Add support for isExpired in configuration store to gate CDN requests… (#61)

* Add support for isExpired in configuration store to gate CDN requests (FF-2048)

* Add info message

* 3.0.4

Author: leoromanovsky

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@eppo/js-client-sdk-common",
-  "version": "3.0.3",
+  "version": "3.0.4",
   "description": "Eppo SDK for client-side JavaScript applications (base for both web and react native)",
   "main": "dist/index.js",
   "files": [

src/client/eppo-client.spec.ts

@@ -639,6 +639,24 @@ describe('EppoClient E2E test', () => {
       expect(variation).toBe(pi);
     });
 
+    it('Does not fetch configurations if the configuration store is unexpired', async () => {
+      class MockStore extends MemoryOnlyConfigurationStore<Flag | ObfuscatedFlag> {
+        async isExpired(): Promise<boolean> {
+          return false;
+        }
+      }
+
+      client = new EppoClient(new MockStore(), requestConfiguration);
+      client.setIsGracefulFailureMode(false);
+      // no configuration loaded
+      let variation = client.getNumericAssignment(flagKey, subject, {}, 0.0);
+      expect(variation).toBe(0.0);
+      // have client fetch configurations
+      await client.fetchFlagConfigurations();
+      variation = client.getNumericAssignment(flagKey, subject, {}, 0.0);
+      expect(variation).toBe(0.0);
+    });
+
     it.each([
       { pollAfterSuccessfulInitialization: false },
       { pollAfterSuccessfulInitialization: true },

src/client/eppo-client.ts

@@ -152,6 +152,14 @@ export default class EppoClient implements IEppoClient {
       this.requestPoller.stop();
     }
 
+    const isExpired = await this.configurationStore.isExpired();
+    if (!isExpired) {
+      logger.info(
+        '[Eppo SDK] Configuration store is not expired. Skipping fetching flag configurations',
+      );
+      return;
+    }
+
     // todo: consider injecting the IHttpClient interface
     const httpClient = new FetchHttpClient(
       this.configurationRequestParameters.baseUrl || DEFAULT_BASE_URL,

src/configuration-store/configuration-store.ts

@@ -28,6 +28,7 @@ export interface IConfigurationStore<T> {
   get(key: string): T | null;
   getKeys(): string[];
   isInitialized(): boolean;
+  isExpired(): Promise<boolean>;
   setEntries(entries: Record<string, T>): Promise<void>;
 }
 
@@ -40,6 +41,7 @@ export interface ISyncStore<T> {
 
 export interface IAsyncStore<T> {
   isInitialized(): boolean;
+  isExpired(): Promise<boolean>;
   getEntries(): Promise<Record<string, T>>;
   setEntries(entries: Record<string, T>): Promise<void>;
 }

src/configuration-store/hybrid.store.spec.ts

@@ -17,6 +17,7 @@ describe('HybridConfigurationStore', () => {
     asyncStoreMock = {
       getEntries: jest.fn(),
       isInitialized: jest.fn(),
+      isExpired: jest.fn(),
       setEntries: jest.fn(),
     };
 
@@ -35,6 +36,21 @@ describe('HybridConfigurationStore', () => {
     });
   });
 
+  describe('isExpired', () => {
+    it("is the persistent store's expired value", async () => {
+      (asyncStoreMock.isExpired as jest.Mock).mockResolvedValue(true);
+      expect(await store.isExpired()).toBe(true);
+
+      (asyncStoreMock.isExpired as jest.Mock).mockResolvedValue(false);
+      expect(await store.isExpired()).toBe(false);
+    });
+
+    it('is true without a persistent store', async () => {
+      const mixedStoreWithNull = new HybridConfigurationStore(syncStoreMock, null);
+      expect(await mixedStoreWithNull.isExpired()).toBe(true);
+    });
+  });
+
   describe('isInitialized', () => {
     it('should return true if both stores are initialized', () => {
       (syncStoreMock.isInitialized as jest.Mock).mockReturnValue(true);

src/configuration-store/hybrid.store.ts

@@ -40,6 +40,11 @@ export class HybridConfigurationStore<T> implements IConfigurationStore<T> {
     return this.servingStore.isInitialized() && (this.persistentStore?.isInitialized() ?? true);
   }
 
+  public async isExpired(): Promise<boolean> {
+    const isExpired = (await this.persistentStore?.isExpired()) ?? true;
+    return isExpired;
+  }
+
   public get(key: string): T | null {
     if (!this.servingStore.isInitialized()) {
       logger.warn(`${loggerPrefix} getting a value from a ServingStore that is not initialized.`);

src/configuration-store/memory.store.spec.ts

@@ -12,6 +12,10 @@ describe('MemoryOnlyConfigurationStore', () => {
     expect(memoryStore.getKeys()).toEqual([]);
   });
 
+  it('is always expired', async () => {
+    expect(await memoryStore.isExpired()).toBe(true);
+  });
+
   it('should return null for non-existent keys', () => {
     expect(memoryStore.get('nonexistent')).toBeNull();
   });

src/configuration-store/memory.store.ts

@@ -48,6 +48,10 @@ export class MemoryOnlyConfigurationStore<T> implements IConfigurationStore<T> {
     return this.servingStore.getKeys();
   }
 
+  async isExpired(): Promise<boolean> {
+    return true;
+  }
+
   isInitialized(): boolean {
     return this.initialized;
   }