feat: Custom fetch per call

[HugeLetters]

Changes

Closes #1369

How to Review

Adds the option to pass in custom fetch as fetchOption on per API call basis. Added a simple test to see that custom fetch overrides the one specified during client initialization.

Checklist

• Unit tests updated
• docs/ updated (if necessary)

[changeset-bot]

🦋 Changeset detected

Latest commit: 1f23659

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

This PR includes changesets to release 1 package

Name	Type
openapi-fetch	Patch

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[HugeLetters]

@drwpow since this change was directly inspired by SvelteKit I would like to add some additional info to docs about making openapi-fetch work with SvelteKit. The issue is not directly related to a custom fetch so perhaps you would prefer a separate PR?

Since your library reads content-length header when parsing a response, if you fetch during SSR SvelteKit will error because it doesn't serialize headers by default.
The fix is rather simple and an error message tells you almost everything you need to know to fix it but I thought adding a small section with a code example in the docs would be nice.

The fix is this

// hooks.server.ts
import type { Handle } from '@sveltejs/kit';
export const handle: Handle = async ({ event, resolve }) => {
	return resolve(event, {
		filterSerializedResponseHeaders(name) {
			return name === 'content-length';
		}
	});
};

Can I add this example to docs in this same PR?

[drwpow]

Docs improvements are always appreciated!

Maybe rather than having that snippet live just in docs, though, putting it in the examples/sveltekit example code itself would mean people don’t miss it when they’re setting up their project. Inline comments can be added if explanation is needed. Beyond that, I’d probably omit it in the docs unless there’s something critical for the reader to understand.

[drwpow]

But re: not serializing headers in SSR, that’s interesting! I’d be open to revisiting that default behavior after understanding why SvelteKit does that better (couldn’t find the “why” in a quick search, just other libraries requiring similar workarounds)

[HugeLetters]

@drwpow I've updated the examples

[drwpow]

This looks great, thank you!

Before releasing this version, though, I want to do a little testing first to make sure the updated types generated from openapi-typescript@7 didn’t introduce any accidental breaking changes from openapi-fetch (it shouldn’t have, but I need to double-check).

[drwpow]

One last thing—could you add a patch changeset to describe the feature? See the comment on this PR for instructions.

[drwpow]

Thank you again!