Micro CORS

cors_headers.rb

class CORSHeaders
  ACCESS_CONTROL_HEADERS = {
    'Access-Control-Allow-Origin'   => '*',
    'Access-Control-Allow-Methods'  => 'OPTIONS,GET,PATCH,PUT,POST,DELETE',
    'Access-Control-Expose-Headers' => '',
    'Access-Control-Max-Age'        => '1728000',
    'Content-Type'                  => 'text/plain'
  }.freeze

  def initialize(app)
    @app = app
  end

  def call(env)
    if env['REQUEST_METHOD'] == 'OPTIONS' and env['HTTP_ACCESS_CONTROL_REQUEST_METHOD']
      headers = ACCESS_CONTROL_HEADERS.merge(
        'Origin'                         => env['HTTP_ORIGIN'],
        'Access-Control-Request-Method'  => env['HTTP_ACCESS_CONTROL_REQUEST_METHOD'],
        'Access-Control-Request-Headers' => env['HTTP_ACCESS_CONTROL_REQUEST_HEADERS']
      )

      [200, headers, []]
    else
      status, headers, body = @app.call(env)
      headers.merge!('Access-Control-Allow-Origin' => '*')
      [status, headers, body]
    end
  end
end