fix: don't fail on immutable headers when using native fetch #10367
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According to the `fetch()`-specification, a header can have an `immutable`-guard which will throw a `TypeError` if the header is changed: https://fetch.spec.whatwg.org/#headers-class When using `fetch()`, the spec requires the response header to be `immutable` (see step 12/4): https://fetch.spec.whatwg.org/#fetch-method This is implemented in undici (used by Node.js for native fetch() under the hood): https://github.com/nodejs/undici/blob/22bdbd8c7820035276b4e876daccef513c29f5c4/lib/fetch/headers.js#L234-L239
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Description
Fixes #10366, related to #10030.
According to the
fetch()-specification, a header can have animmutable-guard which will throw aTypeErrorif the header is changed:https://fetch.spec.whatwg.org/#headers-class
When using
fetch(), the spec requires the response header to beimmutable(see step 12/4):https://fetch.spec.whatwg.org/#fetch-method
This is implemented in undici (used by Node.js for native fetch() under the hood):
https://github.com/nodejs/undici/blob/22bdbd8c7820035276b4e876daccef513c29f5c4/lib/fetch/headers.js#L234-L239
Since PR #9993, a
TypeErroris thrown when using nativefetch()because SvelteKit is trying to change the header from the fetch-response-object.Please don't delete this checklist! Before submitting the PR, please make sure you do the following:
Tests
pnpm testand lint the project withpnpm lintandpnpm checkChangesets
pnpm changesetand following the prompts. Changesets that add features should beminorand those that fix bugs should bepatch. Please prefix changeset messages withfeat:,fix:, orchore:.