Add Streaming Support to Remote Functions

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#14,086 4 comments 39 reactions 0 assignees View on GitHub

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Assessment

Difficulty
5/5
Estimated time
Over a week
Newbie friendliness
30/100
Issue type
Feature
Clarity
Needs clarification
Activity status
Stale
Tech stack
javascript, typescript
Domain
api, backend-api-design, full-stack

Research direction

Start by reading the remote-function entry points in the SvelteKit codebase, then compare the proposed server example in src/lib/server/todos.remote.ts with the client example in src/routes/todos/+page.svelte. Review the alternative +server.ts ReadableStream approach and determine the API, serialization, cancellation, and client-consumption requirements. Done would mean an agreed design and tests covering streamed remote-function values.

Written by the indexing model from the issue text.

Description

Describe the problem

Hi SvelteKit team! Remote functions are awesome for server-client calls. I think adding a stream primitive to $app/server for generators to return ReadableStream would be great for things like real-time data or large datasets.

Describe the proposed solution

A stream export that turns generator yields into a JSON stream, consumable as an async iterable on the client.
Server (src/lib/server/todos.remote.ts):

import { stream } from '$app/server';

export const watchTodos = stream(async function* () {
  yield { id: 1, title: 'Todo 1', completed: true };
  await new Promise(r => setTimeout(r, 1000));
  yield { id: 2, title: 'Todo 2', completed: false };
});

Client (src/routes/todos/+page.svelte):

<script lang="ts">
  import { watchTodos } from '$lib/server/todos.remote';
</script>

<ul>
  {#each watchTodos() as todo}
    <li>{todo.title} - {todo.completed ? 'Done' : 'Pending'}</li>
  {/each}
</ul>
  • Could add cancellation or custom serialization.
  • Please close if this duplicates another issue.

Thanks for considering!

Alternatives considered

Manual ReadableStream in a +server.ts route: Verbose, requires custom fetch handling on the client, and doesn't integrate with remote functions' type safety and simplicity.

// +server.ts
export async function GET() {
  return new Response(new ReadableStream({
    async start(controller) {
      controller.enqueue(JSON.stringify({ id: 1, title: 'Todo 1' }));
      // More enqueues...
      controller.close();
    }
  }), { headers: { 'Content-Type': 'application/json' } });
}
Importance

would make my life easier

Additional Information

No response

Dominant language
JavaScript
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Avg merge
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Merged PRs (30d)
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