Set an experimentation_id cookie on every request

Check if it exists and set it otherwise

app/controllers/application_controller.rb

@@ -14,6 +14,7 @@ class ApplicationController < ActionController::Base
   include SessionlessAuthentication
   include ConfirmEmailWarning
   include Gitlab::Tracking::ControllerConcern
+  include Gitlab::Experimentation::ControllerConcern
 
   before_action :authenticate_user!
   before_action :enforce_terms!, if: :should_enforce_terms?

ee/spec/controllers/ee/dashboard/projects_controller_spec.rb

@@ -37,7 +37,7 @@ describe Dashboard::ProjectsController do
           end
 
           it 'renders the welcome page if it has not dismissed onboarding' do
-            allow(controller).to receive(:cookies).and_return({ 'onboarding_dismissed' => 'false' })
+            cookies[:onboarding_dismissed] = 'false'
 
             get :index
 
@@ -45,7 +45,7 @@ describe Dashboard::ProjectsController do
           end
 
           it 'renders the index template if it has dismissed the onboarding' do
-            allow(controller).to receive(:cookies).and_return({ 'onboarding_dismissed' => 'true' })
+            cookies[:onboarding_dismissed] = 'true'
 
             get :index
 

ee/spec/lib/gitlab/auth/group_saml/failure_handler_spec.rb

@@ -17,7 +17,10 @@ describe Gitlab::Auth::GroupSaml::FailureHandler do
     params = {
       'omniauth.error.strategy' => strategy,
       'devise.mapping' => Devise.mappings[:user],
-      'warden' => warden
+      'warden' => warden,
+      'action_dispatch.key_generator' => ActiveSupport::KeyGenerator.new('b2efbaccbdb9548217eebc73a896db73'), # necessary for setting signed cookies in lib/gitlab/experimentation.rb
+      'action_dispatch.signed_cookie_salt' => 'a4fb52b0ccb302eaef92bda18fedf5c3', # necessary for setting signed cookies in lib/gitlab/experimentation.rb
+      'action_dispatch.cookies_rotations' => OpenStruct.new(signed: []) # necessary for setting signed cookies in lib/gitlab/experimentation.rb
     }
     Rack::MockRequest.env_for(path, params)
   end

lib/gitlab/experimentation.rb

+# frozen_string_literal: true
+
+# == Experimentation
+#
+# Utility module used for A/B testing experimental features. Define your experiments in the `EXPERIMENTS` constant.
+# The feature_toggle and environment keys are optional. If the feature_toggle is not set, a feature with the name of
+# the experiment will be checked, with a default value of true. The enabled_ratio is required and should be
+# the ratio for the number of users for which this experiment is enabled. For example: a ratio of 0.1 will
+# enable the experiment for 10% of the users (determined by the `experimentation_subject_index`).
+#
+module Gitlab
+  module Experimentation
+    EXPERIMENTS = {
+      signup_flow: {
+        feature_toggle: :experimental_separate_sign_up_flow,
+        environment: ::Gitlab.dev_env_or_com?,
+        enabled_ratio: 0.1
+      }
+    }.freeze
+
+    # Controller concern that checks if an experimentation_subject_id cookie is present and sets it if absent.
+    # Used for A/B testing of experimental features. Exposes the `experiment_enabled?(experiment_name)` method
+    # to controllers and views.
+    #
+    module ControllerConcern
+      extend ActiveSupport::Concern
+
+      included do
+        before_action :set_experimentation_subject_id_cookie
+        helper_method :experiment_enabled?
+      end
+
+      def set_experimentation_subject_id_cookie
+        return if cookies[:experimentation_subject_id].present?
+
+        cookies.permanent.signed[:experimentation_subject_id] = {
+          value: SecureRandom.uuid,
+          domain: :all,
+          secure: ::Gitlab.config.gitlab.https
+        }
+      end
+
+      def experiment_enabled?(experiment)
+        Experimentation.enabled?(experiment, experimentation_subject_index)
+      end
+
+      private
+
+      def experimentation_subject_index
+        experimentation_subject_id = cookies.signed[:experimentation_subject_id]
+        return if experimentation_subject_id.blank?
+
+        experimentation_subject_id.delete('-').hex % 100
+      end
+    end
+
+    class << self
+      def enabled?(experiment_key, experimentation_subject_index)
+        return false unless EXPERIMENTS.key?(experiment_key)
+
+        experiment = Experiment.new(EXPERIMENTS[experiment_key].merge(key: experiment_key))
+
+        experiment.feature_toggle_enabled? &&
+          experiment.enabled_for_environment? &&
+          experiment.enabled_for_experimentation_subject?(experimentation_subject_index)
+      end
+    end
+
+    Experiment = Struct.new(:key, :feature_toggle, :environment, :enabled_ratio, keyword_init: true) do
+      def feature_toggle_enabled?
+        return Feature.enabled?(key, default_enabled: true) if feature_toggle.nil?
+
+        Feature.enabled?(feature_toggle)
+      end
+
+      def enabled_for_environment?
+        return true if environment.nil?
+
+        environment
+      end
+
+      def enabled_for_experimentation_subject?(experimentation_subject_index)
+        return false if enabled_ratio.nil? || experimentation_subject_index.blank?
+
+        experimentation_subject_index <= enabled_ratio * 100
+      end
+    end
+  end
+end

spec/controllers/projects/discussions_controller_spec.rb

@@ -189,7 +189,7 @@ describe Projects::DiscussionsController do
 
         context "when vue_mr_discussions cookie is present" do
           before do
-            allow(controller).to receive(:cookies).and_return({ vue_mr_discussions: 'true' })
+            cookies[:vue_mr_discussions] = 'true'
           end
 
           it "renders discussion with serializer" do

spec/lib/gitlab/experimentation_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Gitlab::Experimentation::ControllerConcern, type: :controller do
+  controller(ApplicationController) do
+    include Gitlab::Experimentation::ControllerConcern
+
+    def index
+      head :ok
+    end
+  end
+
+  describe '#set_experimentation_subject_id_cookie' do
+    before do
+      get :index
+    end
+
+    context 'cookie is present' do
+      before do
+        cookies[:experimentation_subject_id] = 'test'
+      end
+
+      it 'does not change the cookie' do
+        expect(cookies[:experimentation_subject_id]).to eq 'test'
+      end
+    end
+
+    context 'cookie is not present' do
+      it 'sets a permanent signed cookie' do
+        expect(cookies.permanent.signed[:experimentation_subject_id]).to be_present
+      end
+    end
+  end
+
+  describe '#experiment_enabled?' do
+    context 'cookie is not present' do
+      it 'calls Gitlab::Experimentation.enabled? with the name of the experiment and an experimentation_subject_index of nil' do
+        expect(Gitlab::Experimentation).to receive(:enabled?).with(:test_experiment, nil)
+        controller.experiment_enabled?(:test_experiment)
+      end
+    end
+
+    context 'cookie is present' do
+      before do
+        cookies.permanent.signed[:experimentation_subject_id] = 'abcd-1234'
+        get :index
+      end
+
+      it 'calls Gitlab::Experimentation.enabled? with the name of the experiment and an experimentation_subject_index of the modulo 100 of the hex value of the uuid' do
+        # 'abcd1234'.hex % 100 = 76
+        expect(Gitlab::Experimentation).to receive(:enabled?).with(:test_experiment, 76)
+        controller.experiment_enabled?(:test_experiment)
+      end
+    end
+  end
+end
+
+describe Gitlab::Experimentation do
+  before do
+    stub_const('Gitlab::Experimentation::EXPERIMENTS', {
+      test_experiment: {
+        feature_toggle: feature_toggle,
+        environment: environment,
+        enabled_ratio: enabled_ratio
+      }
+    })
+
+    stub_feature_flags(feature_toggle => true)
+  end
+
+  let(:feature_toggle) { :test_experiment_toggle }
+  let(:environment) { Rails.env.test? }
+  let(:enabled_ratio) { 0.1 }
+
+  describe '.enabled?' do
+    subject { described_class.enabled?(:test_experiment, experimentation_subject_index) }
+    let(:experimentation_subject_index) { 9 }
+
+    context 'feature toggle is enabled, we are on the right environment and we are selected' do
+      it { is_expected.to be_truthy }
+    end
+
+    describe 'experiment is not defined' do
+      it 'returns false' do
+        expect(described_class.enabled?(:missing_experiment, experimentation_subject_index)).to be_falsey
+      end
+    end
+
+    describe 'feature toggle' do
+      context 'feature toggle is not set' do
+        let(:feature_toggle) { nil }
+
+        it { is_expected.to be_truthy }
+      end
+
+      context 'feature toggle is not set, but a feature with the experiment key as name does exist' do
+        before do
+          stub_feature_flags(test_experiment: false)
+        end
+
+        let(:feature_toggle) { nil }
+
+        it { is_expected.to be_falsey }
+      end
+
+      context 'feature toggle is disabled' do
+        before do
+          stub_feature_flags(feature_toggle => false)
+        end
+
+        it { is_expected.to be_falsey }
+      end
+    end
+
+    describe 'environment' do
+      context 'environment is not set' do
+        let(:environment) { nil }
+
+        it { is_expected.to be_truthy }
+      end
+
+      context 'we are on the wrong environment' do
+        let(:environment) { ::Gitlab.com? }
+
+        it { is_expected.to be_falsey }
+      end
+    end
+
+    describe 'enabled ratio' do
+      context 'enabled ratio is not set' do
+        let(:enabled_ratio) { nil }
+
+        it { is_expected.to be_falsey }
+      end
+
+      context 'experimentation_subject_index is not set' do
+        let(:experimentation_subject_index) { nil }
+
+        it { is_expected.to be_falsey }
+      end
+
+      context 'experimentation_subject_index is an empty string' do
+        let(:experimentation_subject_index) { '' }
+
+        it { is_expected.to be_falsey }
+      end
+
+      context 'experimentation_subject_index outside enabled ratio' do
+        let(:experimentation_subject_index) { 11 }
+
+        it { is_expected.to be_falsey }
+      end
+    end
+  end
+end