feat(proxy): implement proxy backend plugin

plugins/proxy-backend/src/index.ts

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+/*
+ * 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 * from './service/router';

plugins/proxy-backend/src/run.ts

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+/*
+ * 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 { getRootLogger } from '@backstage/backend-common';
+import yn from 'yn';
+import { startStandaloneServer } from './service/standaloneServer';
+
+const port = process.env.PLUGIN_PORT ? Number(process.env.PLUGIN_PORT) : 7000;
+const enableCors = yn(process.env.PLUGIN_CORS, { default: false });
+const logger = getRootLogger();
+
+startStandaloneServer({ port, enableCors, logger }).catch(err => {
+  logger.error(err);
+  process.exit(1);
+});
+
+process.on('SIGINT', () => {
+  logger.info('CTRL+C pressed; exiting.');
+  process.exit(0);
+});

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

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+/*
+ * 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 { errorHandler } from '@backstage/backend-common';
+import { AppConfig } from '@backstage/config';
+import express from 'express';
+import Router from 'express-promise-router';
+import { createProxyMiddleware } from 'http-proxy-middleware';
+import { Logger } from 'winston';
+
+export interface RouterOptions {
+  logger: Logger;
+  config: AppConfig;
+}
+
+export async function createRouter(
+  options: RouterOptions,
+): Promise<express.Router> {
+  const router = Router();
+  router.use(express.json());
+
+  const proxyConfig = options.config.data.proxy ?? {};
+  Object.entries(proxyConfig).forEach(([route, proxyRouteConfig]) => {
+    router.use(createProxyMiddleware(route, proxyRouteConfig));
+  });
+
+  router.use(errorHandler());
+  return router;
+}

plugins/proxy-backend/src/service/standaloneServer.ts

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+/*
+ * 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 { createServiceBuilder } from '@backstage/backend-common';
+import { Server } from 'http';
+import { Logger } from 'winston';
+import { createRouter } from './router';
+
+export interface ServerOptions {
+  port: number;
+  enableCors: boolean;
+  logger: Logger;
+}
+
+export async function startStandaloneServer(
+  options: ServerOptions,
+): Promise<Server> {
+  const logger = options.logger.child({ service: 'catalog-backend' });
+
+  logger.debug('Creating application...');
+
+  logger.debug('Starting application server...');
+  const router = await createRouter({
+    logger,
+  });
+  const service = createServiceBuilder(module)
+    .enableCors({ origin: 'http://localhost:3000' })
+    .addRouter('/proxy', router);
+  return await service.start().catch(err => {
+    logger.error(err);
+    process.exit(1);
+  });
+}
+
+module.hot?.accept();

plugins/proxy-backend/src/setupTests.ts

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+/*
+ * 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.
+ */
+
+require('jest-fetch-mock').enableMocks();
+
+export {};