feat(backend-common): base backend config

app-config.yaml

@@ -4,6 +4,12 @@ app:
 
 backend:
   baseUrl: http://localhost:7000
+  bindPort: 7000
+  bindHost: localhost
+  cors:
+    origin: http://localhost:3000
+    methods: [GET, POST, PUT, DELETE]
+    credentials: true
 
 organization:
   name: Spotify

packages/backend-common/package.json

@@ -29,6 +29,7 @@
     "clean": "backstage-cli clean"
   },
   "dependencies": {
+    "@backstage/config": "^0.1.1-alpha.9",
     "@types/cors": "^2.8.6",
     "@types/express": "^4.17.6",
     "compression": "^1.7.4",

packages/backend-common/src/service/createServiceBuilder.ts

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-import { ServiceBuilderImpl } from './ServiceBuilderImpl';
+import { ServiceBuilderImpl } from './lib/ServiceBuilderImpl';
 
 /**
  * Creates a new service builder.

packages/backend-common/src/service/lib/ServiceBuilderImpl.ts

@@ -14,6 +14,7 @@
  * limitations under the License.
  */
 
+import { ConfigReader } from '@backstage/config';
 import compression from 'compression';
 import cors from 'cors';
 import express, { Router } from 'express';
@@ -21,37 +22,66 @@ import helmet from 'helmet';
 import { Server } from 'http';
 import stoppable from 'stoppable';
 import { Logger } from 'winston';
-import { getRootLogger } from '../logging';
+import { useHotCleanup } from '../../hot';
+import { getRootLogger } from '../../logging';
 import {
   errorHandler,
   notFoundHandler,
   requestLoggingHandler,
-} from '../middleware';
-import { ServiceBuilder } from './types';
-import { useHotCleanup } from '../hot';
+} from '../../middleware';
+import { ServiceBuilder } from '../types';
+import { readBaseOptions, readCorsOptions } from './config';
 
 const DEFAULT_PORT = 7000;
+const DEFAULT_HOST = 'localhost';
 
 export class ServiceBuilderImpl implements ServiceBuilder {
   private port: number | undefined;
+  private host: string | undefined;
   private logger: Logger | undefined;
   private corsOptions: cors.CorsOptions | undefined;
   private routers: [string, Router][];
-  /**
-   * Reference to the module where builder is created
-   * Needed for the HMR
-   */
+  // Reference to the module where builder is created - needed for hot module
+  // reloading
   private module: NodeModule;
+
   constructor(module: NodeModule) {
     this.routers = [];
     this.module = module;
   }
 
+  loadConfig(config: ConfigReader): ServiceBuilder {
+    const backendConfig = config.getOptionalConfig('backend');
+    if (!backendConfig) {
+      return this;
+    }
+
+    const baseOptions = readBaseOptions(backendConfig);
+    if (baseOptions.bindPort) {
+      this.port = baseOptions.bindPort;
+    }
+    if (baseOptions.bindHost) {
+      this.host = baseOptions.bindHost;
+    }
+
+    const corsOptions = readCorsOptions(backendConfig);
+    if (corsOptions) {
+      this.corsOptions = corsOptions;
+    }
+
+    return this;
+  }
+
   setPort(port: number): ServiceBuilder {
     this.port = port;
     return this;
   }
 
+  setHost(host: string): ServiceBuilder {
+    this.host = host;
+    return this;
+  }
+
   setLogger(logger: Logger): ServiceBuilder {
     this.logger = logger;
     return this;
@@ -69,7 +99,7 @@ export class ServiceBuilderImpl implements ServiceBuilder {
 
   start(): Promise<Server> {
     const app = express();
-    const { port, logger, corsOptions } = this.getOptions();
+    const { port, host, logger, corsOptions } = this.getOptions();
 
     app.use(helmet());
     if (corsOptions) {
@@ -89,8 +119,9 @@ export class ServiceBuilderImpl implements ServiceBuilder {
         logger.error(`Failed to start up on port ${port}, ${e}`);
         reject(e);
       });
+
       const server = stoppable(
-        app.listen(port, () => {
+        app.listen(port, host, () => {
           logger.info(`Listening on port ${port}`);
         }),
         0,
@@ -108,6 +139,7 @@ export class ServiceBuilderImpl implements ServiceBuilder {
 
   private getOptions(): {
     port: number;
+    host: string;
     logger: Logger;
     corsOptions?: cors.CorsOptions;
   } {
@@ -118,6 +150,13 @@ export class ServiceBuilderImpl implements ServiceBuilder {
       port = parseInt(process.env.PORT ?? '', 10) || DEFAULT_PORT;
     }
 
+    let host: string;
+    if (this.host !== undefined) {
+      host = this.host;
+    } else {
+      host = process.env.HOST || DEFAULT_HOST;
+    }
+
     let logger: Logger;
     if (this.logger) {
       logger = this.logger;
@@ -127,6 +166,7 @@ export class ServiceBuilderImpl implements ServiceBuilder {
 
     return {
       port,
+      host,
       logger,
       corsOptions: this.corsOptions,
     };

packages/backend-common/src/service/lib/config.ts

@@ -0,0 +1,112 @@
+/*
+ * Copyright 2020 Spotify AB
+ *
+ * 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 { ConfigReader } from '@backstage/config';
+import { CorsOptions } from 'cors';
+
+export type BaseOptions = {
+  bindPort?: number;
+  bindHost?: string;
+};
+
+/**
+ * Reads some base options out of a config object.
+ *
+ * @param config The root of a backend config object
+ * @returns A base options object
+ *
+ * @example
+ * ```json
+ * {
+ *   baseUrl: "http://localhost:7000"
+ *   bindPort: 7000
+ *   bindHost: "0.0.0.0"
+ * }
+ * ```
+ */
+export function readBaseOptions(config: ConfigReader): BaseOptions {
+  return removeUnknown({
+    bindPort: config.getOptionalNumber('bindPort'),
+    bindHost: config.getOptionalString('bindHost'),
+  });
+}
+
+/**
+ * Attempts to read a CORS options object from the root of a config object.
+ *
+ * @param config The root of a backend config object
+ * @returns A CORS options object, or undefined if not specified
+ *
+ * @example
+ * ```json
+ * {
+ *   cors: {
+ *    origin: "http://localhost:3000",
+ *    credentials: true
+ *   }
+ * }
+ * ```
+ */
+export function readCorsOptions(config: ConfigReader): CorsOptions | undefined {
+  const cc = config.getOptionalConfig('cors');
+  if (!cc) {
+    return undefined;
+  }
+
+  return removeUnknown({
+    origin: getOptionalStringOrStrings(cc, 'origin'),
+    methods: getOptionalStringOrStrings(cc, 'methods'),
+    allowedHeaders: getOptionalStringOrStrings(cc, 'allowedHeaders'),
+    exposedHeaders: getOptionalStringOrStrings(cc, 'exposedHeaders'),
+    credentials: cc.getOptionalBoolean('credentials'),
+    maxAge: cc.getOptionalNumber('maxAge'),
+    preflightContinue: cc.getOptionalBoolean('preflightContinue'),
+    optionsSuccessStatus: cc.getOptionalNumber('optionsSuccessStatus'),
+  });
+}
+
+function getOptionalStringOrStrings(
+  config: ConfigReader,
+  key: string,
+): string | string[] | undefined {
+  const value = config.getOptional(key);
+  if (
+    value === undefined ||
+    typeof value === 'string' ||
+    isStringArray(value)
+  ) {
+    return value;
+  }
+  throw new Error(`Expected string or array of strings, got ${typeof value}`);
+}
+
+function isStringArray(value: any): value is string[] {
+  if (!Array.isArray(value)) {
+    return false;
+  }
+  for (const v of value) {
+    if (typeof v !== 'string') {
+      return false;
+    }
+  }
+  return true;
+}
+
+function removeUnknown<T extends object>(obj: T): T {
+  return Object.fromEntries(
+    Object.entries(obj).filter(([, v]) => v !== undefined),
+  ) as T;
+}

packages/backend-common/src/service/types.ts

@@ -14,12 +14,20 @@
  * limitations under the License.
  */
 
+import { ConfigReader } from '@backstage/config';
 import cors from 'cors';
 import { Router } from 'express';
 import { Server } from 'http';
 import { Logger } from 'winston';
 
 export type ServiceBuilder = {
+  /**
+   * Sets the service parameters based on configuration.
+   *
+   * @param config The configuration to read
+   */
+  loadConfig(config: ConfigReader): ServiceBuilder;
+
   /**
    * Sets the port to listen on.
    *

packages/backend/src/index.ts

@@ -55,7 +55,9 @@ function makeCreateEnv(loadedConfigs: AppConfig[]) {
 }
 
 async function main() {
-  const createEnv = makeCreateEnv(await loadConfig());
+  const configs = await loadConfig();
+  const configReader = ConfigReader.fromConfigs(configs);
+  const createEnv = makeCreateEnv(configs);
 
   const catalogEnv = useHotMemoize(module, () => createEnv('catalog'));
   const scaffolderEnv = useHotMemoize(module, () => createEnv('scaffolder'));
@@ -63,10 +65,7 @@ async function main() {
   const identityEnv = useHotMemoize(module, () => createEnv('identity'));
 
   const service = createServiceBuilder(module)
-    .enableCors({
-      origin: 'http://localhost:3000',
-      credentials: true,
-    })
+    .loadConfig(configReader)
     .addRouter('/catalog', await catalog(catalogEnv))
     .addRouter('/scaffolder', await scaffolder(scaffolderEnv))
     .addRouter(