feat: unique connection counting

package.json

@@ -134,6 +134,7 @@
     "hash-sum": "^2.0.0",
     "helmet": "^6.0.0",
     "http-errors": "^2.0.0",
+    "hyperloglog-lite": "^1.0.2",
     "ip-address": "^10.0.1",
     "joi": "^17.13.3",
     "js-sha256": "^0.11.0",

src/lib/db/index.ts

@@ -56,6 +56,7 @@ import { OnboardingStore } from '../features/onboarding/onboarding-store';
 import { createOnboardingReadModel } from '../features/onboarding/createOnboardingReadModel';
 import { UserUnsubscribeStore } from '../features/user-subscriptions/user-unsubscribe-store';
 import { UserSubscriptionsReadModel } from '../features/user-subscriptions/user-subscriptions-read-model';
+import { UniqueConnectionStore } from '../features/unique-connection/unique-connection-store';
 
 export const createStores = (
     config: IUnleashConfig,
@@ -185,6 +186,7 @@ export const createStores = (
         ),
         userUnsubscribeStore: new UserUnsubscribeStore(db),
         userSubscriptionsReadModel: new UserSubscriptionsReadModel(db),
+        uniqueConnectionStore: new UniqueConnectionStore(db),
     };
 };
 

src/lib/features/scheduler/schedule-services.ts

@@ -32,6 +32,7 @@ export const scheduleServices = async (
         frontendApiService,
         clientMetricsServiceV2,
         integrationEventsService,
+        uniqueConnectionService,
     } = services;
 
     schedulerService.schedule(
@@ -179,4 +180,10 @@ export const scheduleServices = async (
         minutesToMilliseconds(15),
         'cleanUpIntegrationEvents',
     );
+
+    schedulerService.schedule(
+        uniqueConnectionService.sync.bind(uniqueConnectionService),
+        minutesToMilliseconds(10),
+        'uniqueConnectionService',
+    );
 };

src/lib/features/unique-connection/fake-unique-connection-store.ts

@@ -0,0 +1,27 @@
+import type { IUniqueConnectionStore } from '../../types';
+import type {
+    TimedUniqueConnections,
+    UniqueConnections,
+} from './unique-connection-store-type';
+
+export class FakeUniqueConnectionStore implements IUniqueConnectionStore {
+    private uniqueConnectionsRecord: Record<string, TimedUniqueConnections> =
+        {};
+
+    async insert(uniqueConnections: UniqueConnections): Promise<void> {
+        this.uniqueConnectionsRecord[uniqueConnections.id] = {
+            ...uniqueConnections,
+            updatedAt: new Date(),
+        };
+    }
+
+    async get(
+        id: 'current' | 'previous',
+    ): Promise<(UniqueConnections & { updatedAt: Date }) | null> {
+        return this.uniqueConnectionsRecord[id] || null;
+    }
+
+    async deleteAll(): Promise<void> {
+        this.uniqueConnectionsRecord = {};
+    }
+}

src/lib/features/unique-connection/unique-connection-service.test.ts

@@ -0,0 +1,169 @@
+import { UniqueConnectionService } from './unique-connection-service';
+import { FakeUniqueConnectionStore } from './fake-unique-connection-store';
+import getLogger from '../../../test/fixtures/no-logger';
+import type { IFlagResolver } from '../../types';
+import { SDK_CONNECTION_ID_RECEIVED } from '../../metric-events';
+import { addHours } from 'date-fns';
+import EventEmitter from 'events';
+
+const alwaysOnFlagResolver = {
+    isEnabled() {
+        return true;
+    },
+} as unknown as IFlagResolver;
+
+test('sync first current bucket', async () => {
+    const eventBus = new EventEmitter();
+    const config = { flagResolver: alwaysOnFlagResolver, getLogger, eventBus };
+    const uniqueConnectionStore = new FakeUniqueConnectionStore();
+    const uniqueConnectionService = new UniqueConnectionService(
+        { uniqueConnectionStore },
+        config,
+    );
+    uniqueConnectionService.listen();
+
+    eventBus.emit(SDK_CONNECTION_ID_RECEIVED, 'connection1');
+    eventBus.emit(SDK_CONNECTION_ID_RECEIVED, 'connection1');
+    eventBus.emit(SDK_CONNECTION_ID_RECEIVED, 'connection2');
+    eventBus.emit(SDK_CONNECTION_ID_RECEIVED, 'connection2');
+    eventBus.emit(SDK_CONNECTION_ID_RECEIVED, 'connection2');
+
+    await uniqueConnectionService.sync();
+
+    const stats = await uniqueConnectionService.getStats();
+    expect(stats).toEqual({ previous: 0, current: 2 });
+});
+
+test('sync first previous bucket', async () => {
+    const eventBus = new EventEmitter();
+    const config = { flagResolver: alwaysOnFlagResolver, getLogger, eventBus };
+    const uniqueConnectionStore = new FakeUniqueConnectionStore();
+    const uniqueConnectionService = new UniqueConnectionService(
+        { uniqueConnectionStore },
+        config,
+    );
+    uniqueConnectionService.listen();
+
+    eventBus.emit(SDK_CONNECTION_ID_RECEIVED, 'connection1');
+    eventBus.emit(SDK_CONNECTION_ID_RECEIVED, 'connection2');
+
+    await uniqueConnectionService.sync();
+
+    eventBus.emit(SDK_CONNECTION_ID_RECEIVED, 'connection3');
+
+    await uniqueConnectionService.sync(addHours(new Date(), 1));
+
+    const stats = await uniqueConnectionService.getStats();
+    expect(stats).toEqual({ previous: 3, current: 0 });
+});
+
+test('sync to existing current bucket from the same service', async () => {
+    const eventBus = new EventEmitter();
+    const config = { flagResolver: alwaysOnFlagResolver, getLogger, eventBus };
+    const uniqueConnectionStore = new FakeUniqueConnectionStore();
+    const uniqueConnectionService = new UniqueConnectionService(
+        { uniqueConnectionStore },
+        config,
+    );
+    uniqueConnectionService.listen();
+
+    uniqueConnectionService.count('connection1');
+    uniqueConnectionService.count('connection2');
+
+    await uniqueConnectionService.sync();
+
+    uniqueConnectionService.count('connection1');
+    uniqueConnectionService.count('connection3');
+
+    const stats = await uniqueConnectionService.getStats();
+    expect(stats).toEqual({ previous: 0, current: 3 });
+});
+
+test('sync to existing current bucket from another service', async () => {
+    const eventBus = new EventEmitter();
+    const config = {
+        flagResolver: alwaysOnFlagResolver,
+        getLogger,
+        eventBus: eventBus,
+    };
+    const uniqueConnectionStore = new FakeUniqueConnectionStore();
+    const uniqueConnectionService1 = new UniqueConnectionService(
+        { uniqueConnectionStore },
+        config,
+    );
+    const uniqueConnectionService2 = new UniqueConnectionService(
+        { uniqueConnectionStore },
+        config,
+    );
+
+    uniqueConnectionService1.count('connection1');
+    uniqueConnectionService1.count('connection2');
+    await uniqueConnectionService1.sync();
+
+    uniqueConnectionService2.count('connection1');
+    uniqueConnectionService2.count('connection3');
+    await uniqueConnectionService2.sync();
+
+    const stats1 = await uniqueConnectionService1.getStats();
+    expect(stats1).toEqual({ previous: 0, current: 3 });
+    const stats2 = await uniqueConnectionService2.getStats();
+    expect(stats2).toEqual({ previous: 0, current: 3 });
+});
+
+test('sync to existing previous bucket from another service', async () => {
+    const eventBus = new EventEmitter();
+    const config = {
+        flagResolver: alwaysOnFlagResolver,
+        getLogger,
+        eventBus: eventBus,
+    };
+    const uniqueConnectionStore = new FakeUniqueConnectionStore();
+    const uniqueConnectionService1 = new UniqueConnectionService(
+        { uniqueConnectionStore },
+        config,
+    );
+    const uniqueConnectionService2 = new UniqueConnectionService(
+        { uniqueConnectionStore },
+        config,
+    );
+
+    uniqueConnectionService1.count('connection1');
+    uniqueConnectionService1.count('connection2');
+    await uniqueConnectionService1.sync(addHours(new Date(), 1));
+
+    uniqueConnectionService2.count('connection1');
+    uniqueConnectionService2.count('connection3');
+    await uniqueConnectionService2.sync(addHours(new Date(), 1));
+
+    const stats1 = await uniqueConnectionService1.getStats();
+    expect(stats1).toEqual({ previous: 3, current: 0 });
+    const stats2 = await uniqueConnectionService2.getStats();
+    expect(stats2).toEqual({ previous: 3, current: 0 });
+});
+
+test('populate previous and current', async () => {
+    const eventBus = new EventEmitter();
+    const config = { flagResolver: alwaysOnFlagResolver, getLogger, eventBus };
+    const uniqueConnectionStore = new FakeUniqueConnectionStore();
+    const uniqueConnectionService = new UniqueConnectionService(
+        { uniqueConnectionStore },
+        config,
+    );
+
+    uniqueConnectionService.count('connection1');
+    uniqueConnectionService.count('connection2');
+    await uniqueConnectionService.sync();
+    await uniqueConnectionService.sync();
+
+    uniqueConnectionService.count('connection3');
+    await uniqueConnectionService.sync(addHours(new Date(), 1));
+    await uniqueConnectionService.sync(addHours(new Date(), 1)); // deliberate duplicate call
+
+    uniqueConnectionService.count('connection3');
+    uniqueConnectionService.count('connection4');
+    await uniqueConnectionService.sync(addHours(new Date(), 1));
+    await uniqueConnectionService.sync(addHours(new Date(), 1)); // deliberate duplicate call
+
+    const stats = await uniqueConnectionService.getStats();
+    expect(stats).toEqual({ previous: 3, current: 2 });
+});

src/lib/features/unique-connection/unique-connection-service.ts

@@ -0,0 +1,99 @@
+import type { IUnleashConfig } from '../../types/option';
+import type { IFlagResolver, IUnleashStores } from '../../types';
+import type { Logger } from '../../logger';
+import type { IUniqueConnectionStore } from './unique-connection-store-type';
+import HyperLogLog from 'hyperloglog-lite';
+import type EventEmitter from 'events';
+import { SDK_CONNECTION_ID_RECEIVED } from '../../metric-events';
+
+// HyperLogLog will create 2^n registers
+const n = 12;
+
+export class UniqueConnectionService {
+    private logger: Logger;
+
+    private uniqueConnectionStore: IUniqueConnectionStore;
+
+    private flagResolver: IFlagResolver;
+
+    private eventBus: EventEmitter;
+
+    private activeHour: number;
+
+    private hll = HyperLogLog(n);
+
+    constructor(
+        {
+            uniqueConnectionStore,
+        }: Pick<IUnleashStores, 'uniqueConnectionStore'>,
+        config: Pick<IUnleashConfig, 'getLogger' | 'flagResolver' | 'eventBus'>,
+    ) {
+        this.uniqueConnectionStore = uniqueConnectionStore;
+        this.logger = config.getLogger('services/unique-connection-service.ts');
+        this.flagResolver = config.flagResolver;
+        this.eventBus = config.eventBus;
+        this.activeHour = new Date().getHours();
+    }
+
+    listen() {
+        this.eventBus.on(SDK_CONNECTION_ID_RECEIVED, this.count.bind(this));
+    }
+
+    count(connectionId: string) {
+        if (!this.flagResolver.isEnabled('uniqueSdkTracking')) return;
+        this.hll.add(HyperLogLog.hash(connectionId));
+    }
+
+    async getStats() {
+        const [previous, current] = await Promise.all([
+            this.uniqueConnectionStore.get('previous'),
+            this.uniqueConnectionStore.get('current'),
+        ]);
+        const previousHll = HyperLogLog(n);
+        if (previous) {
+            previousHll.merge({ n, buckets: previous.hll });
+        }
+        const currentHll = HyperLogLog(n);
+        if (current) {
+            currentHll.merge({ n, buckets: current.hll });
+        }
+        return { previous: previousHll.count(), current: currentHll.count() };
+    }
+
+    async sync(currentTime = new Date()): Promise<void> {
+        if (!this.flagResolver.isEnabled('uniqueSdkTracking')) return;
+
+        const currentHour = currentTime.getHours();
+        const currentBucket = await this.uniqueConnectionStore.get('current');
+
+        if (this.activeHour !== currentHour && currentBucket) {
+            if (currentBucket.updatedAt.getHours() < currentHour) {
+                this.hll.merge({ n, buckets: currentBucket.hll });
+                await this.uniqueConnectionStore.insert({
+                    hll: this.hll.output().buckets,
+                    id: 'previous',
+                });
+            } else {
+                const previousBucket =
+                    await this.uniqueConnectionStore.get('previous');
+                if (previousBucket) {
+                    this.hll.merge({ n, buckets: previousBucket.hll });
+                }
+                await this.uniqueConnectionStore.insert({
+                    hll: this.hll.output().buckets,
+                    id: 'previous',
+                });
+            }
+
+            this.activeHour = currentHour;
+            this.hll = HyperLogLog(n);
+        } else if (currentBucket) {
+            this.hll.merge({ n, buckets: currentBucket.hll });
+        }
+
+        await this.uniqueConnectionStore.insert({
+            hll: this.hll.output().buckets,
+            id: 'current',
+        });
+    }
+}

src/lib/features/unique-connection/unique-connection-store-type.ts

@@ -0,0 +1,14 @@
+export type UniqueConnections = {
+    hll: Buffer;
+    id: 'current' | 'previous';
+};
+
+export type TimedUniqueConnections = UniqueConnections & {
+    updatedAt: Date;
+};
+
+export interface IUniqueConnectionStore {
+    insert(uniqueConnections: UniqueConnections): Promise<void>;
+    get(id: 'current' | 'previous'): Promise<TimedUniqueConnections | null>;
+    deleteAll(): Promise<void>;
+}