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feat(readme-backend): added config to set the cache ttl
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Lines changed: 170 additions & 17 deletions

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‎.changeset/many-baboons-lick.md‎

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---
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'@axis-backstage/plugin-readme-backend': patch
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---
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Added config to set the cache ttl.

‎plugins/readme-backend/README.md‎

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@@ -46,6 +46,20 @@ readme:
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- README.markdown
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```
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To override the default TTL of the internal cache a duration can be set using the `cacheTtl` key. This can be either a string
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or an object. The following examples should be equal.
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```yaml
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readme:
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cacheTtl:
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hours: 2
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```
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```yaml
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readme:
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cacheTtl: '2h'
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```
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### Troubleshooting
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If the backend fails to provide README content for an entity, it could be due to several reasons.

‎plugins/readme-backend/config.d.ts‎

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import { HumanDuration } from '@backstage/types';
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export interface Config {
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/**
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* Configuration options for the Readme backend plugin
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* when looking for a README file and which order to use.
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*/
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fileNames?: string[];
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/**
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* Optional cache TTL, defaults to 1 hour.
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*/
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cacheTtl?: HumanDuration | string;
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};
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}

‎plugins/readme-backend/package.json‎

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"@backstage/backend-plugin-api": "^1.2.0",
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"@backstage/catalog-client": "^1.9.1",
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"@backstage/catalog-model": "^1.7.3",
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"@backstage/config": "^1.3.2",
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"@backstage/errors": "^1.2.7",
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"@backstage/integration": "^1.16.1",
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"@backstage/types": "^1.2.1",
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"@types/express": "*",
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"express": "^4.17.1",
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"express-promise-router": "^4.1.0"
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},
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"devDependencies": {
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"@backstage/backend-test-utils": "^1.3.0",
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"@backstage/cli": "^0.30.0",
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"@backstage/config": "^1.3.2",
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"@types/supertest": "^2.0.12",
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"msw": "^2.7.3",
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"supertest": "^6.2.4"

‎plugins/readme-backend/src/service/config.test.ts‎

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import { mockServices } from '@backstage/backend-test-utils';
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import { getCacheTtl } from './config';
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describe('getCacheTtl', () => {
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it('should return default TTL when cache.ttl is not configured', () => {
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const mockConfig = mockServices.rootConfig({
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data: {},
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});
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const result = getCacheTtl(mockConfig);
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expect(result).toBe(3_600_000); // 1 hour in milliseconds
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});
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it('should return default TTL when readme config section exists but no ttl key', () => {
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const mockConfig = mockServices.rootConfig({
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data: {
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readme: {},
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},
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});
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const result = getCacheTtl(mockConfig);
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expect(result).toBe(3_600_000); // 1 hour in milliseconds
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});
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it('should return configured TTL in seconds', () => {
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const mockConfig = mockServices.rootConfig({
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data: {
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readme: {
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cacheTtl: { seconds: 1800 }, // 30 minutes
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},
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},
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});
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const result = getCacheTtl(mockConfig);
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expect(result).toBe(1_800_000); // 30 minutes in milliseconds
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});
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it('should return configured TTL in minutes', () => {
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const mockConfig = mockServices.rootConfig({
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data: {
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readme: {
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cacheTtl: { minutes: 10 },
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},
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},
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});
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const result = getCacheTtl(mockConfig);
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expect(result).toBe(600_000); // 10 minutes in milliseconds
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});
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it('should return configured TTL in hours', () => {
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const mockConfig = mockServices.rootConfig({
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data: {
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readme: {
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cacheTtl: { hours: 2 },
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},
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},
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});
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const result = getCacheTtl(mockConfig);
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expect(result).toBe(7_200_000); // 2 hours in milliseconds
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});
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it('should return configured TTL as a string value (interpreted as milliseconds)', () => {
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const mockConfig = mockServices.rootConfig({
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data: {
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readme: {
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cacheTtl: '4w',
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},
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},
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});
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const result = getCacheTtl(mockConfig);
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expect(result).toBe(2419200000); // 4 weeks in milliseconds
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});
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it('should handle complex duration configuration', () => {
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const mockConfig = mockServices.rootConfig({
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data: {
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readme: {
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cacheTtl: {
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hours: 1,
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minutes: 30,
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seconds: 45,
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},
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},
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},
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});
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const result = getCacheTtl(mockConfig);
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expect(result).toBe(5_445_000); // 1h 30m 45s in milliseconds
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});
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});

‎plugins/readme-backend/src/service/config.ts‎

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import { Config, readDurationFromConfig } from '@backstage/config';
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import { durationToMilliseconds } from '@backstage/types';
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const CACHE_CONFIG_KEY = 'readme.cacheTtl';
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export const getCacheTtl = (config: Config): number =>
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config.has(CACHE_CONFIG_KEY)
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? durationToMilliseconds(
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readDurationFromConfig(config, { key: CACHE_CONFIG_KEY }),
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)
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: 3_600_000;

‎plugins/readme-backend/src/service/constants.test.ts‎

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import { ConfigReader } from '@backstage/config';
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import { mockServices } from '@backstage/backend-test-utils';
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import { NOT_FOUND_PLACEHOLDER, getReadmeTypes } from './constants';
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describe('constants', () => {
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describe('getReadmeTypes', () => {
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it('should return default readme types when config is empty', () => {
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const config = new ConfigReader({});
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const config = mockServices.rootConfig({
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data: {},
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});
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const readmeTypes = getReadmeTypes(config);
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expect(readmeTypes).toEqual([
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{ name: 'README.md', type: 'text/markdown' },
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});
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it('should return custom readme types from config', () => {
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const config = new ConfigReader({
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readme: {
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fileNames: ['CUSTOM.md', 'CUSTOM.txt'],
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const config = mockServices.rootConfig({
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data: {
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readme: {
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fileNames: ['CUSTOM.md', 'CUSTOM.txt'],
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},
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},
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});
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const readmeTypes = getReadmeTypes(config);

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

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import express from 'express';
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import Router from 'express-promise-router';
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import { isSymLink } from '../lib';
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import { getCacheTtl } from './config';
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import { NOT_FOUND_PLACEHOLDER, getReadmeTypes } from './constants';
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import { ReadmeFile } from './types';
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): Promise<express.Router> {
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const { auth, logger, config, reader, discovery, cache } = options;
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const catalogClient = new CatalogClient({ discoveryApi: discovery });
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const cacheTtl = getCacheTtl(config);
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logger.info('Initializing readme backend');
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logger.info(`Initializing readme backend. Cache TTL: ${cacheTtl}ms`);
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const integrations = ScmIntegrations.fromConfig(config);
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const router = Router();
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router.use(express.json());
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content = (await symLinkUrlResponse.buffer()).toString('utf-8');
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}
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cache.set(entityRef, {
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name: fileType.name,
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type: fileType.type,
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content: content,
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});
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cache.set(
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entityRef,
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{
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name: fileType.name,
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type: fileType.type,
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content: content,
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},
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{ ttl: cacheTtl },
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);
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logger.info(
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`Found README for ${entityRef}: ${url} type ${fileType.type}`,
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);
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}
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}
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logger.info(`Readme not found for ${entityRef}`);
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cache.set(entityRef, {
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name: NOT_FOUND_PLACEHOLDER,
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type: '',
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content: '',
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});
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cache.set(
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entityRef,
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{
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name: NOT_FOUND_PLACEHOLDER,
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type: '',
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content: '',
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},
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{ ttl: cacheTtl },
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);
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throw new NotFoundError('Readme could not be found');
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});
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‎yarn.lock‎

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"@backstage/config": "npm:^1.3.2"
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"@backstage/errors": "npm:^1.2.7"
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"@backstage/integration": "npm:^1.16.1"
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"@backstage/types": "npm:^1.2.1"
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"@types/express": "npm:*"
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"@types/supertest": "npm:^2.0.12"
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express: "npm:^4.17.1"

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