Cancelling fetch request to SvelteKit API route with AbortSignal: timeout() does not work

[eurlexa]

Describe the bug

Trying to use standard AbortSignal: timeout() method: My use-case is to abort internal SvelteKit api route call if server process takes too long to finish. In that case I do the proces client side.

But SvelteKit does not abort the fetch call to its own api route for some reason.

My only workaround was to have a separate second SvelteKit application with the API in matter. Which is quite a hassle.

Reproduction

// routes/+page.svelte
Go to <a href="/roll">roll</a>

// routes/roll/+page.svelte
<script>
	let { data } = $props();
</script>

{data.number}

// routes/roll/+page.server.js
export const load = async ({fetch}) => {
    try {
        let response = await fetch(
            'api/longServerProcess'  // internal api call will not be aborted
            // "http://www.randomnumberapi.com/api/v1.0/randomnumber" //external api call will be aborted as expeted
            , {
        method: 'GET',
        signal: AbortSignal.timeout(100),
        headers: {
            'Content-Type': 'application/json',
        }
    });


    let number = await response.json()
    return {number}
} catch (error) {
     return {
        serverTooSlow: true,
        number: "api call interrupted cos server was too slow"
     }
}
}

// api/longServerProcess/+server.js
import { json } from '@sveltejs/kit';

const asyncTimeout = (ms) => {
  return new Promise((resolve) => {
    setTimeout(resolve, ms);
  });
};

export async function GET() {
    await  asyncTimeout(5000)
    const number = Math.floor(Math.random() * 100) + 1;
	return json(number);
}

Not using SvelteKit fetch but the native one will cause AbortSignal.timeout(...) to abort internal api calls but wont respect the timeout value. The calls are aborted immediately.

export const load = async () => {
    try {
        let response = await fetch(
            'api/longServerProcess'  // is aborted immediately instead of after 10000 ms
            // "http://www.randomnumberapi.com/api/v1.0/randomnumber" // works as expected
            , {
        method: 'GET',
        signal: AbortSignal.timeout(10000), // time does not work, the abortion fires immediately 
        headers: {
            'Content-Type': 'application/json',
        }
    });


    let number = await response.json()
    return {number}
} catch (error) {
     return {
        serverTooSlow: true,
        number: "api call interrupted cos server was too slow"
     }
}
}

Logs

System Info

System:
    OS: Linux 6.12 Pop!_OS 22.04 LTS
    CPU: (4) x64 Intel(R) Pentium(R) CPU 3825U @ 1.90GHz
    Memory: 627.66 MB / 3.74 GB
    Container: Yes
    Shell: 5.1.16 - /bin/bash
  Binaries:
    Node: 20.10.0 - ~/.nvm/versions/node/v20.10.0/bin/node
    npm: 10.2.3 - ~/.nvm/versions/node/v20.10.0/bin/npm
    pnpm: 7.5.2 - /usr/local/bin/pnpm
  npmPackages:
    @sveltejs/adapter-auto: ^6.0.0 => 6.0.1 
    @sveltejs/kit: ^2.16.0 => 2.21.1 
    @sveltejs/vite-plugin-svelte: ^5.0.0 => 5.0.3 
    svelte: ^5.0.0 => 5.33.13 
    vite: ^6.2.6 => 6.3.5

Severity

annoyance

Additional Information

No response