Make cache readTimeout configurable.

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

plugins/techdocs-backend/src/cache/TechDocsCache.test.ts

@@ -15,6 +15,7 @@
  */
 
 import { CacheClient, getVoidLogger } from '@backstage/backend-common';
+import { ConfigReader } from '@backstage/config';
 import { CacheInvalidationError, TechDocsCache } from './TechDocsCache';
 
 const cached = (str: string): string => {
@@ -31,7 +32,7 @@ describe('TechDocsCache', () => {
       set: jest.fn(),
       delete: jest.fn(),
     };
-    CacheUnderTest = new TechDocsCache({
+    CacheUnderTest = TechDocsCache.fromConfig(new ConfigReader({}), {
       cache: MockClient,
       logger: getVoidLogger(),
     });
@@ -55,7 +56,7 @@ describe('TechDocsCache', () => {
       expect(actual).toBe(undefined);
     });
 
-    it('returns undefined if no response after 1s', async () => {
+    it('returns undefined if no response after 1s by default', async () => {
       const expectedPath = 'some/index.html';
       MockClient.get.mockImplementationOnce(() => {
         return new Promise(resolve => {
@@ -66,6 +67,28 @@ describe('TechDocsCache', () => {
       expect(actual).toBe(undefined);
     });
 
+    it('returns undefined if no response after configured readTimeout', async () => {
+      const expectedPath = 'some/index.html';
+      MockClient.get.mockImplementationOnce(() => {
+        return new Promise(resolve => {
+          setTimeout(() => resolve(cached('value')), 20);
+        });
+      });
+
+      CacheUnderTest = TechDocsCache.fromConfig(
+        new ConfigReader({
+          techdocs: { cache: { readTimeout: 10 } },
+        }),
+        {
+          cache: MockClient,
+          logger: getVoidLogger(),
+        },
+      );
+
+      const actual = await CacheUnderTest.get(expectedPath);
+      expect(actual).toBe(undefined);
+    });
+
     it('returns data if cache get returns it', async () => {
       const expectedPath = 'some/index.html';
       MockClient.get.mockResolvedValueOnce(cached('expected value'));

plugins/techdocs-backend/src/cache/TechDocsCache.ts

@@ -14,6 +14,8 @@
  * limitations under the License.
  */
 import { CacheClient } from '@backstage/backend-common';
+import { assertError } from '@backstage/errors';
+import { Config } from '@backstage/config';
 import { Logger } from 'winston';
 
 export class CacheInvalidationError extends Error {
@@ -28,10 +30,29 @@ export class CacheInvalidationError extends Error {
 export class TechDocsCache {
   protected readonly cache: CacheClient;
   protected readonly logger: Logger;
+  protected readonly readTimeout: number;
 
-  constructor({ cache, logger }: { cache: CacheClient; logger: Logger }) {
+  private constructor({
+    cache,
+    logger,
+    readTimeout,
+  }: {
+    cache: CacheClient;
+    logger: Logger;
+    readTimeout: number;
+  }) {
     this.cache = cache;
     this.logger = logger;
+    this.readTimeout = readTimeout;
+  }
+
+  static fromConfig(
+    config: Config,
+    { cache, logger }: { cache: CacheClient; logger: Logger },
+  ) {
+    const readTimeout =
+      config.getOptionalNumber('techdocs.cache.readTimeout') || 1000;
+    return new TechDocsCache({ cache, logger, readTimeout });
   }
 
   async get(path: string): Promise<Buffer | undefined> {
@@ -40,7 +61,7 @@ export class TechDocsCache {
       // temporarily unreachable.
       const response = (await Promise.race([
         this.cache.get(path),
-        new Promise(cancelAfter => setTimeout(cancelAfter, 1000)),
+        new Promise(cancelAfter => setTimeout(cancelAfter, this.readTimeout)),
       ])) as string | undefined;
 
       if (response !== undefined) {
@@ -51,6 +72,7 @@ export class TechDocsCache {
       this.logger.debug(`Cache miss: ${path}`);
       return response;
     } catch (e) {
+      assertError(e);
       this.logger.warn(`Error getting cache entry ${path}: ${e.message}`);
       this.logger.debug(e.stack);
       return undefined;

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

@@ -91,7 +91,7 @@ export async function createRouter(
   const defaultTtl = config.getOptionalNumber('techdocs.cache.ttl');
   if (isOutOfTheBoxOption(options) && options.cache && defaultTtl) {
     const cacheClient = options.cache.getClient({ defaultTtl });
-    cache = new TechDocsCache({ cache: cacheClient, logger });
+    cache = TechDocsCache.fromConfig(config, { cache: cacheClient, logger });
   }
 
   const scmIntegrations = ScmIntegrations.fromConfig(config);