Jake Trent

Set Cookie on Rack Mock Request

Rack apps are generally straightforward to test because of their very basic public interface. But where do we put specific things, in this case, a cookie for the request, on that env argument it takes? Here’s one way.


The env argument that is sent to #call in a Rack app is an variable that represents the environment of the request. It is a hash of CGI-like headers: request method, query params, http headers – that sort of thing.

The HTTP_* keys on the hash will be read as request headers from the environment.

Rack MockRequest Cookies

Rack provides a great little Rack::MockRequest helper object in its library that will help us test our app. This object has a class method called env_for which allows for quick construction of an env var that is a request to a specified url.

On the returned env we will continue to make modifications before passing it to our Rack app. We’ll add our cookie header with a key of HTTP_COOKIE. The value will be of the format cookieName=cookieValue. We can handle multiple cookies by separating the cookies with ;.

Let’s say we’re testing a token authentication middleware with rspec. Our spec may look something like this:

it "accepts an cookie token in the request" do
  middleware = # ... instantiate rack middleware
  env = Rack::MockRequest.env_for("/protected")
  env["HTTP_COOKIE"] = "AUTH_COOKIE=123"
  status, _, _ = middleware.call(env)
  expect(status).to eq(200)

Then in our Rack app source, we can code for the availability of a cookie on the request. It might look like:

# ...
def call(env)
  request = Rack::Request.new(env)
  token = request.cookies["AUTH_TOKEN"]
  # ...

Is this the easiest or best way to set cookies on requests when testing Rack apps? What do you do?