Add dev-proxy to frontend dev server

This adds a reverse proxy to the backend, that automatically
redirects requests that are not handled by the backend to the React
dev server running on port 3001.

The reverse proxy is only enabled when NODE_ENV is set to
'development'.

Signed-off-by: David Mehren <git@herrmehren.de>

src/utils/frontend-integration.ts

@@ -0,0 +1,35 @@
+/*
+ * SPDX-FileCopyrightText: 2021 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+import { NestExpressApplication } from '@nestjs/platform-express';
+import { createProxyMiddleware } from 'http-proxy-middleware';
+
+import { ConsoleLoggerService } from '../logger/console-logger.service';
+import { useUnless } from './use-unless';
+
+export function setupFrontendProxy(
+  app: NestExpressApplication,
+  logger: ConsoleLoggerService,
+): void {
+  logger.log(
+    `Setting up proxy to frontend dev server on port 3001`,
+    'setupFrontendProxy',
+  );
+  const frontendProxy = createProxyMiddleware({
+    logProvider: () => {
+      return {
+        log: (msg) => logger.log(msg, 'FrontendProxy'),
+        debug: (msg) => logger.debug(msg, 'FrontendProxy'),
+        info: (msg) => logger.log(msg, 'FrontendProxy'),
+        warn: (msg) => logger.warn(msg, 'FrontendProxy'),
+        error: (msg) => logger.error(msg, 'FrontendProxy'),
+      };
+    },
+    target: 'http://localhost:3001',
+    changeOrigin: true,
+    ws: true,
+  });
+  app.use(useUnless(['/api', '/public'], frontendProxy));
+}

src/utils/use-unless.ts

@@ -0,0 +1,18 @@
+/*
+ * SPDX-FileCopyrightText: 2021 The HedgeDoc developers (see AUTHORS file)
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+import { NextFunction, Request, Response } from 'express';
+
+export function useUnless(
+  paths: string[],
+  middleware: (req: Request, res: Response, next: NextFunction) => unknown,
+) {
+  return function (req: Request, res: Response, next: NextFunction): unknown {
+    if (paths.some((path) => req.path.startsWith(path))) {
+      return next();
+    }
+    return middleware(req, res, next);
+  };
+}