feat(1.x): add an earlyHints option for 103 Early Hints

[lxsmnsyc]

Closes #1935 on the 1.x line. Same feature as #2350 on main.

Adds an opt-in earlyHints option to defineConfig. With it on, SolidStart sends the page's assets as 103 Early Hints, so the browser can start downloading them while the server is still rendering.

// app.config.ts
export default defineConfig({ earlyHints: true });

Change

• New server/early-hints.ts. sendEarlyHints(event, assets) converts the page's <link> assets to Link values: stylesheets as rel=preload; as=style, scripts as rel=modulepreload, with URLs passed through encodeURI.
  • On Node it uses the response's own writeEarlyHints. 1.x requires Node 22, so that is always available.
  • On other runtimes the values are added as Link headers on the response. Those runtimes run on a node-mock-http response whose writeEarlyHints does nothing, so the check is whether the response has a real socket.
  • h3 v1's writeEarlyHints isn't used: it writes a raw HTTP/1.1 103 straight to the socket and has no Link header fallback.
  • It does nothing outside production, with the option off, or once the response headers are sent.
• 1.x adds route assets in two places during render, so hints are sent from three places:
  • Entry assets: createPageEvent.
  • Route scripts: StartServer, where it collects the matched routes' modulepreload assets.
  • Route stylesheets: lazyRoute's component, which runs on every render. This is guarded by isServer, so it stays out of the client bundle.
• Off by default, like Nuxt's experimental.writeEarlyHints, because some proxies and clients mishandle 1xx responses.

Testing

Production builds of the 1.x basic fixture, with a route CSS file added to /about, and a raw Node HTTP client that logs each 1xx response and the final one:

Setup	Responses for /about
Node, earlyHints: true, stream mode	103 entry CSS + 3 entry JS, 103 about.js, 103 about.css, 200
Node, earlyHints: true, mode: "async"	the same three 103s, then 200
Node, option off	200 only
Bun (server.preset: "bun"), earlyHints: true	no 103; 200 with a Link header holding all 6 values

The hints match the page's own <link> tags, and the client bundle contains no hint code.

• New early-hints.spec.ts (6 tests): the Link values, including encoding a non-ASCII URL. Also, writeEarlyHints for a Node response with a socket, Link headers for a response without one, and nothing sent with the option off, outside production, or after the headers are sent.
• @solidjs/start test:ci (101 tests), typecheck and build pass. apps/tests build, unit:ci and the full Cypress suite against the production build (19) pass.

🤖 Generated with Claude Code

[changeset-bot]

🦋 Changeset detected

Latest commit: 5c04a87

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@solidjs/start	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/@solidjs/start@2351

commit: 5c04a87