fix: remove unnecessary path validation which breaks fetch with custom path base

[goulinkh]

closes #11078

When having a custom base path:

{
  kit: {
  	paths: {
  		base: '/ui'
  	}
  }
}

And making a request to a different server hosted on the same domain, +layout.server.ts:

export const load: LayoutServerLoad = async ({ fetch }) => {
  const workingResponse = await fetch('/ui/api'); // works if api is defined in sveltekit
  const failingResponse = await fetch('/profile'); // returns 404, instead of making request and providing cookies
}

Making a request to the same origin but to a different server not with the configured paths.base, currently doesn't work but this should be allowed and possible as they share the same domain name.

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[PatrickG]

I don't think this is the correct fix.
The request shouldn't even be handled by the respond function.
It must be fixed somewhere in the fetch function in src/runtime/server/fetch.js

Maybe changing

kit/packages/kit/src/runtime/server/fetch.js

Line 58 in 8a59a0d

if (url.origin !== event.url.origin) {

to something like

if (url.origin !== event.url.origin || (paths.base && !decodeURIComponent(url.pathname).startsWith(paths.base))) {

[goulinkh]

Hi @PatrickG, apologies for the quick fix attempt, I lack knowledge in sveltekit codebase but tried to file the fix.

Your suggestion makes sense, I've applied it and it seems to work locally.

Cheers!

[teemingc]

Thanks for the PR! I left a few comments

[teemingc]

Thank you! It's looking good. Just a few suggestions on the added tests and I think we're good to go

[teemingc]

Thank you!