app-backend: some refactoring, renaming, and docs

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

plugins/app-backend/src/lib/assets/StaticAssetsStore.ts

@@ -19,7 +19,7 @@ import { Knex } from 'knex';
 import { Logger } from 'winston';
 import { DateTime } from 'luxon';
 import partition from 'lodash/partition';
-import { StaticAsset, StaticAssetInput } from './types';
+import { StaticAsset, StaticAssetInput, StaticAssetProvider } from './types';
 
 const migrationsDir = resolvePackagePath(
   '@backstage/plugin-app-backend',
@@ -43,7 +43,7 @@ export interface StaticAssetsStoreOptions {
  *
  * @internal
  */
-export class StaticAssetsStore {
+export class StaticAssetsStore implements StaticAssetProvider {
   #db: Knex;
   #logger: Logger;
 

plugins/app-backend/src/lib/assets/createStaticAssetMiddleware.test.ts

@@ -16,16 +16,16 @@
 
 import express from 'express';
 import request from 'supertest';
-import { createStaticAssetsStoreMiddleware } from './createStaticAssetsStoreMiddleware';
+import { createStaticAssetMiddleware } from './createStaticAssetMiddleware';
 import { StaticAssetsStore } from './StaticAssetsStore';
 
 const mockStore = {
   getAsset: jest.fn(),
 } as unknown as jest.Mocked<StaticAssetsStore>;
 
-describe('createStaticAssetsStoreMiddleware', () => {
+describe('createStaticAssetMiddleware', () => {
   const app = express();
-  app.use(createStaticAssetsStoreMiddleware(mockStore));
+  app.use(createStaticAssetMiddleware(mockStore));
   app.use((_req, res) => {
     res.status(404).end('Not Found');
   });

plugins/app-backend/src/lib/assets/createStaticAssetMiddleware.ts

@@ -16,11 +16,16 @@
 
 import { extname } from 'path';
 import { RequestHandler } from 'express';
-import { StaticAssetsStore } from './StaticAssetsStore';
+import { StaticAssetProvider } from './types';
 import { CACHE_CONTROL_MAX_CACHE } from '../headers';
 
-export function createStaticAssetsStoreMiddleware(
-  store: StaticAssetsStore,
+/**
+ * Creates a middleware that serves static assets from a static asset provider
+ *
+ * @internal
+ */
+export function createStaticAssetMiddleware(
+  store: StaticAssetProvider,
 ): RequestHandler {
   return (req, res, next) => {
     if (req.method !== 'GET' && req.method !== 'HEAD') {
@@ -28,6 +33,7 @@ export function createStaticAssetsStoreMiddleware(
       return;
     }
 
+    // Let's not assume we're in promise-router
     Promise.resolve(
       (async () => {
         // Drop leading slashes from the incoming path

plugins/app-backend/src/lib/assets/findStaticAssets.ts

@@ -19,6 +19,11 @@ import globby from 'globby';
 import { StaticAssetInput } from './types';
 import { resolveSafeChildPath } from '@backstage/backend-common';
 
+/**
+ * Finds all static assets within a directory
+ *
+ * @internal
+ */
 export async function findStaticAssets(
   staticDir: string,
 ): Promise<StaticAssetInput[]> {

plugins/app-backend/src/lib/assets/index.ts

@@ -15,6 +15,10 @@
  */
 
 export { StaticAssetsStore } from './StaticAssetsStore';
-export type { StaticAsset, StaticAssetInput } from './types';
+export type {
+  StaticAsset,
+  StaticAssetInput,
+  StaticAssetProvider,
+} from './types';
 export { findStaticAssets } from './findStaticAssets';
-export { createStaticAssetsStoreMiddleware } from './createStaticAssetsStoreMiddleware';
+export { createStaticAssetMiddleware } from './createStaticAssetMiddleware';

plugins/app-backend/src/lib/assets/types.ts

@@ -24,3 +24,7 @@ export interface StaticAsset {
   content: Buffer;
   lastModifiedAt: Date;
 }
+
+export interface StaticAssetProvider {
+  getAsset(path: string): Promise<StaticAsset | undefined>;
+}

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

@@ -30,7 +30,7 @@ import { injectConfig, readConfigs } from '../lib/config';
 import {
   StaticAssetsStore,
   findStaticAssets,
-  createStaticAssetsStoreMiddleware,
+  createStaticAssetMiddleware,
 } from '../lib/assets';
 import {
   CACHE_CONTROL_MAX_CACHE,
@@ -132,7 +132,7 @@ export async function createRouter(
     // Remove any assets that are older than 7 days
     await store.trimAssets({ maxAgeSeconds: 60 * 60 * 24 * 7 });
 
-    staticRouter.use(createStaticAssetsStoreMiddleware(store));
+    staticRouter.use(createStaticAssetMiddleware(store));
   }
 
   if (staticFallbackHandler) {