XMLHttpRequest No 'Access-Control-Allow-Origin' header From SimpleHttpServer

Question

I am writing a rails backend app. I am providing a rest api to the frontend developer who is workng separately. So for time being I have enabled Cross origin resource sharing by adding following in my application.rb:

#todo remove this once ui is integrated into the app. following allows requests from other domains (disble CORS).
    config.action_dispatch.default_headers.merge!({
                                                      'Access-Control-Allow-Origin' => '*',
                                                      'Access-Control-Request-Method' => '*'
                                                  });

I am trying to test out the api by using links on a simple HTML page which I am running off of the python SimplHttpServer. The page is being served at http: // localhost:8000/TestPage.html

When I test one of the links (it sends an ajax request using jquery to the backend which at the moment is running locally as well, on http: // localhost : 3000), I get following error:

GET http://localhost:3000/campaigns/my_campaigns?user_email=swapna%40urbancoding.net&user_token=SNa2kPqkm5ENsZMx7yEi 

XMLHttpRequest cannot load http://localhost:3000/campaigns/my_campaigns?user_email=xyz.xyz.com&user_token=xyz. No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://localhost : 8000' is therefore not allowed access. The response had HTTP status code 500.

What is going on? How can I resolve this?

Answer 1

Turns out the issue was that the url I was sending the request to (http:// localhost:3000/campaigns/my_campaigns) was incorrect. It was matching an action I did not intend it to match. This action was triggering a 'missing template' exception. Somehow this was causing the No 'Access-Control-Allow-Origin' error. Not sure how that happens, but once I fixed my url to go to the intended action, all was well.