sveltekit relative assets fetch bug

Tests

dev mode

run with: pnpm dev

fetch       url
----------+-----
global    + rel: error per definition
global    + abs: true
sveltekit + rel: true
sveltekit + abs: true
read      + rel: true
read      + abs: doesn't make sense
----------------
other     +server: true

node adapter

first swich to adapter node then run with: pnpm build && pnpm preview

fetch       url
----------+-----
global    + rel: error per definition
global    + abs: true
sveltekit + rel: false
sveltekit + abs: false
read      + rel: true
read      + abs: doesn't make sense
----------------
other     +server: true

• probably should use read anyways

cloudflare adapter

first swich to adapter cloudflare then run with: pnpm build && wrangler pages dev .svelte-kit/cloudflare

fetch       url
----------+-----
global    + rel: error per definition
global    + abs: true
sveltekit + rel: false
sveltekit + abs: false
read      + rel: undefined
read      + abs: doesn't make sense
----------------
other     +server: true

Fixes

async read

• con: breaking change

• pro: can work with cloudflare

  • both env.Assests.fetch and fetch (might not work) provide response but asynchroniously

  • would be drop-in implementation

    read: (filename) => {
    	// needed because cloudflare worker does not support relative paths
    	const abs_asset = new URL(req.url);
    	abs_asset.pathname = filename;
    	return env.ASSETS.fetch(abs_asset.pathname).then((res) => res.body);
    };

• vibe check: not passed

  • read (right now) feels like it should be synchronous

add server_assets to is_asset check in server fetch

• pro: no breaking changes

• pro: works with cloudflare & node (probably more)

• pro: feature parity between dev and production

  • right now we end up in kit/src/runtime/server/respond.js:119 and return 404

  • possibly a bug

    • docs say:

      It also allows you to make relative requests, whereas server-side fetch normally requires a fully qualified URL. https://kit.svelte.dev/docs/web-standards#fetch-apis

    • but it doesn't work

• AFICT server_assets is currently only used by read, so using it in server fetch is kind of an async read implementation

• in this case if the static asset is requested "from outside" it is served by the platform (that's why global fetch works?), the problem is when we request from "inside" of sveltekit

---

might be connected:

• sveltejs/kit#3850
• sveltejs/kit#8167

tangentially related:

• sveltejs/kit#11128
• sveltejs/kit#11078