refactor: Separate middleware from Express.

src/server/ExpressHttpServerFactory.ts

@@ -1,5 +1,4 @@
 import type { Server } from 'http';
-import cors from 'cors';
 import type { Express } from 'express';
 import express from 'express';
 import { getLoggerFor } from '../logging/LogUtil';
@@ -17,28 +16,11 @@ export class ExpressHttpServerFactory implements HttpServerFactory {
   }
 
   public startServer(port: number): Server {
-    const app = express();
-    this.setup(app);
-    return app.listen(port);
+    return this.createApp().listen(port);
   }
 
-  protected setup(app: Express): void {
-    // Set up server identification
-    app.use((request, response, done): void => {
-      response.setHeader('X-Powered-By', 'Community Solid Server');
-      done();
-    });
-
-    // Set up Cross-Origin Resource Sharing (CORS)
-    app.use(cors({
-      // Based on https://github.com/solid/solid-spec/blob/master/recommendations-server.md#cors---cross-origin-resource-sharing
-      // By default origin is always '*', this forces it to be the origin header if there is one
-      origin: (origin, callback): void => callback(null, (origin ?? '*') as any),
-      methods: [ 'GET', 'HEAD', 'OPTIONS', 'POST', 'PUT', 'PATCH', 'DELETE' ],
-    }));
-
-    // Delegate to the main handler
-    app.use(async(request, response, done): Promise<void> => {
+  protected createApp(): Express {
+    return express().use(async(request, response, done): Promise<void> => {
       try {
         this.logger.info(`Received request for ${request.url}`);
         await this.handler.handleSafe({ request: guardStream(request), response });

src/server/middleware/CorsHandler.ts

@@ -0,0 +1,26 @@
+import cors from 'cors';
+import type { RequestHandler } from 'express';
+import { HttpHandler } from '../HttpHandler';
+import type { HttpRequest } from '../HttpRequest';
+import type { HttpResponse } from '../HttpResponse';
+
+/**
+ * Handler that sets CORS options on the response.
+ */
+export class CorsHandler extends HttpHandler {
+  private readonly corsHandler: RequestHandler;
+
+  public constructor() {
+    super();
+    this.corsHandler = cors({
+      origin: (origin, callback): void => callback(null, (origin ?? '*') as any),
+      methods: [ 'GET', 'HEAD', 'OPTIONS', 'POST', 'PUT', 'PATCH', 'DELETE' ],
+    });
+  }
+
+  public async handle(input: { request: HttpRequest; response: HttpResponse }): Promise<void> {
+    return new Promise((resolve): void => {
+      this.corsHandler(input.request as any, input.response as any, (): void => resolve());
+    });
+  }
+}

src/server/middleware/HeaderHandler.ts

@@ -0,0 +1,22 @@
+import { HttpHandler } from '../HttpHandler';
+import type { HttpResponse } from '../HttpResponse';
+
+/**
+ * Handler that sets custom headers on the response.
+ */
+export class HeaderHandler extends HttpHandler {
+  private readonly headers: Record<string, string>;
+
+  public constructor() {
+    super();
+    this.headers = {
+      'x-powered-by': 'Community Solid Server',
+    };
+  }
+
+  public async handle({ response }: { response: HttpResponse }): Promise<void> {
+    for (const header of Object.keys(this.headers)) {
+      response.setHeader(header, this.headers[header]);
+    }
+  }
+}