resume(page) }
  request.errback{ f.resume(RestClient::RequestFailed.new) }

  retval = Fiber.yield
  raise retval if retval.is_a? Exception
  return retval
end

Fiber.new{
  results = RestClient.get('http://google.com/search?q=ruby')
}.resume