fix(routing): decode the flash cookie once per request, not per router

[ryansolid]

Rendering a page after a failed no-JavaScript form post hangs the server: the stream retries forever, allocating until the process runs out of memory. Found in examples/todos-server in solidjs/solid (#3717) once the flash cookie had a secret to be written with.

Cause

A server render can re-create the router while it retries a suspension. The trigger is ordinary app code:

<Document>                      // {props.children} in <body>
  <Router>
    {props => (
      <Errored fallback={...}>
        <Header />              // const adds = useSubmissions(addTodo)
        <Loading>{props.children}</Loading>
      </Errored>
    )}
  </Router>
</Document>

useSubmissions in Header's body reads the flash seeding memo, which suspends on the async (encrypted) decode. The server <Errored> escalates a suspension in its children to the nearest retryable hole, and under the hydratable server output that hole is the document's {props.children}, above the router — so each retry renders a new router. The decode was cached on the router instance, so each new router started it again: the read never settled, each pass added a fresh blocking promise, and the stream retried without end. Each new router also appended another one-shot Set-Cookie clear.

The cookie header and its decode now live in a WeakMap keyed by the request event, shared by every router created for that request.

Re-creating components above a suspension on retry is how the server renderer already behaves (core's lazy() asset lookup was made per-request for the same reason); whether <Errored> should widen the retry that far is a separate question I'm raising in solidjs/solid.

Public API changes

None. Behavior: the flash cookie is detected, cleared and decoded once per request instead of once per router instance — a render that re-creates the router now settles, and appends a single Set-Cookie clear.

Tests

• test/server/flash-decode-per-request.spec.tsx: the shape above, streamed with a flash cookie. Asserts the outcome renders, the router was in fact rendered more than once, the decode ran once and the cookie was cleared once. Times out before the fix.
• The server test config now compiles hydratable, as apps do — the hang only reproduces under the hydratable server output. The other server specs pass unchanged under it.

Server suite 77 passed, unit suite 469 passed, tsc clean. Independent of #646.

[changeset-bot]

🦋 Changeset detected

Latest commit: bd4d58c

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

This PR includes changesets to release 1 package

Name	Type
@solidjs/router	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