ng serve does not allow us access to raw 'index.csr.html' when using SSR

[DibyodyutiMondal]

Command

serve

Is this a regression?

• Yes, this behavior used to work in the previous version

The previous version in which this bug was not present was

No response

Description

If I go to http://localhost:4200/, I get a transformed html response which includes my lazy-loaded router-component for the ''path. This is as expected during SSR.

However,
If I go to http://localhost:4200/index.html, I expect to get an html response which is exactly the index.html on disk, without the ssr transformation. But the dev server sends me a "404 Not Found" instead.

Turns out that, for SSR, angular creates 2 index.html - index.csr.html and index.server.html. I am interested in the csr version, because I want to precache it.

However, the angular dev server's middleware prevents me from accessing that file.

This is a screenshot of me debugging the dev-server. The request was for /index.html

In line 25, the middleware tries to search the outputFiles for 'index.html'. The problem is that the outputFile don't have 'index.html'. They have 'index.csr.html' and 'index.server.html'. As a result, rawHtml is going to be always be undefined, and the middleware is going to go to line 27 and skip the middleware.

If I try to go for /index.csr.html, then the middleware will skip out before it even reaches Line 25, due to the if condition on Line 12
Line 12 says that any request that are not '/' or '/index.html' will be ignored.

So we are perpetually denied being served the raw index.html while serving in SSR

Minimal Reproduction

Create a new angular app
Add SSR to it as per the documentation
Add a lazy loaded component for the path '' with the selector test-element and an empty template,
Remove the contents of app.component's template and add a router outlet to app.component.html
Do other task necessary to set up routing
Serve the app with ng serve

Go to http://localhost:4200 and check the response that came on first load. You should see the element <test-element></test-element> in the html. This is ok

Go to http://localhost:4200/index.html. This should result in 404 Not Found. This is ok.

Go to http://localhost:4200/index.csr.html. This should result in 404 Not Found. This is not ok. It should have returned html without the test-element in it.

Exception or Error

No response

Your Environment

Angular CLI: 18.1.0
Node: 20.13.1
Package Manager: pnpm 9.4.0
OS: linux x64

Angular: 18.1.0
... animations, cdk, cli, common, compiler, compiler-cli, core
... forms, language-service, material, material-luxon-adapter
... platform-browser, platform-browser-dynamic, platform-server
... router, ssr

Package                         Version
---------------------------------------------------------
@angular-devkit/architect       0.1702.3
@angular-devkit/build-angular   18.1.0
@angular-devkit/core            18.1.0
@angular-devkit/schematics      18.1.0
@schematics/angular             18.1.0
ng-packagr                      18.1.0
rxjs                            7.8.1
typescript                      5.4.4

Anything else relevant?

angular-cli/packages/angular/build/src/tools/vite/middlewares/index-html-middleware.ts

Lines 30 to 42 in f5c250a

	const pathname = pathnameWithoutBasePath(req.url, server.config.base);
	if (pathname !== '/' && pathname !== '/index.html') {
	next();
	return;
	}
	const rawHtml = outputFiles.get('/index.html')?.contents;
	if (!rawHtml) {
	next();
	return;
	}

This is the part that likely needs to be changed.

• change line 31 to allow index.csr.html
• change line 37 to search for index.csr.html or index.html as per the actual request

[DibyodyutiMondal]

Workaround:

Explanation

During ngOnInit check the route for the existence for a query parameter called __blank_page. If it is present, don't render any routes. Then, wherever you want to cache your empty app shell, use /__blank_page for the url, instead of index.html/index.csr.html

Implementation

In your app.component.ts:

  protected readonly blankPage$ = signal(false);

  private serveBlankPage() {
    this.route.queryParamMap
      .pipe(takeUntilDestroyed(this.dRef))
      .subscribe(params => {
        if (params.has('__blank_page')) {
          console.debug(params);
          this.blankPage$.set(true);
        }
      });
  }

  ngOnInit() {
    this.serveBlankPage();
  }

In your app.component.html:

     <header></header>
    @if (!blankPage$()) {
    <router-outlet></router-outlet>
    }
    <footer></footer>

Finally, for precaching, use the url: /?__blank_page in your precaching manifest

Drawbacks

You can only wrap the router outlet in the @if block. While it is possible to wrap the entire template in the @if, this will interfere with any viewchild.required declarations in your typescript. If you are willing to refactor your typescript to accommodate that, then this is a viable temporary solution

While you can choose to make the

[alan-agius4]

Can you please elaborate on what you mean by "precaching" and what you are trying to achieve with it?

[DibyodyutiMondal]

@alan-agius4 Sorry for the delay in getting back.

So, I use a service worker, and instead of @angular/pwa, I use workbox to implement a custom service worker.

And workbox has the ability to "pre-cache" certain files to ensure that the application always loads, even if offline. To do this, it loads certain files up-front at the time of installation. Usually, this would mean all files in the 'initial' chunk + the index.html file + global styles + polyfills. So for those items, I would need the file names in the build output, then make a list, and pass that to the service worker.

The service worker would then, at install-time, eagerly cache all the files in the list by making a network request. In the case of index.html/index.csr.html, it was returning a 404, and the service worker installation would error out. If used / instead of index.html, it would receive from the server and cache SSR-generated page for the home page (which our default route). If I went offline at this stage, changing routes would cause a very annoying flicker on every navigation, as it would first render the app-component + home-page component, then replace the home-page component with whatever component I am routing to (or fallback to NotFoundComponent). Using the un-altered index.csr.html would get rid of that layout jump in offline scenarios.

https://developer.chrome.com/docs/workbox/modules/workbox-precaching

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