A Rack Middleware to catch errors in Rails API

json_api_public_exceptions.rb

module ActionDispatch
  class JsonApiPublicExceptions < PublicExceptions
    def call(env)
      request = ActionDispatch::Request.new(env)
      status = request.path_info[1..].to_i
      exception = env['action_dispatch.exception']
      message = returned_message(exception, status)
      attribute = exception.try(:param) || :base
      code = convert_to_code(status)

      body = { errors: [ErrorsMapper.single(status: status, attribute: attribute, code: code, message: message)] }

      render(status, request.formats.first, body)
    end

    private

    def returned_message(exception, status)
      if status == 500
        I18n.t('errors.internal_error.message')
      else
        exception.try(:reason)
      end
    end

    def convert_to_code(status)
      Rack::Utils::HTTP_STATUS_CODES.fetch(status, Rack::Utils::HTTP_STATUS_CODES[500]).downcase
    end
  end
end