Remote Functions: deterministic paths

Describe the problem

Sometimes I want to write some internal-use APIs without building a full REST architecture. That way, I can send some cross-origin requests between the applications I own.

The use case that came up is managing logout logic between two applications:

On app.example.com there is a logout form:

<form method="POST" action="accounts.example.com/?/logout">
  <button>Log out</button>
</form>

And on accounts.example.com I can write a traditional SvelteKit Form Action to receive the cross-origin POST request in src/routes/+page.server.ts.

If a remote form named logout exists on accounts.example.com, it's not possible to rely on their path since it may change in between builds. Example generated path: ?/remote=q5s0im%2Flogout.

Describe the proposed solution

Some way to provide deterministic paths for remote form methods ahead of build time; especially if current workarounds may not be made available long-term.

Brainstorming some ways this can be exposed to SvelteKit developers:

1. Remote functions defined anywhere in src/routes/**/*.remote.{ts|js} would generate a path the same way named Form Actions do today; and if there's a conflict with a same-named form action then there would be a build error.
   Example:

   // file: src/routes/auth.remote.ts
   
   import { form } from '$app/server'
   
   // exposed as `accounts.example.com/?/logout`
   export const logout = form(() => { /* do stuff */ }
   

2. A third options parameter is provided for remote functions to set things like { url: '/api/logout' }
3. A config option to make paths determined based on location in the project's file structure and method name, rather than a (seemingly) random hash being generated.
   Example: src/lib/auth.remote.ts#logout -> /_remote/lib/logout
4. (cool, but understandably complex) A generated SDK for all remote functions in a given application. There may need to be considerations for 'private' functions (see https://github.com/sveltejs/kit/issues/15712)

It would be nice to have deterministic paths for query or command as well.

I understand the intent of Remote Functions and RPC in general is to not care too much about endpoint paths and to instead generate an SDK; which in SvelteKit's case is a build-time detail. At least, we could provide a simple escape hatch for these infrequent needs like a single method.

Alternatives considered

• A named Form Action
• A +server.ts POST endpoint

Importance

would make my life easier

Additional Information

This relates to another feature request that would also require deterministic paths:

• #14336

Especially if the 'generated SDK' idea is pursued.

Start by reading the remote functions in src/routes/**/*.remote.{ts|js} and the traditional Form Action in src/routes/+page.server.ts, then review the related issues #14336 and #15712. The issue presents several possible designs, so completion would require an agreed deterministic-path behavior for remote form methods and possibly query or command methods, plus validation of the chosen design.