feat(backend-common): add common code for service shell

packages/backend-common/package.json

@@ -27,12 +27,17 @@
     "clean": "backstage-cli clean"
   },
   "dependencies": {
+    "compression": "^1.7.4",
+    "cors": "^2.8.5",
     "express": "^4.17.1",
+    "helmet": "^3.22.0",
     "morgan": "^1.10.0",
     "winston": "^3.2.1"
   },
   "devDependencies": {
     "@backstage/cli": "^0.1.1-alpha.7",
+    "@types/compression": "^1.7.0",
+    "@types/cors": "^2.8.6",
     "@types/express": "^4.17.6",
     "@types/http-errors": "^1.6.3",
     "@types/morgan": "^1.9.0",

packages/backend-common/src/index.ts

@@ -17,3 +17,4 @@
 export * from './errors';
 export * from './logging';
 export * from './middleware';
+export * from './service';

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

@@ -0,0 +1,117 @@
+/*
+ * 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 compression from 'compression';
+import cors from 'cors';
+import express, { Router } from 'express';
+import helmet from 'helmet';
+import { Server } from 'http';
+import { Logger } from 'winston';
+import { getRootLogger } from '../logging';
+import {
+  errorHandler,
+  notFoundHandler,
+  requestLoggingHandler,
+} from '../middleware';
+import { ServiceBuilder } from './types';
+
+const DEFAULT_PORT = 7000;
+
+export class ServiceBuilderImpl implements ServiceBuilder {
+  private port: number | undefined;
+  private logger: Logger | undefined;
+  private corsOptions: cors.CorsOptions | undefined;
+  private routers: [string, Router][];
+
+  constructor() {
+    this.routers = [];
+  }
+
+  setPort(port: number): ServiceBuilder {
+    this.port = port;
+    return this;
+  }
+
+  setLogger(logger: Logger): ServiceBuilder {
+    this.logger = logger;
+    return this;
+  }
+
+  enableCors(options: cors.CorsOptions): ServiceBuilder {
+    this.corsOptions = options;
+    return this;
+  }
+
+  addRouter(root: string, router: Router): ServiceBuilder {
+    this.routers.push([root, router]);
+    return this;
+  }
+
+  start(): Promise<Server> {
+    const app = express();
+    const { port, logger, corsOptions } = this.getOptions();
+
+    app.use(helmet());
+    if (corsOptions) {
+      app.use(cors(corsOptions));
+    }
+    app.use(compression());
+    app.use(express.json());
+    app.use(requestLoggingHandler());
+    for (const [root, route] of this.routers) {
+      app.use(root, route);
+    }
+    app.use(notFoundHandler());
+    app.use(errorHandler());
+
+    return new Promise((resolve, reject) => {
+      app.on('error', e => {
+        logger.error(`Failed to start up on port ${port}, ${e}`);
+        reject(e);
+      });
+      const server = app.listen(port, () => {
+        logger.info(`Listening on port ${port}`);
+      });
+      resolve(server);
+    });
+  }
+
+  private getOptions(): {
+    port: number;
+    logger: Logger;
+    corsOptions?: cors.CorsOptions;
+  } {
+    let port: number;
+    if (this.port !== undefined) {
+      port = this.port;
+    } else {
+      port = parseInt(process.env.PORT ?? '', 10) || DEFAULT_PORT;
+    }
+
+    let logger: Logger;
+    if (this.logger) {
+      logger = this.logger;
+    } else {
+      logger = getRootLogger();
+    }
+
+    return {
+      port,
+      logger,
+      corsOptions: this.corsOptions,
+    };
+  }
+}

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

@@ -0,0 +1,24 @@
+/*
+ * 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 { ServiceBuilderImpl } from './ServiceBuilderImpl';
+
+/**
+ * Creates a new service builder.
+ */
+export function createServiceBuilder() {
+  return new ServiceBuilderImpl();
+}

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

@@ -0,0 +1,18 @@
+/*
+ * 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.
+ */
+
+export { createServiceBuilder } from './createServiceBuilder';
+export type { ServiceBuilder } from './types';

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

@@ -0,0 +1,65 @@
+/*
+ * 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 cors from 'cors';
+import { Router } from 'express';
+import { Server } from 'http';
+import { Logger } from 'winston';
+
+export type ServiceBuilder = {
+  /**
+   * Sets the port to listen on.
+   *
+   * If no port is specified, the service will first look for an environment
+   * variable named PORT and use that if present, otherwise it picks a default
+   * port (7000).
+   *
+   * @param port The port to listen on
+   */
+  setPort(port: number): ServiceBuilder;
+
+  /**
+   * Sets the logger to use for service-specific logging.
+   *
+   * If no logger is given, the default root logger is used.
+   *
+   * @param logger A winston logger
+   */
+  setLogger(logger: Logger): ServiceBuilder;
+
+  /**
+   * Enables CORS handling using the given settings.
+   *
+   * If this method is not called, the resulting service will not have any
+   * built in CORS handling.
+   *
+   * @param options Standard CORS options
+   */
+  enableCors(options: cors.CorsOptions): ServiceBuilder;
+
+  /**
+   * Adds a router (similar to the express .use call) to the service.
+   *
+   * @param root The root URL to bind to (e.g. "/api/function1")
+   * @param router An express router
+   */
+  addRouter(root: string, router: Router): ServiceBuilder;
+
+  /**
+   * Starts the server using the given settings.
+   */
+  start(): Promise<Server>;
+};