feat: adapter-node shutdown event

This is a small improvement and the missing piece to the recent graceful shutdown feature. After the server has closed gracefully Node will emit the exit event. As others have pointed out however if you have something running in the background the app will continue to run and exit will never be emitted. The exit event isn't ideal anyway because it will close your app as soon as possible so we can't do any custom async cleanup work in a process.on('exit', () => { ... }) handler. That means calling process.exit() to manually emit the exit event isn't an option. It defeats the point of a graceful shutdown. This PR emits a custom event instead that users of adapter-node can listen to and use to perform any kind of cleanup work right after the HTTP server has closed.

process.on('sveltekit:shutdown', async (reason) => {
  await db.close();
  await jobs.stop();
  process.exit();
});

We briefly discussed the option of exporting a function to register a hook instead but with the way adapters work this doesn't seem to be possible today.

Please don't delete this checklist! Before submitting the PR, please make sure you do the following:

[ ] It's really useful if your PR references an issue where it is discussed ahead of time. In many cases, features are absent for a reason. For large changes, please create an RFC: https://github.com/sveltejs/rfcs
[x] This message body should clearly illustrate what problems it solves.
[ ] Ideally, include a test that fails without this PR but passes with it.

Tests

[ ] Run the tests with pnpm test and lint the project with pnpm lint and pnpm check

Changesets

[x] If your PR makes a change that should be noted in one or more packages' changelogs, generate a changeset by running pnpm changeset and following the prompts. Changesets that add features should be minor and those that fix bugs should be patch. Please prefix changeset messages with feat:, fix:, or chore:.

Edits

[x] Please ensure that 'Allow edits from maintainers' is checked. PRs without this option may be closed.

sveltejs / kit