Cross Origin Resource Sharing Rack middleware.

api_settings.rb

# This class should parse a yaml configuration file.
#
require 'ostruct'

class APISettings
  def self.cross_origin_resource_sharing
    OpenStruct.new(allow: ['http://127.0.0.1:8080', 'http://localhost:8080'])
  end
end

cross_origin_resource_sharing.rb

class CrossOriginResourceSharing
  def initialize(app)
    @app = app
    @headers = {
      'Access-Control-Request-Method' => 'GET, POST, PUT, DELETE, OPTIONS',
      'Access-Control-Allow-Headers'  => 'Content-Type, Accept, Cache-Control, Content-Language, Last-Modified, Expires, Origin, x-requested-with, Accept-Language, Access'
    }
  end

  def call(env)
    if env['HTTP_ORIGIN']
      @headers['Access-Control-Allow-Origin'] = access_control_allow_origin(env)

      if env['REQUEST_METHOD'] == 'OPTIONS'
        [200, @headers.merge('Content-Type' => 'text/plain', 'Content-Length' => '0'), []]
      else
        status, headers, body = @app.call(env)
        [status, headers.merge(@headers), body]
      end
    else
      @app.call(env)
    end
  end

  def access_control_allow_origin(env)
    if env['HTTP_ORIGIN'].in?(APISettings.cross_origin_resource_sharing.allow)
      env['HTTP_ORIGIN']
    else
      APISettings.cross_origin_resource_sharing.allow.first
    end
  end
end