Lifecycle hooks for websocket connections

[hampuskraft]

[Deleted for privacy reasons]

[benjie]

You can read about our server hooks support here:

https://www.graphile.org/postgraphile/plugins/#writing-your-own-plugins

We already expose the onOperation hook from the websocket server here:

https://github.com/graphile/postgraphile/blob/3b01d529e7fdc79e14a0bde0bf133e963ecdc088/src/postgraphile/pluginHook.ts#L57

And you can see an example of it in use here:

https://github.com/graphile/persisted-operations/blob/ee2e404ccc5e4f7f7ffe65215a97ac5e6e0fc08e/src/index.ts#L255-L263

---

However, for your derivative stream I think you're actually after something completely separate to that. I suspect you're just not familiar with wrapping an async iterator, which goes a little something like this:

async function* doSomethingWith(asyncIterator, context) {
  console.log("Subscription started");
  try {
    for await (const val of asyncIterator) {
      yield val
    }
  } finally {
    console.log("Subscription ended");
  }
}

(See #1218 (comment) for where doSomethingWith would be called from.)