Question

I’m not sure that I really understand how Sinatra works.

I’d like to get some products from Amazon using their API, in my Rails app. But HTTP requests are blocking the IO. I got the tip to create a Sinatra app and make an Ajax request to there instead.

Ajax: (From my Rails app)

$.ajax({
  url: "http://sinatra.mydomain.com",
  dataType: "json",
  success: function(data) {
    console.log(data);
  }
});

Sinatra app: (I also make use of the Sinatra-synchrony gem)

require 'sinatra'
require 'sinatra/synchrony'
require 'erb'
require 'rest-client'
require 'amazon_product'

Sinatra::Synchrony.overload_tcpsocket!

get '/' do  
  req = AmazonProduct["us"]
  req.configure do |c|
    c.key    = "KEY"
    c.secret = "SECRET"
    c.tag    = "TAG"
  end
  req << { :operation    => 'ItemSearch',
           :search_index => "DVD",
           :response_group => %w{ItemAttributes Images},
           :keywords => "nikita",
           :sort => "" }
  resp = req.get
  @item = resp.find('Item').shuffle.first

  erb :layout, :locals => { :amazon_product => @item }
end

Layout.erb: (renders fine if I go to this Url in the browser)

<%= amazon_product %>

---

Problem:

My Ajax response is a 200 OK but with an empty response.
I’m can’t figure out what’s wrong. Please advise.

Answer 1

It seems that you’ve faced with ajax ‘cross-domain security’ problem. Try to use JSONP (JSON with padding).

Change your sinatra get handler:

get '/' do  
  req = AmazonProduct["us"]
  req.configure do |c|
    c.key    = KEY
    c.secret = SECRET
    c.tag    = TAG
  end
  req << { :operation    => 'ItemSearch',
           :search_index => "DVD",
           :response_group => %w{ItemAttributes Images},
           :keywords => "nikita",
           :sort => "" }
  resp = req.get
  @item = resp.find('Item').shuffle.first

  content_type :json
  callback = params.delete('callback') # jsonp
  json = @item.to_json

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

And change your Ajax request:

$.getJSON("http://address_of_sinatra?callback=?",
  function(data) {
    console.log(data);
});

Or you can add dataType: 'jsonp' to your $.ajax request.
After that you should see data object in js debugger (at least it’s working in my case 😀 )