fix: prefer pages over endpoints when prerendering

[teemingc]

fixes https://github.com/sveltejs/kit/issues/10735

This PR adds an Accept header to the prerender requests, preferring text/html first then whatever with */*. Previously, it would always end up as */* during content negotiation, which invokes the endpoint handler, causing a 405 method not allowed if the GET handler doesn't exist.

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[Rich-Harris]

preview: https://svelte-dev-git-preview-kit-12998-svelte.vercel.app/

this is an automated message

[Rich-Harris]

Is this the right fix? Feels like maybe 405 is the wrong response for a GET request with */* if a page exists. Thoughts?

[teemingc]

Is a test still TODO or is it basically impossable to test?

I chose not to add a test because it's only reproducible by breaking the prerender app build. But I could add a test that just sends a request to the route and see if we get a 405.

Is this the right fix? Feels like maybe 405 is the wrong response for a GET request with */* if a page exists. Thoughts?

An alternative is to await the route.endpoint() call earlier so we can check which methods it has but I'm not sure what kind of impact that will have. Either that, or prefer pages over endpoints during content negotiation (or earlier).

https://github.com/sveltejs/kit/blob/435984bf61b047d1e1a8efe88354ca7ac4e9109f/packages/kit/src/runtime/server/respond.js#L451

[teemingc]

related to content negotiation https://github.com/sveltejs/kit/issues/11794

[teemingc]

Is this the right fix? Feels like maybe 405 is the wrong response for a GET request with */* if a page exists. Thoughts?

Agreed that this PR is the wrong fix. Other people are having a similar issue with bot indexing https://github.com/sveltejs/kit/issues/11794