Cancel cache read if it takes too long

Signed-off-by: Joe Porpeglia <josephp@spotify.com>

plugins/techdocs-backend/src/service/CachedEntityLoader.test.ts

@@ -130,4 +130,19 @@ describe('CachedEntityLoader', () => {
       ttl: 5000,
     });
   });
+
+  it('calls the catalog if the cache read takes too long', async () => {
+    identity.authenticate.mockResolvedValue(identityResponse);
+    cache.get.mockImplementation(
+      () =>
+        new Promise(resolve => {
+          setTimeout(() => resolve(undefined), 10000);
+        }),
+    );
+    catalog.getEntityByName.mockResolvedValue(entity);
+
+    const result = await loader.load(entityName, token);
+
+    expect(result).toEqual(entity);
+  });
 });

plugins/techdocs-backend/src/service/CachedEntityLoader.ts

@@ -30,9 +30,10 @@ export type CachedEntityLoaderOptions = {
 };
 
 export class CachedEntityLoader {
-  private catalog: CatalogClient;
-  private cache: CacheClient;
-  private identity: IdentityClient;
+  private readonly catalog: CatalogClient;
+  private readonly cache: CacheClient;
+  private readonly identity: IdentityClient;
+  private readonly readTimeout = 1000;
 
   constructor({ catalog, cache, identity }: CachedEntityLoaderOptions) {
     this.catalog = catalog;
@@ -45,7 +46,7 @@ export class CachedEntityLoader {
     token: string | undefined,
   ): Promise<Entity | undefined> {
     const cacheKey = await this.getCacheKey(entityName, token);
-    let result = (await this.cache.get(cacheKey)) as Entity | undefined;
+    let result = await this.getFromCache(cacheKey);
 
     if (result) {
       return result;
@@ -68,6 +69,15 @@ export class CachedEntityLoader {
     return result;
   }
 
+  private async getFromCache(key: string): Promise<Entity | undefined> {
+    // Promise.race ensures we don't hang the client for long if the cache is
+    // temporarily unreachable.
+    return (await Promise.race([
+      this.cache.get(key),
+      new Promise(cancelAfter => setTimeout(cancelAfter, this.readTimeout)),
+    ])) as Entity | undefined;
+  }
+
   private async getCacheKey(
     entityName: EntityName,
     token: string | undefined,