Server-side fetch request should have headers

Fetch call made from the server should have the same headers, as the one made from the client.

<!-- index.svelte -->
<script context="module">

export async function load({ fetch }) {
  const { headers }  = await fetch('/content.json').then(res => res.json())
  return { 
    props: { headers }
  }
};

</script>

// content.json.ts
export const get = (request) => ({
  body: {
    headers: request.headers // <- headers: {} if requested during SSR, but populated otherwise
  }
});

In the above case the request.headers are empty ({}) if requested during SSR, but populated when requested from the client on navigation or if requested directly.

The expected behavior is that in both cases the headers are populated and requests look the same.

envinfo:

  npmPackages:
    @sveltejs/adapter-node: next => 1.0.0-next.10 
    @sveltejs/kit: next => 1.0.0-next.60 
    svelte: ^3.29.0 => 3.35.0 

[Rich-Harris]

fetch in onMount is a reasonable workaround, yeah. We’ll get this fixed soon though, it’s a priority

[benwoodward]

Without this feature I have a tree of components that need to wait for a follow up request before they can be rendered. The follow up request fetches the auth token from an endpoint. It slows the performance of the site down a lot, and also increases the complexity of my code.