Add UsageData API

  - Add increment_unique_values

doc/development/telemetry/usage_ping.md

@@ -312,6 +312,34 @@ Implemented using Redis methods [PFADD](https://redis.io/commands/pfadd) and [PF
    end
    ```
 
+1. Track event using `UsageData` API
+
+   Increment unique values count using Redis HLL, for given event name.
+   In order to be able to increment the values the related feature `usage_data<event_name>` should be enabled.
+
+   ```plaintext
+   POST /usage_data/increment_unique_values
+   ```
+
+   | Attribute | Type | Required | Description |
+   | :-------- | :--- | :------- | :---------- |
+   | `name` | string | yes | The event name it should be tracked |
+   | `values` | array | yes | The values counted |
+
+   Response
+
+   Return 200 if tracking failed for any reason.
+
+   - `401 Unauthorized` if not authorized
+   - `400 Bad request` if name parameter is missing
+   - `200` if event was tracked or any errors
+
+   Example usage:
+
+   ```shell
+   curl --header "Authorization: Bearer OAUTH-TOKEN" "https://gitlab.example.com/api/v4/usage_data/increment_unique_users" --data "name=event_name&values[]=value1&values[]=value2"
+   ```
+
 1. Track event using base module `Gitlab::UsageDataCounters::HLLRedisCounter.track_event(entity_id, event_name)`.
 
    Arguments:

lib/api/api.rb

@@ -235,6 +235,7 @@ module API
       mount ::API::Templates
       mount ::API::Todos
       mount ::API::Triggers
+      mount ::API::UsageData
       mount ::API::UserCounts
       mount ::API::Users
       mount ::API::Variables

lib/api/usage_data.rb

+# frozen_string_literal: true
+
+module API
+  class UsageData < Grape::API::Instance
+    before { authenticate! }
+
+    namespace 'usage_data' do
+      desc 'Track usage data events' do
+        detail 'This feature was introduced in GitLab 13.4.'
+      end
+
+      params do
+        requires :name, type: String, desc: 'The event name it should be tracked'
+        requires :values, type: Array, desc: 'The values counted'
+      end
+      post 'increment_unique_values' do
+        event_name = params[:name]
+        values = params[:values]
+
+        increment_unique_values(event_name, values)
+
+        status :ok
+      end
+    end
+  end
+end

spec/requests/api/usage_data_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe API::UsageData do
+  let_it_be(:user) { create(:user) }
+
+  describe 'POST /usage_data/increment_unique_values' do
+    let(:endpoint) { '/usage_data/increment_unique_values' }
+    let(:known_event) { 'g_compliance_dashboard' }
+    let(:unknown_event) { 'unknown' }
+
+    context 'when unauthenticated' do
+      it 'retruns 401 response' do
+        post api(endpoint), params: { values: [user.id] }
+
+        expect(response).to have_gitlab_http_status(:unauthorized)
+      end
+    end
+
+    context 'when name is missing from params' do
+      it 'returns bad request' do
+        post api(endpoint, user), params: { values: [user.id] }
+
+        expect(response).to have_gitlab_http_status(:bad_request)
+      end
+    end
+
+    context 'with correct params' do
+      it 'returns status ok' do
+        post api(endpoint, user), params: { name: known_event, values: [user.id] }
+
+        expect(response).to have_gitlab_http_status(:ok)
+      end
+    end
+
+    context 'with unknown event' do
+      it 'returns status ok' do
+        post api(endpoint, user), params: { name: unknown_event, values: [user.id] }
+
+        expect(response).to have_gitlab_http_status(:ok)
+      end
+    end
+  end
+end