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Returning a native fetch()-response throws TypeError: immutable #10366

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jaylinski opened this issue Jul 11, 2023 · 2 comments · Fixed by #10367
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Returning a native fetch()-response throws TypeError: immutable #10366

jaylinski opened this issue Jul 11, 2023 · 2 comments · Fixed by #10367
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@jaylinski
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jaylinski commented Jul 11, 2023 •
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Describe the bug

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

The change introduced in #9993 will try to mutate the response header in certain scenarios, thus causing a TypeError.

Reproduction

A reproduction via failing test-case can be found in PR #10367.

Logs

No response

System Info

System:
    OS: Linux 5.15 Debian GNU/Linux 11 (bullseye) 11 (bullseye)
    CPU: (6) arm64 unknown
    Memory: 11.31 GB / 15.61 GB
    Container: Yes
    Shell: 5.1.4 - /bin/bash
  Binaries:
    Node: 20.2.0 - /usr/local/bin/node
    Yarn: 1.22.19 - /usr/local/bin/yarn
    npm: 9.6.6 - /usr/local/bin/npm

Severity

blocking an upgrade

Additional Information

This bug was caused by #9993.
This was referenced Jul 11, 2023
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@Conduitry
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Another instance of this was fixed in #10030. This would presumably be fixed in a similar way.

@jaylinski
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Another instance of this was fixed in #10030. This would presumably be fixed in a similar way.

Thanks, that's very helpful. I'll adapt my PR with a fix. :octocat:

@dummdidumm dummdidumm added the bug Something isn't working label Jul 12, 2023
dummdidumm pushed a commit that referenced this issue Jul 12, 2023
fix: don't fail on immutable headers when using native fetch (#10367)
31f27c2 
Fixes #10366, related to #10030.

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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fix: don't fail on immutable headers when using native fetch
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@jaylinski @dummdidumm @Conduitry