Can't get rack-cors working in rails application

I wanted to implement CORS in my rails application, so I googled rack-cors gem for it. And I did everything as was said in README, that is updated Gemfile accordingly and updated application.rb like this:

module YourApp
  class Application < Rails::Application

    # ...

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

  end
end

But it didn't work. No matter what I did, in the browser console I kept getting message:
XMLHttpRequest cannot load https://somewebsite.com. Origin http://0.0.0.0:3000 is not allowed by Access-Control-Allow-Origin.

After reading this blogpost and issue on github, I realized that maybe position of rack-cors middleware in the middleware stack matters. So I did as was told in the github issue:

module YourApp
  class Application < Rails::Application

    # ...

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

  end
end

After that, when I run rake middleware rack-cors is really at the top of the stack.
But It still just simply won't work. I keep getting the same error. Anyone, please help.

I ran into the same problem with heroku. I found this blog with the same rack-cors issue.

Just moved the use Rack::Cors to config.ru, redeployed to heroku and it works.

require ::File.expand_path('../config/environment',  __FILE__)
run Rails.application

require 'rack/cors'
use Rack::Cors do

  # allow all origins in development
  allow do
    origins '*'
    resource '*', 
        :headers => :any, 
        :methods => [:get, :post, :delete, :put, :options]
  end
end

There is a new issue thread for the heroku solution

Instead of using

config.middleware.use Rack::Cors do

try

config.middleware.insert_before ActionDispatch::Static, Rack::Cors do

That worked for me.

I had to create a special route to handle the options requests, the cors gem didn't do it for me like I expected it to. The route I added to the end of routes.rb was:

  match "*path", :to => proc {|env| [200, {
  'Access-Control-Allow-Origin' => '*',
  'Access-Control-Allow-Methods' => 'GET, POST, PUT, DELETE, OPTIONS',
  'Access-Control-Allow-Credentials' => 'true',
  'Access-Control-Request-Method' => '*',
  'Access-Control-Allow-Headers' => 'Origin, X-Requested-With, Content-Type, Accept, Authorization',
'Content-Type' => 'text/plain'

 }, ["CORS Preflight"]] }, :via => [:options]

You just need to un-comment the Rack CORS gem in your Gemfile (gemfile.rb)

# gemfile.rb

gem 'rack-cors'

And then run the code below to install the gem

bundle install

And also ensure that your cors initializer (cors.rb) is set this way # config/initializers/cors.rb

Rails.application.config.middleware.insert_before 0, Rack::Cors do
  allow do
    origins '*'

    resource '*',
      headers: :any,
      methods: [:get, :post, :put, :patch, :delete, :options, :head]
  end
end

Setting origins to '*' should be alright for development, but keep in mind that if you deploy to production you’ll want to change this value to match your front-end’s URI for security reasons.

That's all

I hope this helps.

After all it came out that this gem has some issues with heroku, on the local machine it works perfectly fine.

Make sure you added or uncommented gem 'rack-cors' in the Gemfile

来源：https://stackoverflow.com/questions/18538549/cant-get-rack-cors-working-in-rails-application

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ruby-on-rails