vercel dev doesn't render 404 page when X-Content-Type-Options set to nosniff

[paulrudy]

What version of astro are you using?

2.9.7

Are you using an SSR adapter? If so, which one?

Vercel

What package manager are you using?

pnpm

What operating system are you using?

Mac

What browser are you using?

Chrome, Safari

Describe the Bug

I don't know if this a vercel CLI problem or an @astrojs/vercel adapter issue, but:

In vercel.json, the following entry:

  "headers": [
    {
      "source": "/(.*)",
      "headers": [
        {
          "key": "X-Content-Type-Options",
          "value": "nosniff"
        }
      ]
    }
  ],

causes a custom 404 page to be rendered as raw HTML text, but only when using vercel dev.

Everything works normally when using astro dev and when deployed on Vercel, including with the header in question.

What's the expected result?

Custom 404 page should render.

Link to Minimal Reproducible Example

repo
demo (issue is not present in demo, because issue is only locally when running vercel dev)

Participation

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

[paulrudy]

I see that the 404 and 500 stuff is getting reworked #7754, so perhaps that might address this (admittedly somewhat minor) issue

[natemoo-re]

Is this running vercel dev or astro dev? The vercel.json settings wouldn't change the astro dev settings. #7754 is only updating the build output, which should be what's deployed to Vercel directly.

[natemoo-re]

I'm guessing this is actually unrelated to the vercel.json settings and this just happens anyway? Maybe only if the file is 404.md instead of 404.astro. But I'm pretty sure #7754 will fix this.

[paulrudy]

@natemoo-re thanks for the replies. FYI, I just realized that my minimal reproduction actually doesn't reproduce the issue, sorry about that. Up to you whether you want to leave this issue open or close it, as I may not have time to sort out how to reproduce it minimally. Sorry about the confusion

To answer your questions though, this is only when running vercel dev locally, and removing vercel.json setting does get rid of it. Separately, I'm also noticing that on the live Vercel build, the custom 404 page is rendered but without any styles.

I'll sit tight and see how things shake out after #7754 is merged.

[paulrudy]

Ok, the issue is still present with Astro version 2.9.7. I've updated the issue with a new (and working) minimal repro.

Separately, I'm also noticing that on the live Vercel build, the custom 404 page is rendered but without any styles.

This separate issue also persists, and I've created #7910 to detail and reproduce it

[lilnasy]

Since the issue has to do with vercel.json, which astro code doesn't process, and vercel dev which runs its own server, it would seem there isn't something for astro to fix here.

Feel free to reopen if you find something that suggests otherwise.