refactor: Separate middleware from Express.

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]);
+    }
+  }
+}