Add ability to track unique uses of API endpoints

This MR adds Grape middleware that allows the
tracking of unique users use of any API endpoint.

This MR adds specific support for tracking unique
use of /audit_events.

It also adds the collected data to
the usage ping.

ee/changelogs/unreleased/233786-ppi-unique-audit-events-api.yml

+---
+title: Add ability to track unique uses of API endpoints
+merge_request: 39616
+author:
+type: added

ee/lib/api/audit_events.rb

@@ -3,6 +3,7 @@
 module API
   class AuditEvents < ::Grape::API::Instance
     include ::API::PaginationParams
+    use ::API::UniqueCallTracking, event_name: 'i_compliance_audit_events_api', feature: :track_unique_visits
 
     before do
       authenticated_as_admin!

ee/lib/api/unique_call_tracking.rb

+# frozen_string_literal: true
+
+module API
+  class UniqueCallTracking < Grape::Middleware::Base
+    def visitor_id
+      return context.session[:visitor_id] if context.session[:visitor_id].present?
+      return unless context.current_user
+
+      uuid = SecureRandom.uuid
+      context.session[:visitor_id] = uuid
+      uuid
+    end
+
+    def track_redis_hll_event(event_name, feature)
+      return unless feature_enabled?(feature)
+      return unless visitor_id
+
+      Gitlab::UsageDataCounters::HLLRedisCounter.track_event(visitor_id, event_name)
+    end
+
+    def after
+      track_redis_hll_event(@options[:event_name], @options[:feature])
+      nil
+    end
+
+    private
+
+    def feature_enabled?(feature = :track_unique_visits)
+      Feature.enabled?(feature) && Gitlab::CurrentSettings.usage_ping_enabled?
+    end
+  end
+end

ee/lib/ee/api/groups.rb

@@ -89,6 +89,8 @@ module EE
           end
 
           segment ':id/audit_events' do
+            use ::API::UniqueCallTracking, event_name: 'i_compliance_audit_events_api', feature: :track_unique_visits
+
             before do
               authorize! :admin_group, user_group
               check_audit_events_available!(user_group)

ee/lib/ee/api/projects.rb

@@ -22,6 +22,8 @@ module EE
             end
           end
           segment ':id/audit_events' do
+            use ::API::UniqueCallTracking, event_name: 'i_compliance_audit_events_api', feature: :track_unique_visits
+
             before do
               authorize! :admin_project, user_project
               check_audit_events_available!(user_project)

ee/spec/requests/api/unique_call_tracking_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe API::UniqueCallTracking do
+  describe 'i_compliance_audit_events_api', :clean_gitlab_redis_shared_state do
+    let_it_be(:current_user) { create(:admin) }
+    let_it_be(:group) { create(:group, owner_id: current_user) }
+    let_it_be(:project) { create(:project) }
+
+    before do
+      project.add_user(current_user, :maintainer)
+    end
+
+    context 'after calling all audit_events APIs as a single licensed user' do
+      before do
+        stub_feature_flags(track_unique_visits: true)
+        stub_licensed_features(admin_audit_log: true)
+      end
+
+      subject do
+        travel_to 8.days.ago do
+          get api('/audit_events', current_user)
+          get api("/groups/#{group.id}/audit_events", current_user)
+          get api("/projects/#{project.id}/audit_events", current_user)
+        end
+      end
+
+      it 'tracks 3 separate events' do
+        expect(Gitlab::UsageDataCounters::HLLRedisCounter).to receive(:track_event).exactly(3).times
+                                                                  .with(an_instance_of(String), an_instance_of(String))
+
+        subject
+      end
+
+      it 'reports one unique event' do
+        subject
+
+        expect(Gitlab::UsageDataCounters::HLLRedisCounter.unique_events(event_names: 'i_compliance_audit_events_api', start_date: 2.months.ago, end_date: Date.current)).to eq(1)
+      end
+    end
+  end
+end

lib/gitlab/usage_data_counters/known_events.yml

@@ -16,6 +16,11 @@
   category: compliance
   redis_slot: compliance
   aggregation: weekly
+- name: i_compliance_audit_events_api
+  category: compliance
+  redis_slot: compliance
+  expiry: 42
+  aggregation: weekly
 # Analytics category
 - name: g_analytics_contribution
   category: analytics

spec/lib/gitlab/usage_data_spec.rb

@@ -1013,6 +1013,7 @@ RSpec.describe Gitlab::UsageData, :aggregate_failures do
           'g_compliance_audit_events' => 123,
           'i_compliance_credential_inventory' => 123,
           'i_compliance_audit_events' => 123,
+          'i_compliance_audit_events_api' => 123,
           'compliance_unique_visits_for_any_target' => 543,
           'compliance_unique_visits_for_any_target_monthly' => 987
         }