added app-node with a static fallback handler extension point

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

.changeset/lazy-pugs-wash.md

@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-app-node': minor
+---
+
+Added the `app` plugin node library, initially providing an extension point that can be used to configure a static fallback handler.

plugins/app-node/.eslintrc.js

@@ -0,0 +1 @@
+module.exports = require('@backstage/cli/config/eslint-factory')(__dirname);

plugins/app-node/README.md

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+# @backstage/plugin-app-node
+
+Welcome to the Node.js library package for the app plugin!
+
+_This plugin was created through the Backstage CLI_

plugins/app-node/api-report.md

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+## API Report File for "@backstage/plugin-app-node"
+
+> Do not edit this file. It is a report generated by [API Extractor](https://api-extractor.com/).
+
+```ts
+import { ExtensionPoint } from '@backstage/backend-plugin-api';
+import { Handler } from 'express';
+
+// @public
+export interface StaticFallbackHandlerExtensionPoint {
+  setStaticFallbackHandler(handler: Handler): void;
+}
+
+// @public
+export const staticFallbackHandlerExtensionPoint: ExtensionPoint<StaticFallbackHandlerExtensionPoint>;
+```

plugins/app-node/package.json

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+{
+  "name": "@backstage/plugin-app-node",
+  "description": "Node.js library for the app plugin",
+  "version": "0.0.0",
+  "main": "src/index.ts",
+  "types": "src/index.ts",
+  "license": "Apache-2.0",
+  "publishConfig": {
+    "access": "public",
+    "main": "dist/index.cjs.js",
+    "types": "dist/index.d.ts"
+  },
+  "backstage": {
+    "role": "node-library"
+  },
+  "scripts": {
+    "build": "backstage-cli package build",
+    "lint": "backstage-cli package lint",
+    "test": "backstage-cli package test",
+    "clean": "backstage-cli package clean",
+    "prepack": "backstage-cli package prepack",
+    "postpack": "backstage-cli package postpack"
+  },
+  "devDependencies": {
+    "@backstage/cli": "workspace:^"
+  },
+  "files": [
+    "dist"
+  ],
+  "dependencies": {
+    "@backstage/backend-plugin-api": "workspace:^",
+    "express": "^4.18.2"
+  }
+}

plugins/app-node/src/extensions.ts

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+/*
+ * Copyright 2023 The Backstage Authors
+ *
+ * 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.
+ */
+
+import { createExtensionPoint } from '@backstage/backend-plugin-api';
+import { Handler } from 'express';
+
+/**
+ * The interface for {@link staticFallbackHandlerExtensionPoint}.
+ *
+ * @public
+ */
+export interface StaticFallbackHandlerExtensionPoint {
+  /**
+   * Sets the static fallback handler. This can only be done once.
+   */
+  setStaticFallbackHandler(handler: Handler): void;
+}
+
+/**
+ * An extension point the exposes the ability to configure a static fallback handler for the app backend.
+ *
+ * The static fallback handler is a request handler to handle requests for static content that is not
+ * present in the app bundle.
+ *
+ * This can be used to avoid issues with clients on older deployment versions trying to access lazy
+ * loaded content that is no longer present. Typically the requests would fall back to a long-term
+ * object store where all recently deployed versions of the app are present.
+ *
+ * Another option is to provide a `database` that will take care of storing the static assets instead.
+ *
+ * If both `database` and `staticFallbackHandler` are provided, the `database` will attempt to serve
+ * static assets first, and if they are not found, the `staticFallbackHandler` will be called.
+ *
+ * @public
+ */
+export const staticFallbackHandlerExtensionPoint =
+  createExtensionPoint<StaticFallbackHandlerExtensionPoint>({
+    id: 'app.staticFallbackHandler',
+  });

plugins/app-node/src/index.ts

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+/*
+ * Copyright 2023 The Backstage Authors
+ *
+ * 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.
+ */
+
+/**
+ * Node.js library for the app plugin.
+ *
+ * @packageDocumentation
+ */
+
+export {
+  staticFallbackHandlerExtensionPoint,
+  type StaticFallbackHandlerExtensionPoint,
+} from './extensions';

plugins/app-node/src/setupTests.ts

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+/*
+ * Copyright 2023 The Backstage Authors
+ *
+ * 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.
+ */
+export {};

yarn.lock

@@ -4657,6 +4657,16 @@ __metadata:
   languageName: unknown
   linkType: soft
 
+"@backstage/plugin-app-node@workspace:^, @backstage/plugin-app-node@workspace:plugins/app-node":
+  version: 0.0.0-use.local
+  resolution: "@backstage/plugin-app-node@workspace:plugins/app-node"
+  dependencies:
+    "@backstage/backend-plugin-api": "workspace:^"
+    "@backstage/cli": "workspace:^"
+    express: ^4.18.2
+  languageName: unknown
+  linkType: soft
+
 "@backstage/plugin-auth-backend@workspace:^, @backstage/plugin-auth-backend@workspace:plugins/auth-backend":
   version: 0.0.0-use.local
   resolution: "@backstage/plugin-auth-backend@workspace:plugins/auth-backend"