How to test rails ETag caching?

Question

Is it possible to cover my controller, that is highly depeinding on Etags with unit tests?

Here's what i'm trying to do: in case if page is not stale (meaning that it's fresh), i'm adding some header to response.

When i'm trying to test it all (rspec), no matter how many similar requests i have, i still receive 200 OK instead of 304, and my header doesn't get modified. Furthermore, if i track request.fresh?(response), it's ALWAYS false.

However, it perfectly works in browser. I've already tried to state ActionController::Base.perform_caching = true, it doesn't change the overall situation.

Thank you

Answer 1

Ok, here's a point:

Before hitting the request, read up everything that's related to ETags in Rails code and Don't forget to set:

request.env["HTTP_IF_MODIFIED_SINCE"]
request.env["HTTP_IF_NONE_MATCH"]

Since they're required for ETag testing.

Answer 2

Here's how you can test if second request returns 304 response:

    get action, params
    assert_response 200, @response.body
    etag = @response.headers["ETag"]
    @request.env["HTTP_IF_NONE_MATCH"] = etag
    get action, params
    assert_response 304, @response.body

Answer 3

Rails hashes the :etag you provide:

headers['ETag'] = %("#{Digest::MD5.hexdigest(ActiveSupport::Cache.expand_cache_key(etag))}")

so setting something simple as

frash_when(:etag => 'foo')

would only be triggered by the right digest (the double quotes are necessary)

def with_etag
  if stale?(:etag => 'foo')
    render :text => 'OK'
  end
end

... tested by ...

@request.env['HTTP_IF_NONE_MATCH'] = '"acbd18db4cc2f85cedef654fccc4a4d8"'
get :with_etag
assert_equal 304, @response.status.to_i

same for modified:

def with_modified
  if stale?(:last_modified => 1.minute.ago)
    render :text => 'OK'
  end
end

... tested by ...

@request.env['HTTP_IF_MODIFIED_SINCE'] = 2.minutes.ago.rfc2822
get :with_modified
assert_equal 304, @response.status.to_i

Answer 4

This gist is very useful re etag testing in rspec -

https://gist.github.com/brettfishman/3868277

Answer 5

Rails 4.2 now also takes in to account the digest of the template. For me the following worked:

def calculate_etag(record, template)
  Digest::MD5.hexdigest(ActiveSupport::Cache.expand_cache_key([
    record,
    controller.send(:lookup_and_digest_template, template)
  ])).inspect
end

def set_cache_headers(modified_since: nil, record: nil, template: nil)
  request.if_modified_since = modified_since.rfc2822
  request.if_none_match = calculate_etag(record, template)
end

set_cache_headers(
  modified_since: 2.days.ago,
  record: @book,
  template: 'books/index'
)

Answer 6

At least in Rails 5.2, szeryf's solution fails. This variation does work:

get action, parms
assert_response 200, @response.code
etag = @response.headers["ETag"]
get action, parms, headers: { "HTTP_IF_NONE_MATCH": etag }
assert_response 304, @response.code

See Rails Guides: https://guides.rubyonrails.org/testing.html#setting-headers-and-cgi-variables