Implement a NoStore cache backend, and do not provide a cache backend by default.

Signed-off-by: Eric Peterson <ericpeterson@spotify.com>

app-config.yaml

@@ -26,8 +26,6 @@ backend:
   baseUrl: http://localhost:7000
   listen:
     port: 7000
-  cache:
-    store: memory
   database:
     client: sqlite3
     connection: ':memory:'

packages/backend-common/src/cache/CacheManager.test.ts

@@ -20,6 +20,7 @@ import Keyv from 'keyv';
 import KeyvMemcache from 'keyv-memcache';
 import { DefaultCacheClient } from './CacheClient';
 import { CacheManager } from './CacheManager';
+import { NoStore } from './NoStore';
 
 jest.createMockFromModule('keyv');
 jest.mock('keyv');
@@ -104,21 +105,17 @@ describe('CacheManager', () => {
   });
 
   describe('CacheManager.forPlugin stores', () => {
-    it('returns memory client when no cache is configured', () => {
+    it('returns none client when no cache is configured', () => {
       const manager = CacheManager.fromConfig(
         new ConfigReader({ backend: {} }),
       );
-      const expectedTtl = 3600;
       const expectedNamespace = 'test-plugin';
-      manager.forPlugin(expectedNamespace).getClient({ defaultTtl: expectedTtl });
+      manager.forPlugin(expectedNamespace).getClient();
 
       const cache = Keyv as unknown as jest.Mock;
       const mockCalls = cache.mock.calls.splice(-1);
       const callArgs = mockCalls[0];
-      expect(callArgs[0]).toMatchObject({
-        ttl: expectedTtl,
-        namespace: expectedNamespace,
-      });
+      expect(callArgs[0].store).toBeInstanceOf(NoStore);
     });
 
     it('returns memory client when explicitly configured', () => {
@@ -156,6 +153,7 @@ describe('CacheManager', () => {
       expect(mockCacheCalls[0][0]).toMatchObject({
         ttl: expectedTtl,
       });
+      expect(mockCacheCalls[0][0].store).toBeInstanceOf(KeyvMemcache);
       const memcache = KeyvMemcache as jest.Mock;
       const mockMemcacheCalls = memcache.mock.calls.splice(-1);
       expect(mockMemcacheCalls[0][0]).toEqual(expectedHost);

packages/backend-common/src/cache/CacheManager.ts

@@ -19,11 +19,12 @@ import Keyv from 'keyv';
 // @ts-expect-error
 import KeyvMemcache from 'keyv-memcache';
 import { DefaultCacheClient, CacheClient } from './CacheClient';
+import { NoStore } from './NoStore';
 import { PluginCacheManager } from './types';
 
 /**
  * Implements a Cache Manager which will automatically create new cache clients
- * for plugins when requested. All requested cacheclients are created with the
+ * for plugins when requested. All requested cache clients are created with the
  * connection details provided.
  */
 export class CacheManager {
@@ -34,6 +35,7 @@ export class CacheManager {
   private readonly storeFactories = {
     memcache: this.getMemcacheClient,
     memory: this.getMemoryClient,
+    none: this.getNoneClient,
   };
 
   private readonly store: keyof CacheManager['storeFactories'];
@@ -47,8 +49,8 @@ export class CacheManager {
    */
   static fromConfig(config: Config): CacheManager {
     // If no `backend.cache` config is provided, instantiate the CacheManager
-    // with a "memory" cache client.
-    const store = config.getOptionalString('backend.cache.store') || 'memory';
+    // with a "NoStore" cache client.
+    const store = config.getOptionalString('backend.cache.store') || 'none';
     const connectionString = config.getOptionalString('backend.cache.connection') || '';
     return new CacheManager(store, connectionString);
   }
@@ -82,11 +84,10 @@ export class CacheManager {
   }
 
   private getMemcacheClient(pluginId: string, defaultTtl: number | undefined): Keyv {
-    const memcache = new KeyvMemcache(this.connection);
     return new Keyv({
       namespace: pluginId,
       ttl: defaultTtl,
-      store: memcache,
+      store: new KeyvMemcache(this.connection),
     });
   }
 
@@ -97,4 +98,10 @@ export class CacheManager {
     });
   }
 
+  private getNoneClient(pluginId: string): Keyv {
+    return new Keyv({
+      namespace: pluginId,
+      store: new NoStore(),
+    })
+  }
 }

packages/backend-common/src/cache/NoStore.ts

@@ -0,0 +1,43 @@
+/*
+ * Copyright 2021 Spotify AB
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * Storage class compatible with Keyv which always results in a no-op. This is
+ * used when no cache store is configured in a Backstage backend instance.
+ */
+export class NoStore extends Map<string, any> {
+
+  clear(): void {
+    return;
+  }
+
+  delete(_key: string): boolean {
+    return false;
+  }
+
+  get(_key: string) {
+    return;
+  }
+
+  has(_key: string): boolean {
+    return false;
+  }
+
+  set(_key: string, _value: any): this {
+    return this;
+  }
+
+}