fix(@angular/build): support HTTP HEAD requests for virtual output files

When using the development server, HTTP HEAD requests will now correctly
respond for the virtual output files generated from the Angular build
system.  Previously Vite only handled GET requests for the files. While
HEAD requests are not common in development workflows, it can be needed in
more complex cases with additional servers/proxies/etc. during development.

packages/angular/build/src/tools/vite/middlewares/assets-middleware.ts

@@ -63,6 +63,12 @@ export function createAngularAssetsMiddleware(
       return;
     }
 
+    // Support HTTP HEAD requests for the virtual output files from the Angular build
+    if (req.method === 'HEAD' && outputFiles.get(pathname)?.servable) {
+      // While a GET will also generate content, the rest of the response is equivalent
+      req.method = 'GET';
+    }
+
     // Resource files are handled directly.
     // Global stylesheets (CSS files) are currently considered resources to workaround
     // dev server sourcemap issues with stylesheets.

tests/legacy-cli/e2e/tests/commands/serve/head-request.ts

@@ -0,0 +1,25 @@
+import { ngServe } from '../../../utils/project';
+
+export default async function () {
+  const port = await ngServe();
+  // HTML
+  await checkHeadForUrl(`http://localhost:${port}/index.html`);
+  // Generated JS
+  await checkHeadForUrl(`http://localhost:${port}/main.js`);
+  // Generated CSS
+  await checkHeadForUrl(`http://localhost:${port}/styles.css`);
+  // Configured asset
+  await checkHeadForUrl(`http://localhost:${port}/favicon.ico`);
+}
+
+async function checkHeadForUrl(url: string): Promise<void> {
+  const result = await fetch(url, { method: 'HEAD' });
+  const content = await result.blob();
+
+  if (content.size !== 0) {
+    throw new Error(`Expected "size" to be "0" but got "${content.size}".`);
+  }
+  if (result.status !== 200) {
+    throw new Error(`Expected "status" to be "200" but got "${result.status}".`);
+  }
+}