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fix: infer prerendered MIME types from generated files - #17381

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triage/kit-17380-prerendered-mime
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fix: infer prerendered MIME types from generated files#17381
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triage/kit-17380-prerendered-mime

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@svelte-triage-bot

@svelte-triage-bot svelte-triage-bot Bot commented Oct 8, 2026

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  • Prerendered URL paths omit or misrepresent generated file extensions, leaving HTML absent from builder.mimeTypes unless another asset supplies it.
  • Preserve the shared MIME lookup introduced by #16564, exposed by #16875, and consumed by the build-time static server in #16908, including manifest precedence and the patched icon type.
  • Scan actual prerendered output alongside client output rather than adding only page filenames: the latter misses redirect-only output and retains misleading URL extensions. No runtime MIME database or HTML fallback is needed.
  • Cover pages, redirects, dependencies, generated data and absent prerendered output; retain static HTML alias coverage while adding a no-static-assets variant and nosniff, HEAD and compression regressions.

Fixes #17380

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changeset-bot Bot commented Oct 8, 2026 •
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🦋 Changeset detected

Latest commit: 1c74942

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package
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@sveltejs/kit Patch

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Click here if you're a maintainer who wants to add another changeset to this PR

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pkg-svelte-dev Bot commented Oct 8, 2026 •
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Install the latest version of @sveltejs/kit from 1c74942:

pnpm add https://pkg.svelte.dev/@sveltejs/kit/c/1c7494291b67ed4d451b53a013bca2252779dbb8

Open in pkg.svelte.dev: https://pkg.svelte.dev/repos/kit/pr/17381

Note

This PR is from a fork. A maintainer must approve approve each commit before it can be built and installed.

@dummdidumm

dummdidumm commented Oct 8, 2026

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@svelte-triage-bot do we need the additional test in adapter-node or does the one in core suffice? asking because there is no actual code change in adapter-node itself

@dummdidumm

dummdidumm commented Oct 8, 2026

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(but answered on the issue #17380 (comment) will dig into why)

(I think I would still be in favor of removing the node test to not make everything take even longer)

@theescodes

theescodes commented Oct 8, 2026 •
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Tested this on a production site that hit #17380. The site is fully prerendered, on Kit 3.0.0 and adapter-node 6.0.0, and served through a custom server that wraps handler and sets X-Content-Type-Options: nosniff.

I applied this PR's builder.js change to the installed Kit and rebuilt:

  • mime_types in build/adapter-node.js now includes ".html":"text/html". Before, it had none; .xml was only there because of a prerendered sitemap.
  • /, /about and /imprint are served as text/html;charset=utf-8. Before, they had no Content-Type.
  • Other types are unchanged: sitemap.xml is still text/xml and favicon.ico is still image/x-icon.
  • In Chromium the pages render again instead of showing their source. Client-side navigation works, and the CSP reports no violations.

Thanks in advance for the quick fix!

@teemingc
teemingc marked this pull request as ready for review October 12, 2026 05:56
@teemingc
teemingc merged commit 230d00c into sveltejs:main Oct 12, 2026
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@github-actions github-actions Bot mentioned this pull request Oct 12, 2026
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teemingc added a commit that referenced this pull request Oct 14, 2026
@github-actions @teemingc
Version Packages (#17364)
73bf98c 
This PR was opened by the [Changesets
release](https://github.com/changesets/action) GitHub action. When
you're ready to do a release, you can merge this and the packages will
be published to npm automatically. If you're not ready to do a release
yet, that's fine, whenever you add more changesets to main, this PR will
be updated.


# Releases
## @sveltejs/kit@3.1.0

### Minor Changes

- feat: support `report-sha256`/`report-sha384`/`report-sha512` CSP
hash-reporting keywords
([#17398](#17398))

- feat: emit a `sveltekit.endpoint` span for `+server` handlers when
server tracing is enabled
([#17325](#17325))

### Patch Changes

- fix: don't treat every module as server-only when the project is
inside a `server` directory
([#17376](#17376))

- fix: continue deployment recovery when service worker updates fail
([#17440](#17440))

- fix: infer prerendered MIME types from generated files
([#17381](#17381))

- fix: leave generated files alone when their contents are unchanged
([#17310](#17310))

- fix: leave focus in the parent page when an app in an unfocused iframe
starts or navigates
([#17297](#17297))

- fix: don't warn about Storybook's Vite plugins that use
`transformIndexHtml`
([#17373](#17373))
## @sveltejs/adapter-cloudflare@8.0.1

### Patch Changes

- fix: start the dev server on runtimes such as Deno that define
`caches` as a getter-only global
([#17401](#17401))

- fix: start one platform proxy for concurrent Vite servers and keep it
alive until the last one closes
([#17368](#17368))

- fix: support `Span#setStatus` and `Span#updateName` on local emulation
of Cloudflare `tracing`
([#17400](#17400))
- Updated dependencies:
  - @sveltejs/kit@3.1.0
## @sveltejs/adapter-vercel@7.0.1

### Patch Changes

- fix: keep the detected Bun minor in the resolved runtime
([#17331](#17331))
- Updated dependencies:
  - @sveltejs/kit@3.1.0
## @sveltejs/package@3.0.1

### Patch Changes

- fix: emit component types for the installed Svelte version, rather
than the oldest one the `svelte` dependency range allows
([#17330](#17330))

---------

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Tee Ming <chewteeming01@gmail.com>
dadezzz pushed a commit to dadezzz/events-cash-register that referenced this pull request Oct 18, 2026
Renovate [bot] Forgejo
fix(deps): update dependency @sveltejs/kit to v3.1.0 (#358)
8e6f877 
This PR contains the following updates:

| Package | Change | [Age](https://docs.renovatebot.com/merge-confidence/) | [Confidence](https://docs.renovatebot.com/merge-confidence/) |
|---|---|---|---|
| [@sveltejs/kit](https://svelte.dev) ([source](https://github.com/sveltejs/kit/tree/HEAD/packages/kit)) | [`3.0.1` → `3.1.0`](https://renovatebot.com/diffs/npm/@sveltejs%2fkit/3.0.1/3.1.0) | ![age](https://developer.mend.io/api/mc/badges/age/npm/@sveltejs%2fkit/3.1.0?slim=true) | ![confidence](https://developer.mend.io/api/mc/badges/confidence/npm/@sveltejs%2fkit/3.0.1/3.1.0?slim=true) |

---

### Release Notes

<details>
<summary>sveltejs/kit (@&#8203;sveltejs/kit)</summary>

### [`v3.1.0`](https://github.com/sveltejs/kit/blob/HEAD/packages/kit/CHANGELOG.md#310)

[Compare Source](https://github.com/sveltejs/kit/compare/@sveltejs/kit@3.0.1...@sveltejs/kit@3.1.0)

##### Minor Changes

- feat: support `report-sha256`/`report-sha384`/`report-sha512` CSP hash-reporting keywords ([#&#8203;17398](sveltejs/kit#17398))

- feat: emit a `sveltekit.endpoint` span for `+server` handlers when server tracing is enabled ([#&#8203;17325](sveltejs/kit#17325))

##### Patch Changes

- fix: don't treat every module as server-only when the project is inside a `server` directory ([#&#8203;17376](sveltejs/kit#17376))

- fix: continue deployment recovery when service worker updates fail ([#&#8203;17440](sveltejs/kit#17440))

- fix: infer prerendered MIME types from generated files ([#&#8203;17381](sveltejs/kit#17381))

- fix: leave generated files alone when their contents are unchanged ([#&#8203;17310](sveltejs/kit#17310))

- fix: leave focus in the parent page when an app in an unfocused iframe starts or navigates ([#&#8203;17297](sveltejs/kit#17297))

- fix: don't warn about Storybook's Vite plugins that use `transformIndexHtml` ([#&#8203;17373](sveltejs/kit#17373))

</details>

---

### Configuration

📅 **Schedule**: (UTC)

- Branch creation
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🚦 **Automerge**: Disabled by config. Please merge this manually once you are satisfied.

♻ **Rebasing**: Whenever PR becomes conflicted, or you tick the rebase/retry checkbox.

🔕 **Ignore**: Close this PR and you won't be reminded about this update again.

---

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---

This PR has been generated by [Mend Renovate CLI](https://github.com/renovatebot/renovate).
<!--renovate-debug:eyJjcmVhdGVkSW5WZXIiOiI0NC4xNjUuMSIsInVwZGF0ZWRJblZlciI6IjQ0LjE2NS4xIiwidGFyZ2V0QnJhbmNoIjoibWFpbiIsImxhYmVscyI6W119-->
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adapter-node: prerendered pages are served without a Content-Type

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