Rails cross domain ajax get request (CORS)

I'm trying to implement google places api in my rails app.

This is the error I'm getting when trying to use the function that is fetching the data from the ajax request:

XMLHttpRequest cannot load . Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://localhost:3000' is therefore not allowed access.

I'm using rack-cors gem and I've added this snippet into my config/application.rb file:

config.middleware.insert_before 0, "Rack::Cors" do
      allow do
        origins '*'
        resource '*', :headers => :any, :methods => [:get, :post, :options]
      end
    end

This is the ajax request from my view (coffeescript):

    $.ajax
      url: url
      dataType: "json"
      type: "GET"

I've added this part to my application_controller

before_filter :cors_preflight_check
after_filter :cors_set_access_control_headers

def cors_set_access_control_headers
headers['Access-Control-Allow-Origin'] = '*'
headers['Access-Control-Allow-Methods'] = 'POST, GET, OPTIONS'
headers['Access-Control-Allow-Headers'] = '*'
headers['Access-Control-Max-Age'] = "1728000"
end

def cors_preflight_check
if request.method == :options
  headers['Access-Control-Allow-Origin'] = '*'
  headers['Access-Control-Allow-Methods'] = 'POST, GET, OPTIONS'
  headers['Access-Control-Allow-Headers'] = '*'
  headers['Access-Control-Max-Age'] = '1728000'
  render :text => '', :content_type => 'text/plain'
end
end

and this, to my routes file

 match '*path' => 'application#cors_preflight_check', :via => :options

I've noticed that "cors_preflight_check" method is not triggered by my request. (I make the AJAX request when I click a certain link in my view)

and I've noticed that my request headers remain unchanged.

(Access-Control-Allow-Origin is not added to request headers)

jsonp is not an option because it's not supported by places api

Tried everything that's written in these threads:

https://github.com/cyu/rack-cors/issues/33
Can't get rack-cors working in rails application (config.middleware.insert 0, Rack::Cors do)
https://demisx.github.io/rails-api/2014/02/18/configure-accept-headers-cors.html
POST Method not working in rack-cors rails 4 (adding before & after actions in the app controller)
Add custom response header with Rack-cors and Grape (using :expose key)

I'm trying to implement google places api in my rails app.

You seem confused about what CORS does. If you are trying to perform an ajax call to for example https://maps.googleapis.com the only thing that matters are the CORS headers sent in the response by Google. If this does not work you may be trying to use a outdated api version endpoint.

Instead follow the steps on: https://developers.google.com/maps/documentation/javascript/examples/place-search

If you want your application to be able to provide data to other domains then you would provide CORS headers. But this is not very likely what is causing your issue unless you are doing a Rails api app which is consumed by a separate front-end.

See Using CORS for a tutorial on how CORS works.

The CSP (content security policy) on the other hand allows you to set more permissive rules for cross domain requests. But should not be needed in this case since Google provides CORS headers for their web services.