Navigating to an API handler route 404's in logs.

[Mardoxx]

Describe the bug

Navigating to an API only route yields a 404 in the console. If we do a redirect inside the api route to the app, it does not update the URL correctly.

Reproduction

https://stackblitz.com/edit/sveltejs-kit-template-default-ipxflmtx

1. Open dev console
2. Click the red link
3. Witness error in console
4. Observe URL bar is not at the correct route (/moonlight)

Logs

Error: Not found: /out_there
    SvelteKitError control.js:45
    navigate client.js:1312
    _start_router client.js:2175
    _start_router client.js:2066
    start client.js:314
    async* (index):212
    promise callback* (index):211
.localservice@runtime.c8c182a3.js:26:94631
    error .localservice@runtime.c8c182a3.js:26
    handleError app.js:18
    handle_error client.js:1642
    navigate client.js:1312
    _start_router client.js:2175
    _start_router client.js:2066
    start client.js:314
    <anonymous> (index):212
    (Async: promise callback)
    <anonymous> 

### System Info

```Shell
npx envinfo --system --binaries --browsers --npmPackages "{svelte,@sveltejs/*,vite}"
Need to install the following packages:
envinfo@7.14.0
Ok to proceed? (y) 
 
  System:
    OS: Linux 5.0 undefined
    CPU: (8) x64 Intel(R) Core(TM) i9-9880H CPU @ 2.30GHz
    Memory: 0 Bytes / 0 Bytes
    Shell: 1.0 - /bin/jsh
  Binaries:
    Node: 18.20.3 - /usr/local/bin/node
    Yarn: 1.22.19 - /usr/local/bin/yarn
    npm: 10.2.3 - /usr/local/bin/npm
    pnpm: 8.15.6 - /usr/local/bin/pnpm
  npmPackages:
    @sveltejs/adapter-auto: ^3.3.1 => 3.3.1 
    @sveltejs/kit: ^2.12.1 => 2.12.1 
    svelte: ^5.14.4 => 5.14.4 
    vite: ^6.0.3 => 6.0.3 

### Severity

blocking all usage of SvelteKit

[Mardoxx]

See also #10855 with form actions at API only routes and use:enhance

[teemingc]

I think this is a separate issue from #10855

Essentially, our client router is reporting a 404 because API handlers are not part of the navigable routes list (only pages are). The end result is that we perform a native navigation to the API handler URL and end up being redirected correctly anyway so I think it's fine?

Ideally, a 404 isn't logged since the API handler route is our own. However, I'm not sure it's worth sending that extra information to the client.

A workaround for now is to add data-sveltekit-reload to links that navigate to the API handler route so that it skips trying to find a matching page and won't log a 404. https://svelte.dev/docs/kit/link-options#data-sveltekit-reload

[Mardoxx]

I finally got round to checking this out again data-sveltekit-reload does indeed suppress the error message, thank you.

The action GET /out_there should set the location (or rather, the browser url) to /moonlight but it does not - I think this is still an issue is it? Or is it best to just not call API functions like that?

[Mardoxx]

What I do now is use this pattern for my, e.g. form (post/get pattern) endpoints

./example_login/+page.server.ts

import { redirect } from '@sveltejs/kit';
import type { Actions, PageServerLoad } from './$types';

export const load: PageServerLoad = () => redirect(302, '/');

export const actions: Actions = {
  default: async ({ request, locals }) => {
    // do thing

    return redirect(302, '/');
  }
};

[nickolay]

I'm using <a href="/api/endpoint"> (just like in the testcase above, and as suggested elsewhere) to let the user download a server-generated file.

Changing to <a href="/api/endpoint" data-sveltekit-reload> fixes the 404, as well as adding rel="external".

But what's the point of logging the 404 on the client side at all if you still fall back to native brower's navigation? If there's a 404, it will be reported by the server...