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fix: set cache header for non-immutable build assets #14483

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fix: set cache header for non-immutable build assets #14483

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@TorstenDittmann TorstenDittmann commented Sep 19, 2025 •
edited by teemingc
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When serving client files, ensure non-immutable assets are never cached by browsers by setting a maxage=0 cache header.

When no cache-control header is set, browsers will still cache files and with /_app/version.json and /_app/env.js this causes a lot of issues when deploying new versions using the node adapter.

Similiar to what is done here https://github.com/sveltejs/kit/blob/main/packages/kit/src/runtime/server/respond.js#L291-L294

fixes #9089
fixes #13799

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changeset-bot bot commented Sep 19, 2025 •
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🦋 Changeset detected

Latest commit: 46c5757

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

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Preview: https://svelte-dev-git-preview-kit-14483-svelte.vercel.app/

@TorstenDittmann
Update non-static asset cache-control header
46c5757 
Only static assets should be cached immutably. All other assets should
revalidate to ensure freshness.
@TorstenDittmann TorstenDittmann changed the title fix(node-adapter): set cache header for non-immutable assets fix(node-adapter): set cache header for non-immutable build assets Sep 19, 2025
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Browsers don't generally cache by default, but from a quick glance it looks like the may use a heuristic to decide such as file extension and may possibly cache. Would probably be good to find a more authoritative reference

If this is an issue, I would guess it's not unique to adapter-node and should be fixed everywhere

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Browsers don't generally cache by default, but from a quick glance it looks like the may use a heuristic to decide such as file extension and may possibly cache. Would probably be good to find a more authoritative reference

If this is an issue, I would guess it's not unique to adapter-node and should be fixed everywhere

Yes, they follow https://datatracker.ietf.org/doc/html/rfc7234#section-4.2.2 and at least for cases I have seen those files are cached.

They actually do it based on 200 responses in general when there is a last-modified header:

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teemingc commented Sep 24, 2025 •
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I've always wanted to check if version.json was being cached. Is it possible to check if the other adapters need this too and make the necessary changes there? I also wonder if we need to document these cache related rules for adapter-static where the user or platform is usually responsible for serving those files. Might be growing the scope of this PR too much.

@teemingc teemingc changed the title fix(node-adapter): set cache header for non-immutable build assets fix: set cache header for non-immutable build assets Sep 24, 2025
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generated env.js is missing a cache buster Not found /_app/immutable/assets/xxx
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