Question 1

How do I set up Rack::CORS in a Rails application?

Accepted Answer

Add the gem to your Gemfile, then create an initializer in config/initializers/cors.rb. Use Rails.application.config.middleware.insert_before 0, Rack::Cors to ensure it runs early, as shown in the basic Rails configuration example. This handles dynamic requests from specified origins.

Question 2

Rack::CORS vs setting CORS headers in Nginx: which should I use?

Accepted Answer

Use Rack::CORS for dynamic API requests processed by your Ruby app, as it integrates with middleware for fine-grained control. For static files served by Nginx, configure CORS directly in Nginx since the middleware won't apply, as noted in production static file limitations.

Question 3

Why aren't my CORS headers showing up on static assets in production?

Accepted Answer

Static assets are often served directly by web servers like Nginx in production, bypassing the Rack middleware. To fix this, either serve static files through Rails by setting config.serve_static_assets = true, or add CORS headers in your web server configuration.

Question 4

How can I debug CORS issues with Rack::CORS?

Accepted Answer

Enable debug mode by setting debug: true in the middleware options. This adds X-Rack-CORS headers to responses and logs CORS activity, helping trace origin and resource matching, as explained in the debugging support section.

Question 5

Can I use Rack::CORS with Sinatra or other Rack frameworks?

Accepted Answer

Yes, Rack::CORS is compatible with any Rack-based framework like Sinatra. Configure it in your config.ru file using the use Rack::Cors syntax with allow blocks, similar to the non-Rails examples provided in the README.

Question 6

How to allow multiple origins with different credentials settings?

Accepted Answer

Use separate allow blocks for each origin or condition. For example, one block can allow a specific origin with credentials: true, while another uses a wildcard without credentials, since wildcard origins cannot have credentials enabled due to security constraints.

Rack::Cors

What is Rack::Cors?

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