[@astrojs/cloudflare] Cloudflare Pages Adapter does not Render SSR 404 Page

[Kynson]

Astro Info

Astro                    v5.1.6
Node                     v20.9.0
System                   Linux (x64)
Package Manager          npm
Output                   static
Adapter                  @astrojs/cloudflare
Integrations             none

Describe the Bug

Situation

Setting const prerender = false on the 404 page; other pages are statically generated.

Reproducing:

1. Build and start the preview using wrangler pages dev ./dist
2. Navigate to a non existing page.

Result

The 404 page is not rendered, instead, the index page is rendered.

Possible cause

const { pathname } = new URL(request.url);
if (manifest.assets.has(pathname)) {
  return env.ASSETS.fetch(request.url.replace(/\.html$/, ''));
}
const routeData = app.match(request);
if (!routeData) {
  const asset = await env.ASSETS.fetch(
    request.url.replace(/index.html$/, '').replace(/\.html$/, ''),
  );
  if (asset.status !== 404) {
    return asset;
  }
}

The above is extracted from the generated code (_workers.js/chunks/_@astrojs-ssr-adapter_<hash>.mjs). As the 404 page is server-side rendered, there is no 404.html generated. Hence, Cloudflare Pages assumes the app is a SPA and rewriting all paths to index.html. This leads to an issue that asset.status is 200 instead of 400 and the asset is index.html.

Workaround

1. Don't use SSR for 404
2. Add a fake 404.html to dist

What's the expected result?

The 404 page should be rendered.

Link to Minimal Reproducible Example

https://codesandbox.io/p/devbox/sfgjcf

Participation

• I am willing to submit a pull request for this issue.

[Kynson]

Personally, I think one way to solve this is for the adapter to generate an empty 404.html (possibly configurable by an option in astro.config.mjs? e.g. generate404/ isSPA etc). env.ASSETS.fetch will return 404 when it sees a 404.html and Astro will render the 404.astro.

[alexanderniebuhr]

What you observe is the expected behavior. If Cloudflare doesn't see an static 404.html, it expects SPA mode, and behaves like your described. So far so good. Now the question is how to handle this. One way is to tell users to set prerender = true, the other is to inject an empty page, which could also be a bit unexpected for some. Not sure what the best solution is here. I'll ask the team in Discord :)